Garnet-bearing Granulite Facies Rock Xenoliths from Late Mesozoic Volcaniclastic Breccia, Xinyang, Henan Province

This paper presents the primary results of petrologic, mineralogical and petrochemical studies of garnet-bearing granulite facies rock xenoliths from Xinyang, Henan Province. These xenoliths, which are found in a pipe of late Mesozoic volcaniclastic breccia, are of high density (3.13–3.30 g/cm3) and high seismic velocity (Vp = 7.04–7.31 km/s), being products of underplating of basaltic magmas and had experienced granulite facies metamorphism. The underplating and metamorphism took place before the eruption of the host rock. Petrographical studies and equilibrium T-P calculations show that these xenoliths were captured at a 49 km depth and experienced at least a 16 km uplift before they were captured. The dynamics of the uplift could be related to the continent-continent collision between the North China plate and the Yangtze plate during the Triassic.

徐淮地区镁铁质岩石捕虏体单斜辉石中石榴石和石英的出溶

徐淮地区早侏罗世侵入杂岩中榴辉岩、石榴辉石岩和单斜辉石岩捕虏体单斜辉石中可以观察到丰富的出溶石英针和石榴石、黝帘石及角闪石的出溶叶片。榴辉岩中出溶石英针的绿辉石核部比其边部相对富含FeO和MgO ,贫SiO2 、Al2 O3 和CaO。在石榴辉石岩和单斜辉石岩捕虏体中具有出溶石榴石的单斜辉石 ,从靠近出溶石榴石的一侧向其核部 ,Al2 O3 、Na2 O和TiO2 含量降低 ,MgO、SiO2 和CaO含量增加。单斜辉石中定向石英针的出溶表明曾经存在有超高压条件下 (≥2 5× 10 8Pa)稳定的过硅质绿辉石。单斜辉石中出溶石榴石表明温压条件的降低可能是引起出溶的一个主要原因。捕虏体中的矿物组合和岩相学特征表明它们曾经遭受了榴辉岩相和角闪岩相退化变质作用 ,这与因压力和温度降低引起矿物出溶的结果相吻合。