内蒙古北山地区芨芨台子-小黄山蛇绿岩构造属性及与成矿关系: 来自阿民乌素地幔橄榄岩印证

阿民乌素地幔橄榄岩属芨芨台子-小黄山蛇绿岩带一部分，该构造带南北两侧地质体无明显差异，不具分界断裂的构造特征。本文对阿民乌素地幔橄榄岩与月牙山地幔橄榄岩进行岩石化学、地球化学对比分析，为芨芨台子-小黄山蛇绿岩构造属性提供新依据，并对阿民乌素蛇绿岩成矿潜力进行分析研究。笔者所在团队在地幔橄榄岩上部的辉长岩中获得LA-ICP-MS锆石U-Pb同位素年龄值为462.5±3.2 Ma，属中奥陶世。其上发育奥陶纪-志留纪公婆泉组岛弧拉斑玄武岩。该期地幔橄榄岩轻重稀土之比LR/HR＝1.63~3.68， (La/Sm)N＝1.70~6.92，(Gd/Yb)N＝0.36~0.52，表明岩石轻稀土略富集，稀土配分曲线呈不规则“U”型，估算其为原始地幔橄榄岩经过10%~20%部分熔融的残留物。原始地幔标准化蛛网图富集高场强元素U、Zr、Hf、Yb和大离子亲石元素Rb、Sr，亏损高场强元素Nb、Ti和大离子亲石元素Ba。与月牙山地幔橄榄岩标准化蛛网图对比，最大区别在于阿民乌素地幔橄榄岩明显亏损高场强元素Ti。初步研究认为阿民乌素地幔橄榄岩属SSZ型、高压型蛇绿岩，是岛弧裂谷的产物。该橄榄岩具有形成大型铬铁矿的成矿构造背景，是寻找蛇绿岩型铬铁矿的有利部位。

Tectonic attributes of the Jijitaizi-Xiaohuangshan ophiolite in the Beishan area, Inner Mongolia and in relationship to metallogenesis: Evidence from the Aminwusu mantle perido

The Aminwusu mantle peridotite is part of the Jijitaizi-Xiaohuangshan ophiolite belt in Beishan area of Inner Mongolia. This ophiolite belt displays no significant differences for geological bodies on its north and south sides, untypical of boundary faults. This work compared the petrochemistry and geochemistry of the Aminwusu and Yueyashan mantle peridotites in order to provide new evidence for the tectonic attributes of the Jijitaizi-Xiaohuangshan ophiolite, and further analyzed the metallogenic potential of the Aminwusu ophiolite. The gabbro in the upper mantle peridotite yielded zircon LA- ICP-MS ages of 462.5±3.2 Ma, dating at the Middle Ordovician. The Ordovician-Silurian Gongpoquan island arc tholeiite was developed above the gabbro. This mantle peridotite has LREE/HREE of 1.63~3.68, (La/Sm)N of 1.70~6.92, and (Gd/Yb)N of 0.36~0.52. It has lightly enriched LREE, and shows irregular U-shaped REE distribution patterns. It is estimated that this mantle peridotite is the remnant of the primitive mantle peridotite after 10%~20% partial melting. Standardization of the primitive mantle spider diagram shows enrichment of ?HFSE (U, Zr, Hf, Yb) and LILE (Rb, Sr), and depletion?of HFSE (Nb, Ti) and LILE (Ba). Different from the Yueyashan mantle peridotite, the Aminwusu mantle peridotite is significantly depleted in HFSE (Ti). The Aminwusu mantle peridotite is inferred to be SSZ-type and high pressure-type ophiolite, and is the product of island arc rifting. This peridotite possesses favorable metallogenic tectonic background for large chromite deposits, and is expected to search for ophiolite chromites.