Quick Search:    advanced search

GSW Home   GeoRef Home   My GSW Alerts   Contact GSW   About GSW   Journals List   Help

This Article Figures Only Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Web of Science (13) Citing Articles via Google Scholar Google Scholar Articles by Garzione, C. N. Articles by Basu, A. R. Search for Related Content GeoRef GeoRef Citation

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^,1, Matt J. Ikari² and Asish R. Basu²

¹ Department 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
² Department of Earth and Environmental Sciences, University of Rochester, Rochester, New York 14627, USA

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 _Nd values between –11.8 and –16.1, whereas Paleozoic and Mesozoic plutonic source rocks that intrude the metasedimentary rocks have more positive _Nd values between –3.6 and –11.2. Cretaceous sedimentary source rocks display _Nd 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 _Nd 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 _Nd 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 _Nd 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 (_Nd = –8.6 to –10.5). In addition, the modern Daxia River, which drains the margin of the plateau today, transports clay and silt with _Nd 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 _Nd 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 ¹⁸O 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.

Key Words: Nd isotopes • sedimentary provenance • loess • Tibetan Plateau • paleoclimate • unroofing

This article has been cited by other articles:

				G. Dupont-Nivet, C. Hoorn, and M. Konert Tibetan uplift prior to the Eocene-Oligocene climate transition: Evidence from pollen analysis of the Xining Basin Geology, December 1, 2008; 36(12): 987 - 990. [Abstract] [Full Text] [PDF]

				M. J. Kohn and T. J. Fremd Miocene tectonics and climate forcing of biodiversity, western United States Geology, October 1, 2008; 36(10): 783 - 786. [Abstract] [Full Text] [PDF]

				H. Hong, Z. Li, H. Xue, Y. Zhu, K. Zhang, and S. Xiang OLIGOCENE CLAY MINERALOGY OF THE LINXIA BASIN: EVIDENCE OF PALEOCLIMATIC EVOLUTION SUBSEQUENT TO THE INITIAL-STAGE UPLIFT OF THE TIBETAN PLATEAU Clays and Clay Minerals, October 1, 2007; 55(5): 491 - 503. [Abstract] [Full Text] [PDF]

				J. N. Avila, F. Chemale Jr., G. Mallmann, K. Kawashita, and R. A. Armstrong Combined stratigraphic and isotopic studies of Triassic strata, Cuyo Basin, Argentine Precordillera Geological Society of America Bulletin, September 1, 2006; 118(9-10): 1088 - 1098. [Abstract] [Full Text] [PDF]