Evolution of a crustal‐scale transpressive shear zone in the Albany–Fraser Orogen, SW Australia: 1. P–T conditions of Mesoproterozoic metamorphism in the Coramup Gneiss
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Abstract The Albany–Fraser Orogen in southwestern Australia preserves an important thermo‐tectonic record of Australo‐Antarctic cratonic assembly during the Mesoproterozoic. New petrologic and thermobarometric data from the Coramup Gneiss (a 10 km wide zone of high strain rocks within the NE‐trending eastern Albany–Fraser Orogen) indicate at least two high‐grade metamorphic events during 1345–1140 Ma convergence and amalgamation of the West Australian and Mawson cratons. The first event (M1) involved c . 1300 Ma granulite facies metamorphism of the Coramup Gneiss (M1a: 800–850 °C, 5–7 kbar), followed by burial and recrystallization under high‐ P conditions (M1b: 800–850 °C, c . 10 kbar) prior to high‐ T decompression (M1c: 700–800 °C, 7–8 kbar) and the 1290–1280 Ma emplacement of Recherche Granite sills. The second event (M2) entailed high‐ T , low‐ P metamorphism within dextral D2 shear zones (M2a: 750–800 °C, 5–6 kbar), followed by fluid‐present amphibolite facies M2b retrogression. Subsequent sinistral D3 mylonites and pseudotachylites are considered contemporaneous with similar structures in the adjacent Nornalup Complex that postdate the c . 1140 Ma Esperance Granite. Our petrological and thermobarometric data permit two end‐member P – T ‐time relationships between M1 and M2: (1) a single post‐M1b event involving continuous M1b–M1c–M2a–M2b cooling and decompression, and (2) a two‐stage post‐M1b evolution involving M1c metamorphism during the waning stages of an event unrelated causally or temporally to subsequent M2a metamorphism and D2 deformation. In a companion paper, new structural and U–Pb SHRIMP zircon data are presented to support a two‐stage P – T evolution for the Coramup Gneiss, with M1 and M2, respectively, reflecting thermo‐tectonic activity during Stage I (1345–1260 Ma) and Stage II (1215–1140 Ma) of the Albany–Fraser Orogeny.Keywords:
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Abstract This work presents the results of a fluid inclusion study of an amphibolite‐granulite facies transition in West Uusimaa, S.W. Finland. Early fluid‐inclusions in the granulite facies area are characteristically carbonic (CO 2 ), in contrast to predominantly aqueous early inclusions in the amphibolite facies area. These early inclusions can be related to peak metamorphic conditions (750‐820°C and 3‐5 kbar for peak granulite facies metamorphism). Relatively young CO 2 inclusions with low densities (<0.8g/cm 3 ) indicate that the first part of the cooling history of the rocks was characterized by a near isothermal uplift. N 2 ‐CH 4 inclusions, with compositions ranging between pure CH 4 and pure N 2 (Raman spectral analysis), were found in the whole area. They are probably syn‐ or even pre‐early inclusions. Only nearly critical homogenizing inclusions have been found (low density). Pressure estimates, based on densities of early fluid inclusions, show that the rapid transition of amphibolite towards granulite facies metamorphism is virtually isobaric. Granulite facies metamorphism in West Uusimaa is a thermal event, probably induced by the influx of hot, CO 2 ‐bearing fluids.
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Rodinia
Laurentia
Basement
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Baltic Shield
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A Thesis Submitted to the Faculty of Science
University of the Witwatersrand, Johannesburg
for the Degree of Doctor of Philosophy.
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The southernmost Hidaka metamorphic belt consists mainly of cordierite tonalite intrusions and pelitic metamorphic rocks ranging from the greenschist to the granulite facies. Anatectic migmatites are common in the higher amphibolite and granulite facies zones. Compositional changes in major, rare earth elements and some other trace metals are so small that they are undetectable among the pelitic metamorphic rocks of zones A + B + C and D, but they are large enough to be detected in the higher amphibolite (zone D) to the granulite facies rocks (zone E). The enrichment of Fe, Mg, Na, Eu, and Sc, and the depletion of K, P, La, Ce, Nd, Cs and Rb are statistically significant in pelitic granulites, while heavy REEs are very variable. The chemical variation of pelitic granulite was derived from the accumulation of plagioclase + garnet. This suggests that more than 50-60% of the total volume of pelitic granulite was melted to produce a large amount of tonalitic magma, leaving pelitic granulite as a restite. Migmatites of the higher amphibolite facies are anatexites, and their K, P, Cs, Rb and light REE content is the same as that of lower grade metamorphic rocks. Migmatites of the higher amphibolite facies melted incipiently to segregate only a small amount of melt, and could not produce a large magmatic mass such as the cordierite tonalites. Cordierite tonalites are S-type granites, and their major elements, Cs, Rb and light REE concentrations are similar to those of lower grade metamorphic rocks. The chemical variation of cordierite tonalites is explained by the extraction of plagioclase + garnet from a tonalitic magma and the variation of original sedimentary rocks. The small chemical difference between the cordierite tonalites and the lower grade metamorphic rocks suggests that the former was derived from a massive melting of metapelites or that much of the restite is retained. The material migration among higher amphibolite facies rocks, pelitic granulites, migmatites and cordierite tonalites took place through mineral/melt interaction in the lower crust.
Migmatite
Anatexis
Pelite
Cordierite
Greenschist
Sillimanite
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因为， Grenvillian 造山运动是否发生在华南，仍然保持高度争论高质量，区别数据正在缺乏，因此，解决这件事的钥匙是发现与 Grenvillianorogeny 有关的可确定时代的暴烈或沉积的岩石。如此的岩石在从在中央云南的降低中间的部分 ofKunyang 组的 Fuliangpeng 成员是显然在场的；在这里，单位是厚的超过 100 m 并且由 andesiticignimbrite， tuffite， terrigeous 棒麴霉素和碳酸盐组成。这些暴烈的岩石， Sibao 褶层戳的发达南方系上带子，从中央云南在晚前寒武纪的时间代表最早计算碱的暴烈的活动并且与两个是同时代的在到碳酸盐和在其它地方的 seismite 开发的开始的从岩屑的沉积外形的一个变化。为 SHRIMPanalysis 的二件样品从这个暴烈的单位被收集。从 FuliangpengMember 的底部，样品 G3-29-2 是 ignimbrite，并且从它恢复的大约 100 锆石晶体有 euhedral 形状并且在 cathodoluminescent (CL ) 下面显示相对简单的部门带状配列成像，建议 amagmatogenic 起源。25 锆石被分析， 1032 ± 9 妈的称平均数的 U-Pb 年龄被获得。样品 G3-29-3 从最高 Fuliangpeng 成员的部分是 tuffite，并且许多绕行显然由岩屑形成的锆石被恢复。九这些锆石被分析，并且最旧的单个谷物的 U-Pb 锆石变老，暗示 6 妈在 Cathaysia 开发了的那个 Paleoproterozoic 地下室是 1938 ± 2。标明日期的结果，与关于 FuliangpengMember 的大地构造的研究结合了，导致我们结束那迟了的 Mesoproterozoic orogenic 暴烈的活动发生在华南的西方的部分，并且 Yangtze 和 Cathaysian cratons 的相关碰撞是 Rodinia 的集会的不可分的部分。
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