Just another drip: Re-analysis of a proposed Mesoarchean suture from the Barberton Mountain Land, South Africa
Just another drip: Re-analysis of a proposed Mesoarchean suture from the Barberton Mountain Land, South Africa
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DOI：
10.1016/j.precamres.2014.07.022
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发表时间：
2014-11
影响因子：
3.8
通讯作者：
M. V. Kranendonk;A. Kröner;J. Hoffmann;T. Nagel;C. Anhaeusser
中科院分区：
文献类型：
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作者：
M. V. Kranendonk;A. Kröner;J. Hoffmann;T. Nagel;C. Anhaeusser
对位于南非巴伯顿绿岩带西南部的中太古代缝合线（称为Inyoni剪切带（ISZ））进行的结构分析表明，主要的、陡倾的、NNE走向的组构仅分布在1 km宽的范围内，是晚期（D3），并清楚地叠加了两组较早的组构要素（D1，D2），最初定向在直角的方向提出的碰撞。S2面理化变奥长花岗岩的测年结果表明，D2变形年龄小于3238.2 ± 0.9Ma。ISZ的D3高应变组构局限于紧密折叠的、不规则规模的表壳筏周围，但在远离筏的所有方向上、沿沿着和横跨走向消散。运动学不对称的S3剪切面理的变化，在ISZ的表壳岩的紧，直立F3褶皱的相对的肢体，指示简单的剪切相关的屈曲折叠的更主管表壳岩在矩阵的能力较低的花岗质片麻岩。F3屈曲褶皱是高度非圆柱形的陡峭到近垂直的轴，陷入南部的区域的北方部分和北部的区域的南部，与巢垂直陷入鞘褶皱沿着角闪岩/变花岗岩接触在中心区域。高压（HP），含石榴子石斜长角闪岩仅限于与垂直的D3鞘褶皱密切相关，并不沿走向沿着，结合数据表明，ISZ不是西向俯冲的产物，如前所述。相反，应变和运动学数据表明，ISZ只是另一滴相对较冷，相对刚性的绿岩进入热，韧性花岗岩片麻岩，形成于部分对流翻转的上部（绿岩）和中部（花岗岩）地壳。高压岩石的伸展是沿着与c. 3.1 Ga Kees Zyn Doorns正长岩。
Structural analysis of a proposed Mesoarchean suture located immediately to the southwest of the Barberton Greenstone Belt, South Africa – known as the Inyoni Shear Zone (ISZ) – reveals that the main, steeply dipping, NNE-striking fabric is distributed across only 1 km width, is late (D3), and clearly overprints two earlier sets of fabric elements (D1, D2) that were originally oriented at right angles to the direction of proposed collision. Dating of a S2 foliated meta-trondhjemite is interpreted to indicate that D2 deformation was at, or younger than, 3238.2 ± 0.9 Ma. The D3 high strain fabric of the ISZ is localised around tightly folded, kilometre-scale supracrustal rafts, but dissipates in all directions away from the rafts, along and across strike. The kinematic asymmetry of S3 shear foliations changes across opposing limbs of tight, upright F3 folds of supracrustal rocks in the ISZ, indicative of simple shear related to buckle folding of more competent supracrustal rocks in a matrix of less competent granitic gneisses. F3 buckle folding was highly non-cylindrical on steep to subvertical axes that plunge to the south in the northern part of the zone and to the north in the southern part of the zone, with nests of vertically plunging sheath folds along amphibolite/metagranite contacts in the central area. High-pressure (HP), garnet-bearing amphibolites are restricted to close association with the vertical D3 sheath folds and do not extend along strike.Combined, the data indicate that the ISZ is not the product of west-directed subduction, as previously suggested. Rather, the strain and kinematic data indicate that the ISZ is just another drip of relatively cool, relatively rigid greenstones into hot, ductile granitic gneisses, formed during partial convective overturn of the upper (greenstone) and middle (granitic) crust. Uplift of the HP rocks was along a late (D4), brittle–ductile mylonite zone associated with emplacement of the c. 3.1 Ga Kees Zyn Doorns syenite.