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首页> 外文期刊>Journal of the Geological Society >Detachment faulting and bimodal magmatism in the Palaeoproterozoic Willyama Supergroup, south-central Australia: keys to recognition of a multiply deformed Precambrian metamorphic core complex
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Detachment faulting and bimodal magmatism in the Palaeoproterozoic Willyama Supergroup, south-central Australia: keys to recognition of a multiply deformed Precambrian metamorphic core complex

机译：澳大利亚中南部古元古代Willyama超群的拆离断层和双峰岩浆作用：认识多重变形前寒武纪变质核复合体的关键

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The multiply deformed (D1–D3) Palaeoproterozoic Willyama Supergroup in south–central Australia incorporates upper and lower c. 1700 Ma metasedimentary sequences with contrasting early tectonothermal histories that invite comparisons with the metamorphic core complexes and younger extensional orogens of western North America and Europe. A detachment surface of D1 age separating these two sequences has the deduced geometry of an extensional shear zone, juxtaposing rocks subjected to bimodal magmatism, sillimanite- to granulite-grade migmatization, and Na–Fe metasomatism against a less intensely metamorphosed upper plate lacking both migmatites and bimodal magmatism. Synextensional metamorphism took place under low-pressure–high-temperature conditions, producing regionally extensive andalusite- and sillimanite-bearing mineral assemblages before further high-grade metamorphism accompanying D2 recumbent folding and crustal thickening. D2 folding locally inverted the original D1 thermal structure so that sillimanite-grade lower plate rocks now lie structurally above andalusite-grade rocks of the upper plate, rendering recognition of the original detachment surface and associated thermal structure difficult. U–Pb dating of synextensional metabasites intruded into lower plate rocks just below the detachment surface indicate that extension and related bimodal magmatism peaked around 1690–1670 Ma, some 70–90 Ma earlier than the 1600–1590 Ma age previously inferred for the onset of regional deformation and low-P–high-T metamorphism. A regionally extensive redox boundary associated with the detachment surface served as the locus for several important mineral deposits.
机译：澳大利亚中南部的元古代元古生代Willyama 超群变形变形（D 1 –D 3 ）包括上层 和下层C。 1700 Ma具有较早构造热历史的对比的沉积沉积序列，该序列邀请与北美西部和欧洲西部的变质核复合体和年轻的伸展造山带进行对比。分离这两个序列的 D 1 年龄的分离面具有推导剪切带的推导几何 ，使受 < / sup>双峰岩浆作用，硅线石到粒岩级的成矿作用， 和Na-Fe交代作用，对强度较弱的 上板同时缺乏石和双峰岩浆作用。在低压-高温 条件下发生同伸延伸 同质化，产生了区域广泛的含红柱石和硅线石的矿物组合，随后进一步高变质。 s D 2 伴随的倾斜变质和地壳增厚。 D 2 局部折叠 反转了原始的D 1 热结构，从而使硅线石等级的 下部板岩现在处于结构上上部板块上的红柱石级 岩石之上，使得难以识别原始的 分离表面和相关的热结构。 进入分离表面下方的 下部板岩中的变质岩表明 延伸和相关的双峰岩浆作用在1690–1670 Ma附近达到峰值，大约70-90 Ma早于先前推测的1600-1590 Ma 年龄，是由于区域变形 和低P-高T变质的开始。与脱离表面相关的区域广泛的 氧化还原边界用作 的几个重要矿床的所在地。

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