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Summary: ¶Detailed studies of rocks from the Limpopo (South Africa) and Lapland (Kola-Fennoscandia) high-grade terrains were carried out in order to reveal similar geological and thermodynamic conditions in their formation. Both complexes (1) are situated between Archean greenstone belts, (2) are younger than the belts, (3) are bounded by crustal-scale shear zones, (4) have a similar intrusive-like (harpolith) geometry, and (5) show similar reaction textures that reflect both breakdown and growth of garnet in each high-grade terrain. Local mineral equilibria within the textures indicate their successive formation with cooling of the granulite facies rocks. Some of the textures in the metapelites must have resulted from the following reverse reactions: Grt + Qtz ⇌Opx + Crd and/or Grt + Sil + Qtz ⇌ Crd. Based on these data, both the decompression cooling P-T path and the near-isobaric cooling P-T path were deduced for each HGT. However the near-isobaric cooling P-T path is not a characteristic of the central zones of both complexes studied. Similar structural framework of the high-grade terrains, similar morphologies (shapes of granulitic bodies), similar reaction textures developed in metapelites, and similar shapes of P-T paths suggest similarity in geodynamic history of both complexes.

Summary: ¶The Southern Yenisey Range of Eastern Siberia consists of the granulite facies Kanskiy Complex bordered in the west by the lower-grade Yeniseyskiy and Yukseevskiy Complexes. Three deformational events were recognized in each of the three complexes along the Yenisey River cross-section: a D1 fabric forming event, a D2 shear and folding event, and a D3 shear event. Thrust kinematics across the Southern Yenisey Range suggest that during the D2 event the Kanskiy Complex was thrusted along a regional ductile shear zone onto the lower-grade complexes. This resulted in shearing and folding as well as the development of a dynamic metamorphic zonation. In the low-grade greenstone belt part of the cross section (Yukseevskiy complex) D2 shearing is associated with peak prograde (T ∼ 660 °C and P ∼ 5.8 kbar) metamorphism. The retrograde P-T path of the Yukseevskiy Complex coincides with minimum T of the near-isobaric cooling P-T paths for the adjacent granulites of the Kanskiy Complex (Perchuk et al., 1989). The metamorphism can therefore be attributed to deformation and heat transfer caused by exhumation of the Kanskiy Complex in the time period 2000–1800 Ma which also defines the most significant tectono-thermal event in the Southern Yenisey Range. The tectono-metamorphic pattern and evolution of the low- to high-grade metamorphic complexes of the Southern Yenisey Range is very similar to that described for the ∼ 2600 Ma Limpopo Complex of Southern Africa and the ∼ 1900 Ma Lapland Complex of the Kola Peninsula. Similar geodynamic processes were therefore possibly responsible for the formation of these high-grade terrains suggesting that their formation is linked to a general geodynamic model.

Summary: ¶The petrology and P-T evolution of mica schists from two regional scale tectonic (shear) zones that separate high grade terrains (“mobile belts”) from cratons are described. These are the 2.4–1.9 Ga Tanaelv Belt, a suture zone that separates the Lapland granulite complex from the Karelian craton (Kola Peninsula–Fennoscandia), and the 2.69 Ga Hout River Shear Zone that separates the > 2.9 Ga Kaapvaal craton from the 2.69 Ga South Marginal Zone of the Limpopo high-grade terrain (South Africa). Two metamorphic zones are identified in strongly deformed mica schists from the 1.9 Ga Korva Tundra Group of the Tanaelv belt: (1) a chlorite-staurolite zone tectonically overlaying gneisses of the Karelian craton, and (2) a kyanite-biotite zone tectonically underlying garnet amphibolites of the Tanaelv Belt, which are in tectonic contact with the Lapland granulite complex. The prograde reaction Chl+St+Ms ↠ Ky+Bt+Qtz+H2O clearly defines a boundary between zones (1) and (2). Rotated garnet porphyroblasts from zone (1) contain numerous inclusions (Otz, Chl, Ms), and show clear Mg/Fe chemical zoning, suggesting garnet growth during prograde metamorphism. The metamorphic peak, T = 650°C and P = 7.5 kbar, is recorded in the kyanite-biotite zone and characterized by unzoned snowball garnet. In many samples of mica schists euhedral garnet porphyroblasts of the retrograde stage are completely devoid of mineral inclusions while N Mg decreases from core to rim, indicating a decrease in P-T from 650°C, 7.5 kbar to 530°C, 5 kbar. The Hout River Shear Zone (South Africa) shows metamorphic zonation from greenschists through epidote amphibolites to garnet amphibolites. Rare strongly deformed mica schists (Chl+Grt+Pl+Ms+Bt+Qtz) occur as thin layers among epidote-amphibolites only. Garnet porphyroblasts in the schists are similar to that of the Tanaelv Belt recording a prograde P-T path with peak conditions of T = 600°C and P∼ 5.5 kbar. The retrograde stage is documented by the continuous reaction Prp+2Ms+Phl ↠ 6Qtz+3East recording a minimum T = 520°C and P ∼ 3.3 kbar. Similar narrow clock-wise P-T loops recorded in mica schists from both studied shear zones suggest similarities in the geodynamic history of both shear zones under consideration.

Gold deposits in Archean high-grade terranes are either syngenetic or epigenetic. In the North China craton, the high-grade metamorphic rocks are considered to be the main source of gold for the formation of gold deposits formed during the Proterozoic or Mesozoic eras.The Hadamengou mine is located in the E-W-trending Archean Daqingshan granulite belt at the northern margin of the North China craton. In the mine area, the Archean Wulashan Group rocks were metamorphosed to granulite facies under temperatures of 750-850°C and pressures of 7-9 kbar during the late Archean and subsequently were affected by greenschist to epidote-hornblende facies retrograde metamorphism during the late Proterozoic. Metamorphosed banded iron formation (BIF), i.e., magnetite-quartz granulite and magnetite-garnet-plagioclase- quartz gneiss, is spatially closely associated with gold mineralization. Gold-bearing quartz-K- feldspar veins are the main type of mineralization. A fluid inclusion study demonstrated that K+ and Na+ (with some Mg2+ and Ca2+) were the main cations and Cl-, F- and SiO42- the main anions of the mineral fluid which, in most cases, is a single H2O-rich + CO2 vapor phase. Isotopic geochemistry suggests that the mineralizing fluid is weakly alkaline and oxidizing (pH = 8.3-8.52 and Eh = 231.6-299.2 millivolts) and suitable for gold precipitation. The high-grade meta-morphic rocks in the mine area, which contain high background values of gold, are the most probable source of gold (73%) for the formation of the gold deposit. Granitic magmatism during the late Proterozoic provided additional heat energy and also may have contributed to the mineralizing fluid that resulted in the liberation and eventual precipitation of gold in shear zones. The temperature of mineralization is higher than 200-450°C, as is indicated by a fluid inclusion study. Gold mineralization in the mine area is structurally controlled and all gold lodes are restricted to the hanging wall or north side of an augen-gneissic mylonite zone. This ductile shear zone developed under high-temperature conditions and acted as a conduit for later fluid flow. Late brittle-ductile shear zones, accompanied by retrograde metamorphism of greenschist to epidote-hornblende facies during late Proterozoic, acted as the host structures of gold mineralization. The payshoots are distributed in the foliated zones or fill the fractures in the deformational zones.The Hadamengou deposit is clearly epigenetic and the source of the gold is probably the high- grade metamorphic rocks. In the North China craton, more than 30 gold deposits are located in the high-grade rocks. These deposits formed during late Proterozoic or Mesozoic. It is suggested that Archean high-grade terranes are of similiar importance for gold mineralization and exploration as greenstone belts.