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

该提案描述了一个美国-人民共和国 中国地球科学多学科合作项目。 这项研究涉及三名来自斯坦福大学的研究人员，两名来自 日本和中国各8名。 我们希望继续进行 协调场-岩石学-年代学-构造学 前寒武纪蓝片岩和榴辉岩带的研究 中国中部，以限制这些起源 克拉通内蓝片岩带 最近的报告，许多前- 中华人民共和国中生代-前寒武纪-蓝片岩带 提供了一个很好的机会来测试各种假设， 蓝片岩相变质作用， 这些事件的年龄关系。 中国同事有 确定了4个可能的前寒武纪事件，包括 不连续的、连贯的蓝片岩带，长2000多公里， 认为其成因与深大断裂有关 系统. 榴辉岩是丰富的，有些是与 蓝片岩：其他位于太古代片麻岩夹层中， 含有残余柯石英--一种SiO2的高压多晶型物。 除此之外，人们对它的了解甚少。 中国蓝片岩的相岩石学和矿物共生 和榴辉岩;前寒武纪的可用放射性测年 蓝片岩和榴辉岩变质作用不明确。 拟议 美国的中国项目将解决这些问题;它将涉及 系统的现场观察，共存的微探针分析 矿物+ P-T测量，岩石和K-Ar，U-Pb的大量XRF分析， Nd-Sm和Ar_（39）/Ar_（40）年龄测定 主要目标是： (1)绘制蓝片岩的分布和构造背景图 岩相岩石和榴辉岩;（2）确定矿物学和 变质岩的化学成分;（3）比较 对比不同类型榴辉岩;（4）圈定矿物 蓝片岩和榴辉岩的共生和P-T-时间轨迹 （5）确定了蓝片岩的时代， 榴辉岩变质作用;（6） 阐明公认的 变质、火成岩和构造特征。 程序应该 有助于更好地理解 克拉通内蓝片岩和榴辉岩以及复杂的地质- 中国中部构造组合 我们以前的合作伙伴 与中国地质学家的交流卓有成效。 预计进展会加快，因为 基础工作和许多初步的岩石学和实地研究 已经完成的项目

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.