摘要
新疆北山地区聚集着坡北、罗东、红石山、漩涡岭和笔架山等众多的二叠纪大型镁铁-超镁铁质杂岩体,主要由橄榄岩、辉石岩和辉长岩组成,具有堆晶韵律层,其形成年龄（260.7~289 Ma）与塔里木大火成岩省年龄接近。岩体橄榄石Fo值与Ni含量正相关;与原始地幔相比,微量元素富集Rb、Sr和Pb,亏损Nb、Ta、Ti、Zr和Hf;稀土元素具LREE亏损-平坦型球粒陨石标准化配分曲线。岩石PGE含量低、具IPGE亏损型原始地幔标准化配分型式。SrNd同位素位于亏损地幔（DM）与OIB范围之间,Re-Os同位素组成与地幔柱岩浆作用形成的Noril＇sk铜镍硫化物矿床和峨眉山溢流玄武岩重叠。模拟计算表明,母岩浆Mg O含量高,岩浆初始液相线温度及结晶温度高,岩浆演化过程中经历了分离结晶作用、地壳混染以及早期的硫化物熔离。由此推断北山大型镁铁-超镁铁杂岩体可能是在后碰撞伸展环境叠加地幔柱作用,诱发软流圈上涌、岩石圈底侵,导致俯冲流体交代的岩石圈地幔在高温条件下高程度部分熔融形成的,具有较大的岩浆矿床成矿潜力。
Permian large-sized mafic-ultramafic complexes such as Pobei, Luodong, Bijiashan, Hongshishan and Xuanwoling, are developed as a cluster in Beishan area, Xinjiang. They are mainly composed of peridotite, pyroxenite and gabbro. They have significant cumulate rhythmic layers of magmatic minerals, and are commonly considered to be layered mafic-ultramafic intrusions hosting Ni- Cu sulfide deposits. Their intrusive ages（260.7- 289 Ma） are close to the age of the Tarim large igneous province.Beishan layered mafic-ultramafic intrusions show positive correlation between Fo values and Ni content of olivine minerals. Their trace elements are characterized by negative anomalies of high field strength elements（Zr, Hf, Nb, Ta and Ti）, and richness of Rb, Sr and Pb in comparison with the primitive mantle（PM）. They have LREE- depleted- flat rare earth element（REE） patterns. The rocks display low PGE content and IPGE-depleted PGE primitive mantle normalized distribution patterns. The Sr, Nd isotopes are located between depleted mantle（DM） and OIB ranges, whereas Re-Os isotopic compositions overlap the ranges of mantle plume magmatic Noril＇sk Cu-Ni sulfide deposits and Emeishan basalts. Simulated calculations show that the parental magmas of Beishan complexes had high Mg O content and high magmatic initial liquidus temperature and crystallization temperature, and underwent fractional crystallization and different degrees of crustal contamination in their evolution process. Parental magma experienced sulfide segregation in the mantle source or during the emplacement, and resulted in depletion of PGE. It is inferred that large-sized mafic- ultramafic complexes in Beishan area were formed by high degree of partial melting of lithospheric mantle modified by subduction fluid at high temperature due to lithosphere delamination and asthenosphere upwelling triggered by a superposed mantle plume in a post- collisional extension tectonic setting, and thus show large metallogenic potentials for the formation of magmat
出处
《中国地质》
CAS
CSCD
北大核心
2015年第3期468-481,共14页
Geology in China
基金
国家自然科学基金项目(41372095
41472070)
兰州大学中央高校基本科研业务费专项资金(LZujbky-2015-64)
中国地质调查局项目(12120114044401)
高等学校博士学科点专项科研基金项目(20120211110023)联合资助
关键词
成矿潜力
动力学背景
镁铁-超镁铁质岩体
二叠纪
新疆北山
metallogenic potential
geodynamic setting
mafic-ultramafic intrusions
Permian
Beishan block in Xinjiang
