Geology of Gilgit-Hunza (Field report )

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Geology of Gilgit-Hunza
(Field Report)
Submitted by:
Umair Ali
Reg. No. 2013-KIU-199
Semester 7th
Earth Science
Karakoram International University,

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Gilgit- Baltistan
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D To My dear parents and respectable
teachers. May ALLAH fulfill their life with happiness and give us ability
to live up their expectations. (Ameen)

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Acknowledgement
All the praise to Almighty ALLAH, the Merciful,the Kind and every Grace
of ALLAH to be on the last prophet MUHAMMAD(peace be upon him)
who is an everlasting source ofguidance and knowledge for the whole
mankind in the entire world.
I wishto express my heartfelt thank to the Chairman, Prof.Dr. Haleem
Zaman Magsi who not only managed and provided us all the required
facilities but also his expert guidance, personal interest,sympathetic
attitude always encouragedduring the course of study.
Our deepest appreciation and profound thanks go to extremely patient,
very friendly and most co-operative attitude of our Teacher Sir Asad Ul
Rehmanand Sir Chirag UD din Lecturer,Department of Earth Science
Karakorum International University,Gilgit Balistan
I am very thankful to my parents to pray for the success of me. I am also
very thankful to all other members of my family those support me at
every step of life. I shall be discourteous if I don’t utter a few words of
thanks to my seniors and friends who prayed for me.
Umair ali

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Table of contents
1-Abstract 5
2-Introduction 6
Tectono- Stratigraphy of Gilgit-HunzaArea
Station 1: KohistanBatholith 8
Station 2: ChaltVolcanics 10
Station 3: Yasingroup 11
Station 4: MainKarakoram Thrust 12
Station 5: SouthernMetamorphic complex 13
Station 6: Karakoram Axial Batholith 14
Station7: PassuSlate 15
Station 8: Gojal Dolomite 17
Reference 19

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Abstract.
The Kohistan arc terrene comprises an intra- oceanic island arc of Cretaceous age
separating the Indian plate to the south of the Karakoram(Asian) plateto the
north within the Indus suturezoneof north Pakistan. The intra-oceanic arc
volcanic (Chalt, Dras Group) werebuilt on a foundation of dominantly mid-ocean
ridge basalt (MORB) related amphibolites of the Kamila Group. The sub arc
magma chamber is represented by multiple intrusions of a huge gabbro-norite
complex (Chilas complex), which includes someultramafic assemblages of
residualmantle harzburgiteand dunite,layered cumulates, and hornblendites cut
by late stage dikes of hornblende + plagioclasepegmatites.The Chilas complex
norites intrude the Gilgit met sediments of lower amphibolites and green schist
facies in northern Kohistan, which also formxenolithic roof pendants within the
top of the Chilas complex. Along the southern margin of Kohistan, Jijal and Sapat
complex ultramafics (dunites, harzburgites and websterites) formremnants
uprasubduction zoneophiolitic mantle rocks along the hanging wall of the Main
Mantle Thrust, the Cretaceous abduction plane along which Kohistan was
emplaced onto Indian plate rocks. Garnetgranulites of the Jijal complex formed at
12-14 kbars representoriginalmagmatic lower crustalrocks sub ducted to depths
of at least 45 kmand metamorphosed during high- pressureand high-
temperature subduction of earlier arc- related rocks. Obduction of the Sapato
phiolite and Kohistan arc occurred between 75 and 55 Ma. The closureof the
Shyok suturezoneseparating Kohistan fromthe Karakoramplate must have
occurred prior to 75 Ma, the age of the Jutal basic dikes which crosscuthe
closure- related fabrics, mainly late north directed back thrusting in the lower
Hunza valley. Andean-type granitoid (gabbro- diorite-granodiorite-granite)
emplacement along the Kohistan-Ladakh batholith ended at the time of India-Asia
collision 60-50 Myear ago. Postcollisionalcrustal thickening along the Karakoram
led to multiple episodes of metamorphismfromlatest Cretaceous and throughout

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the Tertiary. Sillimanite grade metamorphismin Hunza was actually pre-India-Asia
collision and may have resulted fromthe earlier Kohistan collision. Localized and
sporadic crustalmelting episodes across northern Kohistan (Indus confluenceand
Parrigranite sheets) and the southern Karakoram(Hunza dikes and Sumayar and
Mango Gusar leucogranites) occurred from51 to 9 Ma and culminated in the
huge Baltoro monzogranite-leucograniteintrusion 25-21 Myear ago. A vast
network of leucogranitic and pegmatitite dikes containing gem quality
aquamarine + muscovitetourmaline garnet biotite quartz areyounger than 5 Ma
and formthe final phaseof intrusion in the Haramosh area and parts of the
southern Karakoramarea.
1. Introduction
The Kohistan arc terrane in north Pakistan is widely regarded as one of the most
complete exposed sections fromthe deep root to the volcanic edifice of an island
arc [Tahirkheliet al., 1979; Tahirkheli, 1982; Bard, 1983; Coward etal., 1987;
Kazmiand Jan, 1997]. TheKohistan arc has been trapped within the Tethyan
suturezones (Shyok suture to the north and Indus sutureto the south) between
India and Asia during the Himalayan collision. The Kohistan arc has been
deformed tilted to the north, uplifted, and eroded following collision, providing
an informativewindow into the deeper levels of the arc crust[Tahirkheli and Jan,
1979; Searleand Asif Khan, 1996]. Notonly is the Kohistan arc superbly well
exposed frombaseto top, but it also reveals the magmatic and structural
evolution of the arc from an intra-oceanic Marianas-typearc system to an evolved
Andean-typemagmatic arc following accretion to the Asian (Karakoram terrane)
plate to the north [Coward et al., 1987; Khan et al., 1989, 1993; Treloar et al.,
1996]. TheKarakoram terranein north Pakistan is equivalent to the Lhasa Block of
south Tibet, and together they formed the southern margin of the Asian plate
prior to the collision of firstKohistan during the Late Cretaceous and then India
are the early Eocene. Although the Karakoramand the Tibetan plateau have a
similar averageelevation of around 5.2 kmabove mean sea level, the geological
exposures arevery different[ Searle, 1991].Tibetis a high, relatively fiat uplifted
plateau which has not been deeply eroded and only reveals upper crustal
sediments and volcanics, whereas the Karakoram has large topographic

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differences (7000-8700mmountain tops to 2500-3000 mvalleys) and has
suffered enormous amounts of deformation and erosion( up to 35 km of erosion
since 35 M year ago; [Searle, 1991; Searleand Tirrul, 1991]. Collision processes
affecting the deep crustof Asia therefore cannot be studied in the surface
geology of Tibet but can be well studied and documented in the Karakoram.

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Area Map
Station 1
Location: Jutal
1-KohistanTerrene:
The Kohistan terrane is sandwiched between the Indian plate (Himalaya) to the
south along the ISZ or MMT, and the Asian plate (Karakoram terrene) to the north
along the Shyok suture zone (SSZ). It is widely regarded as representing a large-
scale Cretaceous intra-oceanic island arc complex which has been obducted onto
the Indian plate to the south along the MMT and subsequently deformed, partly
metamorphosed and intruded by Andean-type granodioritic plutons of the
Transhimalay and batholith. Much of western and central Kohistan remains
unmapped, but pioneering mapping mostly along and around the Karakoram
Highway section was carried out by Tahirkheli [1982], Tahirkheli et al. [1979] and
Bard [1983]. The most recent reviews were written by Treloar et al. [1996], Kazmi
and dan [1997] and Khan et al. [1997].
Stage1The Matum Das pluton, north of Gilgit, which has a poorly constrained
Rb/Srisochron age of 102 + 12 Ma [Peterson and windley, 1985] disrupted basic
dykes from a minor component of this phase. No U-Pb zircon or monazite ages
have been reported from Kohistan granites, although two U- Pb zircon ages of 101
+ 2 and 103 + 2 Ma have been reported from the western Ladakh sectorof the
Trans-Himalayan batholith [Honeggere t at., 1982; Scharere t at., 1984].
Stage 2 intrusions are more acidic granodiorites and granites two plutons of
which have Rb/Sr ages of 54 + 4 Ma (Gilgit granite) and 40 + 6 Ma Shirot
granodiorite [Petterson and Windtey,1985].
Stage 3 Intrusionsarerepresented by compositeaplite-pegmatite bodies(dykes)
intruding meta-sediments at Parri(south of Gilgit) and ‘stage2’ plutons at the
Indus confluence. They yielded 26.2±1.2 Ma (Rb-Sr wholerock Petterson&

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Windley 1985, Georgeetal. 1993) and 34±14 Ma (Rb-Sr wholerock, Petterson&
Windley 1985), respectively.A leucogranitefromthe Indusconfluencearea was
dated at 30.4±0.6 Ma (U-Pb on zircon, Schalteggeretal.2003), which confirmsthe
Rb-Sr ages.
Station 2

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Location: Chalt
2- ChaltVolcanics
Cretaceous and possibly Late Jurassic,pillowed volcanic, tuffs pyroclastic and
minor calcareousrocks underlying the yaseen group. The volcanic are subduction-
related high-Mg tholeiiticandisites, boninites, calc-alkaline andesite’s and rhyolites
metamorphosed to green schistfacies (ivanic et al., 1956; Patterson and windley,
1985; Petersons et at., 1990.)
Station 3

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Location:Chalt
3-Yasin Group
Yasin sedimentary group is youngest tethyan sedimentary rocks composed of
sedimentary and volcanic-clastic rocks represents the northern most part of KIA.
According to Hayden (1914)it is comprised of sandstone, fossilli ferrous shaly
limestone, and conglomerate overlies the volcanic rocks of chalt volcanic .
Tahiekheli (1979) specify the term yasin group for only the sedimentary rocks and
its volcanic constituent include in his chaltvolcanic.
Pudsey et al. (1985b) revised these ages to Late Aptian to Albian. The
Yasin detrital series are interpreted as aturbiditic unit that was
deposited in an intra-arc or back-arc basin of the Kohistan paleo-island
arc (Pudsey 1986, Khan et al. 1995, Treloar et al. 1996).

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Station 4
Location:Chalt
4-Main Karakoram Thrust (MKT)
The Karakoram fault is an oblique-slip fault system in the Himalaya region
across India and Asia. The slip along the fault accommodates radial expansion of
the Himalayan arc northward indentation of the Pamir Mountains, and eastward
lateral extrusion of the Tibetan plateau. Current plate motions suggest that the
convergence between the Indian Plate and the Eurasian Plate are around 44±5 mm
per year in the western Himalaya-Pamir region and approximately 50±2 mm per
year in the eastern Himalayan region.
The Karakoram terrain is joined to the Kohistan Ladakh arc along a suture zone
known in Pakistan as the Northern Suture (Pudsey, 1986) or the Main Karakoram
Thrust, and in India as the Shyok Suture (Tahirkheli, 1982). The Suture zone is 150
m to 4 km wide and contains blocks of volcanic greenstones, Limestone, shale’s,
conglomerates, quartzite’s and serpentinites in northern Pakistan (Karim, 1998).
Station 5

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Location:Nasir Abad
5- Southern Karakorum metamorphic complex
A narrow belt of metamorphic rocks lies to the south of the Karakoram Batholith
and north of the Shyok Suture. These rocks, forming the Karakoram Metamorphic
Complex of Searle (1991), were previously divided by Desio (1979) into the
Dumordu, Ganchen and Askore Groups. The rocks have been studied in several
places. Collectively referred to as the narkot Group (Ivanac et al. 1954, Pudseyet
al. 1985), they display only low grade metamorphism in the western Karakoram. In
Hunza and further east, however, they show up to sillimanite grade metamorphism.
Searle (1991) has provided a detailed integrated account of the rocks.
Station 6
Location:Shishkat

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6-Karakoram Axial Batholith
Karakoram Granitic Belt also known as the Karakoram (Axial) Batholith, this belt
extends for 600 km from southwest to fDrosh to west of Pan gong Lake and attains
a width of up to 30 km.
This is a composite batholiths with many plutons, dykes and veins of variable
composition emplaced over a period exceeding 100m.y. Multiple intrusions can be
observed in many places and, like the Kohistan Batholith, young leucogranites may
occurin swarms. Searle et al. (1989) and Crawford and Searle(1992, 1993) have
proposeda broad subdivision of the Batholith into pre-collision and post-collision
units.
The Hunza Plutonic Complex is reliably dated at 95 ± 5 Ma (D-Pb zircon) with
two K-Ar dates of 46 Ma (hornblende) and 26 Ma (biotite) (Le Fort et al. 1983). It
contains a range of rocks, from quartz diorite to granite, but granodiorite is
predominant.

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Station 7
Location: Hussani
7-Passu Slate
The PassuSlate and Misgar Slate are considered as parts of one formation which
were doubled by the Sostaccident. As a result, Desio & Martina (1972) mapped
these outcrops as PassuSlates on the southern and Misgar Slates on the northern
flank of the fold. No fossil has been reported from the slates horizon so far, but
lithologically these are indistinguishable.
The PassuSlates are light to dark grey, thin to medium bedded and incorporate
slaty shale, slate and phyllitii slate kith subordinate calcareous and arenaceous
part- ings. Sporadic intrusions of granite, diorite, dolerite, aplite and vein quartz in

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the Passu Slates are noteworthy. Their weathered productis splintery.

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Station 8
Location:Khyber
8-Gojal dolomite
The name "Guhjal" was introduced by McMahon (1900) for the carbonaterocks
exposed south of the Upper Hunza Fault. Gaetani et al. (1995) described thesame
unit with corrected and prevailing spelling as Guhjalformation. The formation is
mainly composed of huge mass of carbonate mostly dolostones. The presenceof
megalodontids and colonial scleractinians points to a Late Triassic age, but the
following findings indicate that the unit starts in the Permian.
This tectonostratigraphic unit lying on the northern flank of the Pasu syncline as,
described by Zanchiand Gaetani (1994), is slightly metamorphic slates of the
Gircha formation (Pasu slate of Desio 1963) which passes gradually into the
peritidal dolomites of the Guhjalformation. The transitional lithofacies consists of
slates alternating with 20-50 cmthick marly limestones, increasing upwards with
respect to the slates. The thickness of this lithofacies is about20-30 m. Along the
path leading from Pasu to the rightside of the Batura glacier, a fusilinid
assemblagedominated by Paraiusulina sp. has been found in the marly
limestones of the transitional facies between the Girchaand Guhjalformations
suggesting a middle to Late Permian age. Zanchi and Gactani (1994) added that
"intricacy of the structure, poor accessibility of the outcrops, rarefossils and
metamorphismhamper stratigraphic reconstruction and precisemapping".

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References:
Crawford,
M .B. and Searle,M .P. Field relationsa nd geochemistroyf pre-
collisiona(lI ndia - Asia) granitoid magmatismin the central
Karakoram, northernP akistan. Tectonophysics2,0 6, 171- 192, 1992.
Crawford, M.B. and M.P. Searle, Collision-related granitoidm
agmatism and crustals tructure of the Hunza Karakoram,n orth
Pakistan, in: Treloar, P.J. and Searle, M.P. Himalayan Tectonics edited
by P.J. Treloar and M.P. Searle, Geol. Soc., London, Spec. Publ. 74,
53-68, 1993.
Coward,
M.P., B.F. Windley, R.D. Broughton, I.W. Luff, M.G. PettersonC, .J.
Pudsey,D .C. Rex, and M.A. Khan, Collision tectonics in the NW
Himalayas,i n Collision Tectonics,e dited by M.P. Coward and A.C.
Ries, Spec. Publ. Geol. Soc. London, 19, 203-219, 1986.
Stratigraphy Of Pakistan

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