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Granites, Himalayas, temperature, pressure, Isotopes
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Thank you for answering and suggesting the article Harald G. Dill Sir.
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I'm working on an update to our previous global geochemical database. At the moment, it contains a little over one million geochemical analyses. It contains some basic geochronology data, crystallization dates for igneous rocks and depositional dates for sedimentary rocks. The database differs from GEOROC and EarthChem, in that it includes some interpretive metadata and estimates of geophysical properties derived from the bulk chemistry. I'd like to expand these capabilities going forward.
What would you like to see added or improved?
Here's a link to the previous version:
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It should be able to categorize significant path finder elements for corresponding commodities with anomalous values.
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The metamorphic rock with zoned zircon and Th/U >1 show evidence of Magmatic origin. Can we therefore use the Ti-in-zircon formular to calculate the temperature of crystallisation of magma since the rocks have been subjected to high temperature and pressure?
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IT depends on the zircon textures. If the zircon is still in a good shape, maybe yes. If the Zircon shows evidence of recrystallization and disequilibrium, this method can be applied but results must be evaluated carefully.
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We have carried out a series of works on zircon clasts associated to unlithified terrigenous sediments: for provenance studies and source rock location. We would like to apply Zircon geochronology on consolidated Siliciclastic sedimentary rocks found in some targeted basins (Babouri-Figuil, Mayo Oulo, Mamfe, and Poli) in Cameroon.
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Thanks for these interesting papers
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except for the vitrinite reflectance, conodont and acritarch colour alteration, fission tracks, (U-Th)/He, is there any new methods to reconstruct the thermal history of sedimentary basins?
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Carbonate mineralisation can be used to track thermal histories, utilising U-Pb geochronology (giving you time), in combination with clumped isotopes (giving you temperature).
These papers combine these two methods (and there are many others utilising the methods individually):
Mangenot, X., Gasparrini, M., Gerdes, A., Bonifacie, M. and Rouchon, V., 2018. An emerging thermochronometer for carbonate-bearing rocks:∆ 47/(U-Pb). Geology, 46(12), pp.1067-1070.
Pagel, M., Bonifacie, M., Schneider, D.A., Gautheron, C., Brigaud, B., Calmels, D., Cros, A., Saint-Bezar, B., Landrein, P., Sutcliffe, C. and Davis, D., 2018. Improving paleohydrological and diagenetic reconstructions in calcite veins and breccia of a sedimentary basin by combining Δ47 temperature, δ18Owater and U-Pb age. Chemical Geology, 481, pp.1-17.
Brigaud, B., Bonifacie, M., Pagel, M., Blaise, T., Calmels, D., Haurine, F. and Landrein, P., 2020. Past hot fluid flows in limestones detected by Δ47–(U-Pb) and not recorded by other geothermometers. Geology, 48(9), pp.851-856.
MacDonald, J.M., Faithfull, J.W., Roberts, N.M.W., Davies, A.J., Holdsworth, C.M., Newton, M., Williamson, S., Boyce, A. and John, C.M., 2019. Clumped-isotope palaeothermometry and LA-ICP-MS U–Pb dating of lava-pile hydrothermal calcite veins. Contributions to Mineralogy and Petrology, 174(7), pp.1-15.
Looser, N., Madritsch, H., Guillong, M., Laurent, O., Wohlwend, S. and Bernasconi, S.M., 2021. Absolute Age and Temperature Constraints on Deformation Along the Basal Décollement of the Jura Fold‐and‐Thrust Belt From Carbonate U‐Pb Dating and Clumped Isotopes. Tectonics, 40(3), p.e2020TC006439.
Pan, L., Shen, A., Zhao, J.X., Hu, A., Hao, Y., Liang, F., Feng, Y., Wang, X. and Jiang, L., 2020. LA-ICP-MS U-Pb geochronology and clumped isotope constraints on the formation and evolution of an ancient dolomite reservoir: The Middle Permian of northwest Sichuan Basin (SW China). Sedimentary Geology, 407, p.105728.
Hoareau, G., Crognier, N., Lacroix, B., Aubourg, C., Roberts, N.M., Niemi, N., Branellec, M., Beaudoin, N. and Ruiz, I.S., 2021. Combination of Δ47 and U-Pb dating in tectonic calcite veins unravel the last pulses related to the Pyrenean Shortening (Spain). Earth and Planetary Science Letters, 553, p.116636.
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Is this coral limestone suitable for Sr isotope stratigraphic study to deremine its depositional age? The limestone underlies a turbidite sequece yielding Late Miocene planktonic foraminifera and calcareous nannofossils, and rare Oligocene-Miocene larger benthic foraminifera are obseved in the thin section of the limestone.
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You have to be very careful with the material you use because of potential diagenetic effects. It is best to use skeletal material originally precipitated as low-magnesium calcite, such as oysters for example. Even with low-Mg calcite material you need to be careful to make sure it is pristine. There are a number of petrographic and geochemical steps that can be done to assure you are using unaltered samples. There are numerous papers out there. Here's a paper you can look at to get an idea of the steps done to get good Sr dates. Ortega-Ariza, D., Franseen,E.K., Santos-Mercado, Ramirez-Martinez, W.R., and Core-Suarez, E.E., 2015, Strontium-isotope stratigraphy for Oligocene-Miocene carbonate systems in Puerto Rico and The Dominican Republic: Implications for Caribbean processes affecting depositional history: The Journal of Geology, v. 123, p. 539-560.
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Answers are invited with reference to the characters of IOCG type mineral deposits in terms of their geochronology, geological and tectonothermal evolution, alteration-mineralisation parageneses, and ore geochemistry.
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Dear Dr. Gupta
IOGC (iron-oxide-copper-gold) deposits is a new-fashion classification scheme in economic geology with the number of old and well-known metal deposits categorized as such.
The majority of these deposits and their locus typicus of origin is located in the paleo- and meso Proterozoic settings of the old cratons in Australia and South America. The kick-starter was Olympic Dam a big animal found by the application of mega-shear zones by Western Mining during the early 1980s by Driscoll. While this blind ore body was a new discovery on the Stuart Shelf a lot of well-known deposit such as Kiruna were re-classified and also attributed to this type of deposit. A series of others hosted by Mesozoic and Cenozoic strata in Chile, Peru and different modern fold belts followed suit.
They contain substantial amounts of Fe, they are bound to felsic and intermediate intrusive rocks of the granite clan and lack a special zonation. Their origin is held to be linked to hydrothermal and metasomatic processes affecting large crustal sections so that the above features need not be restricted to one ore body but found within a metal district, see e.g. Kiruna where you have Fe ore bodies like Kiruna Vara, P-enriched ones, e.g. Henry ore body and Cu deposits like Viscaria.
The ore structure is said to be caldera- or maar like with strong faulting all around that controls the accumulation of magnetite and hematite. Brecciation is a common textural feature of IOGC deposits. There is still a lot of debate around this type of deposit as to its link to volcanic and granitic rocks and the related processes which are normally not closely linked in time and space with each other .
The ore mineralization contains chalcopyrite, pyrite, Fe oxides like magnetite and hematite, REE minerals such as orthite, U minerals and gold.
It is the common way of handling new discoveries in economic geology. Olympic Dam also often named as Roxby Downs named after its mining camp is a giant deposit and exceptional in own rights which stands for great success in exploration and could only be brought on-stream by the joint venture with another big animal from the oil and gas business. The logical process was that of finding a plethora of new IOGC deposits worldwide covering now the timespan from 2.0 Ga to 20 Ma simply by re-examining old animals and re-naming it. Thereby you can increase the values of old deposits simply by a hype. As a result of that the features were more and more watered down. And this is why at the beginning I used the term fashion also to shed some light on how the marketing of “economic geology” often works and how it is adopted by those riding the paper tiger in this business.
This is the opinion of a geologist working since more than 40 years in economic geology with facts and data and who is rather skeptical of all these new finds here and there. I was in the early 1980 in Australia when the “genuine” giant type was discovered by one of the smallest mining companies taking a simply handy-craft geological approach was successful and subsequently was draped around by a wealth of ideology.
H.G.D.
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Any discrimination diagram or calculations would be helpful.
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Monazite and zircon are often closely associated with each others in the source rock and in placer deposits, alike. In the study which is available on request for download from the RG server you will find typical X morphological habits and x-y plot for discrimination of their origin and their behaviour during transport:
DILL, H.G., WEBER, B. and  KLOSA, D.  (2012) Crystal morphology  and mineral chemistry  of  monazite–zircon mineral assemblages in continental placer deposits (SE Germany): Ore guide and provenance marker.- Journal of Geochemical Exploration, 112: 322-346.
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Our study group is looking for a geochronological lab where to date Pleistocene (<1 Myr old) Alunite generated by hydrothermal alteration of volcanic systems. This mineralogical phase were identified by XRD at Azufre and Toconce volcanoes, northern Chile
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Dear Harold
Thanks for your answer and the paper.
I know that ia the problem with Alunite, but there are not other minerals to be dating.
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I am considering buying a new shaking table for heavy mineral separation in my lab. I will mostly use the table for zircon separation (and other heavy minerals we use in U-Pb geochronology) from crushed rocks and sands.
Has anyone experience with shaking tables others than Wilfley tables? Any suggestion of alternate (and cheaper?) models I should check?
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Looking at the type of research you do (dust, Loess) you are likely to deal with the smallest of zircons?!?!? The Wilfley table may lead to dust-sized zircon overwash if your rate of water is too high. The Gemini table can be set up so that zircon (the >100 um fraction) stays on the table and you can use a pipette to "suck up" the residual zircon. It may still be likely that some finer zircon flows off the table. The Jasper Canyon Research zircon table is designed so that zircon stays on the table and is collected by pipette. I just purchased one, but have yet to try it because of COVID19 restrictions. It is not a cheaper option but might be more effective. I would maybe ask the vendors to complete a trial sample on each system and see what results they give you.
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Hi everyone,
I am looking for a related material or info regarding how could I model age-depth to extrapolate beyond the dated point in a soil/sediment log.
Thanks in advance
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Hi,
Extrapolation beyond a dated point is always dangerous since you don't have more information. If the sedimentation rate within the dated section remains quite stable and the sedimentology doesn't change too much you could very carefully assume a constant sedimentation rate and extrapolate linearly. However, you'll never be certain and it'll likely be picked up by reviewers as well if the age-depth model in the undated section is important for your overall discussion.
Extrapolation is possible in age depth model scripts such as Bacon ( https://chrono.qub.ac.uk/blaauw/bacon.html ) and Clam ( http://www.chrono.qub.ac.uk/blaauw/clam.html ).
Cheers,
Loic Piret
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In an attempt to better understand the tectonic history of Central America, geochronology will be completed on specific units in my field area. One of these units is interpreted to represent the basement of the South Chortis Terrane. The only known basement exposure of this terrane is a meta-volcanic amphibolite which should be dated. What methods could be conducted on this unit to determine its age of crystallization and/or metamorphism?
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Dear Sean Freeborne: all the dating methods mentioned could work well in an amphibolite (I assume this Chortis amphibolite is in the amphibolite facies, and so it contains hornblende, biotite and garnet, and plagioclase, of course). But a usually overlooked mineral present in mafic and metamafic rocks is also baddeleyite, ZrO2, a monoclinic zirconium dioxide, which can also be dated with the U-Pb method, just a zircon is. In southern Venezuela, and extending to Guyana, Surinam and Brazil, there exists a huge Large Igneous Province in the Guiana Shield: the Avanavero-Roraima LIP, which was intruded in Mesoproterozoic times as thick and extensive diabase sills (and possibly extruded as basalt too, but this volcanic facies has been totally eroded, obviously). Its dating with baddeleyite has given the most correct age of 1.78 Ga for the largest sill located at the base of Mount Roraima. Regards, Sebastian.
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1. Boundaries of Nile craton
2. Its Geochronology
3. Mineralizations
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Dear A.B. Salman!
Some information concerning to the Nile Craton you may find in the following papers:
1) Mohamed G. Abdelsalama,*, Jean-Paul Lieegeoisb, Robert J. Stern 2002. Review The Saharan Metacraton Journal of African Earth Sciences 34 (2002) 119–136
2. Sultan, M., Tucker, R.D., El Alfy, Z., Attia, R., Ragab, A.G., 1994.U–Pb (zircon) ages for the gneissic terrane west of the Nile,southern Egypt. Geologische Rundschau 83, 514–522
3) R. J. Stern - A. Kr6ner • R. Bender - T. Reischmann A. S. Dawoud 1994. Precambrian basement around Wadi Halfa, Sudan: a new perspective on the evolution of the East Saharan Craton. Geol Rundsch (1994) 83: 564- 577
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Most authors agree that the oldest paraconodonts like Protohertzina derive from the "Anabarites trisulcatus - Protohertzina anabarica Zone". According to the geological time-scale 2016 (Ogg et al. 2016), this would yield a minimum age of about 532.7 Ma. Of course, Protohertzina already occurs at the base of this zone, so my question would be are there any earlier "First Appearance Data of Protohertzina" or other early protoconodonts which are bounded below radiometric age or can be reasonable correlate to an interval below 532.7Ma. Your help would be greatly appreciated.
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First Appearance Data of Protohertzina might be constrained to 545–540 Ma according to SSFs (including Protoherzina and other protocodonts) reported from Ust’-Yudoma Formation, Russia. see the ref below:
Zhu M , Zhuravlev A Y , Wood R A , et al. A deep root for the Cambrian explosion: Implications of new bio- and chemostratigraphy from the Siberian Platform. Geology, 2017, 45(5):459-462.
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Hi,
Im searching works and bibliografies about this kind of method.
The main idea is get ages on detrital zircons of volcaniclastic and sedimentary rocks from a retroarc foreland basin, and obtein data of the provienence of this rocks.
Any help will be greatly received.
Regards.
Felipe J.
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You can check these papers as well:
1) Henderson, B., Collins, A.S., Payne, J., Forbes, C. & Saha, D. 2014. Geologically constraining India in Columbia: the age, isotopic provenance and geochemistry of the protoliths of the Ongole Domain, Southern Eastern Ghats, India. Gondwana Research, 26, 888–906.
2) Age-integrated tectonic evolution across the orogen-craton boundary: Age zonation and shallow- to deep crustal participation during Late Cambrian cratonisation of Eastern Ghats Belts, India. DOI: 10.1016/j.lithos.2017.07.020
3) The Neoarchean-Paleoproterozoic basin development and growth of the Singhbhum Craton, eastern India and its global implications: Insights from detrital zircon U-Pb data. DOI: 10.1016/j.precamres.2017.06.008
4) Detrital zircon (U-Pb SHRIMP and LA-ICPMS) geochronology, Nd isotope mapping and sediment geochemistry from the Singhora Group, central India: Implications towards provenance, its shift and regional stratigraphic correlation. DOI: 10.1016/B978-0-12-803386-9.00015-0
5) Detrital zircon geochronology (U–Pb SHRIMP and LA-ICPMS) from the Ampani Basin, Central India: Implication for provenance and Mesoproterozoic tectonics at East Indian cratonic margin. DOI: 10.1016/j.precamres.2016.06.011
Best of luck!!
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I,ev decided do discuss it with my supervisor but wished you may do some helpork is really interesting can you please help me suggesting some geochronological research ideas In western Himalaya, if you have any :-)
I,ev decided do disscuss it with my supervisor but wished you may do some help
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I suggest you contact Dr Abdul Rashid Lone who has done a PhD from University of Delhi. Currently he is working as an Assistant Professor at Kashmir University.
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Thanks for this, I'm only remotely connected to the field, but High Artic gelogy is so fascinating. I did the Boothia work w Okulitch 30 yrs ago. RL Christie explained way back when how hard Zircon geochron was with lines intercepting at low angles giving large uncertainties, apologies for mangling the tech... But this was the best update! Cheers from Cambridge (UK neither MA nor ON lol)
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Thanks for your experience we are happy to work together
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Do you know if there is a mathematical approach (or any publication that came out with something similar) that state the age cut-off between the [(206/238)/(207/206)], and [(206/238)/(207/235)] discordancy degree calculation?
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Several papers have touched on this recently, including:
In my opinion you need to look at your own data to inform this decision.
Nick
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I was reading a past question (https://www.researchgate.net/post/how_to_calculate_the_degree_of_discordance_of_zircon_ages) where people were debating the cutoff age for switching between calculation of discordance/concordance based on either 206/238/207/206 or 206/238/207/235 and the related cutoff age applied when reporting detrital zircon ages. I decided to ask this question to start a debate on the pros and cons of using concordia ages (Ludwig, 1998) which removes the necessity for a cutoff and filters data by probability and MSWD of concordance. The issue has recently been raised by Zimmermann et al (2017) who recommend the latter approach and has been applied as far back as 2004 (perhaps before) by Peter Cawood. The concordia age approach seems to be the most sensible one but I cannot understand why it is not becoming widely adopted by the 'detrital zircon community'. All opinions welcome.
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Hello Jorge,
Thank you for your contribution. I am aware of how ages are determined using the U-Pb isotopic system in zircon. I think, perhaps, you have misinterpreted my question or my question was misleading as it referred to a question about calculation of concordance/discordance. I refer to the concordia age as defined by Ludwig (1998), not specifically concordant ages and how they are calculated. I take the following quote from the Isoplot 3.75 manual (Ludwig, 2012) which provides a concise description of the corcordia age:
"In addition to the usual 206Pb/238U, 207Pb/235U, 207Pb/206Pb ages, you can use any pair of 206Pb/238U - 207Pb/235U or 238U/206Pb - 207Pb/206Pb ratios to calculate a single “Concordia Age” (Ludwig, 1998). A Concordia Age is the most-probable age for a data-point (or weighted-mean data-point) on a concordia-diagram, where the true location of the data point is assumed to fall precisely on the concordia curve."
Most detrital zircon studies will use the 'usual' ages, particularly utilising 206Pb/238U for ages younger than a certain cutoff (e.g. 1.0 Ga) and 207Pb/206Pb for ages older than the cutoff because the latter age tends to be more precise for older ages. However, using the concordia age removes the necessity for a cutoff.
I refer you to the papers referenced in the question and to:
Spencer et al 2016. Strategies towards statistically robust interpretations of in situ U-Pb zircon geochronology. Geoscience Frontiers 7, 581-589.
The above paper provides a discussion on the cutoff age used to switch from 206/238 ages to 207/206 ages.
My question is aimed at starting a discussion on the pros and cons of the adoption of the concordia age method for detrital zircon studies rather than using the more traditional 206/238 and 207/206 method.
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We are studying some plutonic rocks of gabbroic to tonalitic composition of calc-alkaline affinity, intruded within meta-mafic rocks of upper amphibolite metamorphic facies. U-Pb zircon data in the calc-alkaline rocks and Ar-Ar geochronology in meta-mafic rocks are very similar suggesting coetaneous metamorphic and magmatic event.
There are a lot of literature suggesting that partial melting of amphibolite lower crust in continental subduction zone usually result in melts with felsic characteristic.
If some of the tonalitic plutonic rocks are products of partial melting of amphibolite lower crust, what are the most reliable geochemistry evidence of this? We have some whole rock geochemistry data of the calc-alkaline and wall rocks, also we have some zircon trace elements analyses from the felsic rocks. Unfortunately we do not have access to specialized geochemical analysis as Sm-Nd.
Thanks for your help.
Regards
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Hi Cesar Alfredo Tarazona Velasquez:
There is no specific answer to your question, although such petrogenesis for the gabbroic to tonalitic suite is possible. First, conducting detailed bedrock mapping is a critic way to establish temporal and spatial relationships of the felsic pluton(s) in the field with the assistance of geochronology age determination. Second, determining alkalinity and aluminous saturation state of each phases. Third, building up possible petrogenitic linkage between these phases, e.g., partial melting, or fractionation, or absolutely unrelated. With these work done, then you may have better idea to interpret your geolochemical data and origin of the felsic plutonic rocks.
Best regards,
Xue-Ming Yang
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For example is there any way to recognize minerals (augite, plagioclase) as more sodic or calcic?
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For plagioclase there are a few determination charts, based on the extinction angle in the zone normal to (010) - the albite twin plane, as well as the cleavage plane= which function pretty well. Try fpr example this address: eps.mcgill.ca/~courses/c312/Labs/Optlab9-13.doc @ the McGill University
For clinopyroxene it's a bit more complicated because the optical properties depend on several compositional changes, the general idea is that the optical properties and the mineral assemblage offer some clues for the composition of certain phases. Sorry for the quality of typing in this box, I notice it has become very difficult to get what you type..
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Respected Researchers..Can anybode send me a precise paper or suggest me the same for the geochronological aspects of Dalma Formation, East Indian Shield??
Actually the Dalma Formation is composed of meta-sediments and meta-volcanics. The age of the vvolcanics are well reported in Mishra and Johnson, 2004. I need some recent published ages of the metasediments (schists and quartzites).
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Dear Researchers
Thanks for the paper suggestions by you. Went through all of them and also a few more which took me a time of a couple of months to write back to you.
The idea developed from the papers are useful and quite interesting.
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I have learned that baddeleyite occurs in ultramafic and mafic rocks and is used as an alternative to zircon to date these rocks precisely (using U-Pb TIMS/SIMS/LA-ICP-MS/EPMA techniques). My questions are:
(1) What are the optical properties of baddeleyite (ZrO2) which can be used to identify it using a petrological microscope?
(2) How it can be distinguished from zircon and other similar minerals?
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Baddeleyite is also pleochroic and might have a greenish hue apart from the reddish-brownish colours mentioned by Leonid. Please find attached some microscopic images in transmitted (plane polarized and crossed polars) and reflected light. Field width is 180 microns if not stated otherwise. Of course a SEM/EDX investigation would provide more information. The rock containing the Zr phases is a potassic syenite.
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I am endeavouring to reassess some Australian palynostratigraphic zones for the Mesozoic, which no one has done (that I know of) since before the release of the latest geologic time scale (2012). Am I correct in saying that palynostratigraphic zones are determined by their stratigraphic placement in the rock record? So if the timing changes (e.g. the Middle-Late Triassic boundary shift from 229 to 237 Ma), the palynozones would become older like the stratigraphy and not remain where they are relative to the chronologic ages?
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Christopher:
There is no straightforward answer to your question as the subject needs to be explained in detail. However, this link would provide you with basic and useful insights:
Best
Syed
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Hello, everyone, could you tell me how to get the apparant age error when we use Kato et al.(1999)'s method to calculate the apparent age during the EMP monazite dating calculation. I try to use the propagation of the analysis error and age equation to get the error, but I can't get a right result according to the published data. So, could you please teach me how to calculate in a detailed procedure  or share me a calculating software? Thanks a lot!
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@ Jorge de Moura - I'd rather try with Jean-Marc instead of Jean Jacques
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Sm-Nd isotopes can be use for petrogenesis  but what about dating the ultramafic rocks of ophiolite complexes....I have came across very less research paper of these isotopes used for petrogenesis but not for dating......
Can anyone share  publications or expertise in the field of isotope studies of these rock types....
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Dear Dr. Nayak, I've attached an article about Sm-Nd dating technique. Also, if you have gabbro rock samples, you could dating it using U-Pb on zircon, probably, will need 2 to 5 kg, and you can use SHRIMP or LA-ICP-MS methods.
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U-Pb (zicon) Geochronology will be more helpful to reconstruct the Cenozoic tectonic evolution of the Iranian orogenic belts.
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 Your project appears to be focussed on thermochronology and cooling of rocks, and how exhumation may be related to structural evolution.  Thus you may want to focus on fission-track dating, or helium dating of zircon or apatite.  Cooling ages will help constrain the timing of structures and deformation, but may have little bearing on the timing of intrusion. 
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Hello dear RG colleagues can you please tell me that which is the age oldest zircon age of Arabian plate, i have gone through some research papers but still not success to have any satisfactory results. If you have any paper on the Arabian plate and Eurasian plate, regarding U-Pb age dating, please share.
Thanks
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Dear Shakoor,
I still think your question is vague. You are asking for locating a needle in a hay stack. The Arabian-Nubian plate has a complex geologic history.  It is defined on its NE by the Zagros Thrust whereas in the north is juxtaposed against the Anatolian plate. The Arabian-Nubian shield is composed mainly of Neoproterozoic Basement, but there are older rocks going back to 3 billion years. These are overlain by a  Paleozoic to Late Tertiary and Quaternary cover, including one of the largest basaltic provinces.
Do you wish to know about the magmatism in the suture zones or the blocks that collided? From your initial question, I thought you were interested in knowing the age of the Arabian shield!
But having said that, I am no expert to give any suggestion. Why do you not get in touch with the earth scientists in King Abdul Aziz University in Jeddah?
Best, Qasim
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I've been looking for studies applying LA-MC-ICPMS for in situ 230Th–232Th–234U–238U analysis (ie, for 230Th excess measurement) on ferromanganese crusts, and have come up empty. Can anyone help? I want to be thorough. If you think they don't exist, that's also useful. Thanks in advance!
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Excuse me. I can not help it because I just search for stable isotopes of C and O
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The Wüstenquell granites are in West Namibia  bordering the Namib Naukluft Park [GPS co-ordinates are: S22.37.10 E15.21.30] - south of the Erongo Mountains.
I am looking for the age of this formation.
I believe they are part of the Donkerhoek (Donkerhuk) granite suite and should have been intruded in a period between  550 Ma and 450 Ma (Damara granite - Ordovician to Cambrian). Age of the Wüstenquell granites could be around 520 Ma. as they intruded the Kuiseb schist around 520 Ma ago. Any confirmation?
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Good evening Michael,
I don't know if you still need information, but Miller, R. McG. (2008) is sold at the Geological Survey --> http://www.mme.gov.na/gsn/library/ We bought it several times during several field trips, and there still seem to be enough copies.
Maybe they can send you the three volumes.
Best regards,
Andreas
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Semail ophiolite in Oman obducted on southeastern margin of Arabian plate is more or less at the boundary between the Arabian, Eurasian and Indian plate. I want to know if the obduction and post obduction history of ophiolite can be related to regional tectonic frame work of this region. whether the obduction itself is resulted by tectonic uplift, exhumation of Zagros orogeny? or what else? ideas and data? suggestions?
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Munazzam Hello
Your question is not simple. At the same time, I propose that our paper (you can find it in RG DataBase) will be useful for you:
Eppelbaum, L.V. and Katz, Yu.I., 2016. Tectono-Geophysical Zonation of the Near and Middle East and Eastern Africa. International Journal of Geology, 10, 1-10.
Best
Lev
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Is it feasible to use the trace element data extracted from LA- ICP MS for the foreland basin sedimentary rocks; Sandstone?? I have already extracted the U-Pb ages but unknown about the uses of the element data available from the ICP MS ) e.g.;  Si29, Ti49, Y89,Zr90,Nb93,La139,Ce140,Pr141,Nd146,Sm147,Eu153,Gd157 and so on). If you have some papers regarding this type of study then please do suggest me
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You can use Belousova's diagrams for magmatic zircons to determine the nature of your detrital zircons.
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Dear researchers, 
My PhD thesis project is on Mesozoic-Cenozoic magmatism and associated ore deposits in an area (~1000 Km2) to the southern section of the Iranian segment of Neotethys orogen.
U-Pb dating analysis on zircons have accomplished for volcanic and plutonic rocks and yielded interesting results.  
By now we need some dating analysis on garnets through Sm-Nd or U-Pb method.
For more details, please let me know if the researchers are interested and have access to garnet dating analysis facilities. 
Results will be published as a cooperative work, for sure.  
Regards,
M.R. Hosseini 
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Try GFZ potsdam Germany. sure you ll find some one there.
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I know there is zircon FT data from NPHM, some apatite FT and some recent U-Th-He data from Kaghan area. I am interested to know if there is more U-Th-He data,,particularly from northern Pakistan.
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The best is to write to Prof. Peter Zeitler at Lehigh University. In addition to himself, he had several students engaged on Nanga Parbat.
The other would be Prof. Mike Searle at Oxford University-specialist on Karakoram.
I do not know, but Dr Hafiz Rehman >hafiz@sci.kagoshima-u.ac.jp< group in Japan may also be approached.
Cheers
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I am working on palaeoarchean granite of Singhbhum Craton. I have EPMA data of biotite. Whole rock geochemistry of granite showing ferroan characters. Is it possible that the rock is enriched in iron because of biotite?
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Please see the attached paper and the references therein. 
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So I’ve been recently trying to find studies conducted on the possibilities to Amino Acid-date corals. So far I have only found studies that have looked into determining the age of Porites (Erica J. Handy et al., 2012) and Acropora palmata individuals (P. J. Tomiak et al., 2016). I would however be interested in using A. pruinosa individuals, as this is the most abundant species in my field study. I would be using the intra crystallised proteins to analyse the D/L ratio for a few amino acids.  
The main reason why I would be using the AAR method compared to U/Th or Carbon dating is the prices. AAR would be more suitable to my sediment core sampling as I would like to date quite a few samples and Carbon dating would be way too expensive for multiple dating’s. The Uranium Thorium dating method would be also suitable but this method has not proven to be liable in previous studies where I’m working at the moment. Would I however have to carbon date calibrate the A. pruinosa individuals before I start using the AAR method to date all my samples? Or is it possible to determine the ages just based to AAR analysis?
I’m also treating my samples with 60 ° C prior to analysing them. This is because I dry them in the oven after retrieving a sediment core and after the material is sorted. I dry my sample for 48 h, but will this affect the racemization analysis and result? My sample are also collected from the sea floor usually at a 5 m depth. The cores are usually around 40 cm long and I would be dating the bottom, middle and top part of the core using the same species.
Articles:
P.J. Tomiaka, M.B. Andersena, b, , , E.J. Hendya, c, E.K. Potterb, K.G. Johnsond, K.E.H. Penkmane. The role of skeletal micro-architecture in diagenesis and dating of Acropora palmata. Volume 183, 15 June 2016, Pages 153–175
Erica J. Hendy, Peter J. Tomiak,a Matthew J. Collins, John Hellstrom, Alexander W. Tudhope, Janice M. Lough, and Kirsty E.H. Penkmanc. Assessing amino acid racemization variability in coral intra-crystalline protein for geochronological applications. Geochim Cosmochim Acta. 2012 Jun 1; 86(9-2): 338–353.
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Hi Stefan,
In past unpublished studies, I have attempted to determine relative ages of corals using AAR, but have found the results to be far more variable than either mollusks or whole-rock sediment samples.  That said, if the samples are well preserved chemically and mineralogically, and from clear stratigraphic context, it might be worth a pilot study.  AAR will provide only relative ages, but should be able to distinguish Pleistocene from Holocene age samples.  A substantial database of radiometrically calibrated AAR samples would be needed to estimate numerical ages. 
Samples must be air dried and not oven heated to yield reliable results.  The temperature history of the ocean floor location might be available through other proxy methods.  
Best regards,
Paul Hearty
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basaltic melt production from metasomatized mantle is common feature of subduction zones. I want to know if high degree partial melting has occured in Deep Crustal Hot Zones, the basaltic melt likewise can be produced?
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Leonid's comment is very useful. Basalt magmas are commonly believed to originate by partial melting of the upper mantle peridotites. The lower continental crust is generally no more mafic than basalt. It would require unrealistic amount of heat supply to cause high degree of melting to produce basaltic magma. 
Regards,
Qasim
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I had analyzed my sediment sample by X ray diffraction for determining the mineralogy composition for each layer in my sediment core, and I had analyzed the granulometric distribution using grain size analyzer (Malvern, Mastersizer). And I want to etablish the relationship between  mineralogy and sediment size fraction.
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Dear Mrs.Mejjad please see the following link may be help you for this question
PDF]Chapter 7 - Quantitative Mineralogy and Particle-Size Distribution of ...
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I am doing a Project based on xenoliths and megacrysts in kimberlites based on the Monastery mine and other mines in the Free State, South Africa; and would like to know if there are any journals, books, any research work available to look at. I have realized that most research work on acquiring information about the crust and mantle has been mainly focused on using mantle xenoliths as compared to crustal xenoliths. If any, i would love to acquire more information about crustal xenoliths in general as this is also part of my project.
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Thank you very much.
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Dear Researcher,
I want to generate data of zircons by LA-ICP-MS. I have about ten plutons from a Precambrian sield of NE Indiia, having Supercontinental partnership with Columbia and Pan-African assemblies,  whose data are needed in a metallogenc appraisal. There is practically no data on geochronology and crustal history of development. May I have the academic partnership to grow through joint publications? I seek answer from like minded workers who can provide me the facility. This will be trusted one with great honour.
Can Any researcher help me?
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I am potentially interested in collaborating. Info about our lab is here: https://sites.google.com/site/icpgeolucsb/
You can email me for more information: cottle@geol.ucsb.edu
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You can put them in clean aluminum foil. Then it is possible to transfer the pack in boxes or bags, and send them to the lab.
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Can someone please explain the statistics that isoplot uses to identify outliers for rejection when calculating a weighted mean age for a population?
The manual simply notes that checking the box “permits outlier-rejection using a modified 2-sigma criterion”. My experience has been that samples with a tighter age grouping (low MSWD) tend to yield a more aggressive recognition of outliers, whereas those with a spread of ages (higher MSWD) are typically more conservative and do not reject as many apparent outliers. This is obviously a clue as to what’s happening, but I was hoping for a simple explanation for how this is calculated.
Thanks in advance for anyone’s thoughts . . .
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I didn't try it out, but from your description it sounds like what most mass spec software programs also do:
calculate average and standard deviation of your population. Identify which points fall outside of the range from (average - 2*standard deviation) to (average + 2*standard deviation). Reject those points. Recalculate average and standard deviation without those rejected points. This is what you report.
Note: you are not allowed to repeat the exercise a second time in order to improve your uncertainty further. Then it becomes fudging.
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Why such a long gap in the ages of same rock sample? Can anyone please suggest any good paper I can look into? 
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Thank You very much Marwan Wartes
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I have measured the boron isotope of tourmaline in  a borate deposit in northeastern China which hosted mainly in the Paleoproterozoic meta-volcanic and sedimentary rocks. but what is the relationship between the B-11/B-10 and the source of the rock? Thanks!
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Dear Mr Gui,
Palmer and Slack raised expectation to clarify some  questions using the isotope composition of boron in tourmalines. They mentioned as potential controls over the boron isotopic composition of tourmaline the following factors: (1) composition of the boron source, (2) regional metamorphism, (3) water/rock ratios, (4) seawater entrainment, (5) temperature of formation, (6) secular variation in seawater. Trumbull and Chaussidon demostrated that in pegmatite-aplite
dikes the boron ratio is higher than in hydrothermal tourmalines and interpreted their findings as a result of fluid fractionation Apart from the strong dependance of the boron isotope ratios from fluid fractionation there are also some values that can be used as some kind of provenance marker. Values published by Marshall and Ludwig correspond to what is known from S- type granites that have originated by anatectic process from metasedimentary rocks. Martin and De Vito mentioned that the isotopes of boron in tourmaline and danburite reveal clues about the unusual geochemical environment, taking as an example a hybrid pegmatite system from Madagascar. At the end of listing these isotope results and their interpretation, which is by no means complete, the conclusion my be drawn that some indications pointing to a crustal source of boron exist but the wealth of factors on the control of boron isotope ratios renders this highly- sophisticated method of isotope studies less efficient than a classical chemical review conducted as a function of the geological setting.
Best regards
H.G.Dill
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I am looking for suggestions or recommendations for a geochronology laboratory in either that US or Europe that will do U-Th analysis for commercial purposes and accept working under rigorous Quality Assurance standards including audits?
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I run a U-Th/He and U-Pb geochronology lab. Not sure if this is exactly what you want. Let me know.
Bernard
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δ18O of diatoms are usually considered as tracers of past temperature of surface waters. Can these δ18O records of marine sediments devoid of carbonates be used for dating purposes (Marine isotope stages)?
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Try John Barron at the USGS in Menlo Park.  He is a diatom expert and is active in recent climate change research
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I've had 3 "sub-samples" of a sediment core analyzed to ascertain the 10Be concentration levels. The sediment was taken from a closed basin - centripetal drainage pattern. The results indicate that I have a trend from top to bottom, but no age range was offered to me from the lab who ran the analysis. I've been looking for papers regarding this dating method, but I'm hoping that someone on this website maybe able to narrow down my search scope. If you need further information from me - please let me know.
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You may see the attached file. Also the following paper might be useful to your work.
A review of burial dating methods using 26Al and 10Be
Darryl E. Granger
Truly
ARK
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I want to measure a mafic rock age with Sm-Nd isotope system (Sm-Nd  isochron). I have no idea what mineral has low Sm/Nd and what mineral has high Sm/Nd. I need your suggestion. Thank You.
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It may be a problem to get a precise age, since many gabbros and basalts do not contain minerals with high Sm/Nd, which is what you need to get a well-defined isochron. If there is garnet around, you're in luck. Otherwise, it may be a futile exercise, depending on the expected age of the rocks. If you really have no idea of their age, and are happy to know whether they are ca. 500 or 1000 Ma old, take cpx (and/or hbl) and WR; plagioclase contains very little of anything. If you have an alkalu-gabbro, you could use apatite. If you want to know whether the rocks are 400 or 450 Ma, you may have a problem to get an age that is precise enough to be meaningful.
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For trace element analysis I am looking for the trace element data (supplementary) of TH, HH and LH to correlate my data for better interpretation of provenance of the Foreland basin sediments. Any paper/ book?
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Thanks Baerbel and Shannon for your advice...
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I am going to be picking zircons for the first time soon. I have read a lot of literature related to single-zircon LA-ICPMS work for provenance studies. I am concerned about introducing bias when picking, for example: I seem to be able to spot euhedral zircons better than I do rounded ones. Ideally, I would like to pick the "optimal number" (per sample) for a provenance study (Vermeesch, 2004) but how then do you weight the different types of grains within the sample? A modal abundance of different types of zircon grain within the sample could be used to determine what ratio of round to euhedral (or whatever) would be required, but this seems like it can be difficult to estimate, particularly if you do not have a high purity zircon concentrate. I know this may seem trivial to some, but the more I read, the more concerned I become! Any advice would be much appreciated.
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There is considerable good advice above.  But any hand picking will introduce additional bias in any analysis.  If you want the analysis to be as un-biased as possible, make sure your mineral separates are clean, and this may mean refining the separation process.  Then mount everything, image the mount, and then do a random walk from zircon grain to zircon grain.  
Bear in mind that part of your approach should be directed to what you are tying to accomplish.   You may, for example, select euhedral grains because you are interested in the provenance of first-cycle grains only.  Or perhaps only the rounded grains that may be recycled are of interest.    As you note, the euhedral grains are relatively easy to identify, and but zircons get increasingly more difficult to identify if they are broken, frosted, and they have radiation damage.   As such, it is very easy to bias your data by just focussing on the euhedral grains.
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In CHIME method it is best to have intercept of isochron on y-axis is closer to the origin. However, are there any maximum plus and minus values for the intercept of isochron in y-axis? Recently, some of my data sets show the maximum intercept as +0.05. 
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I just added a quick illustration above - this should be applicable to all types of isochrons, regardless of the isotopic system.
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I am trying to substantiate the hypothesis that two different suites of granites, dated 420 and 380 Ma, respectively, were formed after two separated orogenetic events, despite the fact that they are located in nearby areas (scale of tens of kilometers). Beyond dating, I thought that ɛNd vs. ɛSr could be a proper tool to show (or to ascertain) that their source rock was not the same. This would make my hypothesis more robust. However, I cannot find a single article where the aforementioned tool was used for the purpose. People use the ɛ-ɛ plots to characterize basalt source/origin all the time, but not for granites. Is there any specific reason for that? Or, could anyone suggest a study where ɛ-ɛ plots were used to investigate granites? Thank you.
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Perhaps you're too focussed on the epsilon notation? There are plenty of articles where Sr and Nd isotopic ratios have been used to say something about the origin of granites. However, it may not necessarily be true that granites 'image their sources' directly, and that each granite has one single unique source. They can be formed by partial melting of sedimentary rock, or of pre-existing igneous rocks, but a granitic magma could also be produced by assimilation + crystal fractionation of a more mafic magma. Sr and Nd isotopic ratios can certainly help to constrain the source(s) of granites - but major and trace elements are useful too.
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I am trying to look out for a NIST or canadian standard for analysis of trace and REE elements in marine sediment cores. Previously was using MAG-1 Standard from NIST but now it is unavailable so any alternative to that. 
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HI,
A bit late, but info is always handy.
Are you familiar with Particle Induced X-ray Emission (PIXE) and Nuclear Activation Analysis (NAA)? These techniques are to a large extent standard-less and should be of great help to you. Let me have your location and I will direct you to people who WILL/MUST help you. In this regards also search publications of  Lakay, Gihwala and Peisach. Regards.
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Method to date Precambrian Serpentinites.
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I agree with Daniela, that it is difficult to get some ages from serpentinites. However I know that the Stockli's team at Austin (JSG) is trying to develop a method to date serpentinites from magnetite...it seems that it works...but is mainly restricted to thermochronology..
E.H. Goldstein et al.: Magnetite (U-Th)/He Geochronology: Advancements in Sample Preparation and Application to Date Serpentinites, Geological Society of America-South Central, Austin, TX (2013)
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As it is known, sericite is a white mica with tiny and light grains. How is it possible to separate it by using wilfley table and magnetic separator? Does it flow from the 4th or 5th sides of wilfley table? or does it have the same magnetic susceptibility as muscovite? 
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Papering is also a good method to separate micas.  Get a normal clean piece of paper (not folded) and place another piece of paper on the table (to catch the sample).  Hold the papering paper at a gentle slope and sprinkle your sample at the top.  Gently shake tap the paper and the round grains will roll down, while the sheet-like flakes will stick to the paper.  Hands down the cheapest and quickest way to separate micas :)
Any method of Ar-Ar dating using sericite (laser probe, total fusion or step-heating) can be susceptible to 39Ar and 37Ar recoil effects, resulting in mixed too-old and too-young ages.  It's an artifact of the fast-neutron irradiation process to produce 39Ar from 39K, and the fast neutrons can kick some newly formed isotopes out of their positions (think of it like a cue ball hitting other balls in pool/billiards/snooker).  If your grains are generally <50 microns in diameter, and/or interlayered with K-poor minerals (e.g., chlorite in biotite, or K-poor clays in sericite) then you will get disturbed Ar-Ar ages.  This is a great paper to explain the problem:
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Has anyone else conducting U-Pb LA ICP-MS on calcite, zircon or other minerals encountered variable 238U/206Pb ratios with relatively invariant 207Pb/206Pb ratios?
I've analysed a number of other speleothems from other caves in the UK, Canada and Australia, and the data produce proper isochrons, but all of the samples from Borneo have produced data like this and I have no idea what's causing it. The machine setup was operating within normal parameters and all standard analyses (91500, NIST614 and an "in-house" carbonate standard) behave as normal.
If anyone can suggest any possible causes, or recommend any papers that have dealt with or encountered this, that would be a great help.
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Dear Christopher,
I am slightly puzzled by the fact that this particular stalagmite was shown to be in secular equilibrium (>500 ka) by U-230Th method. A simple calculation shows that if you start accumulating radiogenic lead in a speleothem initially having common Pb (206/204~18.5, 207/204~15.6, and 208_204~38.5) and 238U/206Pb=50, then in 3 Ma in a closed system its 207Pb/206Pb will be =0.68, which is a bit lower than your lowest measured 207Pb/206Pb value. Because 238U/206Pb value decreases with time, measured values of ~1000 in your sample may indicate that initial 238U/206Pb was even higher. For the initial 238U/206Pb=1000 207Pb/206Pb will be =0.15 in 3 Ma, which you do not see. Therefore, there are at least 2 natural reasons to explain your data:
(1) Your speleothem is younger than ~ 50 ka
(2) You deal with open U-Pb system. The first scenario would require COMPLETE loss of radiogenic Pb, which is highly improbable. The second scenario would require very recent considerable U gain, which would result in young 230Th/U ages.
Therefore, my suggestion would be (1) to double check U/Th dating results and confirm that the same materials were analyzed for U-Pb and (2) carefully check the accuracy of your U/Pb ration LAICPMS measurements during the analytical sessions when these data were collected.
I hope this would help in resolving your puzzle.
Best,
Leonid
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While I am picking migmatites, I notice an absence of monazite in tourmaline rich ones. Tourmalines are well-developed idiomorphic, brown and can be clearly seen under x2.5 magnification. But in these rocks, monazite couldn't be found. Does it have a meaning chemically and also geologically? How should I use it or interpret it?
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Dear Zehra,
What it often observed is the presence of apatite or xenotime while rock is devoid of monazite. In this case, ihis can be explained by the incorporation of both the Phosphorus and the REE in one mineral instaead of another. To me, the correlation of the presence of tourmaline and the absence of monazite is much more speculalive even if tourmaline may incorporate REE.
Sincerely,
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Does zircon age of meta-sedimentary rocks represent the deposition age or the crystallization age of the magmatic source? If it represent the deposition age, does that mean that the zircon crystallized from metamorphism? In that case, the grade of metamorphism should be higher than 900 degree C.
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Thermochronology of zircons in a high grade metamorphic rock will NOT provide you any information on the depositional age of the protolith, as some have suggested! But will provide you with the history of post-metamorphic cooling, which can postdate metamorphism by hundreds of millions of years (!)
The correct procedure would be to carefully analyse the CL textures of the zircons and date cores and rims - if you find a coherent, younger age population from sector zoned zircon rims, and these ages correspond to low Th/U ratios (e.g. <0.02) then these ages may represent the timing of metamorphism.
The youngest zircon cores which are NOT metamorphic (e.g. oscillatory zoned with high Th/U ratios) may constrain the MAXIMUM age of the sedimentary protolith.
I recommend reading the following paper on zircon textures. Other papers in this volume will also help you a lot.
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Lu-Hf analysis techniques and implication
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Springer just published an Encyclopedia of Scientific Dating Methods, covering all major techniques for the Earth Sciences. There is a search option and you possibly find all sorts of applications/limitations for Lu-Hf
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Does anyone know of an online repository where it's possible to look up updated half-life and decay constant values, with references to who, when and by what methods they were determined? It seems to me that this would be an extremely useful tool for those in the geochronology community, but as of yet, I've not come across anything quite like this.
The closest thing I've found so far is NuDat 2.6, provided by the National Nuclear Data Center, Brookhaven National Laboratory (link at the end), which seems like a credible enough source. However, on closer inspection I've noticed that some of the half-lives for U and Th isotopes appear to be out of date (specifically 230Th and 234U - the recent values for which are http://dx.doi.org/10.1016/j.epsl.2013.04.006). Also, it doesn't seem to cite any sources for where these values have come from. I suspect that if other people using different chronometers were to examine the quotes half-lives for their own geochronologically important isotopes, they might find other discrepancies.
Any help or suggestions would be much appreciated.
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As far as I know, Nudat is strongly connected to the Nuclear Data Sheets, i.e. ENSDF(Evaluated Nuclear Structure Data File). These are _evaluated_ data, i.e. recommended values. Naturally, not every publicated half life can and will be (immediatly) incoporated into ENSDF.
You can find all references in the ENSDF database, also on the nndc webpage.
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I am going to be doing a lot of research involving U-Pb zircon ages as well as Ar-Ar mica ages. So I want to get as clued-up as possible before I undertake any instrument/analytical training. Also I want to learn about pros and cons and data interpretation.
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Atlas of Zircon Textures by F. Corfu may be also helpful if you are going to work with zircons
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Which Sm -Nd values for CHUR and DM are the best for T CHUR and T DM calculations? Which reference? Thanks.
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Hi Nargess,
yes, this is the problem with ANY model age, in that it depends on both your sample and the model source you are comparing it to. Obviously you have mafic or ultramafic samples with very high Sm/Nd (and hence 147Sm/144Nd). In that case the model ages you calculate will be very sensitive to firstly the choice of reservoirs, and the references suggested by others in this discussion are all the best and most up to date. As you point out, it is how to actually interpret these values you are getting, and whether you can actually use the data (ages) calculated.
In essence it depends on what you want. In general we use these ages not, of course, as ages of the rock, but the time it was last in isotopic equilibrium with that reservoir: ie, the time at which we think it was extracted from that portion of the Earth. In that sense, I don't think many people would argue that there is a large, truly chondritic reservoir still inside the Earth that is regularly sourcing large amounts of magmatism on the modern Earth, so T CHUR is not likely to be particularly meaningful for geological applications rocks of Proterozoic or younger ages.
TDM is derived from the evolution of the Depleted Mantle which is the cumulative residue of the upper convecting mantle after extraction of the continents and MORB. Indeed, one isotopic approximation of the DM is to plot the Nd isotopic value of MORB through time, therefore tracking its evolution. What happens when one does this is that we see that there is no "single" DM reservoir, and we need to use a two stage evolution as discussed above. However, I digress- I simply want to illustrate what your data may be telling you, and I attach a graphic that I prepared for other purposes that can outline what your data are saying.
Since the DM reservoir is itself evolving through time as a function of its own Sm/Nd (and hence 147Sm/144Nd) ratio, if your samples have a similar Sm/Nd ratio to the reservoir, then they will define a line that, when you back calculate, will never cross the DM evolution (pale blue line in the figure). In fact it doesn't matter what the present day epsNd value of your sample is, if it has a very high Sm/Nd ratio it will form a sub parallel array with the DM evolution and hence give meaningless ages. Therefore you will not be able to either calculate a TDM or compare it with any of your other samples.
Another case is where your sample has a positive modern day epsNd, but a low Sm/Nd (and hence 147Sm/144Nd) and hence will evolve to give you a TDM, but no TCHUR (since it will never cross the CHUR evolution (dark blue line on figure).
Finally, I have included the "normal" case, say that of Continental crust (CC) which is negative at the present day and will project back to gave both a TCHUR and an TDM- with TCHUR always being younger than TDM. In this case you can start to compare potential sources, extraction ages and mixing, but these all assume a near or below chondritic Sm/Nd (and 147Sm/144Nd) ratio.
I have a pile more examples if you need/are interested, but I think your issue is not the choice of reservoirs, but the Sm/Nd ratio of you samples, rendering model age calculations meaningless.
The final thing you could try is to see whether they plot on an isochron diagram, hence testing whether your ultramafic samples were all derived from a source of the same age, but at different times. I have seen the is for some komatiites and high Mg dolerites which are clearly not of the same magma batch, but are still isochronous.
cheers, and sorry for the long exposition!
Bruce
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Or provide a list of laboratories, the results of which are acceptable for most of the IF journals.
I want to date some sedimentary deposits using 10Be surface exposure dating. However, I have little experience with cosmogenic nuclide laboratories.
Thank you very much for the feedback
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Hi Thomas,
I also suggest my lab, the CEREGE in Aix-en-Provence, France. For exposure dating, you can contact Pr Didier Bourlès (bourles@cerege.fr) the head of our team or Dr Régis Braucher (braucher@cerege.fr).
We organize also the AMS 13th conference at the end of this summer 24-29 August 2014. http://ams13.cerege.fr.
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For example, if zircons in a rock yield an age of 3100±50 Ma, then how this ±50 is calculated?
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Hi there,
This is going to depend exactly on the type of age calculated. Typical ages quoted for zircon would be
1) a mean age
2) an intercept age
3) a concordia age
In the case of a mean age it should be a weighted mean of your age of interest (usually 207/206 for old zircon quoted in your question). Weighted mean ages are pretty easy maths.
Intercept ages are used when you have 2 significant ages (sometimes more but 2 is a simple case) with discordant zircon spread between them. In this case it is a similar calculation but based on your tie line, not a single 'axis'
Concordia ages are calculated based on 'matching age sets' e.g U/Pb-Pb/Pb or U/Pb-U/Pb. These ages are fairly heavy maths to do by hand!
If you are doing lots of this work I would recommend reading the manual for Squid2 (which is a free download) produced by Ken Ludwig at the Berkeley Geochron Centre (download link below). The Squid program processes SHRIMP U-Pb data files and this manual has plenty of info on how it calculates ages.
There is also a GCA paper by Ken Ludwig that goes through lots of the maths in detail for concordia ages, and associated errors that need to be included, titled "On the Treatment of Concordant Uranium-Lead Ages". link below
That should get you started!
Cheers
Rich
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How can you calibrate pMC dates? e.g. what would be the calibration values for 130±2 pMC.
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pMC is percent modern carbon, with modern or present defined as 1950. Of course as calibration is needed anyway you could just apply the formula and give a negative radio carbon age of minus 2150 years bp, but that'd be rather confusing. Since the atmospheric atom bomb tests of the fifties and sixties atmospheric radio carbon values have gone haywire, although they're nearing normal again now. So for anything younger than 1850 AD or so laboratories often do not give an age but the raw radiocarbon measurement as percent of the standard. It is up to you to try and make sense of it in the context of sample.
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Can I use Mb(beta) line in EPMA for Pb, when estimating the age of monazite, instead of Ma(alpha) with Y interference? If I use Mb for Pb then can Y interference be neglected?
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Hi,
You can use Pb Mb to avoid Y interference, but you will loose precision as Pb Mb has a lower count rate than Pb Ma, approximately only 60% of Pb Ma... There are less interferences issue with Pb Mb, although you should check for 2nd order Ce La (minor interference but Ce is a major element in monazite!). Pb Mb is recommended for xenotime analysis (due to the HUGE amount of Y in xenotime), however I would stick with Pb Ma for monazite analysis.
In any case, a critical point about accurate measurement of Pb (which is considered as a trace element) is the background correction. The curvature of the background under both Pb Ma and Mb is significant and can lead to several 10th to 100th of ppm of error!
That being said, and if you decide to go for Pb Ma analysis, you have to be aware of a peak shift issue with Y Lg2,3 between monazite and YPO4 (a typical standard used for Y standardization and peak interference measurement); the shift for YLγ2,3 is measured to about –4.5 × 10–3 Å in monazite relative to YPO4 (~50 * 10-5 sin-theta). There are additional interferences to take into account, such as La La (2nd order) and Th Mz. For more information on precise and accurate monazite dating (including the problem of Y Lg2,3 shift) I can only recommend you to read...
Jercinovic, M.J., Williams, M.L., 2005. Analytical perils (and progress) in electron microprobe trace element analysis applied to geochronology: Background acquisition, interferences, and beam irradiation effects. American Mineralogist 90, 526–546.
and
Jercinovic, M.J., Williams, M.L., Allaz, J., Donovan, J.J., 2012. Trace analysis in EPMA. IOP Conference Series: Materials Science and Engineering 32, 1–22.
You can also subscribe to the Probe for EPMA forum and ask your EMP questions to a bunch of expert in the topic :) Check here:
Good luck,
Julien Allaz
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I am new, but enthusiastic, to the field of geochronology. Want some information before I take up my research in this particular field.
Also I would like to know in which laboratories I can get my samples analyzed.
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Allegre attached !
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I have seen sector zoning in monazite, the rocks belong to Grt-Schist.
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The simple response (without seeing images or knowing more about the rocks) would be that true sector zoning in monazite reflects primary growth. The sector zoning is likely to represent relatively fast growth (as mentioned above). Variable attachment of different elements onto different growth faces will result in your 'sectors', and slow diffusion of elements within monazite retains the zoning. If you are really seeing zoning of that type it would strongly indicate a lack of secondary recrystallisation processes, which play havoc with your monazites in terms of zonation.
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I have seen in my rock sample (Gneiss) which containing phosphorus poor monazite.I was wondering how it loss the phosphorus?
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The most widespread substitution is the huttonite (ThSiO4) substitution: REE_P_ThSi, by which part of the phosphorus in the anionic groups is substituted by silicon. Also the (-2)CO3 and (-2)SO4 anionic groups might be involved in similar heterovalent substitution, but to a lesser extent. The huttonite substitution is actually "good" for geochronology, beacause it is the main mechanism of introducing Th in the monazite lattice (besides the cheralite/brabantite substitution -2REE_CaTh).
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The Deccan Trap breccia at the base of the Panna Formation which is sedimentary clast breccia with matrix of clay.
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the Deccan basalt pile at Mahabaleshwar, Sahyadri (Western Ghats) region.
Along the Sahyadri Range (syn. Western Ghats) beside the west coast and
thins progressively eastward and southeastward, such that along the eastern fringes of the province. Whereas the lava pile in the Western Ghats region and in the interior areas of the province is made up almost completely of fairly evolved, sub-alkaline tholeiitic basalts.
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We are inquiring about the potential archaeological applications of OSL dating. More specifically, we are trying to determine if OSL (or, perhaps, another non-invasive, absolute-dating technique) would be able to determine the date at which the cortex of quartzite cobble was fractured. Recently, we were handed a roughly football-sized quartzite cobble, which has been in a private citizen's collection of artifacts for decades. The cobble is totally unprovenienced and has been totally rinsed clean of whatever sediments originally encased it. However, of note, the cobble is incised with what is unmistakably the profile of a woolly mammoth. This incised drawing could easily be a 19th- or 20th-century forgery of some kind. On the other hand, it may be a piece of Paleoindian art. So, we are trying to determine if there's a non-invasive, absolute dating technique that could determine when the cortex of this particular quartzite cobble was pecked/incised through, to render the mammoth illustration. We look forward to your feedback on this matter. We have already thought about cosmogenics (Beryllium) but that is very destructive. We would destroy the very thing we wish to date.
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It seems like mission impossible with luminescence, because the cobble has been exposed to light. Had it been taken from an excavation and not exposed, you could have tried the exposure dating developed by Reza Sohbati. But even if you now drill a core through the cobble and get a good profile, its interpretation will always be questionable.
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Is it possible do this based on CL images?
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Zircon over/outgrowths generated by multiple processes are well-illustrated in: Köksal, S., Göncüoglu, M. C., Toksoy-Köksal, F., Möller, A., & Kemnitz, H. 2008. Zircon typologies and internal structures as petrogenetic indicators in contrasting granitoid types from central Anatolia, Turkey. Mineralogy and Petrology, 93(3-4), 185-211 and downloadable by ResearchGate.
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When we estimate the equivalent dose of soil samples in 3-6 meters depths we find 400-500 Gy using exp+lin or double exp fit procedures in growth curves. Are these results reliable?
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This depends on your samples. For some quartz grains, these doses are OK. Signals from other samples may be close to saturation. In this case, you have to analyze the shape of the growth curves as mentioned above, and try to find indepentent age controls to determine the reliablility of the ages obtained.
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Dating lab comparison.
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Thanks Renaud,
Your parting comment strikes a chord with me. I once had bones dated by a commercial lab that were just too good to be true so I had the same specimens redated by a research lab who found the bones were devoid of collagen! This made me suspicious of all commercial labs for a while, but the probability that the first set of results could be explained by chance were 1 in 5040! So what did the first lab date and were their ages somehow equivalent to the true age of the bones? I guess the bottom line is that researchers using dating results cannot behave like simple consumers but rather must have a good understanding of the dating and pre-treatment processes used as well as the implications they have on interpretation of dating results.
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I run my zircon (detrital) samples through ICP-MS and found out that we can get REEs and trace element data from those analyses. However, I did not record the detailed procedure. Any suggestions?
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Thanks... I will go through this one ... XIE XIE ni
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What do you recommend the person who studies about precambrian zircons? What are the limitations? Or which method should be used?
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