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

0087919埃利奥特该奖项由极地方案办公室南极地质和地球物理方案提供，支持一个项目，调查与冈瓦瓦兰岛解体有关的岩浆活动的初始阶段。冈瓦瓦兰中生代的裂解是以一次重大的岩浆事件为标志的，在此期间，地表喷发了大量玄武岩岩浆，侵入岩床和岩脉侵位于下伏沉积序列的深层。在南极洲，喷出的岩石包括厚厚的凝灰岩-角砾岩(粗大的火山碎屑岩)，推测是由玄武岩岩浆和含水层中的水发生地下爆炸作用形成的。在现代裂谷环境中，上升的岩浆与含水层中的水或地表的水发生爆炸性相互作用的火山田非常普遍。从矿床的面积范围和厚度、岩浆/水相互作用的深度以及玄武岩凝灰岩-角砾岩的优势等方面来看，这些玄武岩火山碎屑岩与其他已有记载的例子相比，构成了一个独特的火山场。对这些岩石的古火山学研究将为凝灰岩-角砾岩矿床的成因和侵位机制以及凝灰岩-角砾岩占重要组成部分的火山田的演化提供重要的新信息。本研究项目的目的是了解这些特厚凝灰岩-角砾岩的形成过程。这项研究的目的是：(1)记录玄武岩火山碎屑岩的三维结构；(2)建立岩浆/水相互作用的深度；(3)评估含水层补给；(4)确定火山场及其古火山背景的性质和范围；(5)评估这些凝灰岩-角砾岩是火山喷口直接喷发的结果的假说。通过野外研究相(岩石组合)的横向和垂直变化以及与邻近岩石单元的关系，将建立火山碎屑岩的大规模三维关系。将收集岩石样本以检查微观结构和结构，以提供相互作用、喷发和侵位模式的线索。凝灰岩-角砾岩中的沉积岩碎屑将被系统地取样，以对比岩性和孢粉学与下伏岩石序列的岩性和孢粉学，从而建立岩浆/水相互作用深度随时间的变化。在勘察工作的基础上，这项研究结果有望对理解凝灰岩-角砾岩是如何通过镜浆作用(岩浆和水之间的爆炸性作用)形成的及其形成的构造环境具有广泛的意义。这一结果也有望发展出侏罗纪横贯北极山脉的古火山环境。

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.