摘要
在塔里木盆地西北缘的柯坪地区二叠系库普库兹满组和开派兹雷克组玄武岩之间发现厚层长英质火山碎屑岩层序。该层序包括可见含交错层理的空落火山灰层、三层含增生火山砾的火山灰、熔结凝灰岩和再沉积熔结凝灰岩。层序下部为与其准同时喷发的玄武质火山碎屑岩和玄武质熔岩流。利用锆石U-Pb法确定熔结凝灰岩层的喷发年龄为290.9±1.3Ma(MSWD=1.12),该年龄限定了库普库兹满组玄武岩喷发的截止时间。长英质火山碎屑岩层序中的增生火山砾由粒度<250μm的长英质玻屑组成,且长宽比均>1.5。根据形貌、结构和岩相学特征,将增生火山砾分为三类,分别对应热火山碎屑流从起始(TypeⅡ,coated ash pellet)到极盛(TypeⅠ,accretionary lapillus)再逐渐衰弱(TypeⅢ,ash pellet)的过程。由于喷发规模巨大,该火山层序很可能广泛分布于盆地内,可能是确定全盆地溢流玄武岩喷发时限的一个关键标志层。
We report the discovery of an accretionary lapilli-bearing tuff layer from Keping, NW Tarim Basin. There occurs a widely-spread felsic pyroclastic sequence between the Kupukuziman basalts and the Kaipaizileike basalts. The felsic pyroclastic sequence, underlain by synchronous basaltic tuff and basalt lava flows, consists of an air-fall tuff layer with occasional cross beddings, three accretionary lapilli-bearing tuff layers, an ignimbrite layer and a re-sedimented ignimbrite layer. The zircon U-Pb age of an ignimbrite from the felsic sequence is 290.9±1.3Ma （MSWD=1.12）, which determines the cessation time of the Kupukuziman basalt eruption. Based on their structural characteristics, the accretionary lapilli can be classified into three types. They have typical characteristics of ash aggregates formed in co-ignimbrite ash fall deposits, e.g., maximum grain size of accreted ash 〈250μm, and aspect ratio 〉1.5. The stratigraphic evolution of Type Ⅱ-Ⅰ-Ⅲ indicates an undulating strength of a pyroclastic flow that supported the formation of accretionary lapilli.
作者
田伟
王磊
潘路
弓明月
TIAN Wei;WANG Lei;PAN Lu;GONG MingYue(MOE Key Laboratory of Orogenic Belts and Crustal Evolution, School of Earth and Space Sciences, Peking University, Beijing 100871, China;College of Engineering, Peking University, Beijing 100871, China)
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
2018年第1期63-74,共12页
Acta Petrologica Sinica
基金
国家自然科学基金项目(41630205
41272368
41702360)
科技部"973"项目(2010CB808906)联合资助
