United States-China Scientific Cooperative Project: A Petrotectonic Study of Precambrian Blueschist and Eclogite Belts in Central China

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This proposal described a United States - Peoples Republic of China multidisciplinary cooperative project in earth science. The study involves three investigators from Stanford, two from Japan and 8 from China. We wish to continue to conduct coordinated field-petrological-geochronological-tectonic investigations of Precambrian blueschist and eclogite belts in central China in order to constrain the genesis of these intracratonal blueschist belts. Recent reports of many pre- Mesozoic-- even Precambrian -- blueschist belts in the PRC provide an excellent opportunity to test various hypotheses for blueschist facies metamorphism by establishing the tectonic and age relations of these occurrences. Chinese colleagues have identified 4 probable Precambrian occurrences including a discontinuous, coherent blueschist belt more than 2000 km long in central China and suggested its origin is related to deep fault systems. Eclogites are abundant and some are associated with blueschists: other lie within Archean gneiss terranes and contain relict coesite -- a high pressure polymorph of SiO2. Except for reconnaissance surveys, little is known about the phase petrology and mineral parageneses of Chinese blueschists and eclogites; available radiometric dating from Precambrian blueschist and eclogite metamorphism is ambiguous. The proposed U.S. China project will remedy these problems; it will involve systematic field observation, microprobe analyses of coexisting minerals + P-T-ometry, bulk XRF analyses of rocks and K-Ar, U-Pb, Nd-Sm and Ar39/Ar40 age determinations. Primary objectives are: (1) to map the distribution and structural setting of blueschist facies rocks and eclogites; (2) to determine mineralogical and chemical compositions of the metamorphic rocks; (3) to compare and contrast various types of eclogites; (4) to delineate mineral paragenesis and P-T-time paths for blueschist and eclogite metamorphism; (5) to establish the ages of blueschist and eclogite metamorphism through radiometric dating; and (6) to elucidate the genetic relationship between recognized metamorphic, igneous and tectonic features. The program should contribute to a much improved understanding of the genesis of intracratonal blueschists and eclogites and the complex geologic- tectonic assembly of central China. Our previous cooperative exchanges with Chinese geologists have been highly productive. Accelerated progress is anticipated because of the detailed groundwork and many preliminary petrological and field studies that have already been completed.