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A Mainly Crustal Origin for Tonalitic Granitoid Rocks, Superior Province, Canada: Implications for Late Archean Tectonomagmatic Processes 总被引:11,自引:0,他引:11
WHALEN JOSEPH B.; PERCIVAL JOHN A.; McNICOLL VICKI J.; LONGSTAFFE FREDERICK J. 《Journal of Petrology》2002,43(8):1551-1570
The central Wabigoon subprovince of the Superior Province, likemost plutonic domains within Archean cratons, is dominated bygranitoid rocks of the tonalitetrondhjemitegranodiorite(TTG) series. Heterogeneous <2·832·74Ga tonalite gneisses and foliated tonalite to granodiorite units,emplaced at 2·7222·709 Ga, exhibit initial 相似文献
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Water-deficient Calc-alkaline Plutonic Rocks of Northeastern Superior Province, Canada: Significance of Charnockitic Magmatism 总被引:5,自引:0,他引:5
Calc-alkaline batholiths of the Archaean Minto block, northeasternSuperior Province, Canada, have pyroxene- and hornblende-bearingmineral assemblages inferred to have crystallized from hot,water-undersaturated magmas at 2·7292·724Ga. A regional amphibolite- to granulite-facies tectonothermalevent at 2·70 Ga resulted in mild to negligible metamorphiceffects on the dominantly granodioritic units. Geochemical,textural and thermobarometric studies define the crystallizationhistory in compositions ranging from cumulate pyroxenite throughquartz diorite, granodiorite, granite, and syn-magmatic gabbroicdykes. Early magmatic assemblages include orthopyroxene, clinopyroxene,plagioclase, biotite, FeTi oxides and ternary feldspar,indicating crystallization from magmas containing <2 wt %H2O at 1100900°C. Water enrichment in the residualmelt induced hornblende crystallization at 5 ± 1 kbar,800600°C. Characterized by a continuum of large ionlithophile element (LILE)-enriched, high field strength element(HFSE)-depleted compositions, the I-type suite resembles moderncontinental arc batholiths in composition and size but not primarymineralogy. Magmatic arcs produced between 2·75 and 1·85Ga commonly have charnockitic components, possibly because slab-derivedfluids interacted with mantle wedges at ambient temperatureshigher by 100°C than at present, producing large volumesof water-deficient magma. KEY WORDS: granitoid rocks; igneous pyroxenes; water-undersaturated magma; charnockite 相似文献
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The high-grade Archean Ashuanipi complex contains an older sequenceof granulite-facies migmatitic paragneiss and tonalite cut byabundant orthopyroxene-bearing, enclave-laden granitoid bodies(diatexite) of strongly peraluminous (garnet-bearing) and mildlyperaluminous (garnetabsent) granodioritic composition,inferred to be magmatic in origin. Temperature estimates forgarnetorthopyroxenebiotiteplagioclasequartzassemblages in both metamorphic and igneous rock types are mainlyin the range 700 835 ?C, but apparent pressures are higher(0?60?65 GPa) in a wide belt of paragneiss and associatedtonalite than in the enclosing diatexites (0?350?55 GPa),possibly owing to fluid-enhanced retrograde re-equilibrationwithin the crystallizing igneous assemblages. Paragneiss has bulk compositions typical of Archean greywacke(5868 wt. % SiO2), including high Cr (110250 ppm),Ni (20100 ppm), and LREE [(70100) ?chondrites].Garnet-bearing diatexites have compositions virtually identicalto paragneiss whereas garnet-absent diatexites are characterizedby marked HREE depletion. High degrees of fusion of a sourcesuch as paragneiss, with entrainment of crystalline phases suchas garnet and orthopyroxene, are required to explain the compositionof garnet-bearing diatexites, whereas lower amounts of melting,leaving residual garnet, may account for the origin of the garnet-absentvarieties. CO2 may have been a melt component in diatexite, based on severalobservations: (l)the high degrees of fusion implied in the genesisof diatexite require either extreme temperatures (> 1000?C)for which there is no mineralogical evidence, or some fluxingagent other than H2O (cf. Peterson & Newton, 1990); (2)some xenoliths have orthopyroxene-rich (dehydration) margins,implying relatively anhydrous melt conditions; and (3) orthopyroxeneis unaltered, suggesting that low aH2O conditions persistedduring crystallization. UPb zircon geochronology constrains the time for heatingand magma production to <18 Ma (2700 Ma for detrital zirconin paragneiss; 2682 Ma for crystallization of igneous zirconin diatexite). Combined with the evidence for high crustal temperaturesand possible CO2 involvement, the rapid heating implies thatunderplated basaltic magmas played a key role as heat and fluidsources driving high-grade metamorphism and granitoid melt production. 相似文献
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