新疆哈密沁城一带南华系青石峡组地质特征及意义

THE GELOGICAL DARACTER OF NANHUAN SYSTEM QINGSHIXIA FORMATION QIN CHENG HA MI,XIJIANG

在哈密沁城青石峡一带原划为上石炭统居里得能组中解体出一套浅变质火山-沉积岩系,岩石组合为变玄武岩、阳起石片岩、变凝灰岩,变酸性凝灰岩、变火山灰凝灰岩、霏细岩、流纹岩、变岩屑砂岩、千枚岩等,为玄武岩-流纹岩组合,安山岩较少,具双峰式火山岩特征,为裂谷型火山岩组合.火山岩岩石化学特征为碱性玄武岩系列,钠质类型,成熟度低,与裂谷火山岩吻合,稀土元素分布型式为轻稀土富集型,δEu=0.88～0.98,为Eu平坦型,具幔源岩浆特性.微量元素比值蛛网图具大陆板内裂谷玄武岩特征.构造环境判别显示为大陆裂谷环境,具高原火山岩向裂谷演化特点.同位素Sm-Nd测量年龄为707～757 Ma,为早南华世.该套火山岩特征为裂解型的裂谷火山岩,并可与库鲁克塔格地区贝义西组对比,所以这套火山岩时代定为南华纪,新建下南华统青石峡组是古亚洲洋南华纪裂解时产物,为吐哈地块演化提供了新证据.

The Qing Shi Xia zone of Qin cheng Hami rock group is metomorphic bastalt, actinolite schist, metomorphic tuff, Metomorphic acid tuff, me bo morphic volcanic tuff, mebomorphic lithic sandstone, phyllite etc.; Volcanic rock group is basalt-rhyolite group,little andesite, has bimodal valeanie character, belong to rift valcanie group. The chemical character of valcanic rock is alkalit-basalt course, natrium type REE distribution pattern rich in light REE（LREE）, 6Eu=00.88-0.98, is Eu smootheness type, have manble magma charatcer. Trace element have the character of basalt in comtinental plate and tally with rift valley＇s character. The environment of structure shows the character of basalt sufficiently, have the character of evolvement from altiplano effussive rock to rift valley. The year of is otops sm-Nd is 707-757Ma, is early Nanhuan. Nanhuan is globality parting ear, this volcaic rock＇s character is parting type rift valley volconin rock, so this stratum belong to Nanhuan, can contrast to BeiYiXI group of Kuluke TaGe area and New Set up to QingShixia Formation.