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Reconstructing carbonate alteration histories in orogenic sedimentary basins: Xigaze forearc, southern Tibet

Ingalls, Miquela (2019) Reconstructing carbonate alteration histories in orogenic sedimentary basins: Xigaze forearc, southern Tibet. Geochimica et Cosmochimica Acta, 251 . pp. 284-300. ISSN 0016-7037.

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Carbonate clumped isotope thermometry (T(Δ_(47))) and the oxygen stable isotope record (δ^(18)O) provide critical constraints on the temperature of carbonate mineral formation and isotopic composition of ancient waters used in reconstructions of past climate, tectonics, and ecological and environmental change. The robust use of these proxies requires that carbonate minerals in the rock record retain primary isotopic compositions through often complex post-depositional thermal histories. New carbonate clumped isotope thermometry and sedimentology data are paired with existing thermochronology and isotope exchange reaction modeling to provide unique constraints on the alteration history of the carbon and oxygen isotopes in Tethyan marine carbonates (Jialazi Fm, Tso Jianding Group) of the Xigaze forearc, southern Tibet. Within the framework of the textural and isotopic data, the effects of early and late burial alteration on Δ_(47) and δ^(18)O values of marine rocks that were buried to <6 km and uplifted to >4 km above sea level are modeled. The alteration products are considered within two well-studied mechanistic frameworks: water-rock recrystallization and solid-state reordering of ^(13)C-^(18)O bonds at high temperature. The proposed alteration model is as follows: (1) shallow, early diagenesis with water of similar composition and temperature to formation waters infills primary porespace with microspar; (2) high-temperature, rock-buffered water-rock exchange and partial solid-state reordering at >3-4 km depth; and (3) near-surface, low-temperature water-rock exchange on the exhumation pathway. The Δ_(47) heterogeneity within individual samples (0.456 to 0.721) requires significant differential alteration on the retrograde path (high to low temperature, low water-rock ratio) in which primary compositions and compositions inherited during early burial diagenesis are overprinted with modern meteoric values. A low T(Δ_(47)) value is often assumed to record the primary temperature of the depositional environment. However, samples yielding low T(Δ_(47)) values in the Jialazi Fm have undergone extensive high-temperature water-rock alteration, and therefore, require a mechanism for increasing ^(13)C-^(18)O bond ordering on the retrograde pathway while preserving many primary biogenic structures and micritic textures. This study highlights the potential significance of late-stage, low-temperature alteration of carbonates derived from orogenic sedimentary basins for studies of terrestrial paleoenvironments and tectonics. This study also provides an example framework for combining observational and analytical data to reconstruct a carbonate alteration history of a buried sedimentary package.

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Additional Information:© 2019 Elsevier Ltd. Received 28 July 2018, Accepted 4 February 2019, Available online 12 February 2019. MI would like to thank David Rowley and Albert Colman for use of analytical facilities and a great deal of discussion leading to this work, and Brian Currie for assistance with cathodoluminescence imaging. MI thanks Madison Ball for his assistance in the field, and Xu Qiang and Ding Lin for coordination of field logistics in China. MI would also like to thank Devon Orme for discussion of the thermal history of the Xigaze forearc during the development of this work and openness in data sharing prior to publication, Max Lloyd for sharing early versions of reordering models and dolomite reordering kinetics, and Daniel Stolper for discussions of reordering and carbonate diagenesis. Funding for this work was provided by a Geological Society of America Graduate Student Research Grant to MI, Sigma Xi Grants-in-Aid G2016100187643997 to MI, and NSF EAR grants 1111274 to David Rowley and 0923831 to David Rowley and Albert Colman.
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Geological Society of AmericaUNSPECIFIED
Sigma XiG2016100187643997
Subject Keywords:Carbonate alteration; Clumped isotope thermometry; Burial diagenesis; Proxy assessment; Water-rock alteration
Record Number:CaltechAUTHORS:20190212-113826322
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Official Citation:Miquela Ingalls, Reconstructing carbonate alteration histories in orogenic sedimentary basins: Xigaze forearc, southern Tibet, Geochimica et Cosmochimica Acta, Volume 251, 2019, Pages 284-300, ISSN 0016-7037, (
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:92849
Deposited By: Tony Diaz
Deposited On:12 Feb 2019 21:46
Last Modified:25 Mar 2019 22:26

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