Abstract The Nimrod Complex in the Miller and Geologists ranges of the central Transantarctic Mountains comprises Mesoarchean and Palaeoproterozoic crust that was incorporated into the Ross Orogen during metamorphism and deformation along the eastern Gondwanan convergent margin in the late Neoproterozoic and early Palaeozoic. In the Miller Range, boudinaged mafic domains are hosted within upper-amphibolite- to granulite-facies mylonitic rocks that were deformed during the Ross Orogeny. The mafic rocks preserve evidence of a precursor eclogite-facies mineral assemblage containing garnet, omphacite, amphibole, quartz and rutile. Mineral equilibria forward modelling and Zr-in-rutile thermometry indicate that the eclogite assemblage records peak pressure-temperature conditions of 16–18 kbar and 675–760 °C. A secondary metamorphic assemblage of clinopyroxene-plagioclase symplectite, plagioclase coronae rimming garnet, fine-grained amphibole, and interstitial ilmenite orthopyroxene overprint the high-pressure assemblage. Compositions and modal proportions of retrograde garnet, orthopyroxene and amphibole suggest near isothermal exhumation to conditions of 8–10 kbar and 660–840 °C, followed by a long-lived mid-crustal residence. In-situ LA–ICP–MS U Pb dating of zircon and rutile yields concordant ages of 536 ± 14 Ma and 536 ± 20 Ma, respectively. The Cambrian-aged zircons show an absent to weakly negative Eu anomaly signature and flat heavy rare earth element (HREE) distributions that are typical of zircons crystallised in the absence of plagioclase and presence of garnet, and which is diagnostic of eclogite-facies conditions. The Cambrian-aged zircon population contrasts with older, highly discordant Palaeoproterozoic zircons that have negative Eu anomalies and are HREE enriched. These zircons are interpreted to be protolithic, and their ages are consistent with existing geochronology from host rocks in the region. The Cambrian-aged zircon and rutile are inferred to represent eclogite-facies metamorphism associated with Ross orogenesis. The early Palaeozoic eastern Gondwanan margin contains a diverse array of eclogite precursors that document contrasting geodynamic styles. Eclogites in northern Victoria Land and central Tasmania record comparatively warm thermal gradients, short-lived high-pressure conditions, and rapid exhumation within their continental crust hosts, whereas oceanic eclogites in the southern New England Fold Belt record refrigerated, long-lived convergent-margin metamorphism. The Miller Range eclogite-facies rocks in this study appear to have been derived from shallow subduction of ancient continental crust, after which they stalled at thermally elevated mid-crustal depths prior to their final exhumation. The discovery of Cambrian-aged eclogite-facies rocks in the Miller Range expands the spatial footprint of high-pressure metamorphism during the Ross Orogeny along the early Palaeozoic eastern Gondwanan margin.

中文翻译：

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南极东部跨南极山脉中部寒武纪榴辉岩相变质作用：沿冈瓦纳大陆东部边缘扩展早古生代高压变质作用记录

摘要 横贯南极中部米勒和地质学家山脉的宁录杂岩由中太古代和古元古代地壳组成，在新元古代晚期和古生代早期沿冈瓦纳山脉东部收敛边缘变质变形过程中并入罗斯造山带。在米勒山脉，在罗斯造山运动期间变形的上角闪岩至麻粒岩相糜棱岩中存在布丁基镁铁质域。镁铁质岩石保留了榴辉岩相矿物组合的证据，其中包含石榴石、绿辉石、角闪石、石英和金红石。矿物平衡正向建模和 Zr-in-金红石测温表明榴辉岩组合记录了 16-18 kbar 和 675-760 °C 的峰值压力-温度条件。单斜辉石-斜长石辛辉石、斜长石冠镶石榴石、细粒闪石和间质钛铁矿斜方辉石的二次变质组合覆盖在高压组合上。逆行石榴石、斜方辉石和角闪石的成分和模态比例表明，在 8-10 kbar 和 660-840 °C 的条件下，近等温开采，然后是长期存在的中地壳住宅。锆石和金红石的原位 LA-ICP-MS U Pb 测年产生的一致年龄分别为 536 ± 14 Ma 和 536 ± 20 Ma。寒武纪年代的锆石显示无到弱负的 Eu 异常特征和平坦的重稀土元素 (HREE) 分布，这是在没有斜长石和石榴石存在的情况下结晶的锆石的典型特征，并且是榴辉岩相条件的诊断依据。寒武纪时代锆石群与具有负 Eu 异常且富含 HREE 的更老、高度不一致的古元古代锆石形成对比。这些锆石被解释为原石器时代，它们的年龄与该地区主岩的现有地质年代学一致。寒武纪时代的锆石和金红石被推断为代表与罗斯造山作用相关的榴辉岩相变质作用。早古生代东部冈瓦纳边缘包含多种榴辉岩前体，记录了对比鲜明的地球动力学风格。维多利亚州北部和塔斯马尼亚中部的榴辉岩记录了相对温暖的温度梯度、短暂的高压条件和大陆地壳内的快速剥露，而新英格兰褶皱带南部的海洋榴辉岩记录了冷藏，长寿命的收敛边缘变质作用。本研究中的米勒山脉榴辉岩相岩石似乎源自古代大陆地壳的浅俯冲，此后它们在最终折返之前停滞在地壳中部温度升高的深度。米勒山脉寒武纪榴辉岩相岩石的发现扩大了罗斯造山运动期间沿早古生代冈瓦纳东部边缘的高压变质作用的空间足迹。