新疆西准噶尔谢米斯台地区发现早古生代火山岩地层：野外地质学和年代学证据

摘要

The volcanic rocks in the Xiemisitai area of West Junggar was traditionally attributed to the Devonian to Carboniferous. The attribution is mainly based on the regional stratigraphic correlation, which lacks convincing scientific evidence. This paper reports the three profiles of the volcanic rocks and a detailed description of the main volcanic rock types exposed in this area. According to the unconformity contact, rock assemblage and alteration characteristics of the volcanic rocks, two sets of volcanic rocks of different eras were distinguished. Zircons U-Pb dating results show that the volcanic rocks in the Xiemisitai area were formed at (423.6~394.1 Ma), i.e., belonging to the late Silurian-early Devonian. The late Silurian strata mainly are composed of andesite, dacite and minor volcanic tuff and altered sandstone. The Middle Devonian strata consist of andesitic-dacitic volcanic clastic rocks and glutenite. The volcanic rock strata in the Xiemisitai area were likely the products of the late Silurian Boshchekul-Chingiz magmatic arc stretches eastward from East Kazakhstan into China, which constitute parts of a suit of continuous volcanic strata of late Silurian-middle Devonian.%传统上，新疆西准噶尔谢米斯台地区的火山岩地层被归属为泥盆系-石炭系。这种归属主要依据区域地层对比，缺乏确定的科学依据。本文报道了该区火山岩地层的三条剖面，并对区内出露的主要火山岩类型进行了详细描述。根据火山岩地层中岩石的不整合接触关系、岩石组合及蚀变特征将其分为两套不同时代的火山岩，并提供了代表性火山岩的锆石U-Pb测年结果，提出谢米斯台火山岩的时代(423.6~394.1 Ma)属于晚志留世-早泥盆世而不是中晚泥盆世-石炭纪。晚志留世火山岩主要为安山岩和英安岩，夹少量火山凝灰岩和蚀变砂岩。下泥盆统主要为安山质-英安质火山碎屑岩，夹有大量砂砾岩。该区地层的产状总体南倾构成一个单斜。此外本文探讨了该区火山岩地层的大地构造归属及其时空联系性，认为谢米斯台火山岩是东哈萨克斯坦博什库尔-成吉斯早古生代岩浆弧向东的延伸，可与东西两侧的火山岩地层构成一个连续的晚志留世-早泥盆世火山岩带。