中国大陆科学钻探工程主孔100～2000m放射性产热元素的垂向分布特征及其成因  

Vertical distribution characteristics and origin of radiogenic heat-producing elements (HPE) in the first 2000 m of the main hole of the CCSD Project

作　　者：曾令森[1] 刘福来[1] 张泽明[1] 杨经绥[1] 许志琴[1] 

机构地区：[1]中国地质科学院地质研究所,国土资源部大陆动力学重点实验室,北京100037

出　　处：《中国地质》2005年第2期230-238,共9页Geology in China

基　　金：中国地质调查局地质大调查项目(121201056606);国家973基础研究项目(2003CB716500)资助。

摘　　要：地球内部放射性产热元素U、Th及K(HPE)含量如何随深度的变化而变化是固体地球科学中的一个重要参数,在限定地壳的热和流变学结构、地球化学、岩石和构造模型中起关键性的作用。对HPE深部分布的认识主要来自于对大型花岗岩岩基的研究及对地表热流值和产热率之间关系的模拟,对高压-超高压变质地体的HPE随深度的分布缺乏认识。在苏鲁超高压变质带中实施的中国大陆科学钻探工程届时将提供超过5km的岩心,为确定苏鲁超高压带的HPE结构提供了最好的机会。对CCSD的100～2000m岩心的732块样品详细的放射性产热元素含量的测试及现今产热率计算的初步结果表明:(1)花岗质片麻岩具有最高的产热率,平均为1665×10-11W/kg;(2)副片麻岩(变沉积岩)具有中等的产热率,为994×10-11W/kg;(3)金红石榴辉岩及石榴石橄榄岩具有最低的产热率,为17×10-11～20×10-11W/kg;(4)放射性产热元素的浓度及相应的产热率随岩性的变化而变化,呈现阶梯状的分布特征。产热率随深度的变化特征表明CCSD主孔中的HPE三明治结构。该结构可能代表着高压-超高压变质地体中的典型HPE结构,比大型花岗岩岩基的HPE结构更复杂,与传统的HPE指数衰减分布模式不吻合。CCSD主孔中所揭示的三明治式HPE结构是大陆被动陆缘中的基性及超基性岩。How radiogenic heat-producing elements (HPE) are distributed as a function of depth in the Earth is critical to determine the thermal and rheological structure of continental crust and to constrain geochemical, petrological, and tectonic models of crustal evolution. Our knowledge of HPE distribution within the crust has been derived predominantly from studies of large-scale granitic batholiths. The HPE distribution within high-grade metamorphic terrains are not well studied and thus poorly understood. The Chinese Continental Scientific Drilling (CCSD) Project provides us an unparallel opportunity to characterize the vertical HPE distribution in a type example of high- to ultrahigh-pressure metamorphic terrains worldwide. U, Th, and K2O contents have been measured on 734 core samples taken at intervals of 2 to 5 m and used to determine the distribution pattern of radiogenic heat production. Preliminary results show that: (1) the granitic gneisses have the highest heat production with an average of 1665×10-11W/kg; (2) the paragneisses have the intermediate heat production values; (3) the rutile eclogites and garnet peridotites have the lowest and similar values at about 17~20×10-11W/kg;(4) radiogenic HPE concentrations and heat production change stepwise as lithology changes downward. These data reveal a sandwich-like structure for the HPE in the drilling core in which relatively high heat production sections are enclosed by relatively low heat production sections. Such a pattern is not consistent with the downward-decreasing exponential distribution predicted from modeling of surface heat flow data. However, it may represent a typical structure in UHP metamorphic terrains as a result of deformation during or after the exhumation which resulted in the juxtaposition of mafic to ultramafic blocks with felsic blocks.

关 键 词：产热元素 产热率 苏鲁超高压变质带 中国大陆科学钻探工程 流变学结构 

分 类 号：P542.5[天文地球—构造地质学]