摘要:板山坪岩体是北秦岭二郎坪群中的侵入岩。为了查明该岩体的成因，对该岩体进行了锆石U-Pb年代学、锆石原位Hf同位素研究以及矿物化学分析等方面的研究。研究结果表明，板山坪岩体岩性组成主要为石英闪长岩和花岗闪长岩，花岗闪长岩内部存在暗色包体。本次研究获得板山坪石英闪长岩锆石U-Pb年龄为442.7～432.2 Ma，花岗闪长岩锆石U-Pb年龄为436.8～432.7 Ma，暗色包体锆石U-Pb年龄为437.6 Ma。锆石176Hf/177Hf值为0.282 737～0.282 736，εHf（t）值集中分布在8.4～9.4之间，二阶段Hf模式年龄（TDM2）在876～832 Ma之间。石英闪长岩结晶温压分别为673 ℃～745 ℃和0.19～0.54 GPa，花岗闪长岩结晶温压分别为657 ℃～730 ℃和0.48～0.96 GPa，暗色包体结晶温压分别为680 ℃～734 ℃和0.69～1.65 GPa。综合分析认为板山坪岩体为复式岩体，两期结晶年龄分别为496～487 Ma和442～432 Ma。岩石来源于地幔分离出来的新生下地壳。
关键词: 板山坪岩体/
锆石U-Pb年代学/
Hf同位素/
矿物化学
Abstract:The Banshanping pluton is an intrusive rock in the Erlangping Group of the North Qinling. The lithology is mainly quartz diorite and granodiorite. We present zircon U-Pb isotope chronology, mineral chemical analysis and Hf isotopes to study the genesis. The pluton is mainly composed of quartz diorite and granodiorite, and dark inclusions exist in granodiorite. The zircon U-Pb age of the Banshanping quartz diorite is 442.7～432.2 Ma, the zircon U-Pb age of the granodiorite is 436.8～432.7 Ma, and the dark inclusion zircon U-Pb age is 437.6 Ma. The Hf isotopes results show that the 176Hf/177Hf values of the zircons are between 0.282 737～0.282 736, and the εHf（t） values of the zircons are between 8.4 and 9.4, and the two stage Hf model age ranging from 876～832 Ma. The crystallization temperatures and pressures of quartz diorite are 673 ℃～745 ℃ and 0.19～0.54 GPa, granodiorite 657 ℃～730 ℃ and 0.48～0.96 GPa, dark inclusion 680 ℃～734 ℃ and 0.69～1.65 GPa, respectively. According to the comprehensive analysis, the Banshanping pluton is a complex rock mass, and the two phases of crystallization age are 496～487 Ma and 442～432 Ma, respectively. The rock is derived from the new lower crust that is separated from the mantle.
Key words:Banshanping pluton/
Zircon U-Pb chronology/
Hf isotopes/
Mineral chemistry
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