High-precision oxygen isotope analysis of picogram samples reveals 2 m gradients and slow diffusion in zircon
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Abstract:
Ion microprobe analysis with a sub-micrometer diameter spot reveals a sharp, 2 μm gradient in oxygen isotope ratio proving that oxygen diffusion in zircon is slow even under prolonged high-grade metamorphism. The data are consistent with an oxygen diffusion coefficient of 10-23.5±1 cm2/s. Furthermore, this gradient is found in a zircon that contains clear textural evidence of recrystallization in nearby regions. This finding shows that through careful textural and chemical analysis, primary information can be extracted from a zircon that has also undergone partial recrystallization. The oxygen isotope ratios found in zircon have been used to infer magmatic and pre-magmatic histories, including the presence of liquid water on the surface of earliest Earth. Recently, these interpretations have been questioned with the assertion that zircon may not retain its primary oxygen isotope signature through metamorphism. The slow diffusion confirmed by these results supports interpretations that assume preservation of magmatic compositions.Keywords:
Recrystallization (geology)
Microprobe
Metamictization
Research Article| March 01, 2010 Large variations of oxygen isotopes in precipitation over south-central Tibet during Marine Isotope Stage 5 Yanjun Cai; Yanjun Cai * 1State Key Lab of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an 710075, China *E-mail: yanjun_cai@ieecas.cn. Search for other works by this author on: GSW Google Scholar Hai Cheng; Hai Cheng 2Department of Geology and Geophysics, University of Minnesota, Minneapolis, Minnesota 55455, USA Search for other works by this author on: GSW Google Scholar Zhisheng An; Zhisheng An 1State Key Lab of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an 710075, China Search for other works by this author on: GSW Google Scholar R. Lawrence Edwards; R. Lawrence Edwards 2Department of Geology and Geophysics, University of Minnesota, Minneapolis, Minnesota 55455, USA Search for other works by this author on: GSW Google Scholar Xianfeng Wang; Xianfeng Wang 2Department of Geology and Geophysics, University of Minnesota, Minneapolis, Minnesota 55455, USA Search for other works by this author on: GSW Google Scholar Liangcheng Tan; Liangcheng Tan 1State Key Lab of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an 710075, China Search for other works by this author on: GSW Google Scholar Jin Wang Jin Wang 1State Key Lab of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an 710075, China Search for other works by this author on: GSW Google Scholar Author and Article Information Yanjun Cai * 1State Key Lab of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an 710075, China Hai Cheng 2Department of Geology and Geophysics, University of Minnesota, Minneapolis, Minnesota 55455, USA Zhisheng An 1State Key Lab of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an 710075, China R. Lawrence Edwards 2Department of Geology and Geophysics, University of Minnesota, Minneapolis, Minnesota 55455, USA Xianfeng Wang 2Department of Geology and Geophysics, University of Minnesota, Minneapolis, Minnesota 55455, USA Liangcheng Tan 1State Key Lab of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an 710075, China Jin Wang 1State Key Lab of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an 710075, China *E-mail: yanjun_cai@ieecas.cn. Publisher: Geological Society of America Received: 10 Apr 2009 Revision Received: 06 Oct 2009 Accepted: 06 Oct 2009 First Online: 09 Mar 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 © 2010 Geological Society of America Geology (2010) 38 (3): 243–246. https://doi.org/10.1130/G30306.1 Article history Received: 10 Apr 2009 Revision Received: 06 Oct 2009 Accepted: 06 Oct 2009 First Online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation Yanjun Cai, Hai Cheng, Zhisheng An, R. Lawrence Edwards, Xianfeng Wang, Liangcheng Tan, Jin Wang; Large variations of oxygen isotopes in precipitation over south-central Tibet during Marine Isotope Stage 5. Geology 2010;; 38 (3): 243–246. doi: https://doi.org/10.1130/G30306.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Oxygen isotope (δ18O) records of two stalagmites from Tianmen Cave, on the south-central Tibetan Plateau, grew during much of Marine Isotope Stage 5. The Tianmen record, the first cave record from the Tibetan Plateau, characterizes a precipitation δ18O history larger in amplitude but similar in structure to Asian Monsoon records from the adjacent regions, providing essential evidence that the Asian Monsoon system, including the East Asian and Indian Monsoon subsystems, responds largely to changes in Northern Hemisphere summer insolation. Extremely low δ18O values during Marine Isotope Stages 5a, 5c, and 5e suggest that precipitation, rather than temperature, was a major factor controlling δ18O in precipitation on orbital time scales in the south-central Tibetan Plateau. The Tianmen record may help in the interpretation of regional ice core δ18O records. The large range of orbital-scale shifts in meteoric δ18O (>9‰) raises important considerations related to reconstructing the uplift history of the plateau. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
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The origin of the Tsushima Current (TC) is still under debate since direct current observation data are rare and spatial differences in temperature and salinity are too minor to determine the path of the TC. Oxygen isotope is proved to be powerful for tracing the origin of the TC. Oxygen isotope data suggest that there are two water sources of the TC. The TC water could be classified into two water masses with different paths. The depleted oxygen isotope water originates from the Taiwan Strait (T‐TC), whereas the enriched oxygen isotope water originates directly from the Kuroshio (K‐TC).
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Stable isotope analyses of CaCO 3 minerals are very important for investigations of paleoclimate and sedimentary environments For this reason, the experimental calibration of oxygen isotope fractionation factors in the system of CaCO 3 H 2O has been an attractive subject in stable isotope geochemistry since its birth However, there are considerably large differences in the oxygen isotope fractionation factors between CaCO 3 and H 2O measured by different investigators, due to CaCO 3 polymorphs in nature ( i e calcite, aragonite and vaterite) As a result, different temperatures are yielded when these different fractionation factors are applied to isotope geothermometry Thus it is of critical importance in low temperature and environmental geochemistry to make the correct and reasonable choice of oxygen isotope fractionation equations in the calcite water and aragonite water systems In this paper the experimental calibration history, approaches and results of oxygen isotope fractionations in the CaCO 3 H 2O system are systematically summarized and reviewed, and the different expressions about the oxygen isotope fractionation between CaCO 3 and H 2O are unified Salt effect and kinetic effect on oxygen isotope fractionation as well as oxygen isotope inheritance in the processes of polymorph transformation are discussed as well The equilibrium equation of oxygen isotope fractionation between calcite and water is recommended on the basis of reprocessing a large number of the known experimental data and comparing them with theoretical calculations However, the theoretical calculation results concerning the aragonite water system has to be confirmed by further experiments
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