Low-pressure granulite facies metamorphism in the Larsemann Hills area, East Antarctica; petrology and tectonic implications for the evolution of the Prydz Bay area
Low-pressure granulite facies metamorphism in the Larsemann Hills area, East Antarctica; petrology and tectonic implications for the evolution of the Prydz Bay area
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DOI：
10.1111/j.1525-1314.1989.tb00609.x
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发表时间：
1989-07
影响因子：
3.4
通讯作者：
K. Stüwe;R. Powell
中科院分区：
文献类型：
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作者：
K. Stüwe;R. Powell
对南极东部Prydz湾沿岸（73°-79°E, 68°-70°S）不同麻粒岩相区域的热气压研究表明，在1100 Ma左右的晚元古代造山运动中，Larsemann Hills的岩石经历了一个比周围地区更低的压力变质峰。沿着Prydz湾海岸，受此事件影响的岩石包括Vestfold Hills的部分地区以及整个Rauer Group， Larsemann Hills和Munro Kerr Mountains。Vestfold Hills西南角的岩脉在这次事件中重新结晶，在温度不像西南地区（650°C, 6.5 kbar）那么高的温度下几乎没有变形（Collerson et al., 1983）， Rauer群在800°C和7.5 kbar的温度下变质（Harley, 1987a）， Larsemann Hills在750°C和4.5 kbar， Munro Kerr Mountains可能在850°C和5 kbar左右。不同地区的逆行平衡发生在减压至约10公里深度的所有地区，随后在该深度进行等压冷却。本文认为Larsemann Hills的峰值变质作用发生在过低的压力下，不可能是地幔正常热流下过厚地壳热松弛的结果。尽管Prydz湾的其他地区在足够高的压力下变质，因此它们的减压路径与大陆碰撞模式并不矛盾，但推断出的前变质峰历史和与Larsemann Hills一致性的要求，使得碰撞之后的侵蚀驱动减压不太可能是一个合适的模式。我们认为Larsemann Hills地区地壳的热状态是由软流圈的扰动控制的，岩浆侵入地壳。我们认为，Prydz湾以Landing Bluff的花岗岩露头和Larsemann Hills地区的几个K/Ar时代为代表的500 Ma事件是导致地层最终挖掘的原因。
Thermobarometric studies on various granulite facies areas along the Prydz Bay coast, East Antarctica (73°-79°E, 68°-70°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°C, 6.5 kbar) (Collerson et al., 1983), the Rauer Group was metamorphosed at 800°C and 7.5 kbar (Harley, 1987a), the Larsemann Hills at 750°C and 4.5 kbar, and the Munro Kerr Mountains probably at around 850°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.