太行山北段中生代岩基及其包体锆石U-Pb年代学和Hf同位素性质及其地质意义

Zircon U-Pb ages,Hf isotopic compositions and geological significance:a case study of Mesozoic batholiths and mafic enclaves in North Taihang

太行山北段出露大规模中生代岩浆岩带,以中酸性岩为主,普遍含有基性微粒包体。锆石的SHRIMP U-Pb年代学研究表明,包体形成于126Ma左右,与寄主岩石大致同时形成。锆石的LA-MC-ICPMS Lu-Hf同位素原位测量研究表明,基性岩来自富集地幔的部分熔融,并遭受了一定程度的地壳混染;主要的中酸性岩基形成于壳幔岩浆混和过程,而岩基中微粒基性包体是经历分离结晶的基性岩浆注入酸性岩浆房中形成。

Abstract Extensive Mesozoic magmatic rocks were emplaced in the northern part of the Taihang Mountains, which are dominated by intermediate to felsic rocks with minor but widespread mafic microgranular enclaves, accompanied by subordinate mafic bodies. Zircon SHRIMP U-Pb dating yields a weighted mean ^206pb/^238U age of ca. 126Ma for the injection of mafic enclaves, which is identical to the emplacement age of their host rocks. LA-MC-ICPMS in-situ Hf isotopic analysis of zircons suggests that the mafic rocks basically originated from partial melting of an enriched mantle, contaminated by crustal components en route to crustal levels, whereas the dominant intermediate to felsic batholithes formed from a mixing/mingling process between enriched mantle-derived mafic magma and crnstal-derived granitic magma. The mafic macrogranular enclaves in the batholith represent mafic magma that were injected into felsic magma chamber, followed by interaction with the latter.