Structural, Metamorphic and Uplift History of the Prince Charles Mountains

From the abstracts of two of the referenced papers:The low-temperature (ie less than ~120 degrees C) thermal history of the East Antarctic Shield has been assessed by apatite fission-track analysis of 42 Precambrian outcrop samples. Fission-track ages for these samples range from 466 plus or minus 20 Ma to 153 plus or minus 3 Ma and mean track lengths vary from 14.4 plus or minus 0.11 micrometres to 12.41 plus or minus 0.17 micrometres. The variability in the relationship between apatite fission track age and mean track length in data from various geographical regions suggests differences in styles of cooling during the Phanerozoic. Samples from the continental margin east of Prydz Bay are inferred to have cooled during the late Palaeozoic and early Mesozoic, between ~300 and 200 Ma, while samples from the Prince Charles Mountains and from the continental margin west of Prydz Bay are inferred to have cooled more recently in the Mesozoic, at ~150 Ma. Evidence for cooling during the Mesozoic at ~150 Ma is attributed to exhumation associated with the early stages of Gondwana break-up. Cooling during the late Palaeozoic and early Mesozoic may have been associated with an earlier phase of aborted rifting. These preliminary apatite fission track data suggest that the Lambert Graben has had an important influence on the Phanerozoic exhumation history of the East Antarctic Shield, with the region to the west of the Lambert Graben showing the greatest amount of uplift and erosion related to the early stages of Gondwana break-up. ###############Thermobarometric studies on various granulite facies along the Prydz Bay coast, East Antarctica (73 degrees - 79 degrees E, 68 degrees - 70 degrees S), show that, at around 1100 Ma, during a late Proterozoic orogeny, the rocks of the Larsemann Hills suffered a lower pressure metamorphic peak than the surrounding areas. Along the Prydz Bay coast, the rocks affected by this event include parts of the Vestfold Hills block plus all of the Rauer Group, the Larsemann Hills and the Munro Kerr Mountains. The dykes in the south-west corner of the Vestfold Hills were recrystallized during this event with little deformation at temperatures not quite as high as in the areas further south-west (650 degrees C, 6.5 kbar), the Rauer Group was metamorphosed at 800 degrees C and 7.5 kbar, the Larsemann Hills at 750 degrees C and 4.5 kbar, and the Munro Kerr Mountains probably at around 850 degree C and 5 kbar. Retrograde equilibration in the different areas occurred during decompression to about 10 km depth in all areas, followed by isobaric cooling at this depth.This paper shows that the peak metamorphism in the Larsemann Hills occurred at a pressure which is too low to have been the consequence of thermal relaxation of overthickened crust with normal mantle heat flow. Although other areas in Prydz Bay were metamorphosed at sufficiently high pressures so that their decompression paths are not inconsistent with a continental collision model, the inferred pre-metamorphic peak histories and the requirement of consistency with the Larsemann Hills, make it unlikely that collision followed by erosion-driven decompression is an appropriate model. We suggest that the thermal regime of the crust in the Larsemann Hills region was controlled by a perturbation in the asthenosphere, with magma invasion of the crust. We suggest that the 500 Ma event, represented in Prydz Bay by granitic outcrops at Landing Bluff and by several K/Ar ages from the Larsemann Hills area, was responsible for the final excavation of the terrane.

基于两篇参考文献的摘要：
通过对42个前寒武纪露头样品开展磷灰石裂变径迹分析（apatite fission-track analysis），本研究评估了东南极克拉通（East Antarctic Shield）的低温（即约低于120℃）热演化历史。这些样品的裂变径迹年龄介于466±20 Ma至153±3 Ma之间，平均径迹长度则分布于14.4±0.11 μm至12.41±0.17 μm范围内。不同地理区域的样品中，磷灰石裂变径迹年龄与平均径迹长度的关系存在差异，这表明显生宙（Phanerozoic）期间的冷却模式存在区域分异。普里兹湾（Prydz Bay）东侧大陆缘的样品被推断在晚古生代至早中生代（约300 Ma至200 Ma期间）发生冷却，而查尔斯王子山脉（Prince Charles Mountains）及普里兹湾西侧大陆缘的样品则被认为在更晚的中生代（约150 Ma）经历冷却。约150 Ma中生代冷却的证据被归因于与冈瓦纳大陆（Gondwana）裂解早期相关的地壳折返（exhumation）。晚古生代至早中生代的冷却事件可能与早期夭折裂谷作用（aborted rifting）有关。这些初步的磷灰石裂变径迹数据表明，兰伯特地堑（Lambert Graben）对东南极克拉通的显生宙折返历史具有重要影响，其中兰伯特地堑西侧区域因冈瓦纳大陆裂解早期事件而经历了最为强烈的隆升与剥蚀作用。

对东南极普里兹湾沿岸（东经73°~79°，南纬68°~70°）各类麻粒岩相（granulite facies）岩石开展的温压研究（thermobarometric studies）表明，在约1100 Ma的新元古代造山运动（late Proterozoic orogeny）期间，拉瑟曼丘陵（Larsemann Hills）的岩石所经历的变质峰期压力低于周边区域。受该造山事件影响的普里兹湾沿岸岩石包括部分韦斯特福尔丘陵（Vestfold Hills）地块、全部劳尔群（Rauer Group）、拉瑟曼丘陵以及门罗克尔山脉（Munro Kerr Mountains）。韦斯特福尔丘陵西南缘的岩脉在该事件中发生重结晶，变形程度较弱，其变质温度略低于更西南侧的区域（650℃、6.5 kbar）；劳尔群的变质温度与压力分别为800℃与7.5 kbar，拉瑟曼丘陵为750℃与4.5 kbar，门罗克尔山脉则大致为850℃与5 kbar。各区域的退变质平衡（retrograde equilibration）作用均发生于减压至约10 km深度的过程中，随后在该深度发生等压冷却（isobaric cooling）。本研究表明，拉瑟曼丘陵的变质峰期压力过低，无法用具正常地幔热流的加厚地壳热松弛机制来解释。尽管普里兹湾其他区域的变质峰期压力足够高，其减压路径与大陆碰撞模型并不矛盾，但结合推断的变质前峰期演化历史以及与拉瑟曼丘陵数据的一致性要求，碰撞后经剥蚀驱动减压的模型并不适用于该区域。我们认为，拉瑟曼丘陵区域的地壳热状态受软流圈（asthenosphere）扰动及地壳岩浆侵入作用控制。我们认为，500 Ma的地质事件（在普里兹湾以兰丁断崖（Landing Bluff）的花岗岩露头及拉瑟曼丘陵区域的多个钾氩（K/Ar）年龄为代表）是该地块最终抬升剥露的原因。