M. Andreoli, G. Brandl, H. Coetzee, J. Kramers, H. Mouri
{"title":"Intracrustal radioactivity as an important heat source for Neoarchean metamorphism in the Central Zone of the Limpopo Complex","authors":"M. Andreoli, G. Brandl, H. Coetzee, J. Kramers, H. Mouri","doi":"10.1130/2011.1207(09)","DOIUrl":"https://doi.org/10.1130/2011.1207(09)","url":null,"abstract":"","PeriodicalId":281141,"journal":{"name":"Geological Society of America Memoirs","volume":"340 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2011-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131882416","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
K. Mahan, C. Smit, M. L. Williams, G. Dumond, D. D. Reenen
{"title":"Heterogeneous strain and polymetamorphism in high-grade terranes: Insight into crustal processes from the Athabasca Granulite Terrane, western Canada, and the Limpopo Complex, southern Africa","authors":"K. Mahan, C. Smit, M. L. Williams, G. Dumond, D. D. Reenen","doi":"10.1130/2011.1207(14)","DOIUrl":"https://doi.org/10.1130/2011.1207(14)","url":null,"abstract":"","PeriodicalId":281141,"journal":{"name":"Geological Society of America Memoirs","volume":"41 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2011-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114576274","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
J. Huizenga, L. Perchuk, D. D. Reenen, Yvonne Flattery, D. A. Varlamov, C. Smit, T. Gerya
{"title":"Granite emplacement and the retrograde P-T-fluid evolution of Neoarchean granulites from the Central Zone of the Limpopo Complex","authors":"J. Huizenga, L. Perchuk, D. D. Reenen, Yvonne Flattery, D. A. Varlamov, C. Smit, T. Gerya","doi":"10.1130/2011.1207(08)","DOIUrl":"https://doi.org/10.1130/2011.1207(08)","url":null,"abstract":"Petrological and fluid-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 (Grt1,2), cordierite (Crd1,2), and sillimanite (Sil1,2). The first generation defines a gneissic texture, whereas the second generation shows a random mineral orientation. Grt1 and Crd1 show a higher Mg content compared with Grt2 and Crd2. Host rock garnet and Grt1 show K-feldspar micro-veins at the contact with quartz as a result of high-temperature metasomatism. Host rock garnet, Grt1, and Grt2 are zoned and participate in two simultaneously operating reactions: sillimanite + garnet + quartz = cordierite and garnet + K-feldspar + H2O = biotite + sillimanite + quartz. The combination of petrographic, geothermobarometric, and fluid-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 Grt1-Crd1-Sil1 P-T path found in the enclave rocks. The second P-T path is calculated from the Grt2-Crd2-Sil2 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 CO2 and brines. Retrograde infiltration of water in graphite-bearing country rocks under relatively reduced conditions resulted in the formation of a methane-rich fluid.","PeriodicalId":281141,"journal":{"name":"Geological Society of America Memoirs","volume":"23 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2011-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115007359","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Microstructures of melt-bearing regional metamorphic rocks","authors":"R. Vernon","doi":"10.1130/2011.1207(01)","DOIUrl":"https://doi.org/10.1130/2011.1207(01)","url":null,"abstract":"The most reliable microstructural criterion for the former presence of felsic melt in regional migmatites is a three-mineral (quartz, K-feldspar, and sodic plagioclase) aggregate in veinlets. Several other criteria are potentially reliable, namely: (1) euhedral crystals of feldspar (precipitated from liquid) or peritectic minerals (e.g., garnet, cordierite, orthopyroxene, K-feldspar) lining felsic “protoleucosomes”; (2) inclusionfree euhedral overgrowths of feldspar (precipitated from liquid) or peritectic minerals (e.g., garnet, cordierite, orthopyroxene, K-feldspar) on residual grains of the same minerals with abundant inclusions in the mesosome; (3) aligned, euhedral feldspar crystals; (4) simple twinning in K-feldspar; (5) dihedral angles of 60° subtended where a grain of feldspar and/or quartz (inferred to have pseudomorphed former melt) meets two grains of other minerals; (6) cuspate volumes of quartz, K-feldspar or sodic plagioclase, especially where surrounded by grains inferred to have been residual during melting; (7) veinlets of inferred former melt (now mineral pseudomorphs consisting of one of quartz, K-feldspar or sodic plagioclase, preferably, though less commonly, involving two or three of these minerals) along grain boundaries or along inferred former intragranular fractures; (8) biotite pseudomorphed by feldspar; (9) veinlets of plagioclase that is more sodic than plagioclase grains in the adjacent rock; (10) plagioclase with oscillatory zoning; (11) microgranophyric intergrowths of quartz and alkali feldspar in patches or veinlets between primary grains; (12) symplectic replacement aggregates that can be explained by reactions between peritectic grains and cooling melt; and (13) melanosome patches and layers, from which leucosome has been extracted. However, all these criteria must be interpreted with care. Some other proposed criteria are questionable, for example: (1) random mineral distributions; (2) grain-size increase; (3) interstitial grains; (4) corroded relics of inferred reactant mineral grains surrounded by areas of quartz, K-feldspar, or sodic plagioclase; (5) projections into a mineral grain; (6) lobes of myrmekite; and (7) plagioclase rims with a constant sodic composition occurring on plagioclase cores that are more calcic and/or of variable composition.","PeriodicalId":281141,"journal":{"name":"Geological Society of America Memoirs","volume":"47 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2011-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121810336","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Archean magmatic granulites, diapirism, and Proterozoic reworking in the Northern Marginal Zone of the Limpopo Belt","authors":"T. Blenkinsop","doi":"10.1130/2011.1207(13)","DOIUrl":"https://doi.org/10.1130/2011.1207(13)","url":null,"abstract":"The Northern Marginal Zone (NMZ) of the Limpopo Belt, southern Africa, is a high-grade gneiss belt dominated by magmatic granulites of the charnoenderbite suite, which intruded minor mafic-ultramafic and metasedimentary rocks between 2.74 and 2.57 Ga. The intrusive rocks have crustal and mantle components, and occur as elliptical bodies interpreted as diapirs. Peak metamorphism (P ≤800 MPa, T = 800–850 °C) occurred at ca. 2.59 Ga. The highly radiogenic nature of the rocks in the NMZ, supplemented by heat from mantle melts, led to heating and diapirism, culminating in the intrusion of distinctive porphyritic charnockites and granites. Horizontal shortening and steep extrusion of the NMZ, during which crustal thickening was limited by high geothermal gradients, contrast with overthickening and gravitational collapse observed particularly in more recent orogens. The granulites were exhumed by the end of the Archean. The pervasive late Archean shortening over the whole of the NMZ contrasts with limited deformation on the Zimbabwe Craton, possibly owing to the strengthening effect of early crust in the craton. In the southeast of the NMZ, strike-slip kinematic indicators occur within the Transition Zone and the Triangle Shear Zone, where dextral shearing reworked the Archean crust at ca. 1.97 Ga.","PeriodicalId":281141,"journal":{"name":"Geological Society of America Memoirs","volume":"107 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2011-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"132752815","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
C. Smit, D. D. Reenen, C. Roering, R. Boshoff, L. Perchuk
{"title":"Neoarchean to Paleoproterozoic evolution of the polymetamorphic Central Zone of the Limpopo Complex","authors":"C. Smit, D. D. Reenen, C. Roering, R. Boshoff, L. Perchuk","doi":"10.1130/2011.1207(12)","DOIUrl":"https://doi.org/10.1130/2011.1207(12)","url":null,"abstract":"","PeriodicalId":281141,"journal":{"name":"Geological Society of America Memoirs","volume":"14 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2011-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115037998","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"High-pressure and ultrahigh-temperature granulite-facies metamorphism of Precambrian high-grade terranes: Case study of the Limpopo Complex","authors":"T. Tsunogae, D. D. Reenen","doi":"10.1130/2011.1207(07)","DOIUrl":"https://doi.org/10.1130/2011.1207(07)","url":null,"abstract":"","PeriodicalId":281141,"journal":{"name":"Geological Society of America Memoirs","volume":"23 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2011-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127193861","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
D. D. Reenen, C. Smit, L. Perchuk, C. Roering, R. Boshoff
{"title":"Thrust exhumation of the Neoarchean ultrahigh-temperature Southern Marginal Zone, Limpopo Complex: Convergence of decompression-cooling paths in the hanging wall and prograde P-T paths in the footwall","authors":"D. D. Reenen, C. Smit, L. Perchuk, C. Roering, R. Boshoff","doi":"10.1130/2011.1207(11)","DOIUrl":"https://doi.org/10.1130/2011.1207(11)","url":null,"abstract":"","PeriodicalId":281141,"journal":{"name":"Geological Society of America Memoirs","volume":"29 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2011-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123574205","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Fluids in granulites","authors":"J. Touret, J. Huizenga","doi":"10.1130/2011.1207(03)","DOIUrl":"https://doi.org/10.1130/2011.1207(03)","url":null,"abstract":"Since the discovery of CO2 fluid inclusions in granulites, the role of fluids in the formation of these rocks has been widely studied. Owing to the complexity of the tectono-metamorphic history of granulite terrains, fluid inclusion data alone are not sufficient. They need to be integrated with geochemical and mineralogical studies done on the same rock samples. A clear understanding of the tectono-metamorphic history of granulite terranes is also indispensable. The widespread occurrence of CO2 and the later discovered high-salinity aqueous fluid inclusions support the idea that the lower crust underwent fluid flow and that both carbonic and brine fluids played a role in its formation. Both low-H2O-activity fluids play a similar role in destabilizing hydrous mineral phases. Furthermore, experimental studies have shown that brine fluids have a much larger geochemical effect on granulites than initially expected. These fluids are far more mobile in the lower crust compared with CO2 and also have the capability for dissolving numerous minerals. As in the example of the Limpopo Complex, fluid inclusions and many metasomatic features observed in granulite terranes can thus be explained only by large-scale movement of high-salinity aqueous fluids and, to a lesser extent, CO2, implying that lower-crustal granulites are not as dry as previously assumed. Similar brines and CO2-rich fluids are also found in mantle material, most likely derived from deeply subducted supracrustal protoliths.","PeriodicalId":281141,"journal":{"name":"Geological Society of America Memoirs","volume":"73 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2011-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130580463","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"The geochronology of the Limpopo Complex: A controversy solved","authors":"J. Kramers, H. Mouri","doi":"10.1130/2011.1207(06)","DOIUrl":"https://doi.org/10.1130/2011.1207(06)","url":null,"abstract":"","PeriodicalId":281141,"journal":{"name":"Geological Society of America Memoirs","volume":"47 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2011-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123345914","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}