华北克拉通南部王屋山地区太古宙花岗质侵入杂岩的成因及地质意义

The Archean Linshan Complex, a typical early Precambrian terrane in the Wangwushan area, south of the North China Craton, is mainly composed of volcanic-sedimentary sequences (greenstone belt), gneisses, migmatite and syenite. Previous studies mainly focused on preliminary stratum division and rock type classification, but little is known about the age and mechanism of the early continental growth and transformation. Centering on the ages, mechanism and tectonic-thermal regime transition of the early continental evolution, this study will present new zircon U-Pb ages for the Archean granitic plutons (gneissic intrusion and younger granitic suite) to clarify the spatial and temporal distribution of the Archean granitic magmatism and build their chronological framework. This study will further report the whole-rock major and trace elements, and Sm-Nd and zircon in situ Lu-Hf and O isotopic compositions of the gneissic intrusion and younger granitic suite to explore their sources, petrogenesis, and geodynamics, to investigate the associated crust-mantle interaction process, and eventually to constrain the evolution process of the early continental crust from formation, growth to stabilization by their evolution and genetic relationship. Moreover, we will compare the crystalline basement characteristics of the Wangwushan area with those from the adjacent Zanhuang to the north, Zhongtiaoshan to the west, Songshan and Lushan areas to the south to confine the early crustal evolution of the core and southern margin of the North China Craton.

王屋山地区太古宙林山杂岩主要由变火山-沉积岩、片麻岩、混合岩和正长岩等组成，是华北克拉通南部典型的早前寒武纪地质体。已有研究主要针对变质单元的初步划分和岩石类型的厘定，而关于该区早期陆壳演化的时限和机制尚不清楚。本项目围绕早期陆壳生长和改造的时限、方式及其经历的构造-热体制性质等科学问题，研究王屋山地区太古宙花岗质侵入杂岩- - 片麻状侵入岩及其后期的花岗岩，以其记录的构造-热事件的期次和性质为切入点，运用锆石U-Pb年代学，理清这些太古宙花岗质侵入杂岩的岩浆序列，建立其年代学格架；结合岩石学、主、微量地球化学、Sm-Nd和锆石Hf-O同位素特征，探讨岩石的源区、成因和记录的壳-幔作用过程，为揭示研究区早期陆壳从形成、生长到稳定化过程提供有力的岩石学和地球化学证据。同时，以王屋山为中心，与其北部赞皇、西部中条山、南部嵩山和鲁山等邻区的结晶基底进行对比，探讨华北克拉通内部和南缘早期陆壳演化过程。

王屋山太古宙杂岩体岩石类型复杂，早期对岩石组合的厘定并不清楚，也缺少对岩石时代和成因的系统研究。本项目详细研究了王屋山太古宙片麻状侵入岩及花岗岩的时代和成因，并与邻区进行对比，为华北克拉通早前寒武纪陆壳演化机制提供制约。我们首次识别出2569 ± 10-2548 ± 37 Ma TTG片麻岩、2523 ± 17 Ma变火山岩(斜长角闪岩)、2530 ± 27 Ma闪长岩和2530 ± 17-2522 ± 39 Ma富钾花岗岩。TTG为奥长花岗岩，Mg#变化大（36.7-54.8），低Cr和Ni。锆石εHf(t)为1.4-8.8，TDMC模式年龄为2831-2523 Ma，源区为镁铁质下地壳，形成过程可能与汇聚作用有关。斜长角闪岩原岩为亚碱性拉斑玄武岩，高εHf(t)(1.1-7.1)，最年轻的模式年龄(2587 Ma)与其形成年龄接近，源于亏损地幔，形成于弧后环境。闪长岩Nb、Ta负异常不明显。锆石εHf(t)为2.6-8.6，TDMC模式年龄为2830-2527 Ma，说明源区可能为交代岩石圈地幔，形成于弧后环境。钾质花岗岩具有高且一致的SiO2含量，低10000Ga/Al和全岩锆饱和温度(513℃-525℃)，为I型花岗岩。TDMC为2876-2527 Ma，与TTG类似，其源区来自TTG质的长英质地壳，形成于碰撞后环境。王屋山地区在2.60-2.50 Ga存在从挤压碰撞-碰撞后的转换。邻区鲁山地区存在~2840 Ma TTG片麻岩、~2760 Ma SPG花岗岩(sodic-potassic granite)和~2570 Ma钾质花岗岩。TTG高Mg#值，Cr和Ni变化大，最年轻的TDMC (2896 Ma)与形成年龄接近，来自初生洋壳的部分熔融。SPG为I型花岗岩。高Zr/Sm，指示岩浆源区残留石榴石。结合锆石εHf (t) (-4.3-+4.2)及TDMC(3200-2877 Ma)，认为其来自基性下地壳，形成于岛弧环境。钾质花岗岩高SiO2和K2O，低10000Ga/Al和全岩锆饱和温度(670℃)，为高分异I型花岗岩。锆石εHf (t)为-2.0-+4.1，TDMC为2942-2692 Ma，与SPG的形成年龄一致，指示其为主要源区。也有TTG参与，形成于伸展环境。王屋山和鲁山地区的太古宙地质演化存在一定差异，二者在早前寒武纪的演化关系有待进一步解析。