Evolving east Asian river systems reconstructed by trace element and Pb and Nd isotope variations in modern and ancient Red River-Song Hong sediments

Author Posting. © American Geophysical Union, 2008. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry Geophysics Geosystems 9 (2008): Q04039, doi:10.1029/2007GC001867.Rivers in east Asia have been recognized as having unusual geometries, suggestive of drainage reorganization linked to Tibetan Plateau surface uplift. In this study we applied a series of major and trace element proxies, together with bulk Nd and single K-feldspar grain Pb isotope ion probe isotope analyses, to understand the sediment budget of the modern Red River. We also investigate how this may have evolved during the Cenozoic. We show that while most of the modern sediment is generated by physical erosion in the upper reaches in Yunnan there is significant additional flux from the Song Lo, draining Cathaysia and the SW Yangtze Block. Nd isotope data suggest that 40% of the modern delta sediment comes from the Song Lo. Carbonates in the Song Lo basin make this a major control on the Red River Sr budget. Erosion is not a simple function of monsoon precipitation. Active rock uplift is also required to drive strong erosion. Single grain Pb data show a connection in the Eocene between the middle Yangtze and the Red River, and probably with rivers draining the Songpan Garze terrane. However, the isotope data do not support a former connection with the upper Yangtze, Mekong, or Salween rivers. Drainage capture appears to have occurred throughout the Cenozoic, consistent with surface uplift propagating gradually to the southeast. The middle Yangtze was lost from the Red River prior to 24 Ma, while the connection to the Songpan Garze was cut prior to 12 Ma. The Song Lo joined the Red River after 9 Ma. Bulk sample Pb analyses have limited provenance use compared to single grain data, and detailed provenance is only possible with a matrix of different proxies

Research needs for mining and industrial solid waste disposal

Report of a workshop held at Colorado State University, Fort Collins, Colorado, July 22 and 23, 1976.CER76-77JN13.Under the sponsorship of the National Science Foundation, through the initiative of the Embankment Dams and Slopes Committee of ASCE; NSF Grant No. ENG 76-09380

Olivine-poor sources for mantle-derived magmas: Os and Hf isotopic evidence from potassic magmas of the Colorado Plateau

The contribution of olivine-poor lithologies (pyroxenite, eclogite, etc.) in the mantle to the composition of mantle-derived melts is a growing topic of discussion in light of results suggesting that some magmatic characteristics are not easily explained by melt derivation solely from peridotitic sources. To investigate this issue, we have examined the Hf and Os isotopic composition of potassic magmas from the Navajo Volcanic Field of the Colorado Plateau. Most of the magmas have Os isotopic compositions much more radiogenic than observed for any uncontaminated oceanic basalt. The Os isotope compositions of these samples overlap those measured for crustal/upper mantle eclogitic xenoliths carried by nearby intrusions. Compositional and Os isotope systematics, however, suggest that the characteristics of the magmas are not determined by crustal contamination, but rather are the result of melting of pyroxene- and mica-rich veins/layers in the lithospheric mantle beneath the plateau. Once generated, the melts of olivine-poor lithologies interacted with surrounding metasomatized peridotite to create the compositional spectrum from katungite to minette. One component of this compositional variation is the appearance of strong relative depletions of high field strength elements in the minette end-member, suggesting that this chemical signature, common in convergent margin magmas, may be caused by melt-wall rock interaction