TY - JOUR
T1 - P-T paths and tectonic evolution of shear zones separating high-grade terrains from cratons
T2 - Examples from Kola Peninsula (Russia) and Limpopo Region (South Africa)
AU - Perchuk, L. L.
AU - Gerya, T. V.
AU - Van Reenen, D. D.
AU - Smit, C. A.
AU - Krotov, A. V.
PY - 2000
Y1 - 2000
N2 - 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 NMg 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 clockwise P-T loops recorded in mica schists from both studied shear zones suggest similarities in the geodynamic history of both shear zones under consideration.
AB - 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 NMg 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 clockwise P-T loops recorded in mica schists from both studied shear zones suggest similarities in the geodynamic history of both shear zones under consideration.
UR - http://www.scopus.com/inward/record.url?scp=0000297884&partnerID=8YFLogxK
U2 - 10.1007/s007100050020
DO - 10.1007/s007100050020
M3 - Article
AN - SCOPUS:0000297884
SN - 0930-0708
VL - 69
SP - 109
EP - 142
JO - Mineralogy and Petrology
JF - Mineralogy and Petrology
IS - 1-2
ER -
