Increased Magmatic Water Content--The Key to Oligo-Miocene Porphyry Cu-Mo   Au Formation in the Eastern Gangdese Belt, Tibet

Research Article| August 01, 2014 Increased Magmatic Water Content—The Key to Oligo-Miocene Porphyry Cu-Mo ± Au Formation in the Eastern Gangdese Belt, Tibet Rui Wang; Rui Wang † 1 Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta T6G 2E3, Canada †Corresponding author: e-mail, rw5@ualberta.ca Search for other works by this author on: GSW Google Scholar Jeremy P. Richards; Jeremy P. Richards 1 Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta T6G 2E3, Canada Search for other works by this author on: GSW Google Scholar Zengqian Hou; Zengqian Hou 2 Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, PR China Search for other works by this author on: GSW Google Scholar Zhiming Yang; Zhiming Yang 2 Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, PR China Search for other works by this author on: GSW Google Scholar S. Andrew DuFrane S. Andrew DuFrane 1 Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta T6G 2E3, Canada Search for other works by this author on: GSW Google Scholar Author and Article Information Rui Wang † 1 Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta T6G 2E3, Canada Jeremy P. Richards 1 Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta T6G 2E3, Canada Zengqian Hou 2 Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, PR China Zhiming Yang 2 Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, PR China S. Andrew DuFrane 1 Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta T6G 2E3, Canada †Corresponding author: e-mail, rw5@ualberta.ca Publisher: Society of Economic Geologists Received: 28 Jan 2013 Accepted: 30 Sep 2013 First Online: 09 Mar 2017 Online ISSN: 1554-0774 Print ISSN: 0361-0128 © 2014 Society of Economic Geologists. Economic Geology (2014) 109 (5): 1315–1339. https://doi.org/10.2113/econgeo.109.5.1315 Article history Received: 28 Jan 2013 Accepted: 30 Sep 2013 First Online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Rui Wang, Jeremy P. Richards, Zengqian Hou, Zhiming Yang, S. Andrew DuFrane; Increased Magmatic Water Content—The Key to Oligo-Miocene Porphyry Cu-Mo ± Au Formation in the Eastern Gangdese Belt, Tibet. Economic Geology 2014;; 109 (5): 1315–1339. doi: https://doi.org/10.2113/econgeo.109.5.1315 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 SocietyEconomic Geology Search Advanced Search Abstract The eastern Gangdese magmatic belt (between ~88°E and 94°E) in southern Tibet preserves a series of Cenozoic collision-related igneous rocks that have formed since the start of the India-Asia collision at ~55 to 50 Ma. The Paleocene-Eocene intrusive rocks have intermediate La/YbN ratios (average = 12.0 ± 8.6, n = 150, range = 1.15–64.0), intermediate to low Sr/Y ratios (mostly 40), and weak or absent Eu anomalies (Oligocene: average Eun/Eu* = 0.99 ± 0.27, n = 35, range = 0.67–1.58; Miocene: average Eun/Eu* = 0.95 ± 0.13, n = 93, range = 0.44–1.46), and their mineralogy consists mainly of plagioclase, quartz, and amphibole as phenocrysts. These geochemical and mineralogical characteristics suggest that the Paleocene-Eocene magmas were relatively dry and evolved primarily by fractionation of pyroxene and plagioclase, whereas the Oligo-Miocene magmas were more hydrous and fractionated significant amounts of hornblende and lesser plagioclase prior to upper crustal emplacement.Oligocene and Miocene magmatic rocks crop out as small-volume intrusions and are associated with several large- to giant-sized porphyry Cu-Mo ± Au deposits, as well as numerous smaller porphyry and skarn deposits. In contrast, earlier, more voluminous Paleocene-Eocene magmatism is only known to be associated with three small porphyry deposits. Erosional loss of subvolcanic porphyry systems from the older Paleocene-Eocene sequence is not thought to be a controlling factor in this temporal difference of porphyry deposit distribution, because exhumation rates after 55 Ma were relatively low and coeval Linzizong volcanic rocks are extensively preserved in the Gangdese belt. Instead, we suggest that differences in magmatic history and petrogenesis led to this restricted temporal distribution of porphyry deposits. The Paleocene-Eocene magmas were generated during the onset of collision between India and Asia and were triggered by rollback of the Neo-Tethyan oceanic slab. This magmatism records the final stage of subduction of oceanic lithosphere beneath southern Tibet, and the relatively low water contents of these magmas may reflect final dehydration of the remnant Neo-Tethyan slab.After oceanic slab breakoff at ~40 to 38 Ma, the Greater India slab began to subduct beneath the Gangdese belt until hard collision with the Indian continent at ~35 Ma and breakoff of the Greater India slab at ~25 to 10 Ma. This last event is suggested to have caused asthenospheric mantle upwelling and partial melting of subduction-modified, hydrated Tibetan lithosphere. The resultant partial melts may have remobilized metals residual in the deep lithosphere from previous arc magmatism, giving rise to a suite of postsubduction porphyry-type ore deposits in the Oligo-Miocene. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.