TY - CHAP
T1 - Granite emplacement and the retrograde P-T-fluid evolution of Neoarchean granulites from the Central Zone of the Limpopo Complex
AU - Huizenga, Jan Marten
AU - Perchuk, Leonid L.
AU - Van Reenen, Dirk D.
AU - Flattery, Yvonne
AU - Varlamov, Dimitri A.
AU - Smit, C. André
AU - Gerya, Taras V.
PY - 2011
Y1 - 2011
N2 - Petrological and fl uid-inclusion data of high-grade metapelitic gneisses that occur as enclaves and in the immediate surroundings of the 2.612 Ga old Bulai granitoid intrusive are presented in this chapter. The Bulai intrusive is an important time marker in the tectono-metamorphic evolution of the Central Zone of the Limpopo Complex. The host-rock gneisses show one generation of garnet, cordierite, and sillimanite, whereas the enclave gneisses show two different generations of garnet (Grt 1 , 2 ), cordierite (Crd 1 , 2 ), and sillimanite (Sil 1 , 2 ). The fi rst generation defi nes a gneissic texture, whereas the second generation shows a random mineral orientation. Grt 1 and Crd1 show a higher Mg content compared with Grt 2 and Crd 2 . Host rock garnet and Grt 1 show K-feldspar micro-veins at the contact with quartz as a result of high- temperature metasomatism. Host rock garnet, Grt 1 , and Grt 2 are zoned and participate in two simultaneously operating reactions: sillimanite + garnet + quartz = cordierite and garnet + K-feldspar + H 2 O = biotite + sillimanite + quartz. The combination of petrographic, geothermobarometric, and fl uid-inclusion results shows evidence of two different pressure-temperature (P-T) paths in the enclave and a single P-T path in the host rocks. The decompressional cooling P-T path in the host rock is typical of the country rocks throughout the Central Zone. The high-pressure part of the host-rock P-T path overlaps with the Grt 1 -Crd 1 -Sil 1 P-T path found in the enclave rocks. The second P-T path is calculated from the Grt 2 -Crd 2 -Sil 2 assemblage and is found only in the enclave rocks. The two P-T paths in the enclave rocks can be connected by a sub-isobaric heating event of ≃50 °C at 5.5 kbar. This increase in temperature is followed by decompressional cooling but with a lower P-T gradient compared with that of the country rocks caused by the emplacement of the Bulai Pluton. Fluids present during granulite metamorphism include CO 2 and brines. Retrograde infi ltration of water in graphite-bearing country rocks under relatively reduced conditions resulted in the formation of a methane-rich fl uid.
AB - Petrological and fl uid-inclusion data of high-grade metapelitic gneisses that occur as enclaves and in the immediate surroundings of the 2.612 Ga old Bulai granitoid intrusive are presented in this chapter. The Bulai intrusive is an important time marker in the tectono-metamorphic evolution of the Central Zone of the Limpopo Complex. The host-rock gneisses show one generation of garnet, cordierite, and sillimanite, whereas the enclave gneisses show two different generations of garnet (Grt 1 , 2 ), cordierite (Crd 1 , 2 ), and sillimanite (Sil 1 , 2 ). The fi rst generation defi nes a gneissic texture, whereas the second generation shows a random mineral orientation. Grt 1 and Crd1 show a higher Mg content compared with Grt 2 and Crd 2 . Host rock garnet and Grt 1 show K-feldspar micro-veins at the contact with quartz as a result of high- temperature metasomatism. Host rock garnet, Grt 1 , and Grt 2 are zoned and participate in two simultaneously operating reactions: sillimanite + garnet + quartz = cordierite and garnet + K-feldspar + H 2 O = biotite + sillimanite + quartz. The combination of petrographic, geothermobarometric, and fl uid-inclusion results shows evidence of two different pressure-temperature (P-T) paths in the enclave and a single P-T path in the host rocks. The decompressional cooling P-T path in the host rock is typical of the country rocks throughout the Central Zone. The high-pressure part of the host-rock P-T path overlaps with the Grt 1 -Crd 1 -Sil 1 P-T path found in the enclave rocks. The second P-T path is calculated from the Grt 2 -Crd 2 -Sil 2 assemblage and is found only in the enclave rocks. The two P-T paths in the enclave rocks can be connected by a sub-isobaric heating event of ≃50 °C at 5.5 kbar. This increase in temperature is followed by decompressional cooling but with a lower P-T gradient compared with that of the country rocks caused by the emplacement of the Bulai Pluton. Fluids present during granulite metamorphism include CO 2 and brines. Retrograde infi ltration of water in graphite-bearing country rocks under relatively reduced conditions resulted in the formation of a methane-rich fl uid.
UR - http://www.scopus.com/inward/record.url?scp=80051869963&partnerID=8YFLogxK
U2 - 10.1130/2011.1207(08)
DO - 10.1130/2011.1207(08)
M3 - Chapter
AN - SCOPUS:80051869963
SN - 9780813712079
T3 - Memoir of the Geological Society of America
SP - 125
EP - 142
BT - Origin and Evolution of Precambrian High-Grade Gneiss Terranes, with Special Emphasis on the Limpopo Complex of Southern Africa
PB - Geological Society of America
ER -
