鲁西沂山地区新太古代晚期高级深熔混合岩的源区特征

Source characteristics of Late Neoarchean diatexite in the Yishan area,western Shandong

鲁西沂山地区高级深熔混合岩中存在丰富的不同时代、不同类型的岩石包体。在详细野外地质工作基础上,本文对高级深熔混合岩中的包体进行了锆石SHRIMP U-Pb定年和Hf同位素分析及全岩地球化学研究,以期探讨沂山地区高级深熔混合岩的源区性质。英云闪长质片麻岩形成时代为~2.7Ga,存在2.69Ga和2.53~2.51Ga两期基性岩浆作用,并记录了2.52~2.50Ga变质作用。角闪斜长片麻岩与黑云角闪变粒岩互层产出,它们可能为变质火山岩,其岩浆锆石年龄为2.51Ga。变质基性岩的岩浆锆石ε_(Hf)(t)为0~+8.1,一阶段Hf模式年龄为2.83~2.54Ga;变质火山岩的岩浆锆石ε_(Hf)(t)为-1.2~+5.8,一阶段Hf模式年龄为2.89~2.71Ga。结合前人研究,这套高级深熔混合岩的源区组成包括了新太古代早期的英云闪长质片麻岩和变质辉长岩,新太古代晚期的石英闪长质片麻岩、变质火山岩及斜长角闪岩等岩石类型。~2.5Ga基性岩浆作用在鲁西地区发育广泛,为新太古代晚期深熔作用及高级深熔混合岩和壳源花岗岩的形成提供了热源。

There are abundant enclaves of different ages and types within diatexite in the Yishan area,western Shandong.Based on field work,this paper carried out zircon SHRIMP U-Pb dating and Hf isotope analysis and whole-rock geochemical studies on enclaves in the diatexite.A tonalitic gneiss enclave has a formation age of~2.7Ga.Two episodes of Neoarchean mafic magmatism are recognized at 2.69Ga and 2.53~2.51Ga,respectively,and they have metamorphic ages of 2.52~2.50Ga.Hornblende-plagioclase gneiss was interbedded with fine-grained biotite-hornblende gneiss,and these two types of gneisses are considered to be meta-volcanic rocks.The hornblende-plagioclase gneiss has a magmatic zircon age of 2.51Ga.The magmatic zircon from the meta-gabbro hasε_(Hf)(t)values of 0~+8.1 with t_(DM1) of 2.83~2.54Ga,whereas the magmatic zircon from the hornblendeplagioclase gneiss hasε_(Hf)(t)values of-1.2~+5.8 with t_(DM1) of 2.89~2.71Ga.Combined with previous work,it is speculated that the source of the diatexite includes Early Neoarchean tonalitic gneiss and meta-gabbro,and Late Neoarchean quartz diorite gneiss,meta-volcanic rock and amphibolite.~2.5Ga mafic magmatism is widely developed in western Shandong,which provides the heat source for the Late Neoarchean anataxis,resulting in the formation of diatexite and crustally-derived granite.