太行山北段龙门沟基性侵入岩体和幔源包体的岩石学与地球化学：对中生代地幔性质的制约

The destruction of the North China Craton (NCC) is the focus of current geological field. The processes of lithospheric destruction of the NCC is still in controversy in spite of many important achievements. Particularly, the nature of Mesozoic lithospheric mantle of the central NCC has not been well discovered due to less direct samples of the mantle. Fortunately, we have found many mantle xenoliths in Longmengou mafic pluton in the northernTaihang Mountains in 2013. This project will study the mineralogy, petrology and geochemistry of the mafic pluton and the mantle xenoliths . Our aim is to contrian the petrogenesis of the mafic pluton and investigate the composition, formation age and the processes of modification of the lithospheric mantle, and then make a Mosozoic lithospheric mantle comparison among the northern Taihang Mountains, the southern Taihang Mountains and eastern NCC, in order to discover the characteristics of the Mesozoic lithospheric mantle beneath the northern Taihang Mountains, which will provide further evidence for the research of the destruction of the NCC.

华北克拉通破坏是当前地质学界关注的焦点，虽然目前已经取得了许多重要进展，但是关于华北岩石圈破坏的过程仍然存在一些争议，特别是华北克拉通中部中生代岩石圈地幔特征的研究资料较少，其主要原因是直接的地幔样品难以获得。2013年申请者在太行山北段晚侏罗世龙门沟基性侵入岩体中发现了幔源包体，本次项目拟通过对龙门沟基性侵入体和幔源包体进行系统的矿物学、岩石学和地球化学研究，确定龙门沟基性侵入体的岩石成因；查明太行山北段中生代岩石圈地幔组成、时代及其所经历的深部作用过程；通过与中生代期间华北克拉通东部和太行山南段岩石圈地幔的对比，揭示太行山北段中生代岩石圈地幔属性，从而为深入探讨华北克拉通破坏过程提供进一步证据。

LA-ICP-MS锆石U-Pb测年结果显示，花岗闪长岩、石英闪长玢岩和橄榄辉长岩分别形成于129±2.7Ma、128.3±1.9Ma和139.7±2.6Ma，说明王安镇杂岩体形成于早白垩世。在太行山北段龙门沟含橄榄石辉绿岩（锆石U-Pb，138Ma）中首次发现幔源包裹体。根据橄榄石、单斜辉石、斜长石和角闪石的含量，幔源包体可划分三个带：含单斜辉石橄榄石带（纯橄岩）、橄榄石-单斜辉石带和含角闪石钙长石-单斜辉石带。纯橄岩中橄榄石核部具有高Mg#和低Ni的特征，其形成于亏损地幔并受到高Mg#低Ni岩浆/流体改造。具有钛铁矿、磁铁矿出熔棒的橄榄石可能形成于受水交代的石榴子石橄榄岩。高An值（92.0-99.95，平均值97.79）钙长石指示橄榄石受到具有高Ca/Na、Al/Si比值流体交代，其可能形成于在富水情况下超亏损地幔的部分熔融过程。基于前人在太行山地区地幔包体的研究成果，我们认为在中生代太行山地区岩石圈是由超亏损太古代和古元古代地幔。