Kyaw linn oo et al ajes 2015 copy

Journal of Asian Earth Sciences xxx (2015) xxx–xxx
Provenance of the Eocene sandstones in the southern Chindwin Basin,
Myanmar: Implications for the unroofing history of the Cretaceous–
Eocene magmatic arc
Kyaw Linn Oo a,⇑, Khin Zaw b
, Sebastien Meffre b
, Myittac
, Day Wa Aung c
, Chun-Kit Lai b,d
a
PETRONAS Carigali Myanmar Inc. (PCMI), Myanmar
b
ARC Centre of Excellence in Ore Deposits (CODES), University of Tasmania, Hobart, Tasmania, Australia
c
Department of Geology, University of Yangon, Yangon, Myanmar
d
Chinalco Rio Tinto Exploration (CRTX) Co. Ltd., Beijing, China
a r t i c l e i n f o a b s t r a c t
Article history:
Received 12 June 2014
Received in revised form 31 March 2015
Accepted 14 April 2015
Available online xxxx
The Eocene sedimentary rocks, exposed in the southern Chindwin Basin, northern part of Myanmar, are
characterized by a thick sequence of continental clastic units consisting of sandstones with abundant vol-
caniclastic materials, and a subordinate amount of metamorphic lithic fragments. Detrital information
preserved in these Eocene clastic sequences has shed light on the erosional unroofing history of a
Cretaceous to Eocene Andean-type continental magmatic arc related to the India–Asia collision.
An integrated study of the petrography, geochemistry and LA-ICP-MS (Laser Ablation Inductively Couple
Plasma MassSpectrometer) U–Pb zircon geochronology of the late Middle Eocene, volcaniclastic Pondaung
sandstones, combined with the WSW-directed regional mean palaeocurrent direction ( 254 azimuth),
has revealed an older, calc-alkaline, andesitic volcanic arc (detrital U–Pb zircon age: 101–43 Ma), situated
to the NE of the southern Chindwin Basin, possibly related to the Neo-Tethys seafloor subduction beneath
the Eurasia continental margin, i.e., the West Burma Block or Burma (Myanmar) Plate. We suggest that this
arc may have been eroded during the late Middle Eocene(Bartonian) with volcaniclastic detritus deposited
in the fore-arc basin of the Central Myanmar Basin, forming the Pondaung Formation.
2015 Elsevier Ltd. All rights reserved.
Keywords:
Central Myanmar Basin
Chindwin Sub-Basin
Erosionalunroofing
Andean-type continental magmatic arc
Pondaungsandstones
1. Introduction suggested that no such palaeo-river connection existed during
the Paleogene.A significant proportion of volcaniclastic materials
in the Eocene sandstones of the Indo-Burman Ranges (IBR) and
the Central Myanmar Basin (CMB) are considered to have been
derived from the unroofing of a local magmatic arc, which formed
along the eastern Myanmar rather than derived from the
Trans-Himalayan batholiths of Tibet (Allen et al., 2008; Licht
et al., 2013).Wang et al. (2014) have recently proposed, based on
U–Pb and Hf isotope analyses of detrital zircons from the Upper
Cretaceous to Eocene stratigraphic units of the Chindwin Basin,
that the Cretaceousto Eocene Western Myanmar Arc (WMA) was
the southeastern extension of the Trans-Himalayanmagmatic arc
in Tibet (Kohistan-Ladakh-Gangdese arc), which was formed along
the southern Asian margin during the Neo-Tethyansubduction.
Eocenesedimentary rocks constitute 50% of the Cenozoicstrati-
graphicunits in the CentralMyanmarBasin, with a total thickness
of about 13 km (Aung Khin and Kyaw Win, 1969). Among this
sequence, the late Middle Eocene–Upper Eocene, fluvio-deltaic
Pondaung and Yaw formations represent 25% of the entire Eocene
succession. The rest of the Lower- to Middle Eocene units (i.e.,
Since 2008, Myanmar has become a center of attention for
many geoscientists who are investigating sedimentary prove-
nances, tectono-magmatic evolution and palaeo-river reconstruc-
tion in Myanmar by using detrital U–Pb zircon geochronology
and isotopic fingerprinting methods (Allen et al., 2008; Liang
et al., 2008; Mitchell et al., 2012; Licht et al., 2013; Robinson
et al., 2014; Wang et al., 2014). However, advanced technology
alone may not help to reach a complete understanding without
justification from a sound knowledge of regionaland local geology
of Myanmar.
Liang et al. (2008) considered that the Yarlung-TsangpoRiver in
Tibet was connected to the Irrawaddy River in the late Miocene,
whereas Robinson et al. (2014) suggested that the river system
was disconnected in the early Miocene. Licht et al. (2013)
⇑ Corresponding author at: Petronas Carigali Myanmar Inc. (PCMI), 16, Shwe
Taung Kyar, Bahan 11201, Yangon, Myanmar.
E-mail address: linnoo.kyaw@petronas.com.my (Kyaw Linn Oo).
http://dx.doi.org/10.1016/j.jseaes.2015.04.029
1367-9120/ 2015 Elsevier Ltd. All rights reserved.
Please cite this article in press as: Kyaw Linn Oo, , et al. Provenance of the Eocenesandstones in the southern Chindwin Basin, Myanmar: Implications for
the unroofing history of the Cretaceous–Eocene magmatic arc. Journal of Asian Earth Sciences (2015), http://dx.doi.org/10.1016/j.jseaes.2015.04.029
Contents lists available at ScienceDirect
Journal of Asian Earth Sciences
journal homepage: www.elsevier.com/locate/jseaes

2 Kyaw Linn Oo et al. / Journal of Asian Earth Sciences xxx (2015) xxx–xxx
Fig. 1. (A) Simplified geological map of Myanmar and the eastern Himalayan region showing major geotectonic belts, volcanic centers and plutonic rocks of the Western
Myanmar Arc (WMA)in the Central Myanmar Basin (CMB) and granitoid rocks along the MogokMetamorphic Belt (MMB) (modified after Mitchell et al., 2012). Location of
the studied area in the southern part of Chindwin Sub-Basin (CSB) is shown (Fig. 1B). ITSZ, Indus-Tsangpo Suture Zone; MBT, Main Boundary Thrust; EHS, East Himalayan
Syntaxis; GB, Gaoligong Belt; CTFB, Chittagong-Tripura Fold Belt; HSB, Hukaung Sub-Basin; MSB, Minbu Sub-Basin (Salin); PSB, Pyay Sub-Basin; IRSB, Irrawaddy Sub-Basin;
SF, Sagaing Fault; JMB, Jade Mine Belt; SG, Salingyi diorites; MSKD, Mokpalin–Sit-Kinsin Diorites. (B) Geologicalmap of the studied area in the southern Chindwin Basin
(location is shown in Fig. 1A)showing the Middle–Upper Eocene lithostratigraphic units and the sample locations for the current study (after Kyaw Linn Oo, 2008).
Laungshe, Tilin and Tabyinformations in descending stratigraphic
order) are of shallow marine originand are madeup predominantly
of thick shale and mudstone (Aung Khin and Kyaw Win, 1969;
Bender, 1983). The Pondaung Formation is the thickestcontinental
deposit in the Central Myanmar Basin ( 2300 m thick in the
Chindwin Sub-Basin),composed of morethan 70% sandstoneswith
minor conglomerates in the lower part. The Pondaungsandstones
contain abundant volcaniclasticmaterialsand subordinateamount
of low- to medium-grade metamorphic rock fragments (Kyaw Linn
Oo et al., 2009; Licht et al., 2013; Khin Zaw et al., 2014a).
Licht etal. (2013)haverecently conducted a provenancestudyon
the uppermemberof the PondaungFormation( 500 m thick)in the
northeastern MinbuBasin andtheYaw Formation in thenorthwest-
ern Chindwin Basin, using petrography and bulk-sediment Nd–Sr
isotopic analysis. However, about 1500 m thick section of the
fluvial-dominated, lower member of the PondaungFormation has
not been investigated.In this study,we investigatedthe provenance
characteristics of the sandstones from the lower member of the
Pondaung Formation and the Yaw Formation in the southern
Chindwin Basin, based on integrated analyses of detrital modes,
XRF trace element geochemistry, regional mean palaeo-current
data,anddetrital U–Pb zirconages. Our studyalso discussesthetec-
tonic significanceof the volcaniclasticPondaung sandstones in the
context of India–Asia collision in Myanmar, and provides key
chronologicaland palaeogeographical constraints on the erosional
unroofing history of an older volcanicarc in Myanmar.
2. Geological background
2.1. Tectonic framework of the Central Myanmar Basin
Myanmar lies in a tectonically active region, south of the
Himalayan orogenic belt, and east of the Sumatra–Andaman–Ara
Please cite this article in press as: Kyaw Linn Oo, , et al. Provenance of the Eocene sandstones in the southern Chindwin Basin, Myanmar: Implications for

Kyaw Linn Oo et al. / Journal of Asian Earth Sciences xxx (2015) xxx–xxx 3
Table 1
Stratigraphy of the southern Chindwin Sub-Basin in the Central Myanmar Basin, and the stratigraphicintervals of the analyzed samples (modified after Aung Khin and Kyaw Win,
1969; Bender, 1983).
Stratigraphic
age
Stratigraphic units,
depositional
setting, thickness
Stratigraphic age determinations (fauna, flora,
magnetostratigraphy, radiometric dating)
Stratigraphic intervals of the collectedsandstone
samples for this study and the previous studies
Lower
Miocene
Letkat Formation
Fluvial (285 m)
Fossil rare, a palynological assemblage zone indicates the –
early Miocene (Reimann and Aye Thaung, 1981; Engelhardt,
1993)
Oligocene Hiatus: Uplifting of the Chindwin Sub-Basin separated from the Minbu Sub-Basin to the south
Upper
Eocene
Priabonian Yaw Formation Nummulites yawensis, Orthophragmina (Discocyclina) 5 samples for petrographicdata in this study;
petrographic data of the western part of
Chindwin Basin (Licht et al., 2013)
Deltaic–shallow
marine (337 m)
Sella, Operculina sp.cf. canalifera, Velates perversus
Two distinct plynological assemblage zones indicate late
Eocene (Reimann and Aye Thaung, 1981)
Unconformity/Sequence boundary between the Late Bartonian & Early Priabonian (Bar2/Pri 1) at 37.2Ma
Late Middle Bartonian
Eocene
Upper member of
Pondaung Fm.
Fluvio-deltaic
(300 m)
Abundant vertebrate fauna, Anthropoid primate fossil (e.g.,
Pondaungia cotteri), Mammalian fossil correlation = late
Middle Eocene (Bartonian Stage)
Magnetostratigraphic age of the upper member of
Pondaung Fm. in the NE of Minbu Basin = 37.4 Ma (Benammi
et al., 2002)
Fission-tract zircon dating from a tuffaceous bed of the
Basin = 37.2 ± 1.3 Ma (Tsubamotoet al., 2002)
LA ICP-MS U–Pbzircon dating from the same tuffaceous
Petrographicand Nd, Sr bulk-rock isotopic data of
the NE of Minbu Basin (Licht et al., 2013)
upper member of Pondaung Fm. in the NE of Minbu
bed = 40.31 ± 0.65 Ma (Khin Zaw et al., 2014a)
Fossil rare, silicified woods
Youngest detrital LA ICP-MS U–Pb zircon age of this
study = 43.3 ± 4.4 Ma (middle Eocene)
Nummulites acutus
Early Middle Lutetian
Eocene
Lower member of
Pondaung Fm.
Fluvial (2000 m)
Tabyin Fm.
Shallow marine
(760 m)
7 samples for petrographic data in this study
5 samples for U–Pb zircon geochronology and
XRF whole-rockgeochemistry in this study
–
kan Trench (Morley, 2009), i.e., Myanmar portion of the India–
Sunda convergence zone, which forms a transition from oceanic
lithosphere subduction to the continent–continent collision (Le
Dain et al., 1984; Win Swe, 2012). The Indo-Burman Ranges
(IBR), immediate to the east of the ArakanTrench,has been recog-
nized as an accretionary wedge, resulted from oblique subduction
of the India oceanic lithosphere beneath the Burma Plate (Maurin
and Rangin,2009), and as an India–Asia (Myanmar) collision front
during the Cretaceous and Eocene(Ni et al., 1989; Khin Zaw, 1990;
Mitchell, 1993; Hall, 2012).
The Central Myanmar Basin (CMB) lies between the IBR in the
west and the Shan Plateau in the east, i.e., a part of the Sibumasu
Terrane of Metcalfe (2002, 2011, 2013), located in the eastern
Myanmar. The CMB is divided into the eastern (backarc)and the
western (forearc) troughs particularly after the late Miocenewhen
the Central VolcanicLine (CVL) became well established (Bender,
1983; Pivniket al., 1998). The western trough of the CMB is further
subdividedinto a few sub-basins,namely (fromnorth to south) the
Hukaung, Chindwin, Minbu/Salin, Pyay and Irrawaddy sub-basins
(Fig. 1A). The CMB contains a thick succession of the Upper
Cretaceous to Cenozoic sedimentary rocks ( 25 km thick),depos-
ited in fluvio-deltaicsystems and prograded southwards over shal-
low marine depositional environments (Aung Khin and Kyaw Win,
1969; Bender, 1983), in a forearc location (Pivnik et al., 1998).
These sub-basins may have developed as a series of pull-apart
basins since the early Eocene as the Burma Plate moved north-
wards during the motion of India to the north with respect to
Asia (Pivniket al., 1998; Ranginet al., 1999).
At the eastern edge of the CMB, the N-trending active dextral
Sagaing Fault (Win Swe, 1972; Curray et al., 1979) extends for
about 1500km along the western margin of the Shan Plateau,
immediately to the west of the MogokMetamorphic Belt (MMB),
representing a present-day plate boundary between the Burma
Plate (Curray et al., 1979; Curray, 2005) and the Sibumasu
Terrane. The subduction zone, to the west of the IBR (i.e.,
Andaman-Arakan Trench), forms the western margin of the
Burma Plate (e.g., Steckleret al., 2008; Mitchellet al., 2012).
2.2. Western Myanmar subduction zone: Andaman-Arakan Trench
Tomography and earthquake hypocenters delineated an east-
ward dipping subducted slab beneath the Burma Plate, which is
presumed to be a slice of Neo-Tethysoceanic crust from the earlier
phase of subduction (Nielsenet al., 2004; Hall, 2009; Maurinand
Rangin,2009). Except under southernmost Myanmar, the geome-
try of the subductingslab is well established from earthquake focal
depths (hypocenters) of an east-dipping Wadati-Benioff zone,
gradually deepen eastwards following the trajectory of the sub-
ducted oceanic slab up to 200 km beneath the Central Myanmar
Basin (e.g., Ni et al., 1989; Richardset al., 2007; Wang Yu et al.,
2014).
P-wave tomographic depth slices of the Asia region (Bijwaard
and Spakman, 2000) of the upper mantle (at 300 km) indicated
the significant high velocity anomalies, parallel to the present
Sumatra–Andaman-Arakantrenches, interpreted as the principal
lithospheric slabs subducted during the late Cenozoic (Hall,
2009). At depths below 700 km in the lower mantle also showed
the linear high velocityanomalies in the south,north and the east-
ern end of India (i.e., beneath the Burma Plate), interpreted as a
series of subduction zones active during India’s northward move-
ment before collision with Asia (van der Voo et al., 1999;
Aitchisonet al., 2007; Hall, 2009). The velocity anomalies of both
the upper and lower mantle characterize the evidence of
long-term subduction at the Indonesianmargins (Hall, 2009).
The earlier seismologic studies suggested the cessation of sub-
duction beneath the Burma Plate in the western Myanmar (e.g.,
Rao and Kumar,1999) and no evidence of present-day activesub-
duction to the north of the Andaman Islands, as it is shown by

Thrust belt (Radha Krishna and Sanu, 2000; Satyabala, 2003;
Curray, 2005; Nielsen et al., 2004). Than Tin Aung et al. (2008)
described the marine terraces along the Rakhine coast of
Myanmar as evidence for three great earthquakes in the past
3400 years. Radiocarbondating of coral remains suggests that the
oldest terrace emerged three times, during 1395–740 BC, AD
805–1220 and AD 1585–1810 (Than Tin Aung et al., 2008).
In any case, the western Myanmar subduction zone is still
active and accommodated a minor part (ca. 10–15%) of the total
India/Sundaland motion (Pubellier et al., 2003), as indicated by
the infrequent occurrence of moderate to strong historic earth-
quakes along the Rakhine (Arakan) coast (Chhibber, 1934; Sahu
et al., 2006) and the existence of a flight of marine terraces (Than
Tin Aung et al., 2006, 2008). It is implied that the western
Myanmar subduction zone has been active seismically, but less
active than the Sumatran region (Win Swe and Soe Thura Tun,
2008).
2.3. The southern Chindwin Basin
The study area, in the southern part of the ChindwinSub-Basin,
is located about 48 km to the west of Monywa, and about 10 km to
the north of Minbu Sub-Basin (also called Salin Sub-Basin) in the
Central Myanmar Basin (Fig. 1A). The area is covered with fluvial
to deltaic sedimentary units in descending stratigraphic order:
the Tabyin Formation (early Middle Eocene, Lutetian Stage),
Pondaung Formation (late Middle Eocene, Bartonian Stage), the
Yaw Formation (Upper Eocene, Priabonian Stage), and the Letkat
Formation (Lower Miocene?), which are exposed in a regional
north-plunging syncline (Fig. 1B). The Tabyin Formation is poorly
exposed only in the crestalpart of the Pondaung Rangein the stud-
ied area (Fig. 1B). Detailed stratigraphic age determination of the
rock units are shown in Table 1.
The Pondaung Formation (Cotter, 1914) is the thickestand best
exposed fluvial sedimentary sequence in the northern Minbu
Sub-Basin and the southern Chindwin Sub-Basin.It was deposited
in a braided to meandering river system in the southern Chindwin
Sub-Basin (Kyaw Linn Oo, 2008) (Fig. 2C), and a fluvio-deltaic sys-
tem in the northeastern Minbu Sub-Basin(Aung Naing Soe et al.,
2002). The upper member of the Pondaung Formation (Aye Ko
Aung, 1999) in the northeast of the Minbu Sub-Basin is
well-known for hosting important Asian anthropoid primates and
vertebrate mammalian fossils (e.g., Tsubamotoet al., 2002, 2009;
Aung Naing Soe et al., 2002; Khin Zaw et al., 2014a). It is character-
ized by the widespread occurrence of reddish-colored or varie-
gated clay/mudstones of fluvial floodplain palaeosol facies (Aung
Naing Soe et al., 2002; Kyaw Linn Oo and Myitta, 2007; Kyaw
Linn Oo, 2008; Licht et al., 2014b), interbedded with thin to
medium-bedded, fine-grained sandstones. The lower member of
the Pondaung Formation (Aye Ko Aung, 1999) in the studied area
is composed of medium- to thick-bedded, cross-stratified,
medium- to coarse-grained sandstones, gritty to pebbly sand-
stones and conglomerates,interbedded with silty mudstones.
In the southern ChindwinBasin, there is a widespread, trace-
able, highly ferruginous horizon (Stamp, 1922; Kyaw Linn Oo and
Myitta, 2007), i.e., a stratigraphic break or a sequence boundary,
between the late Middle EocenePondaungFormation and the
overlying Upper Eocene Yaw Formation (Fig. 2B). The Yaw
Formation (Cotter, 1914) in the southern ChindwinBasin is inter-
preted to have been deposited in a tide-dominated marginalmar-
ine to deltaic environment, characterized by a thick, prograding
sequence of bluish gray mudstones to dark-colored carbonaceous
to coaly shale units, interbedded with thin- to medium-bedded
sandstones (Kyaw Linn Oo, 2008) (Fig. 2A). The Lower Miocene
(?) fluvial deposit of the Letkat Formation overlies disconformably
on the Yaw Formation.
Fig. 2. (A) A field outcrop of the Upper EoceneYaw Formation (a section of prodelta
mud facies); (B) A region-wide traceable, highly ferruginous horizon between the
Yaw Formation and the underlying Pondaung Formation (Location: 22 070
5700
N,
94 320 2200 E, SE of Sityin village). Note: It is a lithostratigraphic break or a sequence
boundarybetween the end of Bartonianand the early Priabonian stages, correlative
to the major sequence boundary (Bar2/Pr 1, at 37.10 Ma)of Hardenbolet al. (1998),
and also consistent with the petrofacies boundary between the Pondaung
sandstones and the Yaw sandstones. (C) A field outcrop of the late Middle Eocene
Pondaung Formation (a section of fluvial channel and overbank floodplain facies,
the reddish-colored variegated clay or palaeosol).
marine seismic studies to be an active dextral strike-slip margin
(Nielsenet al., 2004). The recent structural and kinematic analysis
of the IBR, based on seismic reflection, geodetic and geologicalfield
data, has indicatedthat the IBR is having right-lateral shearing in
the innermost part and E–W shortening in the outermost part
due to the diffusestrain partitioning, related to the obliqueconver-
gence of the India/Sunda plates (Maurin and Rangin,2009).
However,the still active subduction in the western Myanmaris
confirmed by a number of studies (e.g., Dasgupta et al., 2003;
Satyabala, 2003; Nielsen et al., 2004; Khan, 2005; Socquet et al.,
2006). The Indianplate subducts at a rate of 35–50 mm/yr. beneath
the Burma micro-plate along the western coast of Myanmar,
between the Rakhine (Arakan) trench and Chittagong Fold and

the Supplementary material. Cathodoluminescence (CL) images
of the zircons were also obtained to help with the interpretation
of the U–Pb age data. The images were obtained using a FEI
Quanta 600 SEM housed at the Universityof Tasmania.
Analyses were performed two hours after ignition of the mass
spectrometer to enable the machine to stabilize. Four primary
(Temora standard of Black et al., 2004) and two secondarystan-
dards (91500 standard of Wiedenbecket al., 1995) were analyzed
at the beginningof the sessionand after every12 unknown zircons
(roughly every hour). The data reduction method used was based
on that outlinedin detailby Meffreet al. (2007).The standarderrors
quoted were based on the standard error of the measurements
within the integration intervals,and the errors on themeasurement
of the standards usingsimilar techniques to that outlinedin Paton
et al. (2010). Element abundances were calculated using the
method outlinedby Kosler (2001), using Zr as the internalstandard
element, assuming stoichiometric proportions and using the sec-
ondarystandard 91500to correctfor massbias, usingtraceelement
values from the GeoREM database (Jochumand Nohl, 2008).
The data were not collected to give detailed quantitative or sta-
tistical provenance information, but rather to investigate the age
range for the main magmatic events associated with the volcanic
components observed in the thin sections.The strategy employed
was to combine all the zircon analyses from all of the samples
and focus on the euhedral oscillatoryzoned zircons with Th/U val-
ues > 0.1 (hereby interpreted as magmatic).
3. Analytical methods
3.1. Sampling method
Seventy fresh sandstone samples were collected from seven
stratigraphic measured sections in stream outcrops of the lower
member of the Pondaung Formation and the Yaw Formation,
exposed in both limbs of the regional north-plunging synclinal
structure in the southern ChindwinBasin. Locations of the mea-
sured stratigraphic sections for the analyzed samples are shown
in Fig. 1B. The stratigraphic intervals of the selected samples and
type of analyses performed are also described in Table 1.
3.2. Petrographic analysis
Standard petrographic thin sections were prepared from the 50
medium-grained sandstones and examined under a polarizing
microscope with an attached mechanical stage, out of which 12
representative thin-sections were selected and analyzed by the
modified Gazzi-Dickinsonmethod of point counting(e.g., Ingersoll
et al., 1984; Dickinson,1970, 1985). A totalof 400 framework grains
were identified per thin sectionfor QFL mode and lithic population,
ata spacingof 0.33 mm. Cement,matrix, heavyminerals, carbonate,
mica and miscellaneous grains were included in this count.
Petrographic counting parameters are presented in Table 2. The
Q–F–L plots of McBride(1963) and Dickinson (1985) are used for
classificationand provenancestudy. In addition,the triangularplots
of Dickinson (1985), including Qm–P–K, Qm–F–Lt, and Lm–Lv–Ls
plots are used for discriminatingprobable detrital provenances. 4. Resultsand interpretations
4.1. Petrography of the sandstones
3.3. XRF-whole rock geochemical analysis
Recalculateddetrital modes and lithic percentages are shown in
Table 3. The sandstone modal compositions plotted on ternary
Five volcaniclasticsandstone samples, collected from the Lower
Member of Pondaung Formation, were used for XRF-whole rock
geochemical analysis and LA ICP-MS U–Pb zircon dating. Sample
locations are shown in Fig. 1B. The X-ray Fluorescence (XRF)
method used a PANalytical (Philips) PW 1480 XRF spectrometer
at the ARC Centre of Excellence in Ore Deposits (CODES),
University of Tasmania, Australia. Major elements were measured
from fusion discs, which were prepared at 1100 C in 5%Au/95%Pt
crucibles using 0.500g of sample, 4.500 g of 12–22 Flux (lithium
tetraborate–metaborate mix) and 0.0606g of LiNO3, following
the techniques describedby Watson (1996) and Robinson(2003).
Powdered samples were analyzed for 10 major oxides (SiO2, TiO2,
Fe2O3, MnO, MgO, CaO, Na2O, K2O, P2O5 and loss on ignition)
and 10 trace elements (Y, U, Rb, Th, Pb, As, Bi, Zn, Cu, Ni) using a
ScMo X-ray tube, and another 10 trace elements (Sn, Nb, Zr, Sr, Ba,
Sc, V, La, Ce and Nd) using an Au X-ray tube.
Table 2
Petrographic point-counting parameters for the Pondaung and Yaw sandstones
(modified from Dickinson, 1970; Ingersoll et al., 1984).
Grain categories Recalculated
parameters
Qm
Qp
Cht
Q
Monocrystalline quartz
Polycrystalline quartz
Chert
Total quartzose grains (Qm + Qp + Cht)
Q–F–L:
Q = Qm + Qp + Cht
F = P + K
L = Lv + Lm + Ls
(excluding Qp and
Cht)
Qm–F–Lt:
Qm = Qm F
= P + K
Lt = Qp + Lv + Lm + Ls
P Plagioclase feldspar grains (mainly of
polysynthetic twinned feldspars)
K Potassium feldspar grains (mainly of
untwinned feldspars, simple-twinned
feldspars, microcline and perthitic feldspars)
Total feldspar grains (P + K)
3.4. LA ICP-MS U–Pb zircon dating
U–Pb zircon dating using LA-ICP-MS (Laser AblationInductively
Couple Plasma Mass Spectrometer) is currently the most common
method for analyzing detrital zircons because it achievesthe same
precisionand accuracyas an ion probe (e.g., Kosler et al., 2013) but
is considerably more efficient and cost effective. Detrital U–Pb zir-
con ages can be used to constrainthe age of deposition of the host
sediment, reconstruct provenance, characterize a sedimentary
unit, and characterize many different aspects of source regions
(Gehrels, 2014).
In this study, we used an Agilent quadrupole ICPMS with a
193 nm New Wave Laser at CODES, the University of Tasmania,
for zircon age dating. The zircons were separated using standard
gravityand magnetic techniques, pickedand mounted onto double
sided tape, mounted in epoxy and polished. They were analyzed
using the equipment and techniques described more details in
F Qm–P–K:
Qm = Qm
P = P
K = K
Lm–Lv–Ls:
Lm = Lml + Lmh
Lv = Lvl + Lvm + Lvv
Ls = Ls
Lvl
Lvm
Lvv
Volcanic lithic grain with lathwork texture
Volcanic lithic grain with microlitic texture
Volcanic grain with vitric texture (including
different types of devitrified volcanic glass)
Total volcanic grains (lvl + lvm + lvv)
Totalmetamorphic lithic grains
Totalsedimentary lithic grains
Totalunstable aphanitic lithic grains
(Lm + Lv + Ls), excluding the quartz-related
grains (Qp + Cht)
Total lithic grains (Qp + Lm + Lv + Ls),
Lv
Lm
Ls
L
Lt
including quartz-related grains
Totalgrain parameters and the major plot names are in bold.

Table 3
Recalculatedmodal point-count data of the Pondaung and Yaw sandstones in the southern Chindwin Basin.
Samples Q–F–L % Qm–F–Lt % Qm–P–K % Lm–Lv–Ls % Ratios
Q F L Qm F Lt Qm P K Lm Lv Ls P/F Lv/L Lm/L
Yaw-37
Yaw-35
Yaw-34
Yaw-33
Yaw-39
Average
60
65
51
62
75
63
25
12
32
20
20
22
15
23
17
18
5
15
37
45
38
47
61
46
24
12
32
20
20
22
39
43
30
23
19
32
60
81
54
71
75
68
13
7
10
6
4
8
27
12
36
23
21
24
59
49
80
76
23
57
33
42
20
18
77
38
8
9
0
6
0
5
0.3
0.4
0.2
0.2
0.1
0.2
0.3
0.4
0.2
0.2
0.8
0.4
0.6
0.5
0.8
0.8
0.2
0.6
Pond-9
Pond-3
Pond-30
Pond-29
Pond-26
Pond-25
Pond-15
Average
44
46
24
29
29
49
36
37
29
20
11
14
20
26
32
22
27
34
65
57
51
25
32
41
31
26
6
11
15
30
20
20
30
20
11
10
20
27
32
21
38
54
83
79
65
43
48
59
52
57
36
51
43
52
39
47
38
39
37
22
53
34
54
40
10
4
27
27
4
14
7
13
30
64
6
5
52
16
2
25
65
36
87
94
44
80
98
72
5
0
7
1
4
4
0
3
0.8
0.9
0.6
0.6
0.9
0.7
0.9
0.8
0.7
0.4
0.9
0.9
0.4
0.8
1.0
0.8
0.3
0.6
0.1
0.0
0.5
0.2
0.0
0.2
The average values are in bold and italic.
diagramsof McBride(1963) show typical Q–F–L (Quartz–Feldspar–
Lithic) percentages in the Pondaung sandstone samples (37–22–
41) and the Yaw sandstone samples (63–22–15) (Fig. 3A). The
Pondaung sandstones are feldspathic lithic arenite or feldspathic
volcanic arenite in composition (Fig. 4A–G), whereas the Yaw
sandstones are sub-lithic arenite to sub-arkose,containingabun-
dant monocrystalline quartz and altered K-feldspar grains
(Fig. 5G and H).
The Pondaung sandstones contain abundant volcaniclithic frag-
ments (Lvl, Lvm) and volcanicglass with varyingdegree of devitri-
fication (Lvv). Volcaniclithic fragments with lathwork texture (Lvl)
and microlitic texture (Lvm) show similar characters to basaltic
and andesitic fragments (Fig. 4A–D). The andesitic grains are com-
posed of plagioclase phenocrysts set in an aphanitic groundmass
(Fig. 4E–G). Large euhedral zoned plagioclase feldspars are com-
monly found in association with feldspar-phyric, microlitic, vol-
canic grains (Fig. 4H). Low- to high grade metamorphic lithic
fragments of slate, phyllite and schist (Lm) occur in subordinate
amounts in the Pondaung sandstones (Fig. 5D–F), but become a
dominant lithic type in the Yaw sandstones.
volume of volcanic rocks in the source terrane, during deposition
of the Pondaung Formation in the middle Eocene.The occurrence
of plutonic igneous lithic grains composed of quartz–feldspar–mi
ca aggregates,quartz–mica aggregates,and microcline,perthite
and myrmekite fragments also indicate a plutonic source
(Fig. 5A and B).
4.3. Petrofacies of the Yaw sandstones
The increasing Lm/L ratio, together with significant decreasing
trend of P/F ratio throughout the sandstones of Yaw Formation,
suggests a marked change in source rock composition (Fig. 3B).
Lower value of P/F is typical for detrital sediments derived from
mixed plutonic and metamorphic terranes (Dickinson, 1970;
Ingersoll, 1978). During the deposition of the Yaw Formation, the
associated metamorphic and granitic source inputs were likely to
become more substantial, possibly due to the rapid erosion of a
volcanic arc down to the deeper granitoids, with associated uplift.
In addition,the abundanceof micas suggests an uplifted crystalline
basement terrane composed mainly of micaceous granite or gran-
odiorite, as well as low- to high grade metasedimentary rocks.
4.2. Petrofacies of the Pondaung sandstones
4.4. Provenance of the Pondaung and Yaw sandstones
The Pondaungsandstones and the Yaw sandstones demonstrate
two differenttypes of petrofacies,which are observed clearly when
the compositional variations of the sandstones are plotted on an
area graph (Fig. 3B). The ratios of plagioclase to total feldspar
(P/F) and volcanic lithic to total lithic fragments (Lv/L) are appar-
ently higher in the Pondaung sandstones than in the Yaw sand-
stones (Fig. 3B). The mean value of P/F in the Pondaung
sandstones is more than 0.8. This value is common for most detri-
tal sediments derived from volcanic terranes (Dickinson,1970;
Ingersoll, 1978). The mean value of Lv/L is 0.8, higherthan that
of metamorphic lithic to total lithic fragments (Mean value of
Lm/L = 0.2), also a characteristic for volcanic arc derived materials
(Dickinson, 1970; Ingersoll, 1978). The abundant compositionally
zoned plagioclaseand volcaniclithic fragments were derived pos-
sibly from andesitic rocks,and unaltered euhedral feldsparcrystals
Point-count data of the sandstones plotted on QFL, QmPK,
QmFLt and LmLvLs triangular diagrams (Dickinson and Suczek,
1979; Dickinson,1985), clearly demonstrate that the Pondaung
sandstones fall within the suite of transitional to dissected mag-
matic arc provenances, whereas the Yaw sandstones may have
come from a recycled orogenic provenance (Figs. 6 and 7). The
Q–F–L plots also suggested that provenance of the sandstones
moved from a dissected magmatic arc to recycled orogen or
uplifted basement terrane (Fig. 6).
4.5. XRF major-element geochemistry: sandstone maturity, degree of
chemical weathering and climate condition in source area
The results of XRF majorelements for each Pondaung sandstone
sample are reported in Table 4. For evaluating sandstone maturity, the
Index of Compositional Variability [ICV = (Fe2O3 + K2O +
Na2O + CaO + MgO + MnO)/Al2O3] is commonly used (Cox et al.,
1995). The ICV values of the Pondaung sandstones range from
1.0 to 1.9 (Average = 1.4), indicating that the sandstones are
(Fig. 4H) represent
Cavazza, 1991).
Throughout the
fresh pyroclastic influxes (Ingersoll and
stratigraphic section of the Pondaung
Formation, the amount and character of plagioclase sand fluctu-
ates, but persists up to several meters, suggesting a substantial

Fig. 3. (A) Ternary classiﬁcation diagrams (McBride, 1963) of Pondaung and Yaw sandstones, showing an apparent shift in Q–F–L composition from feldspathic lithic arenite
(Pondaung sandstones) to lithic arkose–sub-arkose (Yawsandstones). (B) Schematic diagram showing the percentages of Quartz, Feldspar and Lithic grains (Q–F–L)of the
sandstone samples taken in stratigraphic positions,together with the ratios of Plagioclase to TotalFeldspar (P/F), volcanic lithic to total lithic (Lv/L) and metamorphic lithic to
total lithic fragments (Lm/L), indicating a two distinct petrofaciesboundary between them. (C) Major-element geochemical plots (SiO2 vs. Al2O3 + K2O + Na2O; after Suttner
and Dutta, 1986) of the Pondaung sandstones to recognizethe chemical maturity as a function of palaeoclimate condition.

Fig. 4. Photomicrographs of the Pondaung sandstones in the southern Chindwin Basin. (A–D) volcanic vitric (Lvv) and volcanic lithic fragments with a characteristic texture of
andesitic basalt to basaltic andesite; feldsparphyric, microlitic volcanic lithic (Lvm) and plagioclase phenocrysts set in a groundmass of plagioclase microlites (Lvl). Figures A
and C are taken under PPL; Figs. B and D are taken under XPL. (E–H) Large, euhedral phenocrysts of zoned plagioclase feldspars (F) are embedded in microlitic volcanic lithic
fragments (Lvl) or vitric groundmass (Lvv) (under XPL).
compositionally immature. A good measure of the degree of
chemical weathering on source rocks can be obtained from the Chemical
Index of Alteration (CIA; Nesbitt and Young, 1982), i.e., CIA (%) =
Al2O3/(Al2O3 + CaO⁄
+ Na2O + K2O) 100. The CIA of the
Pondaung sandstones ranges 44–65% (Average = 57%), indicating that
chemical weathering in the source rock terrane was moderate. A moderate
degree of plagioclase feldspar alteration in the source rock is also indicated
by the Plagioclase Index of Alteration (PIA; Harnois, 1988), i.e.,
PIA (%) = (Al2 O3 K2O)/(Al2O3 + C
aO⁄ + Na2O) 100. The PIA of the PO sandstones ranges from
42% to 64% (Average = 55%). The values of ICV, CIA and PIA are
shown in Table 4. The SiO2 vs. (Al2O3 + K2O + Na2O) plot is used
to recognize the chemical maturity of the Pondaung sandstones as a
function of climate (Suttner and Dutta, 1986).The plot reveals
that the Pondaung sandstones are chemically less mature and
formed under semi-arid to arid climate conditions (Fig. 3C).
4.6. XRF trace-element geochemistry
Results of the XRF trace-element geochemical analyses for the
Pondaungsandstone samples are presented in Table 4. If the detri-
tal grains were transported without much density sorting and con-
sist essentially of volcaniclasticsediments, then it is possible that
they would retain their original volcanic chemical signatures.
Relatively mild chemical weathering in the source area should
not strongly alter the immobile element geochemistry; highly
weathered materials such as laterites and bauxites would lose all
source rock chemical traits (Larue and Sampayo, 1990). Major

Fig. 5. Photomicrographs of the Pondaungsandstones in the southern Chindwin Basin. (A–B) Fresh plutonic fragments; aggregates of polycrystalline quartz with plagioclase
feldspar (Qp–F), hornblende (Hb)and mica (mica), associated with volcanic fragments (Lvv), suggesting a ‘‘volcano-plutonic’’ source (under XPL). (C–D)Elongated fragments
of polycrystalline quartz (Qp) having sutured inter-crystalline boundaries and undulose extinction, suggesting a metamorphic recrystallization (possibly from gneiss);
monocrystalline quartz (Qm) with chains of vacuoles inclusions and tourmaline grain (To) indicating a hydrothermal or vein quartz associated with felsic plutonic source
(under XPL). (D–F) Metamorphic lithic fragments (Lm) of quartz–mica schist are associatedwith Lvv and Lvm grains (Fig. E is taken under PPL, Figure F is taken under XPL). (G,
H) Photomicrographs of the Yaw sandstones showing abundant quartz grains, algae-coated grains (Alg) of monocrystalline quartz (Qm) and altered feldspar grain (F); a
feldspar grain (F) is coated by irregular, crinkle and concentric cortices of algae followed by siderite (Sid) cement, a glaucony grain (Glau), and bioclast fragment suggesting
slow sediment supply, deposited in low energy brackish water in semi-restricted ponds or bay in lower delta plain environment.
element compositionsare routinely used to classify volcanic rocks
in terms of petrogenesis and tectonic setting (e.g., Pearce and
Norry, 1979; Pearce et al., 1984). However, this method is not
applicable to altered volcanic rocks or the volcaniclasticsand-
stones in this study because many of the major elements, espe-
cially Si, Fe, Mg, Ca, Na and K are relatively mobile during
weathering and diagenetic alteration.
The high-ﬁeld-strength elements (HFSE) such as Ti, Zr, Nb, and
Y are relatively immobile during hydrothermal alteration,
diagenesis and weathering, and during regional metamorphism
up to the amphibolite facies. Ratios of these immobile elements
are the basis of many tectono-magmatic discrimination diagrams
(e.g., Pearce and Norry,1979; Winchester and Floyd, 1977). Using
the relatively immobile-element plots of Winchester and Floyd
(1977) and Pearce and Norry (1979), there is a clear assignment
for the composition and tectonic setting of the Pondaung sand-
stones (Fig. 8A and B). Results are also plotted on the two tectonic
discrimination diagrams of Pearceet al. (1984) (Fig. 8C and D). The

Fig. 6. Triangular plots of QFL and QmFLt showing the sandstone suites derived from different provenances (Dickinson, 1985). The Pondaung sandstones fall in the
transitional- to dissected magmatic arc and the Yaw sandstones are distributed toward the recycled orogenicprovenances.
Fig. 7. Triangular plots of the polycrystalline aphanitic lithic fragments Lm–Lv–Ls, and monocrystalline components Qm–P–K (Dickinson, 1985) to characterize source rock
composition. The Yaw sandstones are distributed toward more stable trend as they become more quartzose and mature and contain lower plagioclase content.
present study reveals that the volcaniclasticsandstones of the
Pondaung Formation were derived from calc-alkaline andesitic
volcanic rocks, emplaced in a continental arc setting (Fig. 8A–D).
grains (n = 6) gave older U–Pb ages, e.g., from Proterozoic (n = 3)
to Triassic–Jurassic (n = 3) that are chronologically similar to those
of Sibumasu origin (e.g., Sevastjanovaet al., 2011),suggestingpos-
sible derivation from the Shan Plateau to the east, or the western
part of the Sibumasu Terrane.
Although more zircon grains may be warranted to explainthe
unroofing history of the Cretaceous–Eocenemagmatic arc formed
along the Myanmarcontinental margin, our finding is further sup-
ported by Wanget al. (2014) as they documented the isotopicsig-
natures of the late Cretaceous to Eocene zircons, found in the
stratigraphic units of the western ChindwinBasin, which are cor-
relative to the Gangdesearc in Tibet.
4.7. LA ICP-MS U–Pb zircon geochronology
The total of 60 detrital-zircon grains were separated from the
five volcaniclasticsandstone samples of PondaungFormationand
analyzed by using a Laser Ablation Inductively Couple Plasma
Mass Spectrometer (LA ICP-MS). Analyticalresults are summarized
in Table 5, with each sample analysis illustrated in Concordia dia-
grams (Fig. 9A–F). Comparisons of our results with those of Wang
et al. (2014) are shown in Fig. 10. Most of the zircon grains are
euhedral to subhedral, with distinct oscillatory zones and having
Th/U values > 0.1, the characteristics of magmatic zircons (e.g.,
Hoskin and Schaltegger, 2003) derived from the volcanic lithic
grains (Fig. 10D).
There are two major clusters of the U–Pb zircon ages, observed
in the relative probabilityplot of all analyses (i.e., two majordetri-
tal peaksat 100 Ma and 47 Ma) (Fig. 10C), as well as on each sam-
ple’s Concordia plots, where the major detrital peaks of each
sample are around middle to late Cretaceous (101.7–80.4 Ma),
and the youngest zirconages are between early Palaeoceneto mid-
dle Eocene (65.1–43.0 Ma). The Concordiaplot for all the samples
has yielded 47.75 ± 0.87 Ma, which falls in the Lutetian stage of
the middle Eocene (Fig. 9F). In our study, a few detrital zircon
5. Discussion
5.1. Myanmar Magmatic-Arc
Geochronology and tectonic evolution of the magmatic arcs in
Myanmar (Mitchellet al., 2012)with detrital zirconU–Pb age data
of the present and previous studies are shown in Fig. 11. The late
Neogene–Quaternary volcanic arc of Myanmar is indicated by the
presence of calc-alkaline, Central Volcanic Line (CVL) (Chhibber,
1934; Bender, 1983; Stephenson and Marshall, 1984), running
north–south along the medial part of the Central Myanmar Basin.
The CVL comprises a few isolated, late Miocene–Pleistocene,
extinct volcanoes of Mt. Loimye, Taungthonlon, Monywa and

Table 4
XRF whole-rock geochemical data and values of ICV (Index of Compositional Variability, Cox et al., 1995), CIA (Chemical Index of Alteration, Nesbitt and Young, 1982) and PIA
(Plagioclase Index of Alteration, Harnois, 1988) for the Pondaung sandstones.
1-(PD-21/6) 2-(PD-24/2) 3-(PD-1/5) 4-(PD-28/3) 5-(PD-28/9) Average
Major elements (wt%)
SiO2
TiO2
Al2O3
Fe2O3
MnO
MgO
CaO
Na2O
K2O
P2O5
LOI
Total
ICV
CIA
%
PIA%
62.42
0.54
15.33
4.92
0.08
2.44
4.18
3.12
0.75
0.09
5.63
99.5
1.0
66
64
50.95
0.53
12.35
4.34
0.32
2.88
11.69
2.51
1.12
0.16
12.49
99.34
1.9
45
42
53.65
0.61
11.59
4.57
0.93
1.67
11.67
1.83
0.84
0.1
12.11
99.57
1.9
45
43
66.68
0.43
13.05
4.68
0.07
3
2.75
2.63
1.4
0.1
4.81
99.6
1.1
66
63
65.66
0.52
12.98
4.96
0.07
3.29
3.02
2.72
1.19
0.11
5.13
99.65
1.2
65
63
59.9
0.5
13.1
4.7
0.3
2.7
6.7
2.6
1.1
0.1
8.0
1.4
57.4
55.0
Trace elements (ppm)
Y
U
Rb
Th
Pb
As
Bi
Zn
Cu
Ni
Sn
Nb
Zr
Sr
Cr
Ba
Sc
V
La
Ce
Nd
Zr/Y
Zr/Nb
Nb/Y
10
<1.5
14
2
9
4
<2
59
19
22
<1.5
3
95
582
59
667
15
98
8
19
8
9.5
31.7
0.3
21
<1.5
31
3
16
<3
<2
63
15
58
2
3
79
466
188
394
18
116
19
43
19
3.8
26.3
0.14
24
<1.5
25
2
7
6
<2
54
17
33
<1.5
5
86
300
97
505
18
122
12
30
14
3.6
17.2
0.21
16
2
37
4
13
<3
<2
52
14
85
<1.5
4
79
377
155
422
11
83
14
31
14
4.9
19.8
0.3
16
2
33
3
11
<3
<2
57
15
91
2
4
96
330
247
316
14
114
13
30
17
6
24
0.3
17.4
0.8
28.0
2.8
11.2
2.0
0.0
57.0
16.0
57.8
0.8
3.8
87.0
411.0
149.2
460.8
15.2
106.6
13.2
30.6
14.4
5.6
23.8
0.3
The total values are in bold and italic.
Mt. Popa, fromnorth to south (Fig. 1A). It is continuingsouthwards
into the recently active volcanoes (Narcondam and Barren
Islands) of the Andaman arc and the late Neogene volcanic line
of Sumatra, a part of the active Sunda arc-trench system
(Mitchell, 1993; Win Swe, 2012).
The CVL, together with the granitoids of Wuntho-Saligyi seg-
ment in the north, are named as the Inner Volcanic-magmatic
Arc (Bender, 1983; Khin Zaw, 1990) or Western Granitoid Belt of
Myanmar (Khin Zaw, 1990; Khin Zaw et al., 2014b). It is now com-
monly referred to as the Western Myanmar Arc (WMA) or
Wuntho-Popa Arc (Mitchell, 1993; Mitchell et al., 2012; Wang
et al., 2014). It has long been considered as a Mesozoic to
Cenozoic subduction-related magmatic arc formed by prolonged
east-verging plate convergence (Mitchell, 1977, 1993; Bender,
1983; Khin Zaw, 1990; Mitchell et al., 2012; Win Swe, 2012;
Khin Zaw et al., 2014b; Wang et al., 2014). The magmatic rocks
of the WMA are superimposed on a basement of gneiss, mica
schist, phyllite, amphibolite and ophiolitic ultramafic rocks
(Mitchell, 1993; Pivnik et al., 1998). Similarities in age of the
WMA and Sumatra magmatic arcs, and their absence from the
intervening Andaman Sea, suggestthat the two arcs were continu-
ous in the late Cretaceous (Mitchell,1993).
However, the emplacement history of the late Neogene–
Quaternary volcanic arc of Myanmar is still not clearlyunderstood
(e.g., Hall, 2002). It is generally accepted that the recently active,
northeastward subduction of the India oceanic lithosphere has
resulted in development of a well-defined Wadati-Benioff zone
located at 100–140km beneath Mt. Popa and Monywa
(Guzman-Speziale and Ni, 1996; Satyabala, 1998; Maury et al.,
2004). The depth of the Wadati-Benioffzone below the
calc-alkalic and shoshonitic volcanoes of Mt. Popa and Monywa
is within the typical range for modern arcs and the magmas show
typical subduction-related geochemical signatures (Maury et al.,
2004). The CVL is characterized by high-level intrusions associated
with high-sulfidation Cu (Au) related younger volcanics, e.g.,
Monywa (Khin Zaw et al., 2014b). Recent 39
Ar–40
Ar dating of alu-
nite from Lepadaung at Monywa Cu deposit yielded 19.7 Ma
(Khin Zaw et al., 2014b), and of Mt. Popa yielded K–Ar ages of
0.96–0.80 Ma (Mauryet al., 2004) and 4.30 Ma (Cumming et al.,
2009).

Fig. 8. Geochemical discrimination diagrams for the volcaniclastic Pondaung sandstones. (A) Zr/TiO2 vs. Nb/Y (Winchester and Floyd, 1977) (B) Zr/Y vs. Zr (Pearce and Norry,
1979) (C) Rb vs. Y + Nb (Pearceet al., 1984). (D) Nb vs. Y (Pearceet al., 1984),suggesting that the volcaniclastic materials in the Pondaung sandstones were derived from calc-
alkaline, continental arc andesitic rocks.
However, depth-to-magnetic basement map and seismic
proﬁles of the Salin Sub-Basin in central Myanmar has identiﬁed
the NE–SW striking, basement-involved normal faults and tension
gashes that are coincided with the Mt. Popa and Monywa
volcanics, formed during the Miocene extensional deformation
period (Pivnik et al., 1998; Vigny et al., 2003; Bertrand and
Rangin, 2003). The late Miocene–Pleistocene regional uplift in
the eastern side of the Salin Sub-Basin, during the tectonic
inversion period, may have controlled the extrusion of volcanics
along the reactivated basement-involved normal faults
perpendicular to the NW–SE trending basin-center thrust faults
(Pivnik et al., 1998). It is probably related to the hyper-oblique
convergence of India alongthe western Myanmar;the northward
motion of India coupled with the BurmaPlate and collided with
Asia during Miocene–Quaternary, resulted in extensional to
transpressional deformations in Myanmar (Pivnik et al., 1998;
Ranginet al., 1999).
The northern segment of the arc, the Wuntho Massifand the
Salingyi area (Fig. 1A), contains Cretaceous to Eocene,
calc-alkaline, granodioritic plutons and andesitic volcanics
(United Nations, 1978a; Mitchell,1993; Barley et al., 2003),which
is located at about 100 km northeast of the studied area. Mitchell
(1993) reported that the Middle Cretaceous to early Palaeogene
granodioriticbatholiths intruded a thick, folded sequence of basal-
tic andesites and basalt pillow lavas (i.e., known as Mawgyi
Andesites) in the Banmaukarea of the Wuntho Massif.K–Ar and
SHRIMP zircon dating on the granitoids in the Kanzachaungand
Shangalon areas have yielded 94 Ma and 38 Ma, respectively
(Mitchell, 1993; Barley et al., 1996, 2003), representing the
Cenomanian and Lutetian stages of the middle Cretaceous and
middle Eocene, respectively. It is also suggestedthat the early- to
middle Eocene subduction in Myanmar is indicated by K–Ar ages
of 50.1 Ma on andesite and 52.9 Ma on quartz diorite from the
Shangalon Cu–Mo deposit, located to the south of Banmauk in
the Wuntho Massif area (United Nations, 1978a; Mitchell, 1993).
40
K–40
Ar dating on the granitoids of the Salingyi area gave 106–
91 Ma (United Nations, 1978b; Mitchell, 1993), corresponding to
the Albian to Cenomanian stages of the middle Cretaceous.
The Wuntho-Salingyi segment is also considered to have been
translated northward about 1100km, from its original position in
the Andaman Sea, along the right-lateral movement of Sagaing
Fault since the middle Miocene (Mitchell, 1977, 1993; Mitchell
et al., 2012). Results of isotopic dating of the granitoids and vol-
canic rocks of the Western Granitoid Belt of Khin Zaw (1990) or
the Western Myanmar Arc (WMA) of Mitchell et al. (2012) are
summarized in Table 6.
I-type granitoids found along the western margin of the
Shan-Thai (Sibumasu) Terrane, i.e., along the Mogok
Metamorphic Belt (MMB) and the Myeik (Mergui) Archipelago
(Tenasserim granitoids) in southern Myanmar,are part of the eco-
nomically important W–Sn related Central Granitoid Belt of
Myanmar (Khin Zaw, 1990; Barley et al., 2003), which also belongs
to the Western Granite Province(Peninsular–Thailand–Myanmar)
of Cobbinget al. (1992). The granitoids of this belt are of middle

Table 5
Detrital zircon U–Pb ages for the Pondaung sandstones.
206
Pb/238
U age
(Ma)
206
Pb/238
U 208
Pb/232
Th 207
Pb/206
Pb 207
Pb/235
USample no. Ti Hf Pb Th U Th/U
207
PbcorAnalysis no. ±1SE Ratio %rse Ratio %rse Ratio %rse Ratio %rse Ppm Ppm Ppm Ppm Ppm
1-(PD-21/6)
Fe01l6
Fe01l8
Fe01l12
Fe01l1
Fe01l10
Fe01l11
Fe01l9
Fe01l4
Fe01l7
Fe01l3
Fe01l5
Fe01l2
2-(PD-24/2)
Fe01j6
Fe01j5
Fe01j11
Fe01j10
Fe01j1
Fe01j9
Fe01j7
Fe01j12
Fe01j3
Fe01j2
Fe01j8
Fe01j4
3-(PD-1/5)
Fe01k11
Fe01k1
Fe01k3
Fe01k8
Fe01k10
Fe01k4
Fe01k6
Fe01k7
Fe01k9
Fe01k2
Fe01k12
Fe01k5
4-(PD-28/3)
Fe01m7
Fe01m3
Fe01m11
Fe01m9
Fe01m4
Fe01m8
Fe01m2
Fe01m12
Fe01m5
Fe01m1
Fe01m6
Fe01m10
5-(PD-28/9)
Fe01n10
Fe01n9
Fe01n3
Fe01n8
Fe01n6
Fe01n12
Fe01n11
Fe01n4
Fe01n5
Fe01n7
Fe01n1
Fe01n2
43.3
96.9
97.4
99.4
99.5
99.7
100.4
101.1
103.8
106.2
108.6
203.7
2.2
1.6
1.8
1.5
1.4
1.6
1.5
1.3
1.4
1.8
1.4
2.7
0.0068
0.0152
0.0153
0.0156
0.0156
0.0156
0.0157
0.0158
0.0162
0.0166
0.0170
0.0324
4.8
1.7
1.8
1.5
1.4
1.6
1.5
1.3
1.3
1.6
1.3
1.3
0.0020
0.0047
0.0042
0.0052
0.0047
0.0052
0.0049
0.0048
0.0055
0.0055
0.0063
0.0170
10.0
5.3
7.7
4.8
3.0
4.6
3.8
2.6
3.3
6.7
4.0
4.2
0.054
0.050
0.049
0.050
0.049
0.049
0.049
0.047
0.047
0.047
0.050
0.057
18.6
6.2
7.4
5.5
4.0
5.6
5.1
3.9
4.1
6.3
4.1
3.6
0.038
0.099
0.103
0.102
0.102
0.101
0.102
0.101
0.103
0.102
0.113
0.248
17.5
6.0
7.2
5.3
3.9
5.6
4.7
3.9
3.9
6.0
4.0
3.7
7.9
2.7
3.9
4.1
5.3
4.5
6.7
6.4
3.3
6.3
10.8
14.1
8803
12,468
11,318
11,075
10,553
11,673
10,614
11,798
11,300
11,383
12,274
12,337
1
3
2
3
7
3
5
9
7
3
7
13
110
76
51
90
330
93
148
314
206
43
116
86
107
218
139
218
427
221
304
528
451
168
389
385
1.0
0.3
0.4
0.4
0.8
0.4
0.5
0.6
0.5
0.3
0.3
0.2
46.9
74.1
81.7
83.8
87.7
88.5
89.0
92.3
99.8
107.0
117.5
842.6
1.2
1.2
1.2
1.4
1.9
1.7
1.1
1.5
2.3
2.3
1.5
8.8
0.0074
0.0116
0.0141
0.0131
0.0137
0.0139
0.0140
0.0144
0.0156
0.0166
0.0185
0.1398
2.5
1.6
1.3
1.6
2.1
1.8
1.2
1.6
2.2
2.2
1.3
1.1
0.0025
0.0035
0.0079
0.0044
0.0037
0.0044
0.0045
0.0039
0.0042
0.0055
0.0059
0.0476
7.0
4.4
2.5
3.9
6.4
3.5
3.0
4.3
6.2
6.7
2.9
2.4
0.053
0.051
0.125
0.050
0.049
0.051
0.053
0.049
0.050
0.043
0.052
0.068
9.2
5.8
2.9
6.6
8.4
6.5
3.7
5.7
9.6
8.6
3.9
2.1
0.048
0.077
0.236
0.090
0.087
0.090
0.096
0.095
0.099
0.090
0.125
1.285
8.3
5.7
2.9
6.5
8.3
6.2
3.6
5.4
9.1
8.3
3.9
2.1
6.4
7.7
54.5
10.7
5.1
15.4
4.9
7.1
9.6
7.8
7.0
7.8
11,242
10,898
11,076
10,658
11,417
10,811
12,003
11,001
10,104
8966
10,855
9941
1
3
7
3
2
3
8
4
1
1
6
22
73
137
283
146
45
148
291
174
46
35
190
54
174
272
395
162
111
172
512
238
73
86
308
153
0.4
0.5
0.7
0.9
0.4
0.9
0.6
0.7
0.6
0.4
0.6
0.4
47.2
47.2
48.3
49.5
98.2
98.6
99.1
99.5
100.5
100.7
102.4
503.0
1.0
1.1
0.8
1.1
2.1
1.4
1.5
1.9
1.7
1.9
1.5
4.5
0.0074
0.0075
0.0076
0.0077
0.0156
0.0154
0.0155
0.0156
0.0157
0.0159
0.0160
0.0817
2.0
2.3
1.7
2.2
2.1
1.4
1.4
1.9
1.7
1.9
1.4
0.9
0.0024
0.0020
0.0023
0.0020
0.0053
0.0049
0.0052
0.0048
0.0050
0.0043
0.0052
0.0236
7.2
8.9
3.9
6.8
5.5
3.7
5.6
7.1
6.0
5.9
4.7
2.6
0.053
0.060
0.051
0.049
0.062
0.047
0.051
0.050
0.048
0.054
0.048
0.062
7.4
9.7
5.5
8.6
6.0
5.0
5.2
8.8
6.0
6.0
4.7
1.6
0.052
0.059
0.050
0.048
0.125
0.093
0.102
0.100
0.097
0.112
0.102
0.682
7.6
9.1
5.1
8.3
6.4
5.0
4.9
8.1
6.0
5.9
4.5
1.6
7.7
3.2
8.6
7.4
17.0
6.3
5.8
9.5
5.4
5.7
5.9
11.3
11,030
10,520
9637
10,738
12,737
10,577
12,677
10,932
12,757
9481
13,236
14,549
2
1
3
2
6
5
4
2
3
2
5
58
102
57
289
123
220
152
65
48
70
53
102
88
237
130
402
202
408
347
284
127
222
135
324
745
0.4
0.4
0.7
0.6
0.5
0.4
0.2
0.4
0.3
0.4
0.3
0.1
51.6
66.9
67.6
99.7
101.2
101.4
101.5
101.6
103.1
103.5
173.4
628.1
1.0
1.1
0.9
1.4
1.6
1.2
1.8
1.5
1.4
1.7
3.9
6.4
0.0081
0.0105
0.0106
0.0156
0.0159
0.0159
0.0158
0.0159
0.0161
0.0163
0.0273
0.1023
1.8
1.6
1.3
1.4
1.6
1.2
1.8
1.5
1.3
1.6
2.2
1.0
0.0026
0.0036
0.0033
0.0048
0.0052
0.0052
0.0049
0.0048
0.0053
0.0048
0.0095
0.0309
3.8
4.9
2.6
4.1
3.8
2.8
6.4
5.1
2.5
4.4
6.8
2.1
0.052
0.056
0.050
0.049
0.049
0.049
0.045
0.048
0.049
0.053
0.051
0.060
7.1
5.8
3.6
4.4
5.5
3.1
7.0
5.2
4.6
5.7
7.5
2.0
0.055
0.077
0.071
0.101
0.104
0.104
0.090
0.101
0.103
0.116
0.188
0.821
6.7
5.6
3.6
4.5
5.4
3.2
6.6
5.1
4.4
5.6
7.5
1.9
9.5
14.9
2.8
4.6
7.1
4.7
5.0
3.8
5.6
5.8
5.2
7.7
9378
9950
10,713
12,630
9391
12,118
11,522
12,943
10,717
10,854
10,202
10,740
2
3
9
4
3
8
2
4
6
3
2
23
279
95
604
113
132
218
43
81
321
60
21
82
260
241
754
250
193
521
140
249
335
168
61
229
1.1
0.4
0.8
0.5
0.7
0.4
0.3
0.3
1.0
0.4
0.4
0.4
65.1
78.9
80.9
81.8
97.7
99.1
100.7
132.1
218.4
436.0
487.3
1062.2
1.6
1.4
2.0
1.6
1.4
1.3
1.5
5.4
2.2
4.1
4.3
10.9
0.0103
0.0123
0.0128
0.0128
0.0152
0.0154
0.0158
0.0208
0.0344
0.0700
0.0787
0.1797
2.4
1.8
2.3
1.9
1.4
1.3
1.5
4.1
1.0
1.0
0.9
1.0
0.0032
0.0038
0.0041
0.0035
0.0048
0.0050
0.0047
0.0066
0.0107
0.0216
0.0228
0.0526
6.4
5.7
5.9
6.8
4.1
3.3
4.5
5.9
1.6
2.5
1.5
1.8
0.055
0.046
0.056
0.047
0.046
0.046
0.052
0.052
0.050
0.055
0.059
0.077
8.6
6.1
9.3
7.9
4.9
4.2
5.4
4.6
2.3
1.8
1.6
1.7
0.069
0.077
0.091
0.078
0.092
0.096
0.107
0.152
0.229
0.513
0.613
1.852
8.5
6.2
8.8
7.7
4.9
4.1
5.5
7.5
2.3
1.8
1.6
1.8
4.5
33.3
8.8
4.9
7.9
6.1
3.8
6.5
4.9
0.6
8.8
10.3
9526
10,526
10,647
12,851
11,319
11,851
11,113
10,488
12,472
13,897
9990
10,525
1
2
1
2
5
6
3
5
23
35
45
29
61
77
59
69
124
161
102
130
518
80
423
95
110
198
85
147
317
360
222
268
614
538
535
149
0.6
0.4
0.7
0.5
0.4
0.4
0.5
0.5
0.8
0.1
0.8
0.6
Numbers in bold were used for age calculations.
SE: Standard Error.
207
Pbcor: 207
Pb corrected 206
Pb/238
U age.

Fig. 9. Concordia diagrams (238
U/206
Pb–207
Pb/206
Pb) of the detrital zircons from Pondaung sandstones, southern Chindwin Basin (sample locations are shown in Fig. 1B). (A)
Sample no. 1-(PD-21/6)collected from the uppermost horizon of the lowermember of Pondaung Formation (22 030
29.000
N, 94 340
1.200
E). (B) Sample no. 2-(PD-24/2)collected
fromthe uppermost part of the lowermember of the Pondaung Formation(22 020
11.000
N, 94 280
27.000
E). (C) Sample no. 3-(PD-1/5)collected from the middle part of the lower
member of the Pondaung Formation(22 050
24.200
N, 94 270
22.700
E). (D) Sample no. 4-(PD-28/3)collected from the lower part of the lowermember of the PondaungFormation
(22 050
28.100
N, 94 270
14.500
E). (E) Sample no. 5-(PD-28/9)collected from the lowermost part of the lower member of the Pondaung Formation(22 050
24.200
N, 94 260
59.700
E).
(F) Concordia diagram for all zircon grains from the ﬁve samples gives 47.75 ± 0.87 Ma, the early Eocene(Lutetian).
Cretaceous to the earliest Eocene age (120–50 Ma). LA ICP-MS
U–Pb dating of zircon inclusions in a Mogok ruby gave ages of
31–32 Ma (Khin Zaw et al., 2015). Larue Kyaw Thu (2007) also
dated leucocratic granite intrusions at Mogok using U–Pb zircon
method and yielded ages of 45 and 25 Ma. It is suggested that
prior to the India–Asia collision, an up to 200 km wide
subduction-related magmatic belt (i.e., Trans-Himalayan Arc and
Lhasa Terrane) was extending along the southern Eurasian conti-
nental margin from Pakistan, India, Tibet and Nepal through
Myanmar to Sumatra (Mitchell, 1993; Barley et al., 2003; Searle
et al., 2007, 2012; Mitchell et al., 2012). In fact, Khin Zaw (1990)
ﬁrst speculated the subduction-related arc and back arc basin to

Fig. 10. (A and B) Detrital zircon U–Pb and Hf isotope study of the late Cretaceous–Eocenesamples from the western part of Chindwin Basin (after Wang et al., 2014). (C)
Detrital zircon U–Pbanalysis of the late Middle Eocenesamples from the southern Chindwin (this study). (D) Cathodoluminescence (CL) images of the Pondaungzircons.Note
that the unroofinghistory of the late Cretaceousto Middle Eocenelocal magmatic arc is supported by similar characteristic peaks of U–Pbzircon ages in Wang et al. (2014)
and the present study.
collisional setting along the western margin of MMB as early as
Jurassic based on the distribution and geochemistry of volcanic
and magmatic rocks. This interpretation is later supported by
170 Ma SHRIMP U–Pb age of zircon in orthogneisses near
Mandalay (Barley et al., 2003) suggesting an Andean type
convergent pate margin. Isotopic dating results of the MMB
granitoids are summarized in Table 7.
In the southernpart of the studied area, volcanictuffs and tuffa-
ceous beds are found in the upper member of the Pondaung
Formation, exposed mainly in the Asian anthropoid
primate-bearing locations (i.e., Paukkaung and Bahin villages
located in the northeastern MinbuBasin). Zircon fission-track dat-
ing obtained from a tuffaceous bed gave 37.2 Ma and 38.8 Ma, rep-
resenting the Bartonian Stage of the late Middle Eocene
(Tsubamotoet al., 2002, 2009). Khin Zaw et al. (2014a) recently
reported new LA-ICP-MS U–Pb ages of zirconsfrom the same tuffa-
ceous bed, which yielded 40.31Ma and 40.22Ma. Published and
our new radiometricdata are compiledand summarized in Table 8.
However, published data of the geochemistry and geochronol-
ogy of the granitoids and volcanicrocks in the Wuntho-Massifarea
are too limited to provide a complete history of the
subduction-related, older magmatic arc of Myanmar. The geody-
namics of the India–Asia Collisionproject (GIAC, 1999) suggested
that the Shan volcanic arc may have been built on the Shan
Plateau before 53 Ma, as a result of subduction of the Neo-Tethys
seafloor along the Sundaland active margin (Fig. 12). The arc may
have been destroyed during the early- to middle Eocene (53–
43 Ma) when the western depocenter of the Central Myanmar
Basin was initiated, and the Shan Plateau deformed by crustal
thickening, followed by crustal relaxation due to a change in con-
vergence direction of the Indian Plate from NE to N with respectto
Sundaland (GIAC, 1999). This deformation is also recorded in the
Jurassiczircons that have been partly recrystallized with metamor-
phic overgrowths in the orthogneisses from near Mandalay, which
recorded a period of high-grade metamorphism in the middle
Eocene (i.e., U–Pb zircon age: 43 Ma) (Barleyet al., 2003; Searle
et al., 2007; Mitchellet al., 2012).
5.2. Composition, erosion and weathering condition in source area
Significantchanges in sandstone petrofaciesand gradual transi-
tion of provenances between the Pondaungsandstones and the
Yaw sandstones have clearly demonstrated either a volcanicto
plutonic change in source area or unroofing of a volcanic arc down
to deeper plutons (e.g., Dickinson and Suczek,1979). The apparent
increase in the relative amount of K-feldspar and a significant
decrease in the amount of arc-derived components in the Yaw
sandstones, also indicate that erosion had depleted the volcanics
in the source area. The observed petrofacieschanges from the
Pondaung sandstones to the Yaw sandstones are also consistent
with a major sequence boundary between the underlying
Pondaung Formation and the overlying Yaw Formation (Fig. 2B,
Table 1). This supports a break in sedimentation that may have
attributed to change in source rock composition.
The inferred magmatic arc can be correlated with granitoids
and volcanicrocks found around the Wuntho-Massif and Salingyi

PO, MSB: Pondaung sandstone, Minbu Sub-Basin
(tuffaceous sandstones)
(a)
(b)
(c)
(d)
(e)
(f)
United Na ons (1978)
Khin Zaw (1990)
Tsubamoto et al. (2002, 2009)
Shi et al. (2012)
Mitchell et al. (2012)
Khin Zaw et al. (2014a)
HSB:
CSB:
WTM:
SLG:
MPL:
Hukaung Sub-Basin (volcaniclas c sandstones)
Chindwin Sub-Basin (volcaniclas c sandstones)
Wuntho-Massif (andesite, granodiorite, diorite)
Salingyi diorites
Mokpalin diorites
Fig. 11. Geochronologyand tectonic evolution of the magmatic arcs in Myanmar (modified after Mitchellet al., 2012) with U–Pbdetrital zircon age data of the present study.
area (Table 6), and the I-type granitoids in the MMB (e.g., the
Mokpalin and Sit-Kinsindiorites, Table 7) having a similar isotopic
fingerprints of the Gangdesebatholiths in Tibet (Fig. 11). In addi-
tion, low- to medium-grade metamorphic lithic fragments of con-
tinental margin source are commonly found in the Myanmar
basement terrane (i.e., MMB and JMB shown in Fig. 1A), but are
rarely exposed in the Tibetan Lhasa Terrane (Licht et al., 2013).
Licht et al. (2015a) reject any dramatic provenance shift during
the Middle Eoceneand Pleistocene period in the CMB, but support
a gradual decreasing trend of the volcanicinput and its replace-
ment by a dominant supply from the Myanmarbasement terrane.
The trend is consistentwith the local unroofing of an Andean-type
cordillera (Garzanti and Ando, 2007) that extended onto the
Myanmar continental margin along the flank of the Shan Plateau
(i.e., the MMB at the western foothills of the Shan-Thai or
SibumasuTerrane)where most of the post-collisionaldeformation
of the CMB is located (Licht et al., 2015a). The arc may have been
progressively eroded during the middle Eocene,and experienced
an episode of uplift (e.g., Morley, 2004; Barley et al., 2003; Allen
et al., 2008).
The Pondaung sandstones were likely to have derived from a
tectonically active provenance, such as an active continental arc,
where high relief of uplifted volcano-plutonic and metamorphic
rocks produce fresh or less altered first cycled sediments. During
the middle- to late Eocene, rates of deposition were high
(Metivieret al., 1999; Licht et al., 2013), and the thick sequences

Table 6
Summary of age data of the volcanic and granitoid rocks of Western Myanmar Arc (WMA).
Areas or provinces Sample Method Age (Ma) Geochemistry/tectonicenvironment References
Jade Mine Belt
(JMB)
Jadeitite U–Pb zircon 122.2 ± 4.8
146.5 ± 3.4
163 ± 3.3
Quaternary
– Shi et al. (2009)
Taungthonlon Andesite (hypersthene–
augite–hornblende
Andesite)
Biotite–hornblende,
Granodiorite, Hornblende–
biotite granodiorite
Leucocratic biotite–
hornblende granite
Leucocratic biotite–
hornblende granite
Tonaliteporphyry
Vesicular plagiophyric
epidotised Andesite,
Alteredquartz diorite
Granodiorite
Granodiorite
Feldsparphyric andesite;
flow/dyke
Basalt
– Shoshonitic Stephenson and Marshall
(1984), Maury et al. (2004),
Mitchellet al. (2007)
United Nations (1978a)Wuntho-Massif
Banmauk
K/Ar
Biotite
93.7 ± 3.4
97.8 ± 3.6
–
87
Rb–86
SrKanzachaung
Batholith
90 ± 78 Low Rb/Sr, I-type Darbyshire and Swainbank
(1988)
Barleyet al. (1996, 2003)SHRIMP U–Pbzircon 94.3 ± 1 –
Shangalon Cu–Mo
deposit
K/Ar, Biotite
K/Ar, whole rock
K/Ar, Muscovite
37.9 ± 1.4
50.1 ± 2.5
52.9 ± 2
- United Nations (1978a)
Darbyshire and Swainbank
(1988)
Barleyet al. (1996, 2003)
87
Rb-86
Sr
SHRIMP U–Pb
K/Ar, whole rock
110 ± 63
38.5 ± 0.6
70.7 ± 4.2
Low Rb/Sr, I-type
–Mawgyi Andesite United Nations (1978a)
40
K/40
ArMonywa
Twin Taung
Sabetaung
0.44 ± 0.12 Shoshonitic lavas, low degree melting of
a subduction modified mantle
–
–
Mauryet al. (2004)
Andesite porphyry
Andesite, quartz andesite
and dacitic porphyry
Alunite
Granites
Diorites
Gabbros
Diorite
K/Ar
U–Pb zircon
5.8
13.6 ± 0.1
Kyaw Win and Kirwin (1998)
Lepadaung
Salingyi
Ar/Ar
K/Ar
19.7
103 ± 4
106 ± 7
91 ± 8
105 ± 1.7
–
I-type, Magmatic–volcanic arc,
subduction related
Khin Zaw et al. (2014b)
United Nations (1978b)
Low 87
Sr/86
Sr, High eNd(T) value; Juvenile
mantle origin
High K calc-alkaline, mantle-derived,
continental margin orogenic
environment, subduction related
–
U–Pb zircon Mitchellet al. (2012)
40
K/40
ArMt. Popa Basaltic andesite
Basalt
0.96 ± 0.17
0.80 ± 0.03
Stephenson and Marshall
(1984),Maury et al. (2004)
Hornblende-phyric basaltic
andesite
K/Ar 4.30 ± 0.5 Cumming et al. (2009)
of the Pondaungand Yaw formations represent a significant pro-
portion of the Palaeogene sediments deposited in the Central
Myanmar Basin (United Nations, 1978c; Licht et al., 2013). A thick
sequence of fluvialsediments implies rapid uplift and denudation
in the source area, and also suggests a rapid sedimentation rate
in a subsiding basin. Sourceareas undergoingrapid uplift may gen-
erate large volumes of coarse-grained clastic sediments, with the
development of high-gradient braided or low-sinuosity channel
systems, within the upstream portion of the drainage basin (Cant
and Walker, 1978).
We also take into account the significant effect of tropical
weathering on sandstone composition in provenance study of
the Southeast Asian region, which had attributed to the
compositional maturity in the Eocene sandstones of northern
Borneo (van Hattum et al., 2013). However, geochemical
characteristics of the Pondaungsandstones reflected that there
was no evidence of intense tropical weathering in either of
their original source rocks, during transportation or before
deposition. The low maturity index of the sandstones (ICV),
moderate degree of chemical weathering (CIA), moderate
alteration of plagioclase feldspar in the source rocks (PIA) and
the plot of chemical maturity as a function of climate all
suggest that the Pondaung sandstones were formed under
semi-arid to arid palaeoclimate condition. A seasonal tropical
climate with a significant dry season, prevailed in the late
middle Eocene of Myanmar (Licht et al., 2015b), is further
corroborated by the evidence of faunal and floral assemblages
(Ramdarshan et al., 2010; Licht et al., 2014a), growth arrest
lines in lower jaws of mammalian fossils (Jaeger et al., 2004)
and palaeosoils with carbonate nodules, together with shrinking
and swelling pedogenic features observed in the upper member
of the Pondaung Formation (Licht et al., 2014b).
5.3. Detrital zircon U–Pb geochronology
As the detrital zircons were separated from sedimentary rocks,
deposition age of the host sediment can be no older than the
youngest U–Pb age of the detrital zircons in this study (i.e.,
43.3 ± 4.4 Ma) (Dickinsonand Gehrels, 2009). Several complexities
can result in measured U–Pb dates that are younger than the true
age of deposition due to analytical uncertainties, e.g., Pb loss is one
of the main issuesin many data sets (Gehrels,2014). However, the
present study shows a good correlation between the measured
ages and the stratigraphic positions,i.e., the youngest U–Pb zircon

Table 7
Summary of age data of the granitoids along the MogokMetamorphic Belt (MMB).
Areas or provinces Sample Method Ma Geochemistry/tectonicenvironment References
Mogok Augite–biotite granite,
Leucogranite, Foliated
syenite
Granitic orthogneisses,
Metamorphic
recrystallized zircon
rims
Biotitegranite
Garnet–tourmaline–
leucogranites
LA ICP-MS U–Pb
zircon
129 ± 8.2
32 ± 1
25
170.11 ± 1.09
Calc-alkaline; continental collision
granite (CCG)
Larue Kyaw Thu (2007)
(Unpublished)
Kyanigan Hills SHRIMP U–Pb zircon I-type Barleyet al. (2003)
U–Th–Pb
LA-ICP-MS
(43.37 ± 0.80)
(ca. 59
47–29)
45.5 ± 0.6
171.71 ± 2.05
(47.25 ± 1.28)
33.11 ± 0.93
30.9 ± 0.7)
46.3
114 ± 3
45.9 ± 0.7
44.6 ± 0.5
45.9
59.5 ± 0.9
44.8 ± 2.7
149 ± 21
High-grade metamorphism
Twometamorphic events Searleet al. (2007)
zircon
SHRIMP U–Pb zircon
Syn-metamorphic crustal melting
I-type
High-grade metamorphism
Mandalay Hill Hornblende syenite
Metamorphic
recrystallized zircon
rims
Leucogranite dyke
Augen gneiss,
Pegmatitic granites,
Microdiorite,
Leucogranite dyke
Granite dyke
Granite
Tonalite and
granodiorite
Hornblende–biotite
granodiorite
Granite porphyry
Dacite porphyry
Diorite
Barleyet al. (2003)
Kyaukse
Belin
U–Pb zircon
U–Pb zircon
–
–
Searleet al. (2007)
MEC Granite, North
of Belin
Yebokson
U–Th–Pb zircon
U–Pb zircon
Rb/Sr whole rock
isochron
SHRIMP
U–Pb zircon
–
–
I-type, tonalite–granodiorite, related to
subduction of oceaniccrust
–
Searleet al. (2007)
Cobbing et al. (1992)
121.1 ± 0.9 Barleyet al. (2003)
Payangazu 122 ± 0.2
50 ± 0.6
20.7 ± 0.3
20.7 ± 0.5
128 ± 1
71.8 ± 0.5
48.0 ± 0.9
22 ± 7
Continental crust components
(Sr & Nd isotopes)
Yinmabin-west U–Pb zircon
Nattaung, Sedo Granite U–Pb zircon – Mitchellet al. (2012)
Yesin Dam Magacrystic biotite
syenogranites
Leucocratic biotite
syenogranite
Quartz diorite
Granite
Rb/Sr whole rock
isochron age
SHRIMP
U–Pb zircon
U–Pb zircon
Strongly peraluminous, ilmenite-series,
potassic syenogranites
–
Cobbing et al. (1992)
22.64 ± 0.4 Barleyet al. (2003)
Low 87
Sr/86
Sr, juvenile mantle origin,
Gangdese affinity
Mokpalin, Sit-Kisin,
Kyaikhtiyo
90.8 ± 0.8
63.3 ± 0.6
The range of dating data which are in the rage of Cretaceous-Eoceneare in bold.
ages decrease progressively up-section throughout the lower
member of the Pondaung Formation (Table 8), which suggest a
record of active volcanism during sediment accumulation (e.g.,
Gehrels, 2014).
The detrital U–Pb zircon ages suggest that there were two dis-
tinct episodes of magmatism in Myanmar, during the middle
Cretaceous and the middle Eocene,which also correspond to the
two major tectono-magmatic events as recently proposed by
Mitchellet al. (2012); (1) arc magmatism in Shan Scarps during
Middle- to late Cretaceous, and (2) arc magmatism in
Wuntho-Popa arc (i.e., mainly in Wuntho-Salingyi segment of the
arc) due to the eastward subduction of the Tethys seafloor
(Figs. 11 and 12).
Detrital U–Pb zircon geochronology alone cannot distinguish
the zirconswith similarages derived from different source regions.
More detrital zircon Hf isotope studies need to be carried out to
establish such distinctions (e.g., Belousovaet al., 2006; Clements
et al., 2012) in Myanmar. Although such detailed geochronology,
geochemistry and isotope studies on the volcanic and granitic
rocks of the Wuntho-Salingyi area, and detrital zircons from clastic
Cenozoic strata in the Central Myanmar Basin are required for
future research,our findingis further supported by Hf isotopic data
of detrital zircons of Wanget al. (2014) for the UpperCretaceous–
Eocene stratigraphic units in the western part of Chindwin Basin
which is correlative to the Gangdesearc in Tibet (Fig. 10B).
5.4. Regional mean palaeocurrent data
The results of petrography, geochemistry and geochronology,
combined with the regional mean palaeocurrent direction (i.e.,
253 530
, from ENE to WSW) recorded from the Pondaung and
Yaw formations (Kyaw Linn Oo, 2008) indicate that a
calc-alkaline,continental magmatic arc was situated to the north-
east of the southern ChindwinBasin in the present geographicref-
erence frame. Licht et al. (2013) also described the mean
palaeocurrent direction of the two stratigraphic units, exposed in
the northeast of Minbu Sub-Basin, as unimodal direction toward
243 and 257 .

Table 8
Geochronologicaldata of the volcaniclastic and sedimentary units of the Central Myanmar Basin, the youngest detrital U–Pb zircon ages of the present study decrease progressively upsection, a record of active volcanism during
sediment accumulation in the early Paleocene–middle Eocene.
Location Sample Method Ma Remarks Geochemistry/tectonic
environment
References
Positive eHf(T), juvenile mantle
origin
Positive eHf(T), juvenile mantle
origin
Hukaung Basin Amber (Burmite)-bearing volcaniclastic
fine silty sandstone
Late Cretaceous–Eocene sandstones
SIMS U–
Pb zircon
U–Pb
zircon Hf
isotope
Fission
Track
zircon
LA ICP-MS
U–Pb
zircon
LA ICP-MS
U–Pb
zircon
98.79 ± 0.62 Dacite–Andesitic
clasts
Volcanic clasts in
sandstones
Shi et al. (2012)
NW Chindwin
Basin
110–80, 70–
40
Wang et al. (2014)
NE of Minbu
Basin,
(Primate
localities)
Upper member of the Pondaung Fm. 37.2 ± 1.3 Andesitic arc Tsubamotoet al. (2002, 2009)
Tuff beds in variegated clay unit 38.8 ± 1.4
40.22 ± 0.86
40.31 ± 0.65
43.3 ± 4.4
99.5 ± 1.1
Khin Zaw et al. (2014a)
Southern
Chindwin
Basin
Lowermember of the Pondaung Fm.
Detrital zircons in volcaniclastic
sandstones
1 – (PD-21/6) Andesite–rhyodacite–dacite, calc-
alkaline, continental, volcano-
plutonic arc
Present study
Youngest zircon ages and Major detrital peaks for each
sandstone sample, collected in stratigraphic order from the
lower to upper horizons from sample no. 5 to 1
The youngest U–Pb zircon ages decrease progressively
upsection
46.9 ± 2.4
88.6 ± 1.6
46.9 ± 2.4
100.0 ± 1.2
51.6 ± 2.0
101.7 ± 1.1
65.1 ± 1.6
80.4 ± 1.8
2 – (PD-24/2)
3 – (PD-1/5)
4 – (PD-28/3)
5 – (PD-28/9)
47.75 ± 0.87 Mean U–Pb age
of all five
samples
The major localities are in bold.
KyawLinnOoetal./JournalofAsianEarthSciencesxxx(2015)xxx–xxx19
Please
cite
this
article
in
press
as:
Kyaw
Linn
Oo,,
etal.
Provenance
of
the
Eocene
sandstones
in
the
southern
Chindwin
Basin,Myanmar:
Implications
for
the
unroofing
history

Fig. 12. Schematic diagram (Left) illustrating the geochronology and erosional unroofing history of the Cretaceous–Eocene,magmatic arc formed along the SW-facing
Myanmar continental margin. The schematic map (Right)showing sediment supply from the unroofed Myanmar magmatic arc during the deposition of the Pondaungand
Yaw formations in the middle–late Eocene(after Licht et al., 2013). ITSZ, Indus-Tsangpo Suture Zone; CMB, Central Myanmar Basin, TSS, Tethyan Sedimentary Series; IBR,
Indo-Burman Ranges.
yielded 98.79 Ma, indicating late Cretaceous volcanic activities
occurred in the vicinity of the Hukaung Basin, in the northernmost part of
Myanmar (Shi et al., 2012). U–Pb and eHf isotope analyses of
Robinson et al. (2014) demonstrated that the Middle- to Upper Eocene
sedimentary rocks of the Central Myanmar Basin contain zircons
originating from the Gangdese batholiths of Tibet. Zircons
of similar ages and isotopic signatures are common in the eastern
Trans-Himalayan batholiths from southern Tibet through north-
eastern India to the Western MyanmarArc in Myanmar.
Our current findings support the hypothesis that the Upper
Cretaceous to Eocene deposits (i.e., including Pondaung and Yaw
formations) of the CentralMyanmarBasin may have been derived
from the progressive exhumation and erosional unroofing of the
local Myanmar Andean-typecontinental margin, rather than from
the distal Tibetan region.
6. Conclusions
Our integrated detrital provenance study, focused on the
Middle to Upper Eocene fluvio-deltaic sandstones in the southern
Chindwin Basin of Myanmar, has recorded an erosional unroofing
history of a late Cretaceous to middle Eocene, calc-alkaline,
Andean-type, continental magmatic arc, related to the prolonged,
pre-collisional subduction of Neo-Tethyan oceanic crust beneath
the south Asian margin within Myanmar (Fig. 12). The andesitic
volcanicmaterials and the first-cycled magmatic detrital zircons,
observed in the late Middle Eocene Pondaung sandstones, were
probably derived from the Wuntho-Salingyi segment of the
Western Myanmar Arc (WMA), and some contributionfrom the
I-type plutons of the MMB with similar ages and geochemical sig-
natures to the Gangdesebatholiths in Tibet and Lohit batholiths in
northeastern India (Lin et al., 2013).
Based on the youngest U–Pb detrital zircon ages of the
Pondaung Formation in the Central Myanmar Basin, we suggest
that the latest magmatic activities of the inferred magmatic arc
must have occurred during the late middle Eocene (ca. 40.22–
37.2 Ma). It is also constrained by the distinct petrofacieschanges
occurredat a majorsequenceboundarybetween the late Bartonian
and the early Priabonianstages (Bar 2/Pr 1 at 37.2 ± 0.1 Ma).
This arc originated along the western margin of Shan-Thai or
Sibumasu Terrane (i.e., along the MMB) during the late
Cretaceous and the middle Eocene(Our U–Pb detrital zircon ages:
101.7–43.3 Ma). It is also evident from minor contribution of
Proterozoic to Palaeozoic detrital zircons of Sibumasu origin.
Most parts of the arc were eroded, unroofed and probably
translated northwards from the Andaman sea region to the
present position (i.e., Wuntho-Salingyi segment of the Western
Myanmar Arc) by dextral movement of the SagaingFault during
the Miocene.
In-situ Hf and U–Pb isotope analyses of detrital zircons from the
Irrawaddy riverbank sediments (Bodet and Schärer, 2000) and
from an Upper Miocene sandstone of the Central Myanmar Basin
(Liang et al., 2008) have recorded the late Cretaceous and
Palaeogene zircons with high eHf(T) isotope values, a characteristic
of mantle-derived magmas similar to those of the Gangdesebath-
oliths in southeastern Tibet and the Lohit batholiths in northeast-
ern India. U–Pb dating of magmaticzircons recoveredfrom the
burmite-bearing (Burmese amber) volcaniclastic sandstones
Acknowledgements
This work is a part of the first author’sPhD dissertationsubmit-
ted to the Departmentof Geology, University of Yangon, Myanmar
in 2008. The first author owes his gratitude to his parents and wife
for their financial and moral supports and all his supervisors and
colleagues, including Prof. Aung Naing Soe (Mandalay University
of Foreign Language) for his advice in selecting the field area for
the PhD research, Aung Cho Win (University of Yangon) for assist-
ing throughout the one-month field trip, U Soe Thura Tun
(Myanmar Earthquake Committee and Myanmar Geosciences
Society), U Zaw Naing Oo and U Kyaw Zin Win (Resourcesand
Environment Myanmar Company Limited) for their assistance in
preparing the geological maps and re-drafting the diagrams.
Special thanks are also extended to the ARC Centre of Excellence
in Ore Deposits (CODES), University of Tasmania for sponsoring
the geochemicaland LA ICP-MS U–Pb geochronological analyses.
The authors are also deeply indebted to the reviewers,A.J. Barber
and I. Sevastjanova for their constructive comments and Ian
Metcalfe for his editorial input and handling the paper.
Appendix A. Supplementary material
Supplementarydata associatedwith this articlecan be found, in
the online version, at http://dx.doi.org/10.1016/j.jseaes.2015.04.
029.

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