南秦岭新院岩体位于略阳县城以北约35 km处,呈椭圆形,出露面积约200 km2,主要岩性为花岗闪长岩,岩体中含有大量的铁镁质微粒包体和细晶岩脉.锆石SHRIMP U-Pb定年结果表明,花岗闪长岩的结晶年龄为219.6±4.6 Ma,其中的铁镁质微粒包体的结晶年龄为2 21.5±4.2 Ma,晚于勉县—略阳洋盆闭合时期(242～221Ma).根据岩体及其包体的岩石学、地球化学研究,结合区域地质特征,我们认为,该岩体形成于陆内碰撞造山的构造环境.即印支期扬子板块向北发生俯冲碰撞之后(即主造山期后),岩石圈发生拆沉作用,导致地幔软流圈物质上涌使下地壳发生部分熔融而形成花岗质岩浆,同时,部分幔源基性岩浆上侵到花岗质岩浆房,发生岩浆混合,形成.花岗闪长岩,尚未混合的基性岩浆团块形成包体.%The Xinyuan granitic pluton, located at the North side of the Mianxian-Lüeyang ( Mian-Lüe ) suture zone, Southern Qinling Moutains, occurs in bathollith with an outcrop area of 200 km2. It consists of granodiorite, mafic microgranular enclaves (MME) and granitic aplite. Zircon SHRIMP U-Pb datings yielded an age of 219. 6 ±4. 6 Ma for the granodiorite and 221. 5 ±4. 2 Ma for the MME, which were later than the closing time of the Mian-Lue ocean basin (242~221 Ma). In the basis of the studies on petrology and geochemistry of the granite and enclaves, combined with the regional geological features, we believed that the Xinyuan pluton was formed in intracontinental collision setting after Yangtze plate subduction northward. In that setting, lithospheric delamination led to mantle upwelling with a lot of mantle material and hot energy, causing partial melting of lower crust to generate granitic magma. Partly ascended mantle magma mixed with the granitic magma during the period of transition from compression to extension in orogen, forming the granodiorite and the mafic microgranular enclaves.
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