河北太行山南段符山杂岩体岩浆作用深部过程及其大地构造意义

华北克拉通中生代岩石圈减薄过程中,其深部复杂的壳-幔岩浆过程及深部岩浆房系统研究薄弱,岩石圈减薄过程的浅部响应也存在较大争议。本文以华北克拉通中部的邯邢地区符山杂岩体为研究对象,通过详细的野外地质调查、岩相学观察、岩石地球化学分析、锆石年代学和矿物电子探针分析等研究多重岩浆房系统、岩浆深部作用过程和浅部响应。锆石U-Pb测年结果显示,符山早期岩套中细粒二长岩的年龄为129 Ma,晚期似斑状岩套的斑状角闪二长岩的年龄为122 Ma。岩相学观察及背散射电子(back scatter electron,BSE)图像显示,符山杂岩体的角闪石和斜长石均具有复杂的环带结构,并通过对它们的晶体生长过程分析和环带成因讨论,表明其具有复杂的生长环境和过程。符山杂岩体的高镁、高钾、高Sr 等地球化学特征和角闪石、斜长石的环带成因证明了深部岩浆在幔源流体的活化作用下发生了强烈的岩浆混合作用和多重岩浆房过程。符山杂岩体早期岩套侵入岩定位深度为7 km,晚期岩套侵入岩定位深度为1.5 km,表明在7 Ma内地壳隆升了5.5 km。符山杂岩体中大部分侵入岩具高Sr、低Y及δEu正异常等地球化学特征,表明它们可能形成于加厚陆壳的部分熔融。这些特征表明晚中生代中国东部高原的存在。

Deep magmatic process of the Fushan complex in the southern section of Taihang Mountain,Hebei Province and its tectonic significance

The complex deep crust-mantle interaction in the magmatic process, and the deep magma chamber system during the Mesozoic lithospheric thinning of the North China Craton, is poorly understood, and the shallow response of the deep magma process is also controversial. In this study the Fushan complex in the Han-Xing area in central North China Craton is studied. A detailed petrographical, mineralogical, geochemical and geochronological analysis was carried out to investigate the multiple magma chamber system, the deep magmatic process and its shallow response. Zircon U-Pb dating results show that the age of the fine-grained monzonite from the early Fushan complex suite is 129 Ma, and the age of the porphyritic monzonite from the late porphyry complex suite is 122 Ma. Petrographic observation and back scatter electron (BSE) images indicate both amphiboles and plagioclases in the Fushan complex have a complex annulus structure. Through the analysis of the crystal growth process and discussion on the origin of crystal zoning, we show that the crystal growth environment and process are rather complex. The high Mg, K and Sr contents in the Fushan complex and the origin of crystal zoning in hornblende and plagioclase provided proof that the deep magma underwent strong magmatic mixing and multiple magma chamber process controlled by the activity of magmatic fluids. The depth of the early intrusive suite of the Fushan complex is 7 km, and the emplacement depth of the late suite is 1.5 km, which shows that the crust was uplifted by 5.5 km at 7 Ma. Most of the intrusive rocks in the Fushan complex have high Sr, low Y and positive δEu, indicating they might be formed from partial melting of the thickened continental crust. These observations support the existence of an eastern plateau of China in the Late Mesozoic.