华北克拉通北缘晚志留世末-早泥盆世钾质碱性岩的成因及对区域构造演化的限定

华北克拉通北缘晚志留世末-早泥盆世碱性岩的成因研究可以为古生代古亚洲洋与华北克拉通的相互作用过程提供重要信息.本文以内蒙古达茂旗黄合少正长岩为研究对象,开展了锆石U-Pb年代学、矿物化学、地球化学和Sr-Nd同位素的研究,并综合同带其他代表性岩体的岩石矿物及元素特征,探讨了华北克拉通北缘钾质碱性岩的岩浆体系性质、源区特...

Petrogenesis of the Late Silurian to Early Devonian potassic alkaline rocks on the northern margin of the North China Craton and their constraints on the tectonic evolution

The Late Silurian to Early Devonian potassic alkaline rocks on the northern margin of the North China Craton (NCC) is a key geological unit to understand the interaction processes of the Paleo-Asian Ocean and the NCC in the Paleozoic. In this paper, we report new zircon U-Pb age, mineral chemistry, whole-rock geochemistry and Sr-Nd isotopic compositions from the Late Silurian potassic Huangheshao (HHS) syenties on the northern margin of the NCC, and discuss its petrogenesis. Sensitive high-resolution ion microprobe (SHRIMP) zircon U-Pb dating has revealed a crystallization age of 417.6±4.7 Ma for the HHS pluton. Alkali-feldspar syenite is the main rock type; Aegirine-augite and sanidine (An₀Ab_2~5Or_95~98) are the major minerals, with subordinate albite (An₀Ab_95~100Or_0~5). Aegirine-augites locally transferred into winchite or magnesio-riebeckite. The HHS syenites have high total alkali contents (Na₂O+K₂O=12.79%~15.30%),high Rittmann index (σ=8.48~11.09), high K₂O contents (8.66%~13.78%), and high K₂O/Na₂O ratios (2.10~9.07), suggesting their alkaline, potassic-ultrapotassic affinity. High Sr abundances and radiogenic Sr isotopic compositions (initial ⁸⁷Sr/⁸⁶Sr=0.704 1~0.706 1) argue for an enriched subcontinental lithospheric mantle (SCLM) source for the HHS magmas,which was previously metasomatized by melts/fluids from the subducted sediments on the down-going oceanic crust. The development of the Late Silurian to Early Devonian potassic alkaline rocks on the northern margin of the NCC indicates that the Paleo-Asian oceanic slab had subducted beneath the NCC in the Early Pleozoic, and the subducted materials metasomatised the SCLM, forming a phlogopite/K-amphibole-bearing, fertile mantle source. During the end of the Late Silurian to Early Devonian, due to the accretion or collision of a microcontinent, the northern margin the NCC has entered into a temporary, post-collisional extension tectonic setting.