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

美国加州大学圣克鲁兹分校James Gill与中国科学院地球化学研究所Liang Zhoucheng的合作研究项目为期两年，目的是对东北亚碱性玄武岩的U - Th不平衡进行研究。研究人员将把重点放在265年前中国北方火山喷发的“年轻”玄武岩上。通过放射性同位素研究，研究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。不平衡研究是研究火山岩起源、地幔组成和地幔非均质性形成过程的有用工具。美中合作在几个方面意义重大。不平衡研究需要“年轻”的岩石，研究人员将有机会在中国获得一个独特的来源。分析将在美国和中国的实验室进行，从而实现实验室间样品的校准。研究结果将促进对东北亚（日本、韩国和中国）近期火山喷发性质及其与该地区构造活动的耦合的认识。中美两国实验室的共同努力和互补设施实现了美中项目的主要目标；那就是通过国际合作来推进科学知识。

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.