Terrane accretion in the southwestern Yilgarn Craton: evidence from a deep seismic crustal profile
Terrane accretion in the southwestern Yilgarn Craton: evidence from a deep seismic crustal profile
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耶尔加恩克拉通西南部的地体增生：来自深部地震地壳剖面的证据
DOI：
10.1016/0301-9268(95)00077-1
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发表时间：
1996
影响因子：
3.8
通讯作者：
B. Evans
中科院分区：
文献类型：
--
作者：
S. Wilde;M. Middleton;B. Evans
在珀斯以北约110公里处，对Yilgarn克拉通西缘的地震、重力和磁力导线进行了解释，并结合克拉通西南部新的Rb-Sr和U-Pb年代学数据，重新评价了地质关系，并为该地区建立了一个克拉通增生模型。地球物理数据确定了地壳的三层性质，整个地壳厚度为32-40公里。上地壳的反射层与地表的剪切带相关，被解释为从东部输送地壳切片的主要逆冲断层。这些“鞋底出”在深度约10公里沿着一个明确的滑脱，并表明“薄皮”构造。剪切带定义了三个断层的边界，从西到东，在这里被定义为巴林加普，博丁顿和格雷斯湖断层。巴林居普地体由槽相变质沉积物组成，据信其沉积于2.8Ga，随后在中压角闪岩相条件下变质。该花岗岩中包含了Yilgarn盆地中最年轻的花岗岩类（2612和2527 Ma），这些花岗岩类已被沿着Darling断裂带的晚白垩世运动广泛剪切。东部与博丁顿地体的边界没有精确的界定，部分原因是缺乏暴露。它的标志是在南部的一个狭窄的，100公里长的构造石英二长岩带和更北的花岗岩类的Rb <$Sr黑云母年龄的变化，从400-500 Ma在西部到2300-2600 Ma在东部。Boddington地体包含一系列的Jimperding变质带（Jimperding变质带的一部分），被认为是在3.1 Ga沉积的，并在低压条件下变质为角闪岩-麻粒岩过渡相。这些层序主要发生在平坦的推覆体中，这些推覆体可能是在与格雷斯湖地体组装期间从东部被构造搬运而来的。Boddington地体还包含两个低级绿岩带，形成于2650和2670 Ma之间，并被2640 Ma的花岗岩类侵入。博丁顿地体的东部边界以重力的重大变化为标志，这也与地表的一系列剪切带、构造样式的变化和花岗岩类性质的重大变化相对应。在格雷斯湖地体的这一边界以东，两个年龄的花岗岩类已被确认：charlionkites形成于2640 Ma和后构造花岗闪长岩形成于2580 Ma。变质沉积岩，变质为麻粒岩相，呈筏状和透镜状，具有陡峭的直立褶皱，并被包裹在浅色含石榴子石的花岗质片麻岩中。绿岩，也变质为麻粒岩相和记录年龄约2790马，也被封闭在charcoquitites，因此大大超过低品位的绿岩在Boddington地体的西部。巴林加普和博丁顿花岗岩的组装似乎在2612 Ma的罗格溪花岗岩就位之前就已经完成。博丁顿和格雷斯湖的火山岩在2640 Ma麻粒岩相变质事件后聚集在一起，但组装的精确时间目前还没有限制。它肯定是在2411 Ma前完成的，这是一组主要的东西向基性岩脉（Widgemooltha岩脉套）的侵位时间，这些岩脉延伸超过500 km，横跨Yilgarn岩脉。虽然Widgemooltha Dyke Suite似乎不在Balingup...
Interpretation of a seismic, gravity and magnetic traverse across the western margin of the Yilgarn Craton, undertaken approximately 110 km north of Perth, together with new RbSr and UPb geochronological data from the southwestern portion of the craton, have led to a re-evaluation of the geological relationships and to the development of a terrane accretion model for the region. The geophysical data established the three-layered nature of the crust, with E-dipping reflectors present throughout its thickness of 32–40 km. Reflectors in the upper crust correlate with shear zones mapped at the surface and are interpreted as major thrusts that have transported crustal slices from the east. These ‘sole-out’ at a depth of about 10 km along a well-defined décollement and indicate ‘thin-skinned’ tectonism. The shear zones define the boundaries of three terranes which, from west to east, are herein defined as the Balingup, Boddington and Lake Grace terranes. The Balingup Terrane is composed of trough facies metasediments, believed to have been deposited at ∼ 2.8 Ga and subsequently metamorphosed under medium pressure amphibolite facies conditions. This terrane contains some of the youngest granitoids in the Yilgarn Craton (2612 and 2527 Ma) and these have been extensively sheared by late Archaean movement along the Darling Fault Zone. The boundary with the Boddington Terrane to the east is not precisely defined, partly due to lack of exposure. It is marked in the south by a narrow, 100 km long strip of tectonised quartz monzonite and further north by a change in the RbSr biotite ages of granitoids; from 400–500 Ma in the west to 2300–2600 Ma in the east. The Boddington Terrane contains a sequence of Archaean shelf facies metasediments (part of the Jimperding Metamorphic Belt), believed to have been deposited at ∼ 3.1 Ga, and metamorphosed up to amphibolite-granulite transition facies under low-pressure conditions. These sequences occur mainly in flat-lying nappes, which may have been tectonically transported from the east during assembly with the Lake Grace Terrane. The Boddington Terrane also contains two low-grade greenstone belts, formed between 2650 and 2670 Ma and intruded by 2640 Ma granitoids. The eastern boundary of the Boddington Terrane is marked by a major change in gravity, which also corresponds with a series of shear zones at the surface, a change in structural style and a major change in the nature of the granitoids. East of this boundary in the Lake Grace Terrane, granitoids of two ages have been recognised: charnockites formed at 2640 Ma and post-tectonic granodiorites formed at ∼ 2580 Ma. Metasedimentary rocks, metamorphosed to granulite facies, occur as rafts and lenses with steep upright folds and are enclosed in leucocratic, garnetiferous granitic gneiss. Greenstones, also metamorphosed to granulite facies and recording ages of around 2790 Ma, are also enclosed within the charnockites and are thus substantially older than the low-grade greenstones in the Boddington Terrane to the west. Assembly of the Balingup and Boddington terranes appears to have been completed prior to the emplacement of the Logue Brook Granite at 2612 Ma. The Boddington and Lake Grace terranes came together after the 2640 Ma granulite facies metamorphic event but the precise timing of assembly is not currently constrained. It was certainly completed by 2411 Ma, the time of emplacement of a major set of E-W-trending mafic dykes (the Widgemooltha Dyke Suite) which extend for over 500 km across the Yilgarn Craton. Although the Widgemooltha Dyke Suite appears to be absent from the Balingup …