U.S.-China Cooperative Research (Geochemistry): U-disequili-bria in Northeast Asian Alkali Basalts.

加州大学圣克鲁斯分校的James Gill和中国科学院地球化学研究所梁周成的这一为期两年的合作研究项目的目标是进行东北亚碱性玄武岩的U-Th不平衡研究。调查人员将集中精力研究265年前中国北部火山喷发产生的“年轻”玄武岩。通过放射性同位素研究，调查人员将确定中国玄武岩的来源，研究玄武岩形成过程中的化学分馏，并确定样品的年龄。U-Th不平衡研究是研究火山岩成因、地幔组成和引起地幔不均匀的过程的有用工具。美国与中国的合作在几个方面具有重要意义。铀Th不平衡研究需要“年轻的”岩石，调查人员将有机会接触到中国的一个独特来源。分析将在美国和中国的实验室进行，从而实现实验室之间的样品校准。研究成果将有助于加深对东北亚(日本、韩国和中国)近期火山喷发的性质及其与该地区构造活动的耦合的理解。中美两国实验室的共同努力和互补设施实现了美国-中国计划的主要目标，即通过国际合作促进科学知识。

The objective of this two-year cooperative research project between James Gill, University of California, Santa Cruz and Liang Zhoucheng, Chinese Academy of Sciences' Institute of Geochemistry is to perform U Th disequilibrium studies of Northeast Asian alkali basalts. The investigators will concentrate on "young" basalts from volcanic eruptions in Northern China 265 years ago. Through radioactive isotopic studies the investigators will determine the source of the Chinese basalts, study chemical fractionation during basalt genesis and date the age of the samples. U Th disequilbrium studies are useful tools for studying the origins of volcanic rocks, composition of the earth's mantle and the processes causing mantle heterogeneities. The U.S.-China collaboration is significant in several respects. U Th disequilbrium studies require "young" rocks and the investigators will have access to a unique source in China. Analysis will be performed in both U.S. and Chinese laboratories thereby enabling inter-laboratory calibration of samples. Research results will advance understanding of the nature of recent volcanic eruptions in northeast Asia (Japan, Korea and China) and its coupling to tectonic activities in this region. The combined efforts, complementary facilities of the Chinese and U.S. laboratories fulfill the principal objective of the U.S.-China program; which is, to advance scientific knowledge through international collaboration.