中国大陆科学钻探工程预先导孔中片麻岩-花岗质片麻岩的岩石学和地球化学研究  

Petrology and Geochemistry of Gneiss and Granitic Gneiss from Pre-pilot Drillhole (CCSD-PP1), Chinese Continental Scientific Drilling Project

作　　者：刘福来[1] 许志琴[1] 张泽明[1] 杨经绥[1] 

机构地区：[1]中国地质科学院地质研究所,北京100037

出　　处：《地质学报》2001年第1期70-81,T003,T004,共14页Acta Geologica Sinica

基　　金：中国大陆科学钻探工程选址研究及中华人民共和国连云港幅(I50C002004)1:25万区域地质调查的部分成果。

摘　　要：中国大陆科学钻探工程预先导孔（CCSD－PP1）中岩心的岩性十分复杂，主要由片麻岩－花岗质片麻岩、超基性基、榴辉岩及少量多硅白云母石英片岩、斜长角闪岩及角闪云母片岩组成。其中片麻岩－花岗质片麻岩是最重要的岩石类型。根据片麻岩的岩相学及地球化学特征，确定片麻岩类岩石的地为一套具有较高成熟度的碎屑沉积岩－低成熟度的酸性火山岩、碎屑沉积岩建造，并与在其内部呈夹层形式存在的榴辉岩一起经历了超高压变质作用。花岗质片麻岩可分为三种类型：绿帘黄铁二长花岗质片麻岩、绿帘黑云二长花岗质片麻岩和绿帘二云二长混合片麻岩。绿帘黄铁二长花岗质片麻岩SiO2含量最高，为76．2％－78．86％，具有强烈的负Eu、Ba异常，Eu/Eu^*=0.125,Ba/Ba^*=0.096-0.396，其稀土和微量元素的配分模式与具有极高成熟度碎屑沉积岩部分熔融而成的花岗岩性质十分相似。该类花岗质片麻岩可能在苏鲁超高压变质带形成之前，由具有极高成熟度的碎屑沉积岩部分熔融而成的岩浆，侵入到片麻岩类的表壳岩中，并经历了超高压变质作用。绿帘黑云二长花岗质片麻岩、混合片麻岩的SiO2含量明显偏低，且稀土、微量元素配分模式明显不同于绿帘黄铁二长花岗质片麻岩，该类岩石可能由片磨岩类岩石在超高压变质作用峰期阶段和近等温减压等一阶段深熔作用而成。该项研究对于深入探讨苏鲁超高压变质带变质作用－岩浆作用相互间的成因关系及其动力学过程有着重要的意义。The pre-pilot drillhole CCSD-PP1 of Chinese Continental Drilling Project, with a depth of 432.08 m, is located in Zhimafang, southeastern Donghai County. Core samples from CCSD-PP1 consist mainly of gneiss-granitic gneiss, ultramafic rocks and eclogite with small amounts of phengite quartzite, amphibolite and hornblende-biotite schist. According to the petrographical and geochemical characteristics, the protoliths of gneisses are a sequence of relatively high-maturity clastic sedimentary rocks lower- maturity acid volcanic rocks and clastic sedimentary rocks, which experienced ultrahigh-pressure (UHP) metamorphism together with the eclogites as intercalated layers in the gneisses. The granitic gneisses may be divided into three types: epidote-pyrite mon-zogranitic gneiss, epidote-biotite monzogranitic gneiss and epidote-two mica monzonitic migmatitic gneiss. The SiO2 content of the epidote-pyrite monzogranitic gneiss is the highest, ranging from 76. 72% to 78. 86%, with intense negative Eu and Ba anomalies, Eu/Eu* =0. 125-0. 164 and Ba/Ba* =0. 095-0. 396. The rare earth element (REE) and trace element distribution patterns are silimar to those of granite formed by partial melting of clastic sedimentary rocks with very high maturity. Coesite-bearing UHP mineral inclusions were identified in zircons separated from this kind of granitic gneiss. These features indicate that this kind of granitic gneiss may have been formed by the following genetic mechanism: the magma formed by partial melting of clastic sedimentary rocks with very high maturity, intruded into the supercrustal rocks of gneisses prior to the formation of the Sulu UHP metamorphic belt, and then crystallized and experienced ultrahigh-pressure metamorphism. However, in the epidote-biotite monzogranitic gneiss and migmatitic gneiss, the SiO2 contents are much lower than that of epidote-pyrite monzogranitic gneiss. The REE and trace element distribution patterns are much different from that of epidote-pyrite monzogranitic gneiss. In addition, no-UHP minera

关 键 词：花岗质片麻岩 地球化学 成因机制 预先导孔CCSD- 

分 类 号：P588.345[天文地球—岩石学] P59[天文地球—地质学]