U.S.-China Cooperative Research: Mechanisms of Pluton Emplacement; Study of East China and North America Batholiths

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9507687 Teyssier This award supports collaboration between Christian Teyssier, University of Minnesota, and Wen TianFang, China University of Geosciences on Mechanisms of pluton emplacement. The PI's core research is focused on testing the hypothesis that granitoid plutons are emplaced in the upper crust in tensional bridges between crustal-scale fractures. This research is presently being conducted in the Sierra Nevada batholith, a major continental arc in the Circum-Pacific. The aim of the proposed project is to extend the analysis of pluton-emplacement mechanism to East China in areas that underwent similar tectonic processes as the Sierra Nevada. The methods used in the Sierra Nevada involve structural analysis in the field and in the laboratory, and the analysis of anisotropy of magnetic susceptibility of granitoid rocks in order to retrieve information about magma flow during emplacement. In East China, it will be possible to add a new component to this project, the gravity-anomaly analysis of plutons, in order to define their three-dimensional shape. This technique is difficult to apply successfully within the Sierra Nevada because the rugged topography induces large errors. In contrast, the plutons of East China are exposed in areas of smooth topography, ensuring that this analysis will provide a useful signal above the background noise. Defining the three-dimensional shape of plutons, and particularly the root zones of plutons, is a key element in the hypothesis to be tested. The Chinese group, led by Professor Wan, has corresponded with the PI regularly in the past two years on the methods of pluton emplacement analysis. The two study areas in Eastern China were carefully chosen - in terms of tectonic similarity to the Sierra Nevada, good field exposure, and gentle topography - to insure meaningful results from the analyses and thereby test different models of granitoid emplacement effectively. The Chinese group brings their knowledge of the regional geology and their experience in the field. The American group brings techniques of rock magnetism and gravimetry applied to plutons. All stages of the work, from field analysis to laboratory measurements, will be conducted jointly, and the results will be written collaboratively.