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  • 1
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    Geological and Economic Significance of Supergene Metal Deposits (2015)
    Mineralogical Society of America
    In: Elements
    Details
    Publication Date: 2015-10-08
    Description: Supergene metal deposits form when common rock types or deeply buried primary ore bodies are exposed at or near the Earth's surface and undergo oxidation, dissolution and reconcentration of the metals. Supergene metal deposits are economically interesting because of their accessibility for extraction and increased grades. Scientifically they are attractive because of their mineralogical diversity and what they reveal about surficial history. Apart from supplying mankind's need for metals, supergene metal deposits provide clues about our past climate and offer an unparalleled opportunity to explore the long-term corrosion behavior of natural and man-made materials and their environmental impact.
    Print ISSN: 1811-5209
    Electronic ISSN: 1811-5217
    Topics: Geosciences
    Published by Mineralogical Society of America
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  • 2
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    Rapid change in drift of the Australian plate records collision with Ontong Java plateau (2008)
    Nature Publishing Group (NPG)
    Details
    Publication Date: 2008-08-08
    Description: The subduction of oceanic plateaux, which contain extraordinarily thick basaltic crust and are the marine counterparts of continental flood-basalt provinces, is an important factor in many current models of plate motion and provides a potential mechanism for triggering plate reorganization. To evaluate such models, it is essential to decipher the history of the collision between the largest and thickest of the world's oceanic plateaux, the Ontong Java plateau, and the Australian plate, but this has been hindered by poor constraints for the arrival of the plateau at the Melanesian trench. Here we present (40)Ar-(39)Ar geochronological data on hotspot volcanoes in eastern Australian that reveal a strong link between collision of the Greenland-sized Ontong Java plateau with the Melanesian arc and motion of the Australian plate. The new ages define a short-lived period of reduced northward plate motion between 26 and 23 Myr ago, coincident with an eastward offset in the contemporaneous tracks of seamount chains in the Tasman Sea east of Australia. These features record a brief westward deflection of the Australian plate as the plateau entered and choked the Melanesian trench 26 Myr ago. From 23 Myr ago, Australia returned to a rapid northerly trajectory at roughly the same time that southwest-directed subduction began along the Trobriand trough. The timing and brevity of this collisional event correlate well with offsets in hotspot seamount tracks on the Pacific plate, including the archetypal Hawaiian chain, and thus provide strong evidence that immense oceanic plateaux, like the Ontong Java, can contribute to initiating rapid change in plate boundaries and motions on a global scale.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Knesel, Kurt M -- Cohen, Benjamin E -- Vasconcelos, Paulo M -- Thiede, David S -- England -- Nature. 2008 Aug 7;454(7205):754-7. doi: 10.1038/nature07138.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Earth Sciences, The University of Queensland, St Lucia, Queensland, 4072, Australia. k.knesel@uq.edu.au〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/18685705" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Published by Nature Publishing Group (NPG)
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  • 3
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    Age and Duration of Weathering by 40K-40Ar and 40Ar/39Ar Analysis of Potassium-Manganese Oxides (1992)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 1992-10-16
    Description: Supergene cryptomelane [K(1-2)(Mn(3+)Mn(4+))(8)O(16). chiH(2)O] samples from deeply weathered pegmatites in southeastern Brazil subjected to (40)K-(40)Ar and (40)Ar/(39)Ar analysis yielded (40)K-(40)Ar dates ranging from 10.1 +/- 0.5 to 5.6 +/- 0.2 Ma (million years ago). Laser-probe (40)Ar/(39)Ar step-heating of the two most disparate samples yielded plateau dates of 9.94 +/- 0.05 and 5.59 +/- 0.10 Ma, corresponding, within 2 sigma, to the (40)K-(40)Ar dates. The results imply that deep weathering profiles along the eastern Brazilian margin do not reflect present climatic conditions but are the result of a long-term process that was already advanced by the late Miocene. Weathering ages predate pulses of continental sedimentation along the eastern Brazilian margin and suggest that there was a time lag between weathering and erosion processes and sedimentation processes.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Vasconcelos, P M -- Becker, T A -- Renne, P R -- Brimhall, G H -- New York, N.Y. -- Science. 1992 Oct 16;258(5081):451-5.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/17833140" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 4
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    In situ radiometric and exposure age dating of the martian surface (2013)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2013-12-11
    Description: We determined radiogenic and cosmogenic noble gases in a mudstone on the floor of Gale Crater. A K-Ar age of 4.21 +/- 0.35 billion years represents a mixture of detrital and authigenic components and confirms the expected antiquity of rocks comprising the crater rim. Cosmic-ray-produced (3)He, (21)Ne, and (36)Ar yield concordant surface exposure ages of 78 +/- 30 million years. Surface exposure occurred mainly in the present geomorphic setting rather than during primary erosion and transport. Our observations are consistent with mudstone deposition shortly after the Gale impact or possibly in a later event of rapid erosion and deposition. The mudstone remained buried until recent exposure by wind-driven scarp retreat. Sedimentary rocks exposed by this mechanism may thus offer the best potential for organic biomarker preservation against destruction by cosmic radiation.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Farley, K A -- Malespin, C -- Mahaffy, P -- Grotzinger, J P -- Vasconcelos, P M -- Milliken, R E -- Malin, M -- Edgett, K S -- Pavlov, A A -- Hurowitz, J A -- Grant, J A -- Miller, H B -- Arvidson, R -- Beegle, L -- Calef, F -- Conrad, P G -- Dietrich, W E -- Eigenbrode, J -- Gellert, R -- Gupta, S -- Hamilton, V -- Hassler, D M -- Lewis, K W -- McLennan, S M -- Ming, D -- Navarro-Gonzalez, R -- Schwenzer, S P -- Steele, A -- Stolper, E M -- Sumner, D Y -- Vaniman, D -- Vasavada, A -- Williford, K -- Wimmer-Schweingruber, R F -- MSL Science Team -- New York, N.Y. -- Science. 2014 Jan 24;343(6169):1247166. doi: 10.1126/science.1247166. Epub 2013 Dec 9.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/24324273" target="_blank"〉PubMed〈/a〉
    Keywords: Biomarkers/analysis/chemistry ; *Cosmic Radiation ; *Evolution, Planetary ; *Exobiology ; Extraterrestrial Environment/*chemistry ; Geologic Sediments ; Isotopes/analysis/chemistry ; *Mars ; Noble Gases/*analysis ; Organic Chemicals/analysis/chemistry ; Radiation Dosage ; Radiometric Dating ; Surface Properties
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 5
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    A two-step K-Ar experiment on Mars: dating the diagenetic formation of jarosite from Amazonian groundwaters (2017)
    Wiley
    Details
    Publication Date: 2017-12-07
    Description: Following K-Ar dating of a mudstone and a sandstone, a third sample has been dated by the Curiosity rover exploring Gale Crater. The Mojave 2 mudstone, which contains relatively abundant jarosite, yielded a young K-Ar bulk age of 2.57 ± 0.39 Ga (1σ precision). A two-step heating experiment was implemented in an effort to resolve the K-Ar ages of primary and secondary mineralogical components within the sample. This technique involves measurement of 40 Ar released in low (500 o C) and high (930 o C) temperature steps, and a model of the potassium distribution within the mineralogical components of the sample. Using this method, the high-temperature step yields a K-Ar model age of 4.07 ± 0.63 Ga associated with detrital plagioclase, compatible with the age obtained on the Cumberland mudstone by Curiosity. The low-temperature step, associated with jarosite mixed with K-bearing evaporites and/or phyllosilicates, gave a youthful K-Ar model age of 2.12 ± 0.36 Ga. The interpretation of this result is complicated by the potential for argon loss after mineral formation. Comparison with the results on Cumberland and previously published constraints on argon retentivity of the individual phases likely to be present suggests that the formation age of the secondary materials, correcting for plausible extents of argon loss, is still less than 3 Ga, suggesting post-3 Ga aqueous processes occurred in the sediments in Gale Crater. Such a result is inconsistent with K-bearing mineral formation in Gale Lake, and instead suggests post-depositional fluid flow at a time after surface fluvial activity on Mars is thought to have largely ceased.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 6
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    Discordant K-Ar and Young Exposure Dates for the Windjana sandstone, Kimberley, Gale Crater, Mars (2016)
    Wiley
    Details
    Publication Date: 2016-10-18
    Description: K-Ar and noble gas surface exposure age measurements were carried out on the Windjana sandstone, Kimberley region, Gale Crater, Mars using the Sample Analysis at Mars instrument on the Curiosity rover. The sandstone is unusually rich in sanidine, as determined by CheMin X-ray diffraction, contributing to the high K 2 O concentration of 3.09 ± 0.20 wt % measured by APXS analysis. A sandstone aliquot heated to ~ 915 °C yielded a K-Ar age of 627 ± 50 Ma. Reheating this aliquot yielded no additional Ar. A second aliquot heated in the same way yielded a much higher K-Ar age of 1710 ± 110 Ma. These data suggest incomplete Ar extraction from a rock with a K-Ar age older than 1710 Ma. Incomplete extraction at ~900 °C is not surprising for a rock with a large fraction of K carried by Ar-retentive K-feldspar. Likely variability in the exact temperature achieved by the sample from run to run, uncertainties in sample mass estimation, and possible mineral fractionation during transport and storage prior to analysis may contribute to these discrepant data. Cosmic ray exposure ages from 3 He and 21 Ne in the two aliquots are minimum values given the possibility of incomplete extraction. However, the general similarity between the 3 He (57 ± 49 and 18 ± 32 Ma, mean 30 Ma) and 21 Ne (2 ± 32 and 83 ± 24 Ma, mean 54 Ma) exposure ages provides no evidence for under-extraction. The implied erosion rate at the Kimberley location is similar to that reported at the nearby Yellowknife Bay outcrop.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 7
    Electronic Resource
    Electronic Resource
    K-Ar AND 40Ar/39Ar GEOCHRONOLOGY OF WEATHERING PROCESSES (1999)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Earth and Planetary Sciences 27 (1999), S. 183-229 
    Details
    ISSN: 0084-6597
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Geosciences , Physics
    Notes: Abstract Recent developments in the application of K-Ar and 40Ar/39Ar dating of continental weathering process demonstrate the method's suitability for dating minerals present in weathering profiles. Alunite-group sulfates and hollandite-group manganese oxides, which often precipitate through weathering reactions, were first analyzed by the K-Ar method 30 years ago. Recently these minerals were shown to be suitable to 40Ar/39Ar geochronology, despite their fine-grained habits. The bulk nature of the K-Ar technique and the complex mineral assemblages in weathering profiles restrict K-Ar dating of weathering processes. The single-crystal approach possible with the 40Ar/39Ar method allows the study of weathering profiles where alunite- and hollandite-group minerals occur as minor phases. Step-heating analysis possible with the 40Ar/39Ar method provides information about the Ar and K retention histories, the presence of hypogene contaminants, and possible 39Ar recoil during sample irradiation. Fully automated, modern 40Ar/39Ar systems enable analysis of several samples, providing a comprehensive weathering database. These results are useful in the study of continental paleoclimates and the geochemical, geomorphological, and tectonic histories of an area.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1146/annurev.earth.27.1.183
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  • 8
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    The Paleoclimatic Signatures of Supergene Metal Deposits (2015)
    Mineralogical Society of America
    In: Elements
    Details
    Publication Date: 2015-10-08
    Description: Supergene metal deposits host a comprehensive record of climate-driven geochemical reactions that may span the entire Cenozoic. Products of these reactions can be dated by a variety of radiogenic isotopic methods, such as 40 Ar/ 39 Ar, (U–Th)/He, U–Pb, and U-series. The frequency of mineral precipitation, determined by dating a representative number of samples of a particular mineral collected from distinct parts of the supergene ore body, reflects times in the geological past when weathering conditions were conducive to water–rock interaction. The frequency of mineral precipitation through time permits identifying periods in the geological past when climatic conditions were most conducive to chemical weathering and supergene ore genesis.
    Print ISSN: 1811-5209
    Electronic ISSN: 1811-5217
    Topics: Geosciences
    Published by Mineralogical Society of America
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  • 9
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    New single crystal 40Ar/39Ar ages improve time scale for deposition of the Omo Group, Omo-Turkana Basin, East Africa (2012)
    Geological Society of London
    Details
    Publication Date: 2012-03-08
    Description: Six tuffaceous beds within the Omo Group of the Omo–Turkana Basin have been dated using the 40 Ar/ 39 Ar single crystal total fusion method on anorthoclase, yielding eruption ages. The Omo Group constitutes up to 800 m of subaerially exposed sediments surrounding Lake Turkana within the East African Rift system in northern Kenya and southern Ethiopia. Rhyolitic explosive eruptions produced tuffs and pumice clasts that are considered to have been deposited shortly after eruption. The new age data on feldspars from the pumice clasts range from 4.02 ± 0.04 Ma for the Naibar Tuff of the Koobi Fora Formation to 1.53 ± 0.02 Ma for Tuff K of the Shungura Formation. The Orange Tuff in the KBS Member of the Koobi Fora Formation was dated at 1.76 ± 0.03 Ma, providing good control in this part of the sequence where formerly there was a 〉200 ka gap. Data are consistent with earlier measurements and significantly improve age resolution within the Omo Group, which has yielded many vertebrate fossils, including hominin fossils comprising a number of species. We suggest new age estimates for a limited number of hominin specimens. Supplementary material: Eleven tables and nine figures are available at www.geolsoc.org.uk/SUP18506 .
    Print ISSN: 0016-7649
    Topics: Geosciences
    Published by Geological Society of London
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  • 10
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    A Combined (U-Th)/He and Cosmogenic 3He Record of Landscape Armoring by Biogeochemical Iron Cycling (2018)
    American Geophysical Union
    Details
    Publication Date: 2018-02-01
    Print ISSN: 2169-9003
    Electronic ISSN: 2169-9011
    Topics: Geosciences , Physics
    Published by American Geophysical Union
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