Ferrar Basaltic Tuff-Breccias Formed by Direct Eruption: Evaluating an Hypothesis

0087919艾略特该奖项由极地项目办公室南极地质和地球物理项目提供，支持一个项目，调查与冈瓦纳大陆分裂有关的岩浆活动的初始阶段。中生代冈瓦纳大陆的解体是一个重大的岩浆事件，在此期间，大量的玄武质岩浆在地表喷发，侵入岩床和岩脉在下伏沉积序列的深处就位。在南极洲，喷出岩包括厚厚的凝灰角砾岩（粗火山碎屑岩），推测是玄武岩浆和含水层中的水在地下爆炸相互作用形成的。在现代裂谷环境中，火山区普遍存在，上升的岩浆与含水层或地表的水发生爆炸性相互作用。就沉积物的面积和厚度、岩浆/水相互作用的深度以及玄武凝灰岩角砾岩的优势而言，与其他有据可查的例子相比，南极洲的这些玄武火山碎屑岩构成了独特的火山区。对这些岩石的古火山学研究将提供关于凝灰岩角砾岩矿床的起源和就位机制以及凝灰岩角砾岩构成重要组成部分的火山场演化的重要新信息，本研究项目的目标是了解这些特厚凝灰岩角砾岩形成的过程。研究的目的是：（1）记录玄武质火山碎屑岩的三维结构;（2）确定岩浆/水相互作用的深度;（3）评价含水层的补给;（4）确定火山场的性质和范围及其古火山学背景;（5）对凝灰角砾岩是火山口直接喷发的假说进行了评价。火山碎屑岩的尺寸关系将通过对相（岩石组合）的横向和纵向变化以及与邻近岩石单元的关系的实地检查来建立。将收集岩石样本，以检查微观结构和纹理，为相互作用、喷发和就位的模式提供线索。将对凝灰岩角砾岩中的沉积岩碎片进行系统取样，以便将岩性和孢粉学与下伏岩层序列进行比较，从而确定岩浆/水相互作用深度随时间的变化。这项研究的结果对于理解凝灰岩角砾岩是如何通过蒸汽岩浆作用形成的具有广泛的意义（岩浆和水之间的爆炸性相互作用）和它发生的构造环境。研究结果也有望发展出横贯南极山脉在侏罗纪时期的古火山学背景。

0087919 ElliotThis award, provided by the Antarctic Geology and Geophysics Program of the Office of Polar Programs, supports a project to investigate the initial phase of magmatism associated with the break-up of Gondwanaland. Mesozoic break-up of Gondwanaland was marked by a major magmatic event during which voluminous basaltic magmas were erupted at the surface and intrusive sills and dikes were emplaced at depth within the underlying sedimentary sequence. In Antarctica, the extrusive rocks include thick tuff-breccias (coarse pyroclastic rocks) hypothesized to have formed by subsurface explosive interaction of basaltic magma and water in aquifers. Volcanic fields where rising magmas interact explosively with water in aquifers, or at the surface, are widespread in modern rift settings. In terms of areal extent and thickness of deposits, depth of magma/water interaction, and dominance of basaltic tuff-breccia, in comparison with other well documented examples these basaltic pyroclastic rocks in Antarctica constitute a unique volcanic field. Study of the paleovolcanology of these rocks will yield important new information on the origins and emplacement mechanisms of tuff-breccia deposits and on the evolution of volcanic fields in which tuff-breccias form a significant component.The goal of this research project is to understand the processes involved in the formation of these exceptionally thick tuff-breccias. The objectives of the research are to: (1) document the three-dimensional architecture of the basaltic pyroclastic rocks; (2) establish the depth of magma/water interaction; (3) evaluate aquifer recharge; (4) establish the nature and extent of the volcanic field and its paleovolcanologic setting; and (5) evaluate the hypothesis that these tuff-breccias are the result of direct eruption from volcanic vents.The large-scale three-dimensional relationships of the pyroclastic rocks will be established by field examination of lateral and vertical changes in facies (rock associations), and relationships to adjacent rock units. Rock samples will be collected for examination of microscopic structures and textures that provide clues to the modes of interaction, eruption and emplacement. Sedimentary rock fragments in the tuff-breccias will be systematically sampled for comparison of the lithology and palynology with that of the underlying rock sequence and thus establish the time-dependent changes in depth of magma/water interaction.Building on reconnaissance work, the results of this study are expected to have broad implications for understanding how tuff-breccias are formed by phreatomagmatic processes (the explosive interaction between magma and water) and the tectonic settings in which it occurs. Results are also expected to develop the paleovolcanologic setting of the Transantarctic Mountains during the Jurassic.