Interpretation of an Aneromagnetic Survey Over the Butcher Ridge Igneous Complex, Transantarctic Mountains

对横贯南极山脉屠夫岭火成岩杂岩的风磁测量的解释

• 批准号: 9814036
• 负责人: John Behrendt
• 金额: $ 5万
• 依托单位: University of Colorado at Boulder
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 1999
• 资助国家: 美国
• 起止时间: 1999-08-01 至 2003-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9814036&HistoricalAwards=false
• 关键词: Interpretation; Aneromagnetic; Survey; Over; Butcher

This award, provided by the Antarctic Geology and Geophysics Program of the Office of Polar Programs, supports research to analyze and interpret aeromagnetic data collected over the Butcher Ridge Igneous Complex (BRIC) in the Transantarctic Mountains. These data were collected as a draped aeromagnetic survey in 1997-98 as part of the larger Transantarctic Mountains Aerogeophysical Research Activity (TAMARA) survey. TAMARA was conducted as a cooperative project between US investigators and the German Federal Institute for Geosciences and Natural Resources (BGR).The BRIC, located in the Transantarctic Mountains at about 79 degrees 45 minutes S and 156 degrees E, is exposed in a 10-km-long, 600-m-high scarp, projecting through and bounding the East Antarctic ice sheet. Only part of the BRIC has been mapped geologically because of its inaccessibility. The BRIC appears to be a sill-like hypabyssal intrusion ranging in composition from tholeiitic basalt to rhyolite. A 40Ar/39Ar age of 174 Ma and the chemical character of the basaltic rocks show the BRIC to be part of the widespread Jurassic Ferrar suite of continental tholeiitic rocks. This suite, that extends for over 3000 km across Antarctica, is the result of magmatic activity associated with the Jurassic Transantarctic (failed) rift, and comprises the Ferrar Dolerite sills (the great bulk of the exposures) and dikes, the extrusive Kirkpatrick Basalt flows and the massive gabbroic Dufek intrusion.Significant volumes of crustal-derived rhyolite within the BRIC, requiring a substantial source of advective heat to be formed by melting of crustal rocks, suggested that a major high-level basaltic intrusion might underlie it. In 1990 a single aeromagnetic profile was obtained as part of a BGR-USGS survey over the adjacent Ross Ice Shelf. This profile showed an 8-km-wide positive anomaly with maxima of about 700 and 1000 nT (nano-Tesla), and was interpreted using magnetic models to indicate a gabbroic body beneath the BRIC 2-km thick. This interpretation implied that Ferrar magmatism was accompanied by large, upper crustal magma chambers in which assimilation-fractional crystallization occurred.In 1997-98, a 2.5 by 20-km line spaced, draped aeromagnetic survey was flown by helicopter over the BRIC as part of the TAMARA survey. A preliminary compilation of the aeromagnetic survey over the BRIC shows a 1200-nT amplitude series of anomalies roughly associated with the topography. It is apparent that the high amplitude anomaly pattern, first crossed by the single 1990 profile, is more extensive than the 10-km wide exposed outcrop. The highest amplitude anomalies appear south of the profile acquired in 1990, and extend out of the survey area. The new aeromagnetic data will allow determination of the extent of the thick cumulate body beneath exposures of Beacon sedimentary rock and ice in the survey area as well as beneath the small BRIC exposure. Working in cooperation with the BGR in Germany and the NSF supported PI's of the TAMARA survey, this award supports a detailed analysis and interpretation of the aeromagnetic survey over the area covering Butcher Ridge and the inferred buried extent of the BRIC. Two and three-dimensional models will be calculated, and in cooperation with the USGS, various derivative maps (e.g. pseudogravity gradients and magnetic terraces) will be produced. The models will be interpreted in terms of induced, and if possible, remnant magnetization for the mafic cumulate body inferred to underlie the BRIC and surrounding area.Ultimately, this research will lead to comparisons between the magnetic signature of the BRIC to the patterns of magnetic variation observed over the Ross Sea, the Ross Ice Shelf, and over the ice covered area of the Byrd Subglacial Basin through which the West Antarctic Ice Sheet (WAIS) flows. This comparative work is important to interpretations of possible volcanic features beneath the WAIS that are inferred from magnetic anomaly maps in that region.

该奖项由极地项目办公室的南极地质和地球物理项目提供，支持分析和解释在横贯南极山脉的屠夫岭火成岩杂岩体（BRIC）上收集的航磁数据的研究。这些数据是在 1997-98 年通过航磁调查收集的，是更大规模的横贯南极山脉航空地球物理研究活动 (TAMARA) 调查的一部分。 TAMARA 是美国调查人员与德国联邦地球科学和自然资源研究所 (BGR) 之间的合作项目。金砖四国位于横贯南极山脉，南纬 79 度 45 分，东经 156 度，暴露在 10-10 度的光照下。公里长、600 米高的陡坡，穿过南极东部冰盖并形成边界。由于交通不便，金砖四国仅部分地区绘制了地质图。金砖四国似乎是一种类似窗台的浅成侵入体，其成分范围从拉斑玄武岩到流纹岩。 174 Ma 的 40Ar/39Ar 年龄和玄武岩的化学特征表明金砖四国是广泛分布的侏罗纪费拉尔大陆拉斑玄武岩岩组的一部分。该套件横跨南极洲，绵延 3000 多公里，是与侏罗纪横贯南极（失败的）裂谷相关的岩浆活动的结果，包括费拉尔辉绿岩基岩（大部分暴露）和岩脉、喷出的柯克帕特里克玄武岩流以及大量的辉长岩 Dufek 侵入体。金砖四国需要通过地壳岩石熔化形成大量平流热源，这表明其下方可能存在主要的高层玄武岩侵入。 1990 年，作为 BGR-USGS 对邻近罗斯冰架的调查的一部分，获得了单一航磁剖面。该剖面显示出 8 公里宽的正异常，最大值约为 700 和 1000 nT（纳米特斯拉），并使用磁模型进行解释，表明金砖四国下方有 2 公里厚的辉长岩体。这种解释表明，费拉尔岩浆活动伴随着大型上地壳岩浆室，其中发生了同化分异结晶。 1997-98 年，作为塔玛拉调查。金砖四国航磁勘测的初步汇编显示了与地形大致相关的 1200 nT 幅度异常序列。很明显，1990 年的单一剖面首次穿过的高振幅异常模式比 10 公里宽的裸露露头更广泛。最大振幅异常出现在 1990 年获取的剖面以南，并延伸到调查区域之外。新的航磁数据将能够确定调查区域Beacon沉积岩和冰暴露区以及小金砖四国暴露区下方的厚堆积体的范围。该奖项与德国 BGR 合作以及 NSF 支持 TAMARA 调查的 PI，支持对覆盖屠夫山脊的区域的航磁调查以及推断的金砖四国埋藏范围进行详细分析和解释。将计算二维和三维模型，并与美国地质调查局合作，生成各种导数图（例如伪重力梯度和磁阶）。这些模型将根据推断为金砖四国及其周边地区下方的镁铁质堆积体的感应磁化强度（如果可能的话）进行解释。最终，这项研究将导致金砖四国的磁性特征与磁性模式之间的比较。在罗斯海、罗斯冰架以及西南极冰盖 (WAIS) 流经的伯德冰下盆地的冰覆盖区域上观察到的变化。这项比较工作对于解释 WAIS 下方可能存在的火山特征非常重要，这些火山特征是根据该地区的磁异常图推断出来的。