Thermo-tectonic evolution of the Neoarchaean Southern Marginal Zone of the Limpopo granulite Complex (South Africa)

被引:0
|
作者
Van Reenen, D. D. [1 ,2 ]
Smit, C. A. [1 ,2 ]
Huizenga, J. M. [2 ,3 ,4 ]
Tsunogae, T. [2 ,5 ]
Safonov, O. [2 ,6 ,7 ]
机构
[1] Univ Johannesburg, Natl Res Fdn Ctr Excellence Integrated Mineral &, Dept Sci & Technol, POB 524, ZA-2006 Auckland Pk, South Africa
[2] Univ Johannesburg, Dept Geol, POB 524, ZA-2006 Auckland Pk, South Africa
[3] Norwegian Univ Life Sci, Fac Environm Sci & Nat Resource Management, POB 503, NO-1432 As, Norway
[4] James Cook Univ, Coll Sci & Engn, Econ Geol Res Inst EGRU, Townsville, Qld 4811, Australia
[5] Univ Tsukuba, Fac Life & Environm Sci Earth Evolut Sci, Tennoudai 1-1, Ibaraki 3058572, Japan
[6] Russian Acad Sci, Korzhinskii Inst Expt Mineral, Academician Ossipian Str 4, Chernokalovka 142432, Russia
[7] Moscow MV Lomonosov State Univ, Dept Petr & Volcanol, Vorobevy Cory, Moscow 142432, Russia
基金
俄罗斯科学基金会; 新加坡国家研究基金会;
关键词
CRUSTAL; BELT; FLOW;
D O I
10.25131/sajg.126.0027
中图分类号
P5 [地质学];
学科分类号
0709 ; 081803 ;
摘要
Combined geophysical, structural geological, metamorphic, geochronological, and stable isotope information is employed to elucidate the Neoarchaean thermo-tectonic evolution of the Southern Marginal Zone (SMZ) within the Limpopo Complex (South Africa) during the Limpopo orogeny (2.72 to 2.62 Ga). The complex evolutionary history of the SMZ was controlled by an allochthonous SMZ granulite nappe that was extruded from a rising granulite diapir through a process of mid-crustal heterogeneous channel flow. This granulite nappe with its embedded structures (steeply plunging reclined folds and steep shear zones) was formed during emplacement of the diapir to mid-crustal level (6 kbar, 20 km depth) from where it was thrust south-westwards along the Hout River shear zone (HRSZ) sole thrust against the Kaapvaal Craton (KVC) at 2.72 to 2.69 Ga. Evidence for the thermo- tectonic interaction of thegranulite nappe with the KVC includes (1) thrust complexes (referred to as hot-iron zones) that are developed at the frontal ramp sections of the HRSZ juxtaposed against the granite-greenstone belts of the KVC, and (2) strike-slip shear deformation associated with the lateral ramp section of the HRSZ, which developed against the KVC devoid of greenstone belts. The emplacement of the post-tectonic Matok granitic pluton at 2.68 Ga into the SMZ signified the end of the thermo-tectonic event that established the regional fold- and shear deformational framework of the granulite facies SMZ. Post-Matok secondary shear zones reflect evidence for HRSZ-linked tectonism that continued intermittently to 2.65 to 2.62 Ga. Low H2O-activity fluids (H2O activity of 0.1 to 0.3) released from devolatilisation of underthrust greenstone material passively infiltrated and interacted with the overlying cooling granulites. This established a retrograde anthophyllite-in isograd at 6 kbar and 620 degrees C that subdivides the SMZ into a northern granulite domain and a southern retrograde hydrated granulite domain. Simultaneously, gold-bearing fluids focused into these minor shear zones established shear zone-hosted orogenic gold mineralisation at 2.65 to 2.62 Ga. Emplacement of the posttectonic Palmietfontein granite at 2.46 Ga and associated sub-volcanic granitic dykes into both the retrograde hydrated granulite domain and the granulite domain signifies the end of all thermo-tectonic activity in the SMZ. A Palaeoproterozoic thermal overprint at 2.1 Ga is recorded by Rb-Sr biotite and phlogopite ages derived from various rocks from the SMZ and adjacent KVC. This thermal event is not associated with deformation and did not result in the formation of new mineral assemblages. Integrated data presented and discussed in this paper contradict the interpretation of age and petrological data utilised to support alternative models for the evolution of the SMZ, including a proposed 2.1 Ga Palaeoproterozoic polymetamorphic amphibolite-grade thermo-tectonic event.
引用
收藏
页码:373 / 406
页数:34
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