溧水中生代橄榄安粗岩系的构造环境及演化关系  

ANALYSES OF TECTONIC SETTING FOR OCCURRENCE OF LISHUI MESOZOIC SHOSHONITE SERIES AND ITS EVOLUTIONAL RELATIONSHIP

作　　者：周金城[1] 赵太平[1] 陈克荣[1] 

机构地区：[1]南京大学地球科学系

出　　处：《南京大学学报（自然科学版）》1994年第3期504-510,共7页Journal of Nanjing University（Natural Science）

摘　　要：溧水中生代橄榄安粗岩系中橄辉玄粗岩的不相容元素对原始地幔的配分曲线与东非裂谷相应岩石的配分曲线相近似，而与典型岛弧地区橄辉玄粗岩的配分曲线明显不同．溧水橄榄安粗岩系的产出与下扬子地区中生代时期地壳的减薄、地幔的上涌、长江深断裂的发育，即与“陆内拉张”的构造环境有关．本文并用成岩模拟计算证实了橄榄安粗岩系内不同类型岩石间的相互演化关系．The Mesozoic volcanic sequences in the Lishui basin include Longwangshan, Dawangshan, Guanshan and Jiashan formations, which constitute associated K-rich cafe-alkaline series and shoshonite series. To discern tectonic setting of the Lishui Mesozoie volcanic magmas, authors compared the trace elements and REE abundances of shoshonitic mafic rocks in Lishui and Luzhong basins from the Lower Yangtzefault depression zone with those from other different tectonic environments. Theincompatible elements patterns normalized by hypothetical primordial mantle compositions for absarokite from Lishui and Luzhong are distinctly different from that of island arc area. The patterns of absarokite from Lishui and Luzhong have Rb, Th, Ce, Nd and Zr spikes (similar to that of East Africa rift). In contrast, the pattern of island arc has depletions for these elements. On the other hand, the patterns of absarokite from Lishui and Luzhong have depletions for Ba, Sr, and p(also similar to that of East Africa rift), that of island arc, howover, has spikes for these elements. In general, the patterns of Lishui and Luzhong are situated between those of East Africa rift and island arc, and keep basically synchronous variations with that of the former.Our trace elements model calculation verified possible assimilation-fractional crystallization (AFC) processes which cause magmatic diversity in the Lishui basin. In first model calculation, alkaline olivine basalt, which have modal composition of plagioclase (Pl)+olivine (01)+augite (Aug)+magnetite (Mt) in the ratio 62:10:20:8 and bulk partition coefficients DRb = 0.0478, DBa = 0.1018, is used as starting composition. The modal composition is taken as fractional assemblage in the calculation. Spinel garnet mica schist (Sgms) enclave in the Precambrian granites from Jiangnan ancient island arc is used as assimilant with the mass assimilated/ mass fractionated (R)=0.25. Variations of both Rb and Ba selected as represents of incompatible elements have been calculated by the method of Depaolo. Cal

关 键 词：橄榄安粗岩系 构造环境 演化关系 

分 类 号：P588.14[天文地球—岩石学]