关键词: 镁铁-超镁铁杂岩, 年代学, 造山后, 岩石成因, 红旗岭地区

Abstract: Mafic-ultramafic complexes are widespread in Hongqiling area in central Jinlin Province,NE China. The Hongqiling complex comprises pyroxenite,olivine websterite,lherzolite,gabbro and leucogabbro. Based on the latest geochronological results,these intrusions yield a zircon U-Pb age of about 216Ma BP,which implicates they emplaced in late Triassic and the mafic-ultramafic complexes are post-orogenic in origin. These ages are coeval with the emplacement of A-type granites in the area,but slightly younger than syn-orogenic granitic magmatism. The composition of the parent magma during the equilibration of the cumulate olivine crystallizing is basaltic with high MgO,and it comes from depleted or juvenile lithospheric mantle according to the results of trace elements and Sr-Nd isotopes. Amount of crustal material contaminated the magmatic source,implying that mafic-ultramafic rocks originate from the mixing product of crust-and mantle-derived magma. So the magmatic source was contaminated by an amount of crustal material,and the subsequent crystal fractionation resulted in the Cu Ni mineralization. Dynamic analyses indicate that,after the collision of the North China Craton and Jiamuqi Massif,the lithospheric delamination during post-orogeny resulted in the upwelling of asthenosphere and the intruding of the mass of mantle-derived magma and the underplating of mantle-derived magma,which led to forming the primary mafic-ultramafic magma due to mantle-derived magma and partial melting of the lower crust. This result suggests that the mafic-ultramafic complexes belong to a typically important magmatic suite that evolved during post-orogenic processes,and they exposed as mafic-ultramafic dyke swarms that existed in the post-orogenic extension environment. It also implies the orogenic process finished ultimately in this regional geological setting. The widespread occurrence of mafic ultramafic complexes in the Xing'an Mongolian Orogenic Belt of NE China and in the Altay Tianshan Junggar Orogenic Belt of Northern Xinjiang indicates that mafic intrusions are an important magmatic suite that evolved during post-orogenic processes. Portions of this mafic magma could have underplated the lower crust,and served as the heat source for associated late-stage granitic magmas.

Key words: mafic-ultramafic complexes, geochronology, post-orogenic processes, petrogenesis, Hongqiling area