辽东黄花甸地区古元古代花岗质岩浆作用及其地质意义

发布时间：2019-01-17 13:17

【摘要】：胶-辽-吉古元古代造山/活动带的辽东黄花甸地区出露大量古元古代花岗质岩石,前人将该区的花岗质岩石统称为花岗质混杂岩。本文通过详细的野外地质调查和室内综合研究,将该套花岗质混杂岩解体为时代及性质完全不同的两类花岗岩——黑云母二长花岗岩和花岗闪长岩。其中黑云母二长花岗岩具有块状、条痕状、片麻状的不同构造类型,均显示富SiO_2(72.37%~77.44%)、贫Al_2O_3(11.69%~13.21%)、富K_2O(3.97%~5.11%)的特征,Na_2O/K_2O=0.64~1.08,TiO_2含量在0.18%~0.34%之间,MnO、MgO和P_2O_5的含量较低,分别为0.01%~0.07%、0.12%~0.32%和0.01%~0.06%,铝饱和指数A/CNK集中分布在1.33~1.45之间,A/NK在1.49~2.60之间,属于过铝质高钾钙碱性系列;微量元素Sr、Ba、Ti、P强烈亏损,具有明显的Eu负异常,具有A型花岗岩的特征。黑云母二长花岗岩的锆石大部分为具有清晰震荡环带结构的岩浆锆石,从3个样品获得LA-ICP-MS锆石U-Pb谐和年龄分别为2185±29Ma、2183±13Ma、2166±10Ma,据目前所获得南辽河群碎屑锆石年龄(1.95~2.15Ga),本文认为黑云母二长花岗岩的侵位时代要早于南辽河群地层沉积的时间,构成了南辽河群地层沉积的基底。花岗闪长岩呈岩枝状侵入黑云母二长花岗岩和里尔峪组地层中,富SiO_2(72.54%~74.31%)、Al_2O_3(15.01%~16.17%),全碱(K_2O+Na_2O)平均7.77%,相对富钠(Na_2O/K_2O=1.27~2.82),贫钙、镁,MgO平均为0.26%,CaO平均为1.59%,Mg#值平均为54.0,铝饱和指数A/CNK集中分布在1.61~1.78之间,A/NK在1.49~2.60之间,属于过铝质钙碱性系列,具明显的Eu正异常,Y/Yb低,Sr/Y高,而且强烈亏损Th、Ta、Nb、Ti等高场强元素,富集Ba、K、Rb、Sr等低场强元素,具有埃达克质花岗岩的特征。花岗闪长岩的锆石大部分为具有清晰震荡环带结构的岩浆锆石,从2个样品获得LAICP-MS锆石U-Pb年龄分别为1995±18Ma、1995±13Ma。可以推断花岗闪长岩的侵位时代为2.0Ga左右。本文认为具有A型特征的黑云二长花岗岩是陆块内部拉伸减薄-裂解过程中下部地壳部分熔融的产物,具有埃达克质特征的花岗闪长岩是俯冲过程中所形成火山弧或活动大陆边缘岩浆活动的产物。以上研究表明胶-辽-吉古元古代造山/活动带可能经历了在2.2~2.15Ga左右的拉伸裂解过程和2.0Ga左右俯冲挤压的构造演化过程。
[Abstract]:A large number of ancient Gu Yuan granitic rocks were exposed in Huanghuadian area of the Jiao-Liaoji-Jiguo Paleoproterozoic orogenic / active belt, and the granitic rocks in this area were generally called granitic melange. Based on detailed field geological investigation and laboratory comprehensive study, the granitic melange is disintegrated into two types of granitoids, biotite monzogranite and granodiorite, which are of completely different ages and properties. Among them, biotite monomorphic granites are of block, stripe and gneiss types, all of which are rich in SiO_2 (72.37%) and poor in Al_2O_3 (11.6910%, 13.21%), and are rich in SiO_2 (77.44%) and poor in Al_2O_3 (13.21%). The content of Na_2O/K_2O=0.64~1.08,TiO_2 is between 0.18% and 0.34%, and the contents of MnO,MgO and P_2O_5 are lower, 0.01and 0.07%, respectively. 0.12 0.32% and 0.01% respectively. The aluminum saturation index (A/CNK) was distributed in the range of 1.33 ~ 1.45 and the A/NK was in the range of 1.49 ~ 2.60, belonging to the peraluminous high-potassium calc-alkaline series. The trace element Sr,Ba,Ti,P is strongly depleted and has obvious negative Eu anomaly, which is characterized by A-type granite. The zircon of biotite monzonitic granite is mostly magmatic zircon with clear concussion ring structure. The U-Pb harmonic age of LA-ICP-MS zircon is 2185 卤29 Ma, 2183 卤13 Ma, 2166 卤10 Ma, respectively, from three samples. According to the zircon age (1.95~2.15Ga) of the South Liaohe Group, it is believed that the emplacement age of biotite monzogranites is earlier than that of the South Liaohe Group, which constitutes the basement of the South Liaohe Group. The granodiorite intruded into the formation of biotite monzogranite and Lianyu formation in the form of branching, rich in SiO_2 (72.54 and 74.31%), Al_2O_3 (15.01%) and K _ 2O Na_2O (7.77% on average). Relative sodium rich (Na_2O/K_2O=1.27~2.82), poor calcium, magnesium, MgO were 0.26% Cao, the average value of Mg# was 54.0, and the A/CNK of aluminum saturation index was 1.61 ~ 1.78, respectively. A/NK is between 1.49 and 2.60, belongs to peraluminous calc-alkaline series, with obvious positive Eu anomaly, low Y/Yb, high Sr/Y, and strong loss of Th,Ta,Nb,Ti and other high field strength elements, enriched Ba,K,Rb,. Sr and other low field elements have the characteristics of adakitic granite. The zircon of granodiorite is mostly magmatic zircon with clear concussion ring structure. The U-Pb age of LAICP-MS zircon obtained from two samples is 1995 卤18Ma1995 卤13Ma. It can be inferred that the emplacement age of granodiorite is about 2.0Ga. In this paper, it is considered that the black cloud monzogranite with A-type characteristics is the product of partial melting of the lower crust in the process of extensional thinning and splitting of the continental block. The granodiorite with adakitic characteristics is the product of volcanic arc or active continental margin magma formed during subduction. The above studies indicate that the Jiao-Liaojianguo Proterozoic orogenic / active belt may have undergone the process of tensile cracking around 2.2~2.15Ga and the tectonic evolution of subduction and compression around 2.0Ga.
【作者单位】：吉林大学地球科学学院;中国地质科学院地质研究所;
【基金】：国家自然科学基金重点项目(41430210) 中国地质调查局地质调查项目(DD20160121)联合资助
【分类号】：P588.1

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