Archaean fluid-assisted crustal cannibalism recorded by low δ 18 O and negative ε Hf(T) isotopic signatures of West Greenland granite zircon

摘要: The role of fluids during Archaean intra-crustal magmatism has been investigated via integrated SHRIMP U–Pb, δ18O and LA-MC-ICPMS 176Hf isotopic zircon analysis. Six rock samples studied are all from the Nuuk region (southern West Greenland) including two ~3.69 Ga granitic trondhjemitic gneisses, a 3.64 augen gneiss, 2.82 granodioritic Ikkattoq migmatite with late Neoarchaean neosome homogeneous granite 2.56 Qorqut Granite Complex (QGC). All grains were thoroughly imaged to facilitate analysis magmatic growth domains. Within analysed, there is no evidence for metamictization. Initial eHf values (n = 63) largely sub-chondritic, indicating host magmas generated by remelting older, un-radiogenic crustal components. Zircon some displays more than one 207Pb/206Pb age, correlated 176Hf/177Hf compositions can trace multiple phases or recrystallization Archaean. Model ages calculated using Lu/Hf arrays each sample indicate that parental rocks granites, granodiorites trondhjemites segregated chondrite-like reservoir at an earlier time Archaean, corresponding known formation periods primitive tonalite–trondhjemite–granodiorite (TTG) gneisses. granite, QGC contains Eoarchaean cores chondritic mantle-like compositions. age geochemical signatures these inherited components identical those surrounding tonalitic further suggesting genesis granites broadly protoliths. oxygen 62) over nine populations (six igneous three inherited) have weighted mean ranging 5.8 ± 0.6 3.7 0.5‰. gneiss highest mildly supra-mantle composition 0.6‰. Inherited TTG-derived shows values. Igneous other samples, spanning billion years time, record low sub-mantle These first reported represent formed metamorphism older following high-temperature hydrothermal alteration meteoric water. Meteoric fluid ingress coupled extension, associated high heat flow melting viable mechanism production here. Both may in extensional environments distinct Phanerozoic I-type plutonic systems, which typified increasing reworking. This suggests processes here subtly different operating on modern Earth involved tectonic regimes predominance hydrothermally altered crystalline basement.