大地热流研究揭示的中国地壳成分横向变化

LATERAL VARIATION OF CRUSTAL COMPOSITION IN CHINA AS REVEALED BY HEAT FLOW STUDY

依据大地热流值、地壳厚度以及大陆壳 /幔热流比与地下流体氦同位素比值的相关关系 ,计算出中国主要构造单元地壳生热率 .同时 ,根据Rudnick和Fountain( 1995 )的数据得到地壳生热率和SiO2 质量分数的线性关系 ,进而利用生热率数据得到地壳SiO2 质量分数 .此方法得到的中国东部地壳生热率和SiO2 质量分数与基于地震波速的成分模型相符 .中国大陆地壳生热率和SiO2 质量分数横向变化明显 ,东部地区地壳为中性成分 ,相对富集强不相容元素 ;而西北部盆地地壳成分偏于中基性 .华北、扬子和塔里木地壳成分差异较大 ,克拉通内部表现出明显的成分非均匀性 ,褶皱带地壳一般较克拉通略富长英质组分 .

The crustal heat generation rate of major tectonic units in China are calculated on the basis of heat flow, crustal thickness as well as the inverse relation between the heat flow ratio of continental crust/mantle and the helium isotopic composition of underground fluid. Meanwhile, the linear relation between heat generation (A) and SiO2 content (w(SiO2)) of the bulk crust is obtained from the data of Rudnick and Fountain (1995). Then, the w(SiO2) of China's crust are derived from the w(SiO2) - A relation. The derived w(SiO2) and A are in agreement with the values obtained from the seismic velocity-based composition models. There exhibits an obvious lateral variation of heat production and w(SiO2) in China's crust. The eastern China crustal composition, intermediate, contains relatively concentrated strong incompatible elements, but the crustal composition of the northwestern China basins is prone to be intermediate to mafic. The crustal compositions in North China, Yangtze craton and Tarim platform are different from each other to a relatively great extent. Obvious lateral variation of composition is also present within cratons. The orogenic crust often contains slightly more felsic components than does craton.