This document provides an overview of 40Ar/39Ar geochronology methods, challenges, and applications. It discusses:
- Justifications for using 40Ar/39Ar to date mafic igneous rocks given suitable minerals and sample size requirements.
- Methodological approaches including sample preparation, irradiation, mass spectrometry, and testing results using standards.
- Difficulties posed by alteration and approaches to overcome them such as comparing untreated and acid-treated aliquots.
- Successful studies dating mafic magmatism in Australia, Brazil, and altered volcanic rocks both onshore and offshore.
- Current projects and developments including improving dating of hydrothermally altered samples.
Infrared Spectroscopy and its potential for estimation of soil propertiesExternalEvents
The second lab managers’ meeting of the South-East Asia Laboratory NETwork (SEALNET) took place on 19 - 23 November 2018 in ICAR-IISS (Indian Institute of Soil Science), Bhopal, India.
Dr. K M Hati, Principal Scientist, ICAR-IISS, Bhopal, India (1st Day)
Infrared Spectroscopy and its potential for estimation of soil propertiesExternalEvents
The second lab managers’ meeting of the South-East Asia Laboratory NETwork (SEALNET) took place on 19 - 23 November 2018 in ICAR-IISS (Indian Institute of Soil Science), Bhopal, India.
Dr. K M Hati, Principal Scientist, ICAR-IISS, Bhopal, India (1st Day)
XRF for Analysis of Contaminated Soil and Environmental Applications Olympus IMS
This presentation reviews:
- Contaminated soil and environmental applications and market
- Pollutants in soils and standards and regulation in Europe
- Examples of applications and case studies
- Use of XRF handheld analyzer for soil analysis
For more information about portable XRF, visit: https://www.olympus-ims.com/en/xrf-xrd/xrf-handheld/
Techniques for Rapid and Accurate Sample Analysis in the FieldOlympus IMS
For more than 10 years, portable X-ray fluorescence (pXRF) has evolved into a standard industry technique for quickly generating near real-time geochemistry in all aspects of geoscience including environmental, academia and research, mineral exploration, mining, mineral processing and laboratories. In addition, recent advances in portable powder X-ray diffraction (pXRD) has delivered quantitative mineralogy to geoscientists in the field, something that was previously only possible in the lab.
Together, these two novel techniques are changing the speed, resolution, and cost of decision-making data and transforming geochemistry and mineralogy in the field.
In this webinar, we will outline the basic concepts of pXRF and pXRD and then focus on some of the innovative and exciting case studies delivered by our large and diverse customer base around the globe. This webinar is intended for anyone involved in the collection of geo-scientific samples for geochemical and mineralogical characterisation and aims to showcase what can be achieved with Olympus’ portable analysers.
For more information, visit: https://www.olympus-ims.com/en/innovx-xrf-xrd/
This slide is all about proximal sensing of soil properties including lab techniques and proximal remote sensing. Hope it will help soil science scholars and acade
Of Henges, Rock Art & Lasers; An application of Laser-Scanning techniques at ...Paul Cripps
A presentation given in May 2005 at the McDonald Institute for Archaeological Research, University of Cambridge, on behalf of the Stonehenge Laser Scan project team. The presentation was aimed at highlighting some of the results and well as the technologies used.
PROPERTIES MINERALOGICAL, STRUCTURAL AND ELECTRONIC OF SOIL SAMPLES DISORIENTED CULTIVATED WITH SUGAR CANE USING ANALYSIS: PHYSICAL-CHEMICAL, X-RAY DIFFRACTION (XRD) AND MÖSSBAUER SPECTROMETRY (MS)
A geomatics approach to the interpretation of Ground Penetrating Radar (GPR)Stuart Glenday
Presentation to Dept. of Geogrpahy, Queen Mary University of London. Use of 3d visualisation and Geomatics techniques to support interpretation of GPR data.
XRF for Analysis of Contaminated Soil and Environmental Applications Olympus IMS
This presentation reviews:
- Contaminated soil and environmental applications and market
- Pollutants in soils and standards and regulation in Europe
- Examples of applications and case studies
- Use of XRF handheld analyzer for soil analysis
For more information about portable XRF, visit: https://www.olympus-ims.com/en/xrf-xrd/xrf-handheld/
Techniques for Rapid and Accurate Sample Analysis in the FieldOlympus IMS
For more than 10 years, portable X-ray fluorescence (pXRF) has evolved into a standard industry technique for quickly generating near real-time geochemistry in all aspects of geoscience including environmental, academia and research, mineral exploration, mining, mineral processing and laboratories. In addition, recent advances in portable powder X-ray diffraction (pXRD) has delivered quantitative mineralogy to geoscientists in the field, something that was previously only possible in the lab.
Together, these two novel techniques are changing the speed, resolution, and cost of decision-making data and transforming geochemistry and mineralogy in the field.
In this webinar, we will outline the basic concepts of pXRF and pXRD and then focus on some of the innovative and exciting case studies delivered by our large and diverse customer base around the globe. This webinar is intended for anyone involved in the collection of geo-scientific samples for geochemical and mineralogical characterisation and aims to showcase what can be achieved with Olympus’ portable analysers.
For more information, visit: https://www.olympus-ims.com/en/innovx-xrf-xrd/
This slide is all about proximal sensing of soil properties including lab techniques and proximal remote sensing. Hope it will help soil science scholars and acade
Of Henges, Rock Art & Lasers; An application of Laser-Scanning techniques at ...Paul Cripps
A presentation given in May 2005 at the McDonald Institute for Archaeological Research, University of Cambridge, on behalf of the Stonehenge Laser Scan project team. The presentation was aimed at highlighting some of the results and well as the technologies used.
PROPERTIES MINERALOGICAL, STRUCTURAL AND ELECTRONIC OF SOIL SAMPLES DISORIENTED CULTIVATED WITH SUGAR CANE USING ANALYSIS: PHYSICAL-CHEMICAL, X-RAY DIFFRACTION (XRD) AND MÖSSBAUER SPECTROMETRY (MS)
A geomatics approach to the interpretation of Ground Penetrating Radar (GPR)Stuart Glenday
Presentation to Dept. of Geogrpahy, Queen Mary University of London. Use of 3d visualisation and Geomatics techniques to support interpretation of GPR data.
Mineral potential mapping as a strategic planning tool in the eastern Lachlan...Kenex Ltd
The Geological Survey of New South Wales (GSNSW) is undertaking a statewide mineral potential mapping project driven by the need to provide justifiable land use planning advice to key government stakeholders and to highlight the exploration potential of the state’s major mineral systems at a regional scale. Following delivery of mineral potential data packages for the Southern New England Orogen in 2017, and the Curnamona Province and Delamerian Thomson Orogen in 2018, the eastern Lachlan Orogen was selected as the next area for a review of key mineral systems and mineral potential. The study area covers the Lachlan Orogen east of the Gilmore Fault and the study mapped the mineral potential for porphyry Cu–Au, polymetallic skarn, Kanimblan orogenic Au, Tabberabberan orogenic Au, and VAMS mineral systems.
The full report and data package can be downloaded from: https://search.geoscience.nsw.gov.au/product/9253
2015 Broken Hill Resources Investment Symposium - Geological Survey of South...Symposium
"Curnamona Proterozoic Geochronology".
Liz Jagodzinski, Geochronologist, Geological Survey of South Australia.
Technical presentation at 2015 Broken Hill Resources Investment symposium.
RESULTS OF THE APPLICATION OF DIRECT-PROSPECTING TECHNOLOGY OF SATELLITE IMAG...Dr. Arzu Javadova
The results of reconnaissance studies within the Shakal and Halabja exploration blocks in Kurdistan are presented. Experimental studies were carried out using a mobile direct-prospecting technology, including modified methods of frequency-resonance processing and decoding of satellite images and photo images, vertical electric resonance scanning of the cross-section and a method of integral assessment of the oil and gas potential of large prospecting blocks and license areas. At the local survey site within the Shakal block, responses from oil, condensate, phosphorus and limestone were recorded. The lower boundary of the limestones was established at a depth of 4676 m. By scanning the cross-section from 2770 m, step 1 cm, the responses of oil from limestones were obtained from the intervals: 1) 2771-2794 m, 2) 2795.3-2815.45 m, 3) 2834.40-2854 m. During processing the image of the entire Halabja block, signals were recorded at the frequencies of oil, condensate, phosphorus gas, bacteria, sodium chloride and dolomite. At the 57 km hydrocarbon synthesis boundary, responses from oil, condensate and gas were recorded. When scanning the cross-section from 480 m to 4 km, step 50 cm, responses from oil were obtained from two intervals: 1) 1140-1200 m, and 2) 3310-3340 m. Within the local fragment of the block by scanning up to 5 km with a step of 1 m responses of oil from salt were recorded from the intervals: 1) 295-350 m, 2) 1190-1260 m, 3) 2015-2320 m). The response intervals within the 1st and 3rd horizons have been refined by scanning with a step of 5 cm. The results of experimental studies show that practical application of direct-prospecting methods and technologies will accelerate and optimize the exploration process for oil and gas.
Tracking subduction through geological time and dating the onset of plate tec...Richard Palin
Summary of past and current research on subduction throughout geological time and brief review of evidence for the timing of onset of plate tectonics on Earth
Sedimentology and Geochemical Evaluation of Campano-Maastrichtian Sediments, ...Premier Publishers
The Cretaceous sediments in the Anambra Basin (SE Nigeria) consist of a cyclic succession of coals, carbonaceous shales, silty shales, siltstones and sandstones interpreted as deltaic deposits. Statistics reveals a graphic mean range from 1.5 to 2.8, sorting range from 0.45 to 1.58, skewness range from -0.58 to 0.32 and kurtosis between 0.38 and 2 for the Ajali Sandstone. From these results, the sandstones in the area are dominated by medium to coarse grains, poorly to moderately sorted, coarse skewed and very platykurtic sediments. Further sedimentological evaluation in six localities indicates fluvial-flood plain-marginally marine facies for the Mamu and Nsukka Formations and marine for the Nkporo and Enugu Shales. The geochemical evaluations show that total organic carbon (TOC) (8.95wt%) of the samples constitutes that of good to excellent source rock with oil, oil/gas, gas prones for kerogen types I, II/III, III indicated by Rock-Eval S2/S3 (9.13). The high oxygen index (OI) (42.61 mgCO2g-1TOC) suggest deposition in a shallow marine environment. The Tmax (430oC), indicate the immaturity to onset of maturity of these source rocks. Potential reservoir units occur in the fluvial sandstones of the Ajali Formation and in the marginal marine and flood plain sandstones of the Mamu Formation. The shales and claystones of the Nsukka and Imo Formations may provide regional seals.
Each group should plot on graph paper the ½ life of the radioisotope.pdfdeepakarora871
Each group should plot on graph paper the ½ life of the radioisotopes using the special graph
paper supplied by the teacher. The y-axis has a log scale and begins at 100% of the parent
radioisotope present; the next point is 100/ 2, or 50% parent radioisotope present; the next point
is 50/2, or 25%; and so on.). For example, if the ratio of C-14 to C-13 is 1:3 than the fossil is
how old? 5600 +5600. Correct? For each of the radioisotopes listed above, make a radiometric
graph going to 3 half-lives. Be sure to make one graph using uranium-lead and potassium-argon
dating to one half life. This will become useful later. Why?
Uranium-Lead dating method
Very careful measurements in laboratories, made on VERY LARGE numbers of U-235 atoms,
have shown that each of the atoms has a 50:50 chance of decaying during about 704,000,000
years. In other words, during 704 million years, half the U-235 atoms that existed at the
beginning of that time will decay to Pb-207. This is known as the half life of U- 235. Many
elements have some isotopes that are unstable, essentially because they have too many neutrons
to be balanced by the number of protons in the nucleus. Each of these unstable isotopes has its
own characteristic half life. Some half lives are several billion years long, and others are as short
as a ten-thousandth of a second.
The uranium-lead radiometric dating scheme has been refined to the point that the error margin
in dates of rocks can be as low as less than two million years in two-and-a-half billion years. An
error margin of 2–5% has been achieved on younger Mesozoic rocks.
One of its great advantages is that any sample provides two clocks, one based on uranium-235\'s
decay to lead-207 with a half-life of about 700 million years, and one based on uranium-238\'s
decay to lead-206 with a half-life of about 4.5 billion years, providing a built-in crosscheck that
allows accurate determination of the age of the sample even if some of the lead has been lost.
Potassium-argon dating method
This involves electron capture or positron decay of potassium-40 to argon-40. Potassium-40 has
a half-life of 1.3 billion years, and so this method is applicable to the oldest rocks. Radioactive
potassium-40 is common in micas, feldspars, and hornblendes, though the closure temperature is
fairly low in these materials, about 125°C (mica) to 450°C (hornblende).
#1-23 meters deep from top of hill (limestone)
#2-18 meters deep from top of hill (limestone/volcanic ash)
#3-34 meters deep from base of hill (sandstone)
#4-39 meters deep from top of hill (sandstone)
#5- 50 meters deep from bottom of hill (slate)
#6-26 meters deep (limestone)
#7-10 meters into hill (basalt)
#8-50 meters deep from base of hill (pegmatite)
#9- 3 meters deep into hill (erosion surface of limestone)
#10-52 meters deep from top of hill (pegmatite)
#11- on bank of stream (in shale)
#12- from base of hill 63 meters deep (in granite)
#13-47 meters deep from base of hill (pegmatite)
#14- 2 meters de.
DERIVATION OF MODIFIED BERNOULLI EQUATION WITH VISCOUS EFFECTS AND TERMINAL V...Wasswaderrick3
In this book, we use conservation of energy techniques on a fluid element to derive the Modified Bernoulli equation of flow with viscous or friction effects. We derive the general equation of flow/ velocity and then from this we derive the Pouiselle flow equation, the transition flow equation and the turbulent flow equation. In the situations where there are no viscous effects , the equation reduces to the Bernoulli equation. From experimental results, we are able to include other terms in the Bernoulli equation. We also look at cases where pressure gradients exist. We use the Modified Bernoulli equation to derive equations of flow rate for pipes of different cross sectional areas connected together. We also extend our techniques of energy conservation to a sphere falling in a viscous medium under the effect of gravity. We demonstrate Stokes equation of terminal velocity and turbulent flow equation. We look at a way of calculating the time taken for a body to fall in a viscous medium. We also look at the general equation of terminal velocity.
The ability to recreate computational results with minimal effort and actionable metrics provides a solid foundation for scientific research and software development. When people can replicate an analysis at the touch of a button using open-source software, open data, and methods to assess and compare proposals, it significantly eases verification of results, engagement with a diverse range of contributors, and progress. However, we have yet to fully achieve this; there are still many sociotechnical frictions.
Inspired by David Donoho's vision, this talk aims to revisit the three crucial pillars of frictionless reproducibility (data sharing, code sharing, and competitive challenges) with the perspective of deep software variability.
Our observation is that multiple layers — hardware, operating systems, third-party libraries, software versions, input data, compile-time options, and parameters — are subject to variability that exacerbates frictions but is also essential for achieving robust, generalizable results and fostering innovation. I will first review the literature, providing evidence of how the complex variability interactions across these layers affect qualitative and quantitative software properties, thereby complicating the reproduction and replication of scientific studies in various fields.
I will then present some software engineering and AI techniques that can support the strategic exploration of variability spaces. These include the use of abstractions and models (e.g., feature models), sampling strategies (e.g., uniform, random), cost-effective measurements (e.g., incremental build of software configurations), and dimensionality reduction methods (e.g., transfer learning, feature selection, software debloating).
I will finally argue that deep variability is both the problem and solution of frictionless reproducibility, calling the software science community to develop new methods and tools to manage variability and foster reproducibility in software systems.
Exposé invité Journées Nationales du GDR GPL 2024
Toxic effects of heavy metals : Lead and Arsenicsanjana502982
Heavy metals are naturally occuring metallic chemical elements that have relatively high density, and are toxic at even low concentrations. All toxic metals are termed as heavy metals irrespective of their atomic mass and density, eg. arsenic, lead, mercury, cadmium, thallium, chromium, etc.
Salas, V. (2024) "John of St. Thomas (Poinsot) on the Science of Sacred Theol...Studia Poinsotiana
I Introduction
II Subalternation and Theology
III Theology and Dogmatic Declarations
IV The Mixed Principles of Theology
V Virtual Revelation: The Unity of Theology
VI Theology as a Natural Science
VII Theology’s Certitude
VIII Conclusion
Notes
Bibliography
All the contents are fully attributable to the author, Doctor Victor Salas. Should you wish to get this text republished, get in touch with the author or the editorial committee of the Studia Poinsotiana. Insofar as possible, we will be happy to broker your contact.
Professional air quality monitoring systems provide immediate, on-site data for analysis, compliance, and decision-making.
Monitor common gases, weather parameters, particulates.
1. 40Ar/39Ar geochronology of mafic
magmatism: problems, solutions,
and applications
Paulo M. Vasconcelos – The University of Queensland
paulo@earth.uq.edu.au
Isabela O. Carmo – Petrobras S.A.
icarmo@petrobras.com.br
Contributions: David Thiede,Allan Gomes, Karine Carvas, Tracey Crossingham,
Ben Cohen, Kurt Knesel, Zorano Souza, Umberto Cordani, Leila Marques, Emanuel
Jardim de Sá, Marcos Nascimento, João Marinho de Morais Neto.
2. Roadmap:
• brief introduction to UQ-AGES and TANG3O
• justify why 40Ar/39Ar geochronology is useful, necessary, or sometimes the only method
• illustrate the methodological approaches in 40Ar/39Ar
• show some of the difficulties
• show steps to overcome some of the difficulties
• illustrate some successful studies in Australia
• illustrate some successful studies in NE Brazil
• illustrate some successful studies in southeasthern Brazil
• illustrate some advantages in dating altered volcanic rocks (on shore and offshore)
• current projects
• developments
18. Test of the reliability of the 40Ar/39Ar
results
• Analysis of an international standard
with known age:
GA1550 biotite,
age 98.8 ±
0.5Ma (McDougall
& Harrison 1999)
19. Irradiation at OSU Reactor
http://radiationcenter.oregonstate.edu
Approach and Methods
20. Noble Gas Mass Spectrometry:
• Single collector
• Peak Hopping
Approach and Methods
21. Why date mafic igneous rock
by 40Ar/39Ar geochronology?
• Mineralogy:
- mafic magmas are often devoid or poor in U-rich minerals suitable for U-Pb
geochronology (zircon, baddeleyite)
- zircons may occur as xenocrysts in volcanic sequences
- rich in various minerals (feldspars, biotite, amphibole) datable by 40Ar/39Ar
- both phenocrysts and matrix datable
- datable by whole rock analysis
• Mass:
- need several kgs to extract zircon or baddeleyite
- only small fragments (< 2-3 mm) needed for 40Ar/39Ar geochronology
• Process:
- 40Ar/39Ar method provides information on timing of extrusion/cooling
- 40Ar/39Ar method also provides information on susequent re-heating and/or
alteration
• Intercomparison:
- date all samples by the same method in a magmatic province
Disadvantages: K-minerals susceptible to alteration and diffusional losses
22. 40Ar/39Ar Geochronology
High Precision-High Accuracy Geochronological Method for:
• Extrusive Igneous Rocks and Minerals
• Rapidly Cooled Intrusive Igneous Rocks and Minerals
• Rapidly Cooled Metamorphic Rocks and Minerals
• Rapidly Cooled Hydrothermal Rocks and Minerals
• Chemical Sediments
• Diagenetic Minerals
• Weathering Minerals
40Ar/39Ar Geochronology
23. Closure temperature (Tc) is the temperature at which a system (rock, mineral, etc.)
becomes closed to gains and losses of parent and daughter isotopes for a given isotopic
system, assuming an stable and monotonic
cooling history.
For the K-Ar system,
closure temperature is given by:
Tc
E
{Rln[A(D0 /a2
)]}
Tc = closure temperature
Ea = activation energy for molecular diffusion
(in kJ/mol or kcal/mol)
R = Universal Gaas Constant (8.31441 J/mol/K)
A = geometric factor
D0 = frequency factor (in cm2/s),
a = radius of diffusion domain
T = dT/dt = cooling rate
{[RTc
2
]/[E(dT /dt)]}
27. 40Ar/39Ar Thermochronometry
Application of 40Ar/39Ar method to any K-bearing
earth material that formed above and slowly cooled
below its closure temperature.
Thermochronometric method used to study:
• Slowly cooled intrusive igneous rocks and minerals
• Slowly cooled metamorphic rocks and minerals
• Slowly cooled hydrothermal phases
• Sediments with complex thermal histories
• Any rock or mineral that underwent re-heating after
its formation
35. 3 Decades on…
(where do we go from here?)
Compilation in:
Vasconcelos, Knesel, Cohen & Heim, AJES (2008)
36. & Why?
Provides a powerful tool for testing & informing plate
reconstructions & for unraveling tectonic events
37. Working hypothesis:
This collision should have caused a
change in the motion of the
Australian plate
&
this change should be recorded in
hotspot tracks
38. • 15 volcanic centres
spanning c. 800km
• > 300 mineral grains
& groundmass
fragments from ~ 100
samples by laser
incremental heating
Our 40Ar/39Ar experiment
Cohen, Vasconcelos & Knesel, AJES (2007)
Knesel, Cohen, Vasconcelos, & Thiede, Nature (2008) and …..
many more…
40. 25
Westward deflection + reduced
migration rate
provide strong evidence for
first contact between the OJP & Melanesian arc at 26 Ma.
41. Slower plate velocity explains
why SE Qld area is anomalous
The volcanoes erupted between 26-23 Ma are
anomalous:
larger
overlap
have more crustal melts
Slower plate velocity enabled greater time over hotspot
for volcano construction & to melt crust
Knesel, Cohen, Vasconcelos, Thiede, Nature 2008
SRTM data: www2.jpl.nasa.gov/srtm
Tweed Digital Elevation Model
Many of the volcanoes are
quite big – the largest is
Tweed, which is ~100 km
across
64. Paraná Flood Basalts:
Rapid Extrusion Hypothesis
Supported by New 40Ar/39Ar Results
School of Earth Sciences
David S.Thiede &
Paulo M. Vasconcelos
65. The Controversy
• Duration of the volcanism in the Paraná continental
flood basalt province has two conflicting sets of 40Ar/39Ar
geochronology data.
• One set of results [Renne et al., 1992] indicates that the
Paraná flood volcanism began at 134±1 Ma (corrected for
the currently used value of 28.02±0.09 Ma for the Fish
Canyon fluence monitor) and lasted less than 1 Ma.
• Another set of results [Turner et al., 1994; Stewart et al.,
1996] indicates an interval of 10 Ma, beginning at ca. 138
Ma and ending at ca. 128 Ma.
68. The Possible Causes
• each group of researchers collected and analyzed their own sample
suite and employed different 40Ar/39Ar methodologies.
• Renne et al. (1992):
- samples collected from four vertical Serra Geral sections;
- incremental-heating method on plagioclase and whole rock grains;
- geochronological information from plateau ages in % 39Ar release
spectra.
• Turner et al. (1992) and Stewart et al. (1994):
- sampled a broader region in Brazil, Paraguay, and SE Uruguay
- used a combination of laser and furnace stepped heating on single
crystals, whole rock grains, and in situ laser total fusion extraction
of Ar from various spots in their samples;
- derived age information by plotting the results from stepped
heating or spot analysis onto an 39Ar/40Ar vs. 36Ar/40Ar isotope
correlation diagram (inverse isochron method).
69.
70.
71. UV Pulsed Laser
50-200 µm
laser fusion pit
Laser Total-Fusion Spot Analysis:
• selected areas in the grain are instantaneous fused
72. Visible (blue-green) Continuous Ar Laser
1-2 mm
defocused laser beam
Laser Incremental-heating Analysis:
• the whole grain is incrementally and homogeneously heated
73. UQ-AGES Approach
• we re-dated, by the laser incremental-heating
method, three samples previously analyzed by
Turner et al., 1994 and Stewart et al., 1996.
• we dated three 1-2 mm total rock grains extracted
from the exact same hand specimens analyzed by
these authors (supplied by Marcel Regelous), which
represented the oldest [138.4±1.3 (1s) Ma, sample
PAR-1] and youngest [127.7±4.6 (1s) Ma, sample
DSM23; 129.4±1.3 (1s) Ma, sample DSM05A]
samples in the 10 Ma age range reported by Turner
et al. (1994) and Stewart et al. (1996).
74.
75.
76. Conclusions
• widespread age distribution obtained by Turner et al. (1994)
and Stewart et al. (1996) is an artifact of the methodology
used, and it does not record a true age spread.
• all nine grains analyzed in this study are within error from
each other and correspond, within error, to the ages obtained
by Renne et al. (1992) suggesting that the duration of the
Paraná volcanism was less than 2 Ma.
• geological models that assume that the Paraná flood basalt
volcanism extends for more than 2 Ma are not supported by
geochronological information currently in the literature.
84. Best age determination for each sample:
All 40Ar/39Ar ages are within the main emplacement stage of
134.7 ± 1 Ma proposed by Renne (2015).
Sample
Thiede and
Vasconcelos (2010)
Present study
DSM-05A 134.2 ± 0.8 Ma 135.01 ± 0.35 Ma
DSM-23 134.6 ± 1.1 Ma 134.96 ± 0.36 Ma
PAR-01 134.8 ± 0.7 Ma 135.18 ± 0.33 Ma
• Untreated sample;
• 1 year after irradiation.
• Both untreated and acid-
treated samples;
• 6 months after irradiation.
Take Home Message: Baksi’s Concerns not Justified
96. MBB-211
Idade de cristalização da lava basáltica
(fenocristal de plagioclásio)
MBB-211 (Plagioclase)
Fresh
Ca-plagioclase
phenocryst
Plagioclase phenocryst
Plateau age compatible with
isochron and probability ages.
113.4 ± 0.5 Ma
Fresh plagioclase
(bytownite/labrad
orite)
113.3 ± 0.4 Ma
Fresh matrix
101. Post-salt intrusion – 40Ar/39Ar Geochronology
89 ± 5 Ma
85.4 ± 0.7 Ma
78.4 ± 0.8 Ma
amphibole
biotite
plagioclase
gabbro
102. Diffusion
• Mechanism for Ar loss from a mineral over geologic
residence time
• Governed by the Arrhenius equation:
diffusion rate (D/a2) = (D0/a2) e-Ea/RT
Activation Energy (Ea)
higher = more retentive
Diffusion Constant (D0/a2)
lower = more retentive
• A measure of the ‘conductance’ of diffusion paths in a mineral
- Musset, 1969
103.
104. • systematic variations in diffusive behavior with apparent closure
temperatures for 0.1–1 mm grains of 200–400 °C (assuming a 10 °C/Ma
cooling rate)
• there is no broadly applicable set of diffusion parameters that can be
utilized in feldspar thermal modeling
• sample-specific data are required
• considerable inaccuracies may exist in published thermal histories obtained
using multiple diffusion domain (MDD) models fit to Arrhenius plots for
exsolved alkali feldspar
105. Determine the most probable thermal history
40Ar/39Ar modelling of K-feldspar experiment on resistance furnace
Resistance furnace experiment
Calculate fractions of 39Ar released
Determine diffusion parameters
Plot/Interpret Arrhenius diagrams
Use diffusion coefficients and activation energy
(+ thermochronological constraints) to invert data
From Morais Neto
116. Take Home Message:
• South Atlantic offshore basins offer a
great new frontier of opportunities in the
refinement and application of 40Ar/39Ar
geochronology