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Origin of the Cenozoic porphyry Cu deposits in southern Tibet Open Access

Descriptions

Other title
Subject/Keyword
Porphyry deposit
Gangdese, Tibet
Miocene
Paleocene-Eocene
Type of item
Thesis
Degree grantor
University of Alberta
Author or creator
Wang, Rui
Supervisor and department
Jeremy Richards (Earth and Atmospheric Sciences)
Examining committee member and department
Robert Creaser (Earth and Atmospheric Sciences)
Tom Chacko (Earth and Atmospheric Sciences)
Jeremy Richards (Earth and Atmospheric Sciences)
Martyn Unsworth (Earth and Atmospheric Sciences & Physics)
Kevin Ansdell (Geological Sciences)
Department
Department of Earth and Atmospheric Sciences
Specialization

Date accepted
2014-05-16T14:05:12Z
Graduation date
2014-11
Degree
Doctor of Philosophy
Degree level
Doctoral
Abstract
The Gangdese magmatic belt features extensive Cenozoic magmatic rocks that record geodynamic changes related to the India–Asia collision starting at ~55–50 Ma. Paleocene–Eocene magmas throughout the belt have similar continental arc features. Their intrusive rocks have intermediate [La/Yb]N and intermediate-to-low Sr/Y ratios, negative Eu anomalies, and consists mainly of pyroxene and plagioclase. These geochemical and mineralogical characteristics suggest that the Paleocene–Eocene magmas were relatively dry and evolved primarily by fractionation of pyroxene and plagioclase. In addition, their magmas were also less oxidized (ΔFMQ -1.2 to +0.8). The relatively low water contents and oxidation state of these magmas may reflect final dehydration of the remnant Neo-Tethyan slab, and with the result that only three small porphyry Cu-Mo deposits associated to this suite. The Oligo-Miocene igneous rocks show a sharp longitudinal distinction of petrography, magmatic geochemistry, and association with porphyry-type mineralization. The eastern Gangdese group (east of ~89°E) is characterized by mainly intermediate–felsic calc-alkaline plutons related to porphyry Cu-Mo±Au deposits, and minor potassic rocks. Their intrusive igneous rocks have high [La/Yb]N and Sr/Y ratios, weak or absent Eu anomalies, and amphibole as common phenocrysts. Their magmas were more hydrous and fractionated significant amounts of hornblende and lesser plagioclase prior to upper crustal emplacement. In addition, their magmas were also more oxidized (ΔFMQ+0.8 to +2.9). In contrast, the western group is characterized by potassic volcanic rocks with relatively high Th and K2O contents, low Sr/Y ratios, and low εNdi values. There are only one small-sized porphyry Cu deposit to the west of ~89°E. We propose that the sharp longitudinal distinction between magmatism and metallogenic potential in the Oligo-Miocene Gangdese belt reflects the variable extent of underthrusting of the Indian plate continental lithosphere beneath Tibet. Where subduction-modified Tibetan lithosphere was partially melted by upwelling asthenosphere following slab breakoff in the east, hydrous, oxidized magmas with the result to generate several large porphyry deposits. In contrast, underthrusting of the Indian plate to the west limited the involvement of asthenospheric melts and limited the extent of lithospheric partial melting, with the result that few porphyry deposits are associated with these magmas.
Language
English
DOI
doi:10.7939/R3BK16X8N
Rights
Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.
Citation for previous publication
Wang, R., Richards, J.P., Hou, Z.Q., and Yang, Z.M., 2014, Extent of underthrusting of the Indian plate beneath Tibet controlled the distribution of Miocene porphyry Cu–Mo ± Au deposits: Mineralium Deposita, v. 49, p. 165–173. DOI 10.1007/s00126-013-0507-y.Wang, R., Richards, J.P., Hou, Z.Q., Yang, Z.M., and DuFrane, S.A., 2014, Increased magmatic water content–the key to Oligo-Miocene porphyry Cu–Mo ± Au formation in the eastern Gangdese belt, Tibet: Economic Geology, in press.Wang, R., Richards, J.P., Hou, Z.Q., Yang, Z.M., Gou, Z.B., and DuFrane, S.A., 2014, Increasing magmatic oxidation state from Paleocene to Miocene in the eastern Tibetan Gangdese belt: Implication for collision-related porphyry Cu–Mo±Au mineralization: Economic Geology, in press.

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