Post-Archean granitic rocks: contrasting petrogenetic processes and tectonic environments

Janoušek, Vojtěch; Bonin, Bernard; Collins, William J.; Farina, Felicia; Bowden, Peter

doi:10.1144/sp491-2019-197

Cited by 21 publications

(21 citation statements)

References 81 publications

(63 reference statements)

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“…The continued extension is typically associated with intrusion of mafic magmas at depth, which leads to (a) a weakened lithosphere that enhances extension and basin subsidence and (b) an increased heat flow and/or extensive fractional crystallization resulting in felsic magma generation (see Hinchey, 2021a, and references therein). These early melts are felsic with ferroan (A‐type) signatures (high Na 2 O + K 2 O, HFSEs, and REE (except for Eu) values; and their production in significant volumes can act as mid‐crustal barriers to the ascent of co‐magmatic mantle‐derived mafic magmas (Janoušek et al., 2020, and references therein). Ultimately, continued intrusion of mafic magmas enables the felsic barrier to be breached, allowing a more widespread ascent of mafic magma and the onset of basaltic volcanism.…”

Section: Discussionmentioning

confidence: 99%

Localized Backarc Extension in an Overall Compressional Setting During the Assembly of Nuna: Geochemical and Isotopic Evidence From Orosirian (1883–1848 Ma) Mafic Magmatism of the Aillik Group, Labrador, Canada

Hinchey

2021

Earth and Space Science

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Protracted assembly of the Paleoproterozoic supercontinent Nuna resulted in localized extension in an overall compressional setting  Backarc settings produce geochemical and isotopic variability in mafic volcanic rocks that obscure understanding of their tectonic setting  Paleoproterozoic accretionary orogens comprise multiple diachronous, compressional and extensional events along a long-lived active margin Accepted ArticleThis article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. Please cite this article as

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Section: Discussionmentioning

confidence: 99%

Localized Backarc Extension in an Overall Compressional Setting During the Assembly of Nuna: Geochemical and Isotopic Evidence From Orosirian (1883–1848 Ma) Mafic Magmatism of the Aillik Group, Labrador, Canada

Hinchey

2021

Earth and Space Science

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“…With their more differentiated counterparts (Mg-K-rich monzodiorite to qtz-monzonite and mela-syenites), they collectively form a magmatic series referred to as durbachites (Moyen et al, 2017;Soder & Romer, 2018;Von Raumer et al, 2014). These durbachites presumably derived from melting of a metasomatized mantle source, enriched by melts derived from a subducted mature continental crust (Janoušek et al, 2019(Janoušek et al, , 2020Janoušek & Holub, 2007). We therefore speculate that type-II metasomatism is related to percolation in the mantle of the primary magmas from which the durbachites are derived.…”

Section: A Refractory Mantle Refertilized By Melts and Fluidsmentioning

confidence: 94%

Discovery of Variscan orogenic peridotites in the Pelvoux Massif (Western Alps, France)

Jacob¹,

Janots²,

Cordier³

et al. 2023

BSGF - Earth Sci. Bull.

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Small bodies of mantle-derived peridotites and other ultramafic rocks are commonly found in exhumed lower crustal units of collisional orogens. They provide a direct record of the complex evolution of the upper mantle before and during an orogeny, and are therefore key markers of the geodynamic evolution of an orogen. We report here the discovery of such mantle-derived peridotites in high-grade Variscan lower crust exposed in the Pelvoux massif (External Western Alps), which occur as fragmented enclaves in migmatites. A wide petrographic diversity has been observed, from very fertile, garnet-bearing lherzolites, to more depleted spinel/chromite-bearing harzburgites. Thermobarometric calculations on a garnet lherzolite indicate an initial stage at 3.0 ± 0.5 GPa and 973 ± 50°C, followed by exhumation to 0.8-1.3 GPa and 800-850°C, while the harzburgites do not show any evidence of equilibration in the garnet field and sample shallower mantle (<2.0 GPa). Petrological observations, whole-rock geochemistry and in-situ mineral compositions suggest the peridotites have undergone a complex history prior to their incorporation in the lower crust during the Variscan Orogeny. They derive from refractory mantle domains, which have experienced variable degrees of melt depletion, and have then been extensively refertilized. Cryptic metasomatism is observed in all samples. It is characterized by an enrichment in fluid-mobile incompatible elements relative to immobile ones (LILE vs HFSE), leading to the development of pronounced negative anomalies Nb and Ta, and is presumably related to percolation of hydrous fluids in the mantle. In addition, strong enrichment in incompatible LREE relative to HREE is observed in some samples, commonly associated with modification of the modal composition (crystallization of phlogopite and/or pargasite with accessory chromite and apatite). This modal metasomatism is attributed to percolation by a K2O-P2O5-Cr2O3-rich silicate melt, which might be at the source of syn-collisional ultrapotassic magmas (durbachites) emplaced in the crust during the middle-upper Carboniferous. These geochemical characteristics are in line with whole-rock Nd isotopic compositions, which indicate enrichment of the mantle by a continental crust component, presumably related to Variscan subductions. This evolution is consistent with that of other Variscan peridotites in the eastern Alps (Ulten) and the Bohemian massif, where multiple metasomatic episodes related to melts or fluids released in Variscan subduction zones have been documented.

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“…The majority of the samples plot in the field of syncollision granites in the Nb + Y versus Rb tectonic discriminant diagram (as do other Himalayan leucogranites), with a few samples straddling the field boundary between collision granite and volcanic-arc granite (Figure 6b). The available petrogenetic studies on granites (particularly on Himalayan leucogranites) show that the granites that form in the syn-collision field are generally peraluminous in nature and may be derived from the hydrated bases of continental thrust sheets (Collins, Huang, Bowden, & Kemp, 2020;Harris et al, 1986;Huang & Jiang, 2014;Janoušek, Bonin, Collins, Farina, & Bowden, 2020). The Rb/Sr versus Rb/Ba diagram (Figure 6c) of the Bomdila gneisses demonstrates that the granites may have been derived from metasedimentary (pelite-dominated) source rocks.…”

Section: Petrogenesismentioning

confidence: 99%

Magmatic and metamorphic history of the Proterozoic Lesser Himalayan Crystallines from Bomdila area, Arunachal Pradesh, NE Lesser Himalaya, India: Constraints from whole rock and mineral chemistry

et al. 2022

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The excellent exposures of plentiful Proterozoic granitic bodies in the north-east Himalaya offer a chance to explore the evolution of continental crust in the Early Proterozoic period. The present comprehensive study from Bomdila area, western Arunachal Pradesh, NE India documents petrogenesis of Palaeoproterozoic Bomdila granite gneiss and metamorphic history of the region using the whole rock and mineral chemistry, and suitable mineral thermobarometry. The gneisses, with quartz, k-feldspar, plagioclase, and mica mineralogy, are characterized by enrichment in rare earth elements (total REE up to 290 ppm), Rb, Ba, Th, and depletion in mafic elements (Ni, Cr, V, Sc). The gneisses are subalkaline and peraluminous with A/CNK (Al 2 O 3 /CaO + Na 2 O + K 2 O) > 1.1, indicating S-type nature of the granites. The gneisses show fractionated REE patterns (La N /Yb N = up to 22) with LREE enrichment and HREE depletion. Geochemical characteristics such as enriched SiO 2 , Al 2 O 3 , alkalis, LREE, high incompatible element ratios (Rb/Sr and Ba/Sr), and depleted mafic contents with noticeable negative Eu anomalies (Eu/Eu* = 0.2 -0.6) suggest an origin of gneisses through high-temperature (>800 C) shallow crustal melting of a pelitic source similar to the metasedimentary enclaves within the gneisses. Mineral thermobarometric calculations suggest a tightly constrained P-T condition of 7.5-8.6 kbar and 560-590 C for the gneiss and schist from the study area. Almost identical P-T conditions of metamorphism from different lithologies attests that the Bomdila area may have attained an upper amphibolitic facies condition, possibly concomitant to the Himalayan Orogeny. Though rudimentary, temperature estimates from Ti-in biotite thermometer suggest an increase in metamorphic grade towards the Main Central Thrust.

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Post-Archean granitic rocks: contrasting petrogenetic processes and tectonic environments

Cited by 21 publications

References 81 publications

Localized Backarc Extension in an Overall Compressional Setting During the Assembly of Nuna: Geochemical and Isotopic Evidence From Orosirian (1883–1848 Ma) Mafic Magmatism of the Aillik Group, Labrador, Canada

Localized Backarc Extension in an Overall Compressional Setting During the Assembly of Nuna: Geochemical and Isotopic Evidence From Orosirian (1883–1848 Ma) Mafic Magmatism of the Aillik Group, Labrador, Canada

Discovery of Variscan orogenic peridotites in the Pelvoux Massif (Western Alps, France)

Magmatic and metamorphic history of the Proterozoic Lesser Himalayan Crystallines from Bomdila area, Arunachal Pradesh, NE Lesser Himalaya, India: Constraints from whole rock and mineral chemistry

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