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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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Geochemical and Isotopic (O, Nd, Pb and Sr) Constraints on A-type Granite Petrogenesis Based on the Topsails Igneous Suite, Newfoundland Appalachians 总被引:24,自引:2,他引:22
WHALEN JOSEPH. B.; JENNER GEORGE A.; LONGSTAFFE FREDERICK J.; ROBERT FRANCINE; GARIPY CLMENT 《Journal of Petrology》1996,37(6):1463-1489
The voluminous, bimodal, Silurian Topsails igneous suite consistsmainly of A-type peralkaline to slightly peraluminous,hypersohnis to subsolvus granites with subordinate syenite,onzonite and diabase, plus consanguineous basalts and highsilicarhyolites. Nd(T) values from the suite range from 1.5to +5.4; most granitoid components exhibit positive Nd(T) values(+1.1 to +3.9). Granitoid initial 87Sr/86Sr and most 18 O valuesare in the range expected for rocks derived from mantle-likeprotoliths (0.7010.706 and +6 to +80/). Restricted 207Pb/204Pbvariation is accompanied by significant dispersion of 206Pb/204Pband 208Pb/204Pb. Superficially, petrogenesis by either direct(via fractionation from basalt) or indirect (via melting ofjuvenile crust) derivation from mantle sources appears plausible.Remelting of the granulitic protolith of Ordovician are-typegranitoids can be ruled out, because these rocks exhibit negativeNd(T) and a large range in 207Pb/204Pb. Geochemical and isotopicrelationships are most compatible with remelting of hybridizedlithospheric mantle generated during arc-continent collision.A genetic link is suggested among collision-related delaminationor slab break-off events and emplacement of post-erogenicgranite suites. A-type granites may recycle previously subductedcontinental material, and help explain the mass balance notedfor modern arcs. However, they need not represent net, new,crustal growth. KEY WORDS: A-type granites; juvenile crust; isotopes; Newfoundland
*Telephone: (613) 995-4972. Fax: (613) 995-7997. e-mail: jwhalen{at}gsc.emr.ca 相似文献
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Geochemistry of an Island-Arc Plutonic Suite: the Uasilau-Yau Yau Intrusive Complex, New Britain, P.N.G 总被引:2,自引:0,他引:2
In the Uasilau-Yau Yau intrusive complex of central New Britain,Papua New Guinea, there is a compositional continuum in intrusiverock-types from gabbro to granodiorite and K-Ar mineral agesof the most mafic and most felsic components are not significantlydifferent (29?0.6 Ma versus 28.3?0.5 Ma, respectively). Tonaliteporphyry, the progenitor of porphyry copper mineralization inthe complex, represents a significantly younger intrusive eventat 24 Ma. Relatively calcic (An9550) plagioclase coresand salite to augite composition clinopyroxene are texturallyearly phases in the intrusive rocks. The main mafic mineral,calcic amphibole, generally has corroded clinopyroxene coresand may, like biotite, K-feldspar and quartz, generally be alate-stage, not a primary liquidus phase. Petrographic featuresindicate that the mafic minerals in the plutonic rocks crystallizedfrom melt, rather than being restite phases. The intrusive rocks cover an extensive silica range (4575wt. per cent), do not exhibit simple straight-line variationon Harker diagrams for many elements (e.g. TiO2, FeO, P2O5 andSr), and most are relatively depleted in incompatible traceelements (Rb, Zr, and REE). Major and trace element modellingsupports derivation of the complex by shallow level fractionalcrystallization dominated by removal of the phases calcic plagioclase,clinopyroxene, and magnetite from a parental magma closely resemblingrecent basaltic rocks in New Britain. The fact that the plutonicrocks are almost chemically indistinguishable from late Cainozoiccalc-alkaline volcanic rocks of New Britain supports fractionalcrystallization as a viable mechanism for generating these island-arcvolcanic rocks and indicates an analogous origin for the initialmagma. Granites, such as those of the Uasilau-Yau Yau intrusive complex,which are probably generated by partial melting of subductedoceanic crust or the overlying mantle, may be termed mantleor M-type granites. Documentation of the characteristics ofM-type versus normal I-type granites may enable the recognitionof M-type plutonic rocks in older, possibly more deeply erodedgeologic terrains. This would, by analogy to their volcanicequivalents, be very helpful in tectonic interpretations. Also,such plutonic rocks have known potential for Cu-Au mineralization. 相似文献
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