摘要
根据对火山岩岩石成份空间变异特征与中生代构造格局间关系的分析和实验岩石学成果,作者认为中国东部中生代陆相火山岩岩石成份主要受构造应力和基底组份的控制,而且基底岩石的重熔也受构造应力控制,也就是说,构造应力场是火山岩成份变异的主要因素。
The Mesozoic volcanic rocks widespread in eastern China arc a part of the marginal-Pacific igneous rock belt and may be divided into three NNE-trending zones and one E-W-trending zone and some subzones and provinces according to their spatial distribution,rock associations and controlling structures.In this paper the average chemical compositions of the volcanic rocks of the zones,subzones and provinces and the whole of eastern China are given.The volcanic rocks of eastern China belong to quatz andesite(SiO_(2)65.94,Na_(2)O 3.40,K_(2)O 4.24,and Rittmann normσ2.54)and are characterized by enrichment in alkalis,especially potassium,although the volcanic rocks in some areas are enriched in sodium.The Mesozoic volcanic rocks may be divided into the alkali basalt-basalt is trachyandesite-trachyandesite-trachyte(or phonolite),basalt-andesite-dacite-rhyolite,and rhyolite-dacite-(andesitebasalt)associations and the northern,central and southern provinces that are characterized by different chemical compositions and volcanic rock associations.Besides,based on the volcanic rock associations,chemical composition,Sr isotopic and REE characteristics and their structural positions,the Mesozoic volcanic rocks may be divided into two genetic types:(1)mantle-derived type or mixed mantle-and crust-derived type,and(2)crust-derived type.Abundant geological data and results of experimental petrology show that the basaltic magma mainly originated in the tensile structural environment and the rhyolitic magma tended to form in the compressive structural environment.The author considers that the problem on the genesis of the Mesozoic volcanic rocks in eastern China must be approached in respects of formation(upper mantle and lower crust or basement)and the deformation(structural stress),and it is very likely that the structural stress played the dominant role.The Mesozoic volcanic rocks in eastern China are the products of the evolution of East Asia into the marginal-Pacific tectonic domain and their formation is closely related to the reciprocal motion of the Asian continent and the Pacific plate,but such motion is expressed by two manners:the westward subduction of the Pacific plate beneath the Asian continental plate and the southward sliding of the Central Asian continent relative to the Pacific basement,and the latter further led to the generation of a gigantic NNE-trending Tancheng-Lujiang deep wrench fault at the inner margins of the continent.The magmatism in the South China region was controlled by the westward com-pressive stresses exerted by the Pacific plate since the region is close to the subduction zone and the magma was generated by the anatexis of the lower crust,but the coastal areas were partially influenced by the magma derived from the subduction zone.The magmatism in Northeast China was mainly dominated by the compressive stresses derived from the southward sliding of the Asian continent and chiefly resulted from the anatexis of the lower crust.The magmatism in the Yanshan Mountains,southern Jilin-eastern Liaoning,Shandong and the lower Yangzi(Chang-jiang)River valley was closely related to the sinistral shearing and rifting of the Tancheng-Lujiang fracture belt.Of the above-mentioned regions,those located in the tensile stress field mainly contain the mantle-derived or mixed mantle-and crust-derived intermediate-basic volcanic rocks,while those situated in the compressive stress field mainly contain intermediate-acid volcanic rocks.
作者
徐志刚
Xu Zhigang(Institute of Mineral Deposits,Chinese Academy of Geological Sciences)
出处
《地质学报》
1985年第2期109-126,共18页
Acta Geologica Sinica
