Eastern margin of the Ross Sea Rift in western Marie Byrd Land, Antarctica: Crustal structure and tectonic development
Eastern margin of the Ross Sea Rift in western Marie Byrd Land, Antarctica: Crustal structure and tectonic development
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南极洲玛丽伯德地西部罗斯海裂谷东缘：地壳结构和构造发育
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发表时间：
2003
期刊：
影响因子：
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通讯作者：
C. Siddoway
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作者：
B. Luyendyk;Douglas S. Wilson;C. Siddoway
西南极洲玛丽伯德地（wMBL）的罗斯海裂谷基底岩石和构造出露。变薄、伸展的大陆地壳形成了西地中海和罗斯海东部大陆架，断层控制着区域盆地和山脉型地形，间距为120公里。在wMBL的福特山脉和洛克菲勒山脉的岸上，基底岩石由早古生代变杂砂岩和混合岩化等效物组成，被泥盆纪-石炭纪和白垩纪花岗岩类侵入。海洋地球物理剖面表明，这些地质构造在罗斯海东部之下继续向西延伸，并被冰川和冰川海洋沉积物覆盖。wMBL上空的航空重力和雷达探测表明，北方福特山脉的北部和东部内陆有较厚的地壳和较平滑的基底。在100-94 Ma之间从中地壳深度挖出的混合岩杂岩表明，在罗斯海东部边缘东北约300 km处的扩展地壳内侧边界附近存在深刻的地壳不连续性。在此极限附近，航磁测绘显示，福特山脉以东有一个大面积的高振幅异常区，可以解释为冰下火山区。重力数据模拟表明，罗斯海东部和西大洋边界层的伸展地壳比内部大洋边界层薄8-9 km（β = 1.35）。重力模型还勾勒出了低密度（2300-2500 kg m−3）埋藏基底岩石的广泛区域，这些岩石比地表暴露的岩石轻。这些区域被解释为以垂直分离的贯通东西断层为界。这些埋藏的低密度岩石可能是早古生代变杂砂岩的低密度相，或白垩纪花岗岩的低密度浅成相，或冰碛中已知的长英质火山岩。wMBL地区陆地上的这些地球物理特征和构造保存了罗斯海裂谷中、晚白垩世发育的记录。来自基底岩石和近海地层的热年代学数据表明，西太平洋裂谷边缘形成，大部分伸展发生在白垩纪中期和晚期，在西太平洋裂谷和坎贝尔高原之间的海底扩张开始之前。wMBL中的白垩纪构造记录与形成西部裂谷边缘的横贯南极山脉形成对比，在那里，在第三纪中期形成了显著的裂谷侧翼起伏。
The basement rock and structures of the Ross Sea rift are exposed in coastal western Marie Byrd Land (wMBL), West Antarctica. Thinned, extended continental crust forms wMBL and the eastern Ross Sea continental shelf, where faults control the regional basin‐and range‐type topography at ∼20 km spacing. Onshore in the Ford Ranges and Rockefeller Mountains of wMBL, basement rocks consist of Early Paleozoic metagreywacke and migmatized equivalents, intruded by Devonian‐Carboniferous and Cretaceous granitoids. Marine geophysical profiles suggest that these geological formations continue offshore to the west beneath the eastern Ross Sea, and are covered by glacial and glacial marine sediments. Airborne gravity and radar soundings over wMBL indicate a thicker crust and smoother basement inland to the north and east of the northern Ford Ranges. A migmatite complex near this transition, exhumed from mid crustal depths between 100–94 Ma, suggests a profound crustal discontinuity near the inboard limit of extended crust, ∼300 km northeast of the eastern Ross Sea margin. Near this limit, aeromagnetic mapping reveals an extensive region of high amplitude anomalies east of the Ford ranges that can be interpreted as a sub ice volcanic province. Modeling of gravity data suggests that extended crust in the eastern Ross Sea and wMBL is 8–9 km thinner than interior MBL (β = 1.35). Gravity modeling also outlines extensive regions of low‐density (2300–2500 kg m−3) buried basement rock that is lighter than rock exposed at the surface. These regions are interpreted as bounded by throughgoing east‐west faults with vertical separation. These buried low‐density rocks are possibly a low‐density facies of Early Paleozoic metagreywacke, or the low‐density epizonal facies of Cretaceous granites, or felsic volcanic rocks known from moraines. These geophysical features and structures on land in the wMBL region preserve the record of middle and Late Cretaceous development of the Ross Sea rift. Thermochronology data from basement rocks and offshore stratigraphy suggest that the wMBL rift margin formed and most extension occurred in mid‐ and Late Cretaceous time, before seafloor spreading initiated between wMBL and the Campbell Plateau. The Cretaceous tectonic record in wMBL contrasts with the Transantarctic Mountains that form the western rift margin, where significant rift‐flank relief developed in middle Tertiary time.