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

该奖项由极地方案办公室南极地质和地球物理方案提供，支持分析和解释在横跨北极山脉的屠宰岭火成岩(BRIC)上收集的航磁数据的研究。这些数据是1997-98年作为跨北极山脉航空地球物理研究活动(TAMARA)调查的一部分进行的一项覆盖航空磁力调查收集的。塔玛拉是美国调查人员和德国联邦地球科学及自然资源研究所的合作项目。金砖四国位于横跨南极的山脉上，位于东经79度45分，东经156度，暴露在一个10公里长，600米高的疤痕中，突出并环绕着南极东部冰盖。由于无法进入，金砖四国只有一部分被绘制了地质地图。金砖四国似乎是一个地台状的浅成侵入体，成分从拉斑玄武岩到流纹岩不等。174 Ma的40Ar/39Ar年龄和玄武岩的化学特征表明，金砖四国属于广泛分布的侏罗纪拉斑玄武岩套的一部分。该套岩套在南极洲绵延3000多公里，是与侏罗纪横贯北极(断裂)裂谷有关的岩浆活动的结果，由费勒榴辉岩岩床(大部分暴露)和岩脉、喷出的柯克帕特里克玄武岩流动和大规模的辉长岩杜费克侵入岩组成。金砖四国内部大量的壳源流纹岩，需要大量的平流热源通过地壳岩石的熔融形成，这表明它可能是一个主要的高级别玄武岩侵入体。1990年，作为BGR-USGS在邻近的罗斯冰架上进行的调查的一部分，获得了一个单一的航磁剖面。这一剖面显示了一个8公里宽的正异常，最大值约为700和1000 nT(纳米特斯拉)，并被磁学模型解释为在2公里厚的金砖四国之下有辉长体。这一解释表明，费拉尔岩浆活动伴随着大型的地壳上部岩浆室，其中发生了同化-分离结晶。1997-98年，作为塔玛拉调查的一部分，一项2.5x20公里长的线间距为2.5x20公里的覆盖航磁调查被直升机空运到金砖四国上空。对金砖四国航磁调查的初步汇编显示，与地形大致相关的异常幅度为1200-nT。很明显，高幅度异常模式，首先由单一的1990年剖面交叉，比10公里宽的露头更广泛。最大幅度异常出现在1990年采集的剖面以南，并延伸到调查区之外。新的航磁数据将可以确定调查区域Beacon沉积岩和冰暴露下以及金砖四国小规模暴露下厚厚堆积体的范围。与德国的BGR和NSF支持的Tamara调查的PI合作，该奖项支持对覆盖Butcher Ridge区域的航磁调查以及推断的金砖四国的埋藏范围进行详细的分析和解释。将计算二维和三维模型，并与美国地质勘探局合作，制作各种导数图(例如伪重力梯度和磁梯田)。这些模型将被解释为金砖四国及其周边地区的镁铁质堆积体的感应剩余磁化强度，如果可能的话，这项研究将导致将金砖四国的磁性特征与罗斯海、罗斯冰架以及西南极冰盖流经的伯德冰下盆地的冰盖区域观测到的磁性变化模式进行比较。这项比较工作对于解释从该地区磁异常图推断出的WAIS之下可能的火山特征很重要。

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.