Geochemical characteristics and tectonic setting of the Tuerkubantao mafic-ultramafic intrusion in West Junggar, Xinjiang, China

Mineral chemistry, whole-rock major oxide, and trace element compositions have been determined for the Tuerkubantao mafic-ultramafic intrusion, in order to understand the early Paleozoic tectonic evolution of the West Junggar orogenic belt at the southern margin of the Central Asian orogenic belt. The Tuerkubantao mafic-ultramafic intrusion is a well-differentiated complex comprising peridotite, olivine pyroxenite, gabbro, and diorite. The ultramafic rocks are mostly seen in the central part of the intrusion and surrounded by mafic rocks. The Tuerkubantao intrusive rocks are characterized by enrichment of large ion lithophile elements and depleted high field strength elements relative to N-MORB. In addition, the Tuerkubantao intrusion displays relatively low Th/U and Nb/U (1.13–2.98 and 2.53–7.02, respectively) and high La/Nb and Ba/Nb (1.15–4.19 and 37.7–79.82, respectively). These features indicate that the primary magma of the intrusion was derived from partial melting of a previously metasomatized mantle source in a subduction setting. The trace element patterns of peridotites, gabbros, and diorite in the Tuerkubantao intrusion have sub-parallel trends, suggesting that the different rock types are related to each other by differentiation of the same primary magma. The intrusive contact between peridotite and gabbro clearly suggest that the Tuerkubantao is not a fragment of an ophiolite. However, the Tuerkubantao intrusion displays many similarities with Alaskan-type mafic-ultramafic intrusions along major sutures of Phanerozoic orogenic belts. Common features include their geodynamic setting, internal lithological zoning, and geochemistry. The striking similarities indicate that the middle Devonian Tuerkubantao intrusion likely formed in a subduction-related setting similar to that of the Alaskan-type intrusions. In combination with the Devonian magmatism and porphyry mineralization, we propose that subduction of the oceanic slab has widely existed in the expansive oceans during the Devonian around the Junggar block

新疆阿尔泰南缘大东沟铅锌矿区火山岩LA-ICP-MS锆石U-Pb定年及地质意义/LA-ICP-MS U-Pb dating of volcanic rocks from Dadonggou ore district on southern margin of Altay in Xinjiang and its geological implications[J]

大东沟铅锌矿位于新疆阿尔泰南缘的克兰盆地,赋存于康布铁堡组上亚组火山-沉积岩系,矿体直接围岩为变质钙质砂岩及不纯的大理岩,矿体呈层状、似层状、透镜状分布,与地层产状一致.利用LA-ICP-MS锆石U-Pb测年法,获得矿区2件康布铁堡组上亚组变质流纹岩加权平均年龄分别为(388.9±3.2) Ma(MSWD=3.3)和(400.7±1.6) Ma(MSWD=1.3).结合前人的年龄数据,将克兰盆地康布铁堡组的时代厘定为晚志留世末期至早泥盆世(413～389Ma).大东沟铅锌矿为火山岩容矿的喷流沉积型矿床(VMS),2件变质流纹岩年龄限定大东沟铅锌矿的成矿作用发生在早泥盆世(401～389Ma)

阿尔泰造山带伟晶岩型稀有金属矿化类型与成岩成矿时代/Types,Intrusive and Mineralization Ages of Pegmatite Rare-element Deposits in Chinese Altay[J]

新疆阿尔泰地区是世界闻名的稀有金属伟晶岩产区，其成岩成矿时代尚存很大争议。伟晶岩就位时代的厘定对该区伟晶岩型矿化的期次、类型划分和产出构造背景的研究及矿产评价至关重要。在典型伟晶岩脉系统调查基础上，通过对阿尔泰代表性稀有金属矿化伟晶岩和伟晶岩型稀有金属矿床的锆石LA-ICP MS U-Pb定年，获得一批新的年龄结果：阿斯喀尔特Be矿床(200.7±6.5) Ma、可可托海矿集区的可可托海3号脉Li-Be-Nb-Ta-Cs矿床180~186 Ma、柯鲁木特-吉得克矿集区的柯鲁木特112号脉(191.8±1.4) Ma、库卡拉盖650号脉(207.9±5.1) Ma和群库尔Be矿床(194.3±1.6) Ma、卡拉额尔齐斯矿集区的虎斯特Be矿化伟晶岩(195.9±2.4) Ma、大喀拉苏-可可西尔矿集区的大喀纳苏Be-Nb-Ta矿床(231.8±7.4) Ma、小卡拉苏-切别林矿集区的小喀纳苏Li-Nb-Ta矿床(296.3±9.0) Ma和苇子沟Be矿床(248.2±2.2) Ma。阿尔泰伟晶岩型稀有金属矿床可划分为加里东期、海西期、印支期至燕山早期4期。阿尔泰造山带北西和南东端矿集区的形成时代集中在370~480 Ma，其他矿集区伟晶岩时代集中在180~250 Ma。造山作用峰期(加里东期与海西早期)形成的伟晶岩多为工业白云母型和REE-Nb型，造山后与非造山阶段(二叠纪-中侏罗世)形成的伟晶岩多为稀有金属型(矿化类型包括Be，Li，Li-Be-Nb-Ta-Cs组合)