摘要
中国大陆科学钻探工程主孔(CCSD-MH)3000~3500m深度范围内的岩心揭示的主要岩石类型以正、副片麻岩为主,夹少量的榴辉岩、片岩及斜长角闪岩等。正片麻岩可进一步划分为钾长花岗质片麻岩和二长花岗质片麻岩。地球化学研究表明,花岗质片麻岩的SiO2含量普遍高,为73.56%~79.01%,Al2O3含量为10.49%~13.75%;TiO2、Fe2O3、FeO、MnO和MgO的含量明显偏低,其中Fe2O3为0.26%~2.56%,FeO为0.09%~1.13%,MgO为0.01%~0.63%;岩石明显富含Na2O、K2O,强烈贫钙,Na2O K2O的含量为6.20%~9.15%,K2O的含量为1.26%~5.67%,CaO的含量为0.08%~1.59%。花岗质片麻岩在洋脊玄武岩标准化蛛网图上都表现出强烈富集大离子亲石元素(K、Rb、Th)的特点,高场强元素Ti、Ta和Nb表现为明显的负异常,而Hf和Zr则为明显正异常。3000~3500m花岗质片麻岩的原岩具A型花岗岩的特征,形成于大陆裂谷环境,记录了Rodinia超大陆裂解时苏鲁地区的花岗岩浆事件,表明新元古代晚期扬子板块北缘的构造属性为大陆裂谷环境。
The main drill hole CCSD-MH, Chinese Continental Scientific Drilling Project (CCSD), with depth of 5000 m, is located in the Donghai area, southwestern Sulu terrane. The 3000~3500 m recovered cores in CCSD-MH are mainly comprised of orthgneiss (granitic gneiss) and paragneiss, with thin layers of eclogite, chist and amphibolite. The orthgneiss.can be subdivided into two groups: K-feldspar granitic gneiss and monzonitic granitic gneiss. The SiO_2 and Al_2O_3 contents of analyzed granitic gneiss samples range from 73.56% to 79.01%, and from 10.49% to 13.75%, respectively. All the analysis show lower abundance of TiO_2, Fe_2O_3, FeO, MnO and MgO; Fe_2O_3=0.26%~2.56%, FeO=0.09%~1.13% and MgO=0.01%~0.63%. The analyzed orthogneiss samples are richer in Na_2O and K_2O contents, but poor in CaO content, with vary intervals of Na_2O K_2O=6.20%~9.15%, K_2O=1.26%~5.67% and CaO=0.08%~1.59%. In the MORB normalized spider diagram, the granitic gneiss is relatively riched in K, Rb, Th, Zr and Hf, but evident depleted in Ti, Ta and Nb. The major and trace element compositions indicate that the preexisting rock of granitic gneiss belong to A-type granite protolith, formed in the continental rift surrounding related to Neoprotorozoic Rodinia supercontinent breakup event.