东准噶尔喀拉托别地区火山岩地质特征及地层厘定

Geological Characteristics and Stratigraphic Determination of Volcanic Rocks in the Kalatobe Area,East Junggar

位于准噶尔盆地东南缘的喀拉托别-乌宗布拉克地区广泛分布以火山岩为主的陆相火山-沉积地层,对于其形成时期及岩石地层单位归属久存争议。在进行详细野外调查和岩石学、岩石化学与地球化学、同位素年代学等综合研究,并开展区域对比的基础上,认为该区火山岩应划分为上下两个层位并归属不同的岩石地层单位。下部层位为本区火山岩的主体,岩性以基性、中酸性火山岩及其火山碎屑岩为主,局部夹层理层纹明显的沉凝灰岩、凝灰质砂岩及砾岩等火山-沉积岩;岩石为钙碱性,微量元素和稀土元素分析表明,岩浆来源于地幔-下地壳,形成于“大陆边缘弧”构造环境;在其安山岩中获得锆石U-Pb年龄为326.9±8.8Ma,表明火山岩形成于早石炭世晚期;各项特征均与卡拉麦里地区等准噶尔东北部典型的石炭纪火山岩相同或相似,将其岩石地层单位厘定为巴塔玛依内山组。上部火山岩零星覆盖于下部火山-沉积岩地层之上,岩性为流纹岩、英安斑岩及霏细岩,局部见气泡状、球粒状构造。前人曾在流纹岩中获得Rb-Sr等时线年龄278±2Ma,属中二叠世早期,结合区域对比研究,将上部层位火山岩划属卡拉岗组。该区火山岩的解体及地层单位的厘定,为研究准噶尔地块及周边区域的岩浆活动与构造演化提供了新的信息和证据。

Continental volcanic-sedimentary strata dominated by volcanic rocks are exposed in theKalatobe-Uzunbulk region on the northeastern margin of the Junggar basin.The volcanic rocks may be divided into 2 horizons.The lower horizon is determined as Batamayinei Formation which consists of basic and intermediate-acid volcanic and pyroclastic rocks derived from the mantle-lower crust and formed in continental margin arc environment and partially intercalated with tuffite,tuffaceous sandstone and conglomerate,with zircon U-Pb ages of 326.9±8.8Ma.The upper horizon consists of rhyolite,dacite porphyry and felsites with Rb-Sr isochronal ages of 278±2Ma for the rhyolite.These provide new information and evidence for magmatic activity and tectonic evolution of the Junggar Massif and its surrounding area.