【作者】 郑培玺；

【导师】 金巍；

【作者基本信息】 吉林大学 ， 矿物学、岩石学、矿床学， 2009， 博士

【摘要】 冀东-辽西地区分布有大面积的太古代花岗质岩石,是研究华北克拉通地壳起源与演化的理想地区之一。通过详细的野外地质调查,将该地区太古代花岗质岩石划分为三类:英云闪长岩-花岗闪长岩组合、黑云母二长花岗岩组合和黑云母花岗岩组合,并初步划分出各类岩石组合的分布范围。LA-ICP-MS锆石U-Pb年代学研究显示,三类花岗质岩石形成时间基本一致,集中在2.50-2.56Ga。地球化学特征显示,英云闪长岩-花岗闪长岩和黑云母二长花岗岩组合源于高压下玄武质地壳的部分熔融,黑云母花岗岩组合来源于浅部层次硅铝质地壳的部分熔融。锆石Hf同位素显示,本区主要存在多期壳幔分异事件,最主要的壳幔分异事件发生在2.7-2.9Ga之间。2.5-2.6Ga壳幔分异事件与锆石的结晶年龄(2.50-2.52Ga)基本一致,表明本区花岗质岩石形成过程中有源自地幔分异的新生地壳物质的加入。根据前人研究成果和本文的工作推断,本区新太古代晚期以花岗质岩石为代表的大规模地壳重熔事件与幔源岩浆的底板垫托作用(underplating)相关。更多还原

【Abstract】 The North China Craton is the largest and oldest known cratonic block in China. The Precambrian rocks distributed abroad, and developed complete. It recorded the very complex evolution process on earth with more than 30 hundred million years in geology history. In recent years, the North China Craton is tectonically divided into two major Archean to Paleoproterozoic blocks, named Eastern blocks and western blocks, separated by a Paleoproterozoic orogen, named the Central zone. The eastern Hebei and western Liaoning area belongs to the Eastern blocks in tectonic attribute, with large area of late Archean granitic rock exposure. This is an idea area for the evolution research of Archean lithosphere in North China Craton.In eastern Hebei and western Liaoning area, the Archean granitic rocks mainly are Suizhong granites, Anziling gneisses, Wangchang gneisses, Liugezhuang diorites and Qinhuangdao granites. Based on petrography and geochemistry characteristics, the granitic rocks in this area could mainly be divided into three types: tonalite-granodiorite(TTG), biotite adamellite and biotite granite. Based on field investigation, the distribution ranges of kinds of rocks are preliminary divided. Tonalite-granodiorite is distributed in west Anziling and Wangchang area. Biotite granite is distributed in north Qinhuangdao and south Suizhong area. And biotite adamellite is distributed between the two of them, in Heshangfangzi- Kuanbang area. There is a gradual change in the three of granitic rocks, without obviously boundary.In eastern Hebei and western Liaoning area, the zircon in granitic rocks generally have obviously fine-scale oscillatory growth zoning and high Th/u ratios, with the mode of depleted in light rare earth and enriched in heavy rare earth, suggesting magmatic origin. LA-ICPMS zircon U–Pb age shown that the granitic rocks age is 2500-2560Ma, indicated the mainly era of the continental crust accretion in this area is in late Archean, which is consistent with the mainly tectonic-magma events in North China Craton. Simultaneously, the age indicated that the three mainly granitic rocks basically have accordant form age, without obviously time interval.Geochemical characteristics indicated that tonalite-granodiorite and biotite adamellite all have high Mg#, low Rb/Sr ratios, Y and Yb, enriched in large ion lithophile elements and depleted in high field strength elements, shown as the product of basaltic crust partial melted at high pressure. However, tonalite-granodiorite have higher MgO, Cr, Ni, V, and lower SiO2, low light-heavy rare earth fractionation, suggesting early magmatic evolution. Biotite granite have high SiO2, K2O, low MgO, Cr, Ni, and high Rb/Sr ratios, suggesting a higher degree evolution of K-rich granite. And biotite granite have Eu negative anomaly,and depleted in Ba, Sr, suggesting the molten residuum are plagioclase. In addition, rock and zircon’s rare earth characteristics all shows relatively strong light-heavy rare earth fraction, and high Yb, Y. All these geochemistry characters indicated the product of partial melting salic crustal at low pressure.To discuss the source region characteristics and evolution of different granitic rocks in late Archean, especially discuss the continental crust accretion mechanism and the old continental crust’s characteristics, based on the zircon U-Pb chronology, corresponding zircons are carefully tested of Hf isotopes in situ. The test result indicated that: 1) Four periods of crust-mantle differentiation events as 3.7Ga, 3.0Ga-3.4Ga, 2.7-2.9Ga and 2.5-2.6Ga existed, the mainly event happed between 2.7Ga and 2.9Ga. 2) Partial zircon’s crystallization age are consistent with Hf model age (2.5-2.6Ga), indicated new crust substance from mantle differentiation added when granite formed. 3) Confirmed inconsistency of the crust-mantle differentiation from the three granite rocks. Biotite granite reflected Eoarchean-mo crust-mantle differentiation events (3.7Ga, 3.0-3.4Ga, 2.9Ga). Tonalite-granodiorite and biotite adamellite reflected middle-late Archean crust-mantle differentiation events (2.7-2.9Ga、2.5-2.6Ga). 4) Presumed mainly crust-mantle differentiation and a few products of granitic magma in 2.7-2.9Ga, mainly granic magma generated in 2.5-2.6Ga and a few crust-mantle differentiation happened.According to the previous research results, the paper speculated that: 1) The Archean granitic rocks in this area distributed in planar, with a lot of amphibolite, pyroxenite and other mafic enclaves. 2) The formation age of the Archean granitic rocks in this area is 2.50-2.56Ga, indicated a large-scale crust transformation event mainly happed in 2.50-2.56Ga. 3) Metamorphsim rocks in this area generally have equal pressure cool-down type anticlockwise P-T path characteristics, suggesting a additional heat source from out crust (mantle). This may related with lots of magmatic emplacement from mantle differentiation. 4) The Hf isotope model age of zircon shown mantle differentiation simultaneously happed when large-scale granitic rocks generated in 2.5-2.6Ma. According to above characteristics, it is speculated that the large-scale magmatic events in late Archean in this area are related with mantle magma’s underplating.更多还原