The Murchison Greenstone Belt, South Africa: Accreted slivers with contrasting metamorphic conditions
The Murchison Greenstone Belt, South Africa: Accreted slivers with contrasting metamorphic conditions
复制标题
南非默奇森绿岩带：具有对比变质条件的增生碎片
DOI：
10.1016/j.precamres.2012.03.005
复制
发表时间：
2013
影响因子：
3.8
通讯作者：
Paquette. J.-L.
中科院分区：
文献类型：
--
作者：
Poujol;Jaguin;Paquette. J.-L.
本文介绍了位于南非卡普瓦尔盆地的3.09-2.92Ga默奇森绿岩带（MGB）的新的岩石学和年代学数据，并讨论了它们的大地构造意义。MGB由三个构造变质单元组成：Silwana Amphibolites，Murchison Unit和La France Formation。它们经历了对比鲜明的顺时针压力-温度-变形（P-T-D）历史，并通过相对狭窄的高应变剪切带相互分离，具有左旋，逆冲自上而下的运动，与整个带观察到的变形模式一致。这些模式是由一个N-S挤压应力场，影响默奇森带之间的2.97和2.92 Ga。新的岩石学研究结果表明，默奇森单元的超镁铁质至长英质火山-沉积岩在最大P-T条件（5.6± 0.6 kbar，570°C）下经历了绿片岩至低角闪岩相变质作用，沿着相对较热的最小表观地热（1030 °C/km）。相比之下，Silwana斜长角闪岩和La France组的变质峰温分别为8.7- 10 kbar，630-670°C和8- 9 kbar，600-650°C，需要的视地热为20°C/km。一个逆行的，近等温减压P-T路径，其次是等压冷却也推断为法国组。构造-变质叠加的时间在2.97和2.90Ga之间，这分别受到Murchison单元内的同变形花岗岩和变形后的Maranda花岗岩的U-Pb锆石年龄的限制。La France变质岩中的独居石和磷钇矿产生了更年轻的年龄。2.75Ga，在2.92Ga时继承组分较少。他们指出，MGB的后期激活，可能与Rooiwater复杂和Pietersburg绿岩带的构造热事件有关。Silwana和La France岩石中记录的相对较冷的表观地温、不同单元之间的对比峰值P-T条件以及La France组的近等温减压表明，Kaapvaal克拉通地壳一定足够冷，从而能够使地壳显著增厚，应变沿沿着狭窄的剪切带局部化，因此，在不同地壳深度变质的岩石的快速构造并置。这些特征与沿着古生代或现代斜向俯冲-碰撞带所观察到的特征相似，但与热大陆省的特征不同。因此，我们解释的MGB代表的一部分，一个倾斜的碰撞区之间的两个地形的卡普瓦尔克拉通：威特沃特斯兰德和彼得斯堡地形。
This paper presents new petrological and geochronological data for the ∼3.09–2.92Ga Murchison Greenstone Belt (MGB), located in South Africa's Kaapvaal Craton, and discusses their geotectonic implications. The MGB is made of three tectono-metamorphic units: the Silwana Amphibolites, the Murchison Unit and the La France Formation. They underwent contrasting clockwise pressure–temperature–deformation (P–T–D) histories, and are separated from each other by relatively narrow, high-strain shear zones, with a sinistral, transpressive top-to-the-south movement, consistent with the deformation patterns observed throughout the belt. These patterns are explained by a N–S compressional stress field, affecting the Murchison Belt between 2.97 and 2.92Ga. Results of new petrological investigations indicate that ultramafic to felsic volcano-sedimentary rocks of the Murchison Unit underwent a greenschist- to lower-amphibolite-facies metamorphism at maximum P–T conditions of 5.6±0.6kbar at 570°C, along a relatively hot, minimum apparent geotherm of ∼30°C/km. In contrast, the Silwana Amphibolites and the La France Formation were metamorphosed at much higher peak metamorphic conditions of 8.7–10kbar, 630–670°C, and 8–9kbar, 600–650°C, respectively, and require a colder apparent geotherm of ∼20°C/km. A retrograde, nearly isothermal–decompression P–T path followed by isobaric cooling is also inferred for the La France Formation. The timing of the structural–metamorphic overprint is bracketed between 2.97 and 2.90Ga, which is constrained by U–Pb zircon ages of a syn-deformation granite within the Murchison Unit and the post-deformation Maranda granite, respectively. Monazite and xenotime from La France metapelites yield much younger ages of ca. 2.75Ga, with few inherited components at 2.92 Ga. They point to a later activation of the MGB, perhaps related with tectono-thermal events in the Rooiwater Complex and the Pietersburg Greenstone Belt. The relatively cold apparent geotherms recorded in the Silwana and La France rocks, the contrasted peak P–T conditions between the different units, and the near isothermal decompression of the La France Formation indicate that the Kaapvaal craton crust must have been cold enough to enable significant crustal thickening and strain localisation along narrow shear zones and, as a consequence, fast tectonic juxtaposition of rocks metamorphosed at different crustal depths. These features are similar to those observed along Palaeozoic or modern day, oblique subduction–collision zones, but different to those of hot Archaean provinces. We therefore interpret the MGB as representing part of an oblique collision-zone between two terrains of the Kaapvaal craton: the Witwatersrand and Pietersburg terrains.
登录
查看更多内容
南非巴伯顿花岗岩-绿岩地形最古老的部分：3.5 至 3.7 Ga 之间地壳形成的证据
影响因子：
3.8
作者：
A. Kröner;E. Hegner;J. Wendt;G. Byerly
通讯作者：
G. Byerly
南非巴伯顿山区早期太古代花岗岩-绿岩演化的年代学，基于单锆石蒸发的精确测年。
影响因子：
5.3
作者：
A. Krüner;G. Byerly;D. Lowe
通讯作者：
D. Lowe
南非卡普瓦尔克拉通默奇森片岩带锑线相关结构
DOI：
--
发表时间：
1988
期刊：
影响因子：
--
作者：
J. Vearncombe;P. E. Cheshire;J. H. Beer;A. M. Killick;W. S. Mallinson;S. Mccourt;E. Stettler
通讯作者：
E. Stettler
印度中北部邦德尔坎德克拉通不含石英的高镁、铝金云母-绿泥石片岩中新太古代高压玛格丽特-白云母-绿泥石电晕刚玉
DOI：
--
发表时间：
2011
期刊：
影响因子：
--
作者：
L. Saha;N. Pant;J. K. Pati;D. Upadhyay;J. Berndt;A. Bhattacharya;M. Satynarayanan
通讯作者：
M. Satynarayanan
南非卡普瓦尔克拉通太古代默奇森带的结构和变质作用
DOI：
--
发表时间：
1988
期刊：
影响因子：
--
作者：
J. Vearncombe
通讯作者：
J. Vearncombe