Abstract The Rauer Group in East Antarctica is a typical high- to ultrahigh-temperature (HT–UHT) granulite-facies terrane. As UHT metamorphism has been recognized only in Mg–Al-rich pelitic granulites from the Mather Paragneiss, the regional extent of UHT metamorphism remains uncertain, which has hindered our understanding of the genesis and tectonic setting of UHT metamorphism in the Rauer Group. In this study, representative samples of mafic granulite were selected from Archean crustal domains to constrain the peak metamorphic conditions and P–T path and to assess the regional extent of UHT metamorphism in the Rauer Group. Integrated results from mineral reaction histories, thermobarometry, and phase equilibria modeling indicate a multi-stage clockwise P–T evolution for mafic granulites involving pre-peak compression, heating to UHT peak conditions, post-peak near-isothermal decompression under UHT conditions, and subsequent decompressional cooling. The pre-peak prograde history is based mainly on the inclusion assemblage of clinopyroxene + plagioclase + amphibole + quartz + ilmenite ± orthopyroxene ± k-feldspar within porphyroblastic garnet and clinopyroxene and records the transformation from a quartz-present to quartz-absent system. The UHT peak conditions are well constrained at 930°C–1030°C and 10.6–12.8 kbar on the basis of the stability field of the observed peak assemblage of (orthopyroxene–quartz)-free garnet + clinopyroxene + plagioclase + amphibole + ilmenite + melt, as well as measured mineral compositions, including the high Ti content in amphibole (Ti = 0.38–0.42 p.f.u.), the anorthite content of coarse-grained plagioclase cores (XAn = 0.35–0.42), and the grossular content in garnet (XGrs = ~0.21) in P–T pseudosections. The peak T conditions are consistent with thermometric estimates in the range of 930°C–1030°C obtained from garnet–clinopyroxene, garnet–orthopyroxene, and Ti-in-amphibole thermometers, and are slightly lower than estimates (1020°C–1120°C) obtained from thermometers based on rare earth elements. The near-isothermal decompression under UHT conditions can be divided into two stages. The early stage is recorded by coronae of orthopyroxene + plagioclase around clinopyroxene and core–mantle/rim anorthite-increasing zoning in plagioclase. The late stage is identified from symplectites of orthopyroxene + plagioclase ± amphibole around porphyroblastic garnet, which were formed at the expense of garnet at 915°C–950°C and 7.6–8.2 kbar as inferred from the amphibole–plagioclase thermometer. The subsequent decompressional cooling to fluid-absent solidus conditions (~875°C and ~6.5 kbar) is indicated by the growth of biotite, which formed at the expense of symplectic minerals, reflecting back-reaction of melt with symplectite minerals. The peak UHT metamorphic conditions and clockwise P–T path of the studied mafic granulites from the Archean crustal domains are similar to those of Mg–Al-rich pelitic UHT granulites from the Mather Paragneiss. The UHT conditions recorded by the mafic granulites, combined with previously identified isolated UHT localities in the Rauer Group, imply that UHT metamorphism in the Rauer Group occurred over a much wider region than previously thought and probably extends over the whole Archean crustal domain. Our findings have general significance in understanding the regional extent of other UHT granulite-facies terranes worldwide.
We provide a principal Hugoniot of cryogenic liquid deuterium at a pressure of $27<P<240$ GPa, with reflected-shock data of up to $\ensuremath{\sim}830$ GPa. The maximum density reaches $\ensuremath{\sim}1.49$ $\mathrm{g}/{\mathrm{cm}}^{3}$, about 8.7 times the initial density. Our independent principal Hugoniot experimental data broadly support the wide-regime equation of state (WEOS) model, which well matches Fernandez-Pa\~nella et al. [Phys. Rev. Lett. 122, 255702 (2019)] and Knudson et al. [Phys. Rev. Lett. 118, 035501 (2017)] experimental data over the observed pressure range up to 550 GPa, and most of three sets of reflected shock data are in accordance with our theory up to 1 TPa. Our high-precision experimental results establish an important benchmark equation of state of deuterium and conform to the WEOS model quite well. Our work is useful for the development of the high-pressure response of hydrogen's isotopes, directly related to inertial confinement fusion, planetary science, and metallization.
东南极拉斯曼丘陵斯图尔内斯半岛及邻区发育不同类型的片麻岩。本文结合岩相学、相平衡模拟以及年代学分析等方法对该地区石榴石斜方辉石片麻岩（样品LSM178-2）和石榴石夕线尖晶石片麻岩（样品LSM302-10）进行综合研究，结果显示片麻岩经历了中低压高温麻粒岩相变质作用。样品LSM178-2峰期温压条件为T=830~870℃，P=6.1~8.9kbar，后期退变至T<705℃，P=3.6~5.4kbar。石榴石夕线尖晶石片麻岩（LSM302-10）保存的峰期温压范围为T=860~1050℃，P=4.8~10.2kbar，之后退变至T=820~840℃，P=4.7~5kbar。样品LSM178-2主要矿物组合对应的变质年龄为~543±5.7Ma。样品LSM302-10中锆石暗灰色边年龄为531±5.7Ma，浅灰色边年龄为509±5.9Ma，这些变质年龄可能反映了持续较长时间的泛非期构造热事件（ca.540~510Ma）。结合相关区域已有资料分析，拉斯曼丘陵西部斯图尔内斯半岛及邻区片麻岩记录的中低压高温麻粒岩相变质作用可能反映了造山作用后期的抬升与伸展。;Different types of gneiss are exposed in the Stornes Peninsula and its adjacent region of the Larsemann Hills, East Antarctica. In this paper, a comprehensive study of garnet-orthopyroxene gneiss (Sample LSM178-2) and garnet-sillimanite-spinel gneiss (Sample LSM302-10) is carried out by combining petrography, phase equilibrium modelling and geochronological analysis. The results indicate that the gneisses experienced medium-low pressure high-temperature granulite facies metamorphism. The estimated peak P-T conditions of the Sample LSM178-2 are T=830~870℃, P=6.1~8.9kbar, which retrogressed to T<705℃, P=3.6~5.4kbar. The peak P-T ranges of the garnet-sillimanite-spinel gneiss (Sample LSM302-10) are T=860~1050℃, P=4.8~10.2kbar, followed by retrograde conditions of T=820~840℃, P=4.7~5kbar. The metamorphic age corresponding to the development of the major mineral assemblage of Sample LSM178-2 should be ~543±5.7Ma. The age for the dark gray rim of zircon in Sample LSM302-10 is 531±5.7Ma and the age for the light gray rim is 509±5.9Ma. The metamorphic ages may reflect Pan-African tectonic thermal event that lasted for a relatively long period of time (ca. 540~510Ma). Combined with the existing data in the relevant regions, the medium-low pressure high-temperature granulite facies metamorphism recorded by the gneisses in the Stones Peninsula and its adjacent region in the west of the Larsemann Hills may reflect the uplift and extension during the late stage of orogenesis.
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