Li G.,Institute of Surficial Geochemistry |
Li G.,University of Cambridge |
Pettke T.,University of Bern |
Chen J.,Institute of Surficial Geochemistry
Geology | Year: 2011
The time and rate of Tibetan uplift is critical in understanding both the geodynamics of plateau growth and the influence of mountain building on climate change. Models predict that the uplift of the north Tibetan Plateau (NTP) occurred later than uplift of the south and central Tibetan Plateau; uplift of the NTP is believed to have initiated the aridity in the interior of Asia, and to have critically affected the evolution of Asian monsoon and, ultimately, global climate. The history of NTP uplift has remained uncertain, however; scenarios range from Early Miocene to the past million years. This work provides new evidence by relating the Nd isotopic evolution of Asian dust to NTP uplift. The sources of the Asian dust are located in the arid lands between the NTP and the Central Asia orogen. Mass balance calculations indicate that the decreasing εNd values, from -8.2 to -10.4 for Pacific dust since 15 Ma, reflects increasing relative contribution of NTP materials (40% to 70%) to the dust source. As paleoelevation in the Central Asia orogen has largely remained constant, the increasing relative NTP detritus contribution is interpreted to reflect the progressive surface uplift of the NTP at a rate of at least 0.12 mm yr-1 since 15 Ma. © 2011 Geological Society of America.
Zhou W.,Institute of Surficial Geochemistry |
Chen L.,Institute of Surficial Geochemistry |
Zhou M.,Institute of Surficial Geochemistry |
Balsam W.L.,University of Texas at Arlington |
Ji J.,Institute of Surficial Geochemistry
Geoderma | Year: 2010
Goethite (Gt) is an important iron mineral in soils and sediments. Conventional measurements cannot effectively identify it at the low concentrations typical of soils and sediments. In this paper we demonstrate that diffuse reflectance spectroscopy (DRS) in conjunction with thermal treatment provides a definitive technique for identifying Gt in soil and sediments. The DRS pattern of Gt exhibits diagnostic changes of the first derivative value (FDV) peaks after heating to 300 °C, whereas hematite (Hm) displays no shift in peak wavelength after heating. The degree of thermal changes induced in a sample depends on the concentration of both Gt and Hm. Application of this technique to natural soils and sediments demonstrates that it can effectively detect Gt even at very low concentrations in soils and sediments. © 2010 Elsevier B.V. All rights reserved.