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中国东南部晚中生代花岗质火山-侵入杂岩特征与成因

王德滋, 周金城, 邱检生, 范洪海   

  1. 南京大学 地球科学系, 江苏 南京 210093
  • 收稿日期:2000-12-20 修回日期:2000-12-20 出版日期:2000-12-20 发布日期:2000-12-20

Characteristics and Petrogenesis of Late Mesozoic Granitic Volcanic-Intrusive Complexes in Southeastern China

WANG De-zi, ZHOU Jin-cheng, QIU Jian-sheng, FAN Hong-hai   

  1. Department of Earth Sciences, Nanjing University, Nanjing 210093, China
  • Received:2000-12-20 Revised:2000-12-20 Online:2000-12-20 Published:2000-12-20

摘要: 晚中生代期间,中国东南部岩浆活动十分强烈。 由内陆向沿海,花岗岩、火山岩的时代越来越新。花岗岩 与酸性、中酸性火山岩在成因上存在密切联系。在时间、空间和成岩物质来源一致的条件下 ,花岗岩可视为流纹岩、英安岩所构成的中心式火山机构的“根”,形成所谓的花岗质火山-侵入杂岩。中国东南部的花岗质火山-侵入杂岩可以区分为同熔型、陆壳重熔型和A 型三类,它们具有不同的构造环境、形成机制和物质来源。同熔型火山-侵入杂岩主要分布 于沿海,陆壳重熔型火山-侵入杂岩一般分布于内陆,而 A型花岗质火山-侵入杂岩主要受浙闽沿海长乐-南澳断裂带控制。 以桐庐和相山两个典型杂岩体为代表剖析了花岗质火山-侵入杂岩 体的时、空、源一致性,所揭示的规律对于认识整个中国东南部晚中生代花岗质火山-侵入 杂岩的成因具有普遍意义。

Abstract: During the late Mesozoic, magmatic activities in southe astern China were very intensive. In the products of magmatism, the gra nites-rhyolites are predominant, and the andesitic-basaltic rocks are less imp ortant. The statistica l data on the isochron ages for over 200 granite and volcanics samples show that the earl y Cretaceous ages make up about 60% of age population; and the late Jurassic, 20 %; the late Cretaceous, 10%; the middle Jurassic, 10%. The ages of Mesozoic volcanic s and related granites in southeastern China have a tendency of getting younger from the inland toward the coast. In some cases, granites and associated acid ic and interm ediate volcanic rocks are comagmatic. Under the condition of uniformity in time, space and source materials, the granities can be considered as the “roots” of t he central type volcanic apparatuses composed of rhyolites and dacites, forming so -called granitic volcanic-intrusive complexes. The granitic volcanic-intrus i ve complexes in southeastern China may be divided into three types, i.e., syntex is type, continental crust remelting type and A-type. Their petrogenesis is cont rolled by different tectonic settings, rock-forming mechanisms and source materials. The syntexis t ype is dominantly distributed in the coastal area, w hereas the continental crust remelting type is mainly located in the inner land. Th is spatial pettern is constrained by two factors: the composition of b asement rocks and the intensity of crust-mantle interactions. Underplating of basaltic magma took place more intensively in the coastal area of Zhejiang and Fujian provinces during the late Mesozoic. Therefore, the crust-mantle interaction was also more intensive in the coastal area than i n the inner l and. In the west of Wuyishan Mts., the continental crust usually possesses highe r maturity. The meta-igneous materials, such as amphibolites, are rare or absent in the baseme nt rocks of the area. The combining constraints of these two factors led t o a regular spatial distribution of above-mentioned two types of granitic volcani c-intrusive c omplexes in southeastern China. The distribution of A-type granitic volcanic-i ntru sive complexes is mainly controlled by Changle-Nanao fault zone in the coastal a rea of Zhejiang and Fujian provinces. The thickness of both lithosphere and cont inental cr ust is obviously thinned and the asthenosphere is upwelled in this r egion. It is evident that A-type granitic volcanic-intrusive complexes were fo rmed in a extensional tectonic setting and display the post-orogenic features. Since then, the Yanshanian magmatic activities were toward the end. In this pap e r, the authors show the uniformity in emplacement time, space and source mate rials for granitic volcanic-intrusive complexes, taking both Tonglu and Xiangsh an complexes as examples. Some regularities summarized may be very important for un de rstanding the genesis of granitic volcanic-intrusive complexes in southeastern China.