佳木斯地块东部早古生代花岗岩的成因及其构造意义

发布时间：2018-08-13 15:57

【摘要】：佳木斯地块是中亚造山带在中国东北的一个重要构造单元，也是兴蒙造山带若干变质地体中最著名的一个，地处西伯利亚克拉通和华北克拉通之间。同整个中亚造山带一样，佳木斯地块经历了多期次、多阶段的复杂构造演化，形成了大量的花岗质岩石。新的锆石U Pb年龄测定表明，佳木斯地块很多原被认为形成于元古代的花岗岩，实际上形成于晚古生代，而早古生代花岗岩的时空展布、岩石组合和成因目前尚不清楚，因而有必要加强对早古生代花岗岩的研究。本文通过对佳木斯地块东部花岗岩的年代学、全岩地球化学和锆石Hf同位素特征的研究，确定花岗质岩石的形成时代及成因，并进一步探讨佳木斯地块早古生代花岗岩形成的地球动力学背景。锆石LA ICP MS U Pb结果表明，佳木斯地块东部早古生代花岗岩的侵位年龄在530~484Ma之间。地球化学特征显示：SiO2=64.66%~79.17%、K2O=3.08%~7.33%、MgO=0.14%~2.63%、CaO=0.37%~3.87%、A/CNK=0.89~1.10、 u=0.16~1.77，，富集大离子亲石元素（Rb、Nd），亏损高场强元素（Nb、Ta、P、Ti）；锆石原位Hf同位素分析显示花岗岩的εHf（t）值介于-5.8~+2.3之间，二阶段Hf模式年龄介于2.4~1.3Ga之间。表明其原始岩浆起源于古-中元古代增生的下地壳物质的部分熔融。此外，根据地球化学及同位素组成的变化，这些花岗岩的岩浆锆石记录了一致的锆石U Pb年龄和不一致的εHf（t）比值，暗示在岩石成因过程中存在分离结晶作用和地壳混染作用。结合区域研究资料，佳木斯地块曾发生过大规模的泛非期岩浆活动，且该期岩浆事件至少持续了50Ma，这些花岗岩属于壳源成因的碰撞后花岗岩，为加厚的造山带发生垮塌性伸展导致下地壳物质的部分熔融而形成的花岗质岩石，反映了佳木斯地块该期应处于碰撞后的伸展构造环境。
[Abstract]:The Jiamusi massif is an important tectonic unit of the Central Asian orogenic belt in northeast China and one of the most famous metamorphic terraces in the Xingmeng orogenic belt, located between the Siberian Craton and the North China Craton. Like the whole Central Asian orogenic belt, the Jiamusi massif underwent multiple stages of complex tectonic evolution and formed a large number of granitic rocks. The new zircon U-Pb dating indicates that many of the Jiamusi blocks were originally considered to have formed in the Proterozoic granite, but in fact they were formed in the late Paleozoic, while the space-time distribution, rock assemblage and genesis of the early Paleozoic granites are still unclear. Therefore, it is necessary to strengthen the study of early Paleozoic granite. Based on the study of geochronology, geochemistry and zircon HF isotopic characteristics of granites in the eastern Jiamusi massif, the forming age and genesis of granitic rocks are determined in this paper. The geodynamic background of the early Paleozoic granite formation in the Jiamusi block is also discussed. The results of zircon ICP and MS U / Pb indicate that the emplacement age of the early Paleozoic granites in the eastern Jiamusi block is between 530~484Ma. The geochemical characteristics show that 79.17K _ 2O-3.08 is 7.33mg _ O _ (0.14) and 2.63 ~ 0.37K ~ 0.370.891.10, U ~ (0.16N) 1.77, enriched in large ion lithophile element (Rbndd), depleted high field strength element (NbLi _ TaPnTi), zircon in-situ HF isotopic analysis shows that the 蔚 Hf (t) value of the granite is between -5.8 ~ 2.3, and the age of the second stage HF model is between -5.8 ~ 2.3, and the age of the second stage HF model is between 2.4~1.3Ga. It is indicated that the primitive magma originated from partial melting of the materials of the lower crust that were accreted in the Paleo-Mesoproterozoic. In addition, according to the changes of geochemistry and isotopic composition, the magmatic zircon of these granites recorded a consistent zircon U-Pb age and inconsistent 蔚 Hf (t) ratio, suggesting that there were segregation crystallization and crustal mixing in the genesis of the rocks. In combination with regional research data, the Jiamusi massif experienced large-scale Pan-African magmatic activity, and the magmatic event lasted at least 50 Ma.These granites belong to post-collision granites of crustal origin. The granitic rocks formed by the collapse extension of the thickened orogenic belt and the partial melting of the material in the lower crust reflect that the Jiamusi massif should be in the post-collision extensional tectonic environment in this period.
【学位授予单位】：吉林大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P588.121

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