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Permanent link (DOI): https://doi.org/10.7939/R3WP9TM45

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Biogenic and Abiotic Carbonates in Altered Oceanic Crust (AOC) and Implications to Subduction Zone Carbon Cycle Open Access

Descriptions

Other title
Subject/Keyword
Biogenic Carbonate
Subduction Zone Carbon Cycle
Diamond
Altered oceanic crust (AOC)
Carbon Budget
Type of item
Thesis
Degree grantor
University of Alberta
Author or creator
Li,Kan
Supervisor and department
Li, Long (Earth and Atmospheric Sciences)
Examining committee member and department
Muehlenbachs, Karlis (Earth and Atmospheric Sciences)
Stachel, Thomas (Earth and Atmospheric Sciences)
Department
Department of Earth and Atmospheric Sciences
Specialization

Date accepted
2017-09-22T11:18:12Z
Graduation date
2017-11:Fall 2017
Degree
Master of Science
Degree level
Master's
Abstract
Altered oceanic crust (AOC) is an important carbon reservoir for subduction-zone carbon recycling. However, the character of the carbon reservoir (e.g., total budget and isotopic signatures) in AOC has not been well constrained. Here, based on analyses of contents and isotope compositions of 73 DSDP/ODP/IODP samples (22 pillow basalts, 7 sheeted dikes, 22 gabbros and 22 peridotites) and 7 gabbro samples from the Oman Ophiolite, we show that carbonates in gabbros and peridotites were all precipitated at near surface low temperature conditions instead of being precipitated at their corresponding depths in the deeper oceanic crust, and thus cannot represent the true values of the lower oceanic crust sections. Our modeling yielded a new value for carbon input flux in AOC of 1.3 × 1012 moles C/year, which is only 30-60% of previous estimates. We also observed that carbonate in some oceanic crust segments, such as the Cocos plate (ODP/IODP Site 1256D) and the Southwest Indian Ridge (ODP Site 735B), is predominately biogenic in origin with weighted average δ13C values of -20.4‰ to -6.3‰. If such AOC is subducted and provides a carbon source for diamond formation, the diamond can inherit the “organic”-like δ13C values but maintain normal mantle δ15N values. This may provide an alternative explanation for the decoupled δ13C and δ15N signatures in some eclogitic diamonds.
Language
English
DOI
doi:10.7939/R3WP9TM45
Rights
This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for the purpose of private, scholarly or scientific research. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.
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