Jurassic Volcanic Rocks in the Transantarctic Mountains: A Test of a Model for Continental Flood Basalt Magmatism in Antarctica

横贯南极山脉的侏罗纪火山岩：南极洲大陆洪水玄武岩岩浆作用模型的检验

• 批准号: 9420498
• 负责人: David Elliot
• 金额: $ 27.42万
• 依托单位: Ohio State University Research Foundation -DO NOT USE
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 1995
• 资助国家: 美国
• 起止时间: 1995-06-01 至 1999-11-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9420498&HistoricalAwards=false
• 关键词: Jurassic; Volcanic; Rocks; Transantarctic; Mountains

Abstract This award supports a project to study the Jurassic volcanic rocks which overlie the Permian to Triassic Gondwana sequence in Antarctica. These rocks constitute the Antarctic part of the magmatic record of the break-up of the supercontinent Gondwana. These Jurassic rocks, which occur along the length of the Transantarctic Mountains, include both silicic and tholeiitic compositions. The most complete stratigraphic record of the time interval from the Late Triassic termination of deposition in the Beacon foreland basin to the Middle Jurassic eruption of the flood basalts of the Ferrar Group is located in the central Transantarctic Mountains. In that region, the upper Falla Formation is dominated by volcanogenic rocks including plinian airfall tuffs and phreatomagmatic deposits. The overlying Prebble Formation is dominated by fine to coarse grained phreatomagmatic deposits, including accretionary lapilli tuffs and breccias. Compositionally the rocks are bimodal with silicic activity initiating volcanism and continuing into the flood basalt eruptive episode, whereas the basaltic activity begins with explosive eruptions in the Prebble and changes to quiet effusion of lava. The basaltic pyroclastic rocks are comagmatic with the lavas, having the same geochemical characteristics. The silicic rocks are probably anatectic. Coarse quartzose sandstones with large angular clasts and the presence of monoclinal structures active late in the magmatic activity, indicate contemporaneous basement block faulting. Stratigraphic, structural, petrologic and paleovolcanologic data indicate that these igneous rocks accumulated in a tectono-magmatic rift setting. In south Victoria Land, the correlative strata include flood lavas, basaltic pyroclastic deposits and some recently reported silicic pyroclastic rocks. At one locality a major disconformity separates the basaltic pyroclastic rocks from the underlying Beacon. The relations of the silicic tuffs to the basalt ic pyroclastic rocks and to the disconformity are unclear. The silicic tuffs are reported to include an ignimbrite. The objectives of this project are to gather data to test the tectono- magmatic model proposed for the Jurassic magmatism in Antarctica. Specifically, the objectives are to: 1) establish a detailed stratigraphic framework for the Jurassic pyroclastic rocks in order to assess syndepositional extensional normal faulting, 2) investigate the paleovolcanology of the rocks, in particular the rocks formed by phreatomagmatic processes, in order to understand the physical environment, 3) further characterize the geochemistry of the rocks in order to better define time dependent changes in magma compositions, relations between silicic and basaltic rocks, and source region characteristics of the silicic magmas, and 4) establish the age of onset of the silicic volcanism. These data will be used to validate or modify the proposed model and to assess the model's applicability to continental flood basalt magmatism in general.

摘要 该奖项支持了一个研究南极洲二叠纪至三叠纪冈瓦纳层序上覆侏罗纪火山岩的项目。 这些岩石构成了冈瓦纳超大陆分裂的岩浆记录的南极部分。 这些侏罗纪岩石沿着横贯南极山脉的长度出现，包括玄武岩和拉斑玄武岩成分。 从晚三叠世毕肯前陆盆地沉积终止到中侏罗世费拉尔群溢流玄武岩喷发的最完整的地层记录位于中横贯南极山脉。 在该地区，上部Falla组主要是火山岩，包括普利尼亚气降凝灰岩和蒸汽岩浆沉积。 上覆的Prebble地层主要为细粒至粗粒的蒸汽岩浆沉积物，包括增生的火山砾凝灰岩和角砾岩。 岩石的成分呈双峰状，硅活动引发火山活动并持续到洪水玄武岩喷发阶段，而玄武岩活动则从普雷布尔的爆炸性喷发开始，然后转变为熔岩的安静渗出。 玄武质火山碎屑岩与岩浆同源，具有相同的地球化学特征。 这些岩石可能是深源岩。 粗粒石英砂岩中含有大角度碎屑，且在岩浆活动晚期存在活动的单斜构造，表明存在同期基底块断作用。 地层学、构造学、岩石学和古火山学资料表明，这些火成岩是在构造-岩浆裂谷环境中形成的。 在南维多利亚地，与之相关的地层包括泛滥熔岩、玄武质火山碎屑沉积和一些新近报道的火山碎屑岩。 在一个地方，一个主要的不整合面将玄武质火山碎屑岩与下面的灯塔分开。 凝灰岩与玄武质火山碎屑岩和不整合面的关系尚不清楚。 据报道，凝灰岩中含有熔结凝灰岩。 该项目的目标是收集数据，以检验为南极侏罗纪岩浆活动提出的构造-岩浆模型。 具体而言，目标是：1）建立侏罗纪火山碎屑岩的详细地层格架，以评估同沉积伸展正断层，2）调查岩石的古火山学，特别是由蒸汽岩浆作用形成的岩石，以了解物理环境，3）进一步描述岩石的地球化学特征，以便更好地确定岩浆成分随时间的变化、岩浆岩与玄武质岩石之间的关系以及岩浆的源区特征，（4）确定了古火山作用的起始时代。 这些数据将被用来验证或修改所提出的模型，并评估该模型的适用性大陆洪水玄武岩岩浆作用一般。