太行山阜平杂岩中麻棚-赤瓦屋岩体的时代、侵位深度及构造意义

摘要

It is known that Mesozoic magmatism generated a series of granitic plutons in the northern segment of the Taihang Mountains. Among others, the Mapeng-Chiwawu pluton just crops out in the central part of the Neoarchean-Paleoproterozoic Fuping Complex, showing I-type calc-alkaline affinity, with low SiO2 and high AL2O3 and alkali content. The pluton consists of quartz diorite, granodiorite and granite from edge to core, and these intrusions yielded LA-ICP-MS zircon U-Pb ages of 126.4 ±2.4 Ma, 125.4 ±2.0 Ma and 126.2 ± 2.0 Ma, indicating that the pluton was emplaced in a short time around 126 Ma (Early Cretaceous). The total amount of Al in hornblende is 1.018, 0.880 and 0.871 for quartz diorite, granodiorite and granite, and accordingly the crystallization pressure of hornblende is 0.183, 0.118 and0.114 GPa, with an average of 0.141 GPa, indicating a depth of ca. 5 km. This is significantly smaller than the thickness of Proterozoic to Jurassic sequences around the Fuping Complex, suggesting a dome-shaped structure for the Fuping Complex before the Early Cretaceous. Combined with other data, an average uplift rate of 0.07～0.08 km/Ma can be obtained for the Tai-hang Mountains since the Early Cretaceous.%中生代岩浆活动在太行山北段形成了一系列花岗岩体,其中的麻棚-赤瓦屋岩体侵位于穹窿状的阜平杂岩中,具有贫硅、富碱、高铝的钙碱性I型花岗岩特征.岩体分带明显,由边部向核部可以划分为石英闪长岩、花岗闪长岩、似斑状花岗岩3个相带,它们的锆石LA-ICP-MS U-Pb年龄分别为126.4±2.4 Ma、125.4±2.0 Ma和126.2±2.0Ma,在误差范围内一致,指示岩体在早白垩世期间快速侵位、结晶.各相带样品的角闪石全铝平均值分别为1.018、0.880和0.871,对应的角闪石平均结晶压力分别为0.183、0.118和0.114 GPa,均值为0.141GPa,对应的侵位深度约5km,明显小于区域内元古界至侏罗系的地层厚度,表明在岩体侵位之前,阜平杂岩就已经具有穹窿状构造特征.结合相关资料,估计太行山早白垩世以来的平均隆升速率为0.07～0.08 km/Ma.