Source of Oligocene to Pliocene sedimentary rocks in the Linxia basin in northeastern Tibet from Nd isotopes: Implications for tectonic forcing of climate

Research Article| September 01, 2005 Source of Oligocene to Pliocene sedimentary rocks in the Linxia basin in northeastern Tibet from Nd isotopes: Implications for tectonic forcing of climate Carmala N. Garzione; Carmala N. Garzione 1Department of Earth and Environmental Sciences, University of Rochester, Rochester, New York 14627, USA, and Department of Geological Sciences and Cooperative Institute for Research in Environmental Science, University of Colorado, Boulder, Colorado 80309, USA Search for other works by this author on: GSW Google Scholar Matt J. Ikari; Matt J. Ikari 2Department of Earth and Environmental Sciences, University of Rochester, Rochester, New York 14627, USA Search for other works by this author on: GSW Google Scholar Asish R. Basu Asish R. Basu 2Department of Earth and Environmental Sciences, University of Rochester, Rochester, New York 14627, USA Search for other works by this author on: GSW Google Scholar Author and Article Information Carmala N. Garzione 1Department of Earth and Environmental Sciences, University of Rochester, Rochester, New York 14627, USA, and Department of Geological Sciences and Cooperative Institute for Research in Environmental Science, University of Colorado, Boulder, Colorado 80309, USA Matt J. Ikari 2Department of Earth and Environmental Sciences, University of Rochester, Rochester, New York 14627, USA Asish R. Basu 2Department of Earth and Environmental Sciences, University of Rochester, Rochester, New York 14627, USA Publisher: Geological Society of America Received: 13 Oct 2004 Revision Received: 19 Feb 2005 Accepted: 10 Apr 2005 First Online: 02 Mar 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (2005) 117 (9-10): 1156–1166. https://doi.org/10.1130/B25743.1 Article history Received: 13 Oct 2004 Revision Received: 19 Feb 2005 Accepted: 10 Apr 2005 First Online: 02 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 Carmala N. Garzione, Matt J. Ikari, Asish R. Basu; Source of Oligocene to Pliocene sedimentary rocks in the Linxia basin in northeastern Tibet from Nd isotopes: Implications for tectonic forcing of climate. GSA Bulletin 2005;; 117 (9-10): 1156–1166. doi: https://doi.org/10.1130/B25743.1 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 SocietyGSA Bulletin Search Advanced Search Abstract We used Nd isotopes and trace element data to determine the provenance of sedimentary rocks in the Linxia basin, northeastern Tibet, whose Oligocene through Pliocene sedimentation history has been interpreted to reflect deposition in a flexural basin associated with contractional deformation along the northeastern margin of the Tibetan Plateau. Paleozoic–early Mesozoic metasedimentary source rocks from the Kunlun-Qaidam and Songpan-Ganzi terranes have ϵNd values between −11.8 and −16.1, whereas Paleozoic and Mesozoic plutonic source rocks that intrude the metasedimentary rocks have more positive ϵNd values between −3.6 and −11.2. Cretaceous sedimentary source rocks display ϵNd values of −9.7 and −9.9 in the Maxian Shan, north of the Linxia basin, and −15.3 in the plateau margin south of the basin. With ϵNd values that range between −8.4 and −10.4 before ca. 15 Ma, and −6.2 and −11.8 after ca. 14 Ma, sedimentary rocks of the Linxia basin are less negative than metasedimentary rocks, which are dominant source rocks within the margin of the Tibetan Plateau today. The relatively positive ϵNd values of Linxia basin sedimentary rocks could reflect several possible sources, including (1) a mixture of plutonic and metasedimentary rocks within the northeastern margin of Tibet, (2) Cretaceous sedimentary rocks derived from the north, or (3) loess derived from central Asian deserts. A mass balance calculation indicates that plutonic rocks are not volumetrically significant enough to generate the ϵNd values observed in Linxia basin sedimentary rocks through mixing of plutonic and metasedimentary sources.Rare earth element patterns suggest that Cretaceous rocks were not a dominant source of sediment. The Nd isotopic composition and rare earth element pattern of Quaternary loess are similar to older deposits in the Linxia basin and reflect loess deposited elsewhere in the Loess plateau and the North Pacific (ϵNd = −8.6 to −10.5). In addition, the modern Daxia River, which drains the margin of the plateau today, transports clay and silt with ϵNd values of −10.5 to −10.8 despite the river's source in more negative metasedimentary rocks of the Kunlun-Qaidam and Songpan-Ganzi terranes, which indicates that the modern fine-grained sedimentary budget is dominated by recent loess deposits. Considering the slow sedimentation rates in the Linxia basin, it is likely that loess sources have contributed a significant volume of fine-grained sediment to this basin throughout its history. An increase in the range of ϵNd values at ca. 14 Ma in the Linxia basin may reflect increased unroofing of the northeastern margin of Tibet, which slightly preceded a change in climate between ca. 13 and 12 Ma in the Linxia basin. A 1.5‰ increase in baseline δ18O values of lacustrine carbonates has been interpreted as the result of reorganization of atmospheric circulation and an increase in aridity on the northeastern margin of the Tibetan Plateau, perhaps associated with the plateau having achieved an elevation sufficient to block moisture from the Indian Ocean and/or Pacific Ocean. Similar timing of exhumation and climate change suggests that northeastward and eastward propagation of the plateau margin was responsible for the middle Miocene climate change observed in the Linxia basin. 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