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

[00:879 . 19]这个奖项是由极地项目办公室的南极地质和地球物理项目提供的，用于支持一个研究与冈瓦纳大陆分裂有关的岩浆作用初始阶段的项目。冈瓦纳大陆中生代分裂的标志是一次大型岩浆活动，在此期间，大量玄武岩岩浆在地表喷发，侵入岩岩和岩脉在下伏沉积层序的深处就位。在南极洲，喷出的岩石包括厚厚的凝灰岩角砾岩（粗糙的火山碎屑岩），假设是由玄武岩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，上升的岩浆与含水层或地表的水发生爆炸性相互作用的火山场非常普遍。从矿床的面积范围和厚度、岩浆/水相互作用的深度和玄武岩凝灰岩角砾岩的主导地位来看，与其他有充分记录的例子相比，南极洲的玄武岩火山碎屑岩构成了一个独特的火山场。对这些岩石的古火山学研究将对凝灰岩角砾岩矿床的成因和侵位机制以及以凝灰岩角砾岩为重要组成部分的火山场演化提供重要的新信息。这个研究项目的目标是了解这些异常厚的凝灰岩角砾岩的形成过程。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/水相互作用深度；(3)评价含水层补给；(4)确定火山场的性质、范围及其古火山环境；(5)评价凝灰岩角砾岩为火山直接喷发产物的假说。火山碎屑岩的大规模三维关系将通过实地考察相（岩石组合）的横向和垂直变化以及与邻近岩石单元的关系来建立。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，将其岩性和孢粉学与下伏岩石层序进行比较，从而确定岩浆/水相互作用深度的随时间变化。在勘测工作的基础上，这项研究的结果有望对了解凝灰岩角砾岩是如何通过呼吸岩浆过程（岩浆和水之间的爆炸性相互作用）形成的以及它发生的构造环境产生广泛的影响。研究结果也将有助于发展横贯南极山脉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.