scholarly journals U-Pb evidence for late Neoarchean crustal reworking in the Southern São Francisco Craton (Minas Gerais, Brazil)

2003 ◽  
Vol 75 (4) ◽  
pp. 497-511 ◽  
Author(s):  
José C.S. Campos ◽  
Maurício A. Carneiro ◽  
Miguel A.S. Basei
Keyword(s):  
Granulite Facies ◽  
Minas Gerais ◽  
Metamorphic Complex ◽  
Granulite Facies Metamorphism ◽  
Sialic Crust ◽  
Facies Metamorphism ◽  
Minimum Age ◽  
Crustal Reworking ◽  
Metamorphic Complexes

The Passa Tempo Metamorphic Complex is one of several metamorphic complexes that form the Archean sialic crust of the southern São Francisco Craton. It encompasses hypersthene-bearing gneissic rocks, with subordinateNW- or EW-trending mafic-ultramafic bodies and granodioritic to alkali-granitic, weakly foliated, and light-colored granitoids. These granitoids are the product of generalized migmatization that followed granulite-facies metamorphism. To determine the ages of the granulite-facies metamorphism and granitoid genesis, we obtained U-Pb ages on zircon extracted from the mesosome and leucosome of the migmatitic gneisses. For the mesosome, a discordia that intercepts Concordia at 2622 ± 18 Ma is interpreted as a minimum age for granulite-facies metamorphism. For the leucosome, the upper intercept of discordia at 2599 ± 45 Ma corresponds to migmatization and granitoid genesis. Contemporaneous metamorphism and magmatism have been documented elsewhere in the São Francisco Craton, especially in the southern portion, demonstrating vast and vigorous reworking of sialic crust by the end of the Neoarchean.

Tectonic history of the Grenville-age Trenton Prong inlier, Central Appalachians, USA: Evidence from SHRIMP U–Pb geochronology

2021 ◽  
Author(s):  
Richard Volkert ◽  
John N. Aleinikoff
Keyword(s):  
Granulite Facies ◽  
Small Population ◽  
Local Source ◽  
Thermal Activity ◽  
Granulite Facies Metamorphism ◽  
Magmatic Arc ◽  
Tectonic History ◽  
Facies Metamorphism ◽  
Minimum Age ◽  
History Of

New zircon U–Pb geochronologic data from the Grenville-age Trenton Prong provide information on the age of magmatism, timing of metamorphism, and post-metamorphic history of the inlier. Diorite gneiss (1318 ± 13 Ma) of the Colonial Lake Suite temporally correlates to magmatic arc sequences that formed along the eastern margin of Laurentia at <1.4 Ga. Metasedimentary gneisses yielded detrital zircon ages of ca. 1319-1133 Ma and ca. 1370-1207, consistent with sediment derived from a similar local source of Laurentian affinity. A small population of zircon (either detrital or igneous in origin) in one sample yielded ages of ca. 1074-1037 Ma. Possible interpretations for their formation are explored. Ca. 1060 Ma overgrowths on zircon in the northern part of the inlier constrain the timing of granulite-facies metamorphism to the Ottawan phase of the Grenvillian Orogeny. The undeformed Assunpink Creek Granite (1041 ± 6 Ma) intruded country rocks as small bodies of late-orogenic syenogranite. It provides a minimum age for amphibolite-facies metamorphism and Ottawan orogenesis elsewhere in the inlier. Regionally, zircon rim ages of ca. 1010–960 Ma record continued thermal activity during the Rigolet phase of the orogen that resulted in migmatization of paragneiss at ca. 1004 Ma and juxtaposition of upper- and mid-crustal rocks during orogenic collapse. The lithologic ages and tectonic history of the Trenton Prong correlate to those in other Appalachian Mesoproterozoic inliers, and parts of the Canadian Grenville Province, confirming it is not an exotic terrane that was accreted to eastern Laurentia during Grenvillian orogenesis.

scholarly journals Unravelling the origins and P-T-t evolution of the allochthonous Sobrado unit (Órdenes Complex, NW Iberia) using combined U-Pb titanite, monazite and zircon geochronology and REE geochemistry

2020 ◽  
Author(s):  
José Manuel Benítez-Pérez ◽  
Pedro Castiñeiras ◽  
Juan Gómez-Barreiro ◽  
José Ramón Martínez Catalán ◽  
Andrew Kylander-Clark ◽  
...  
Keyword(s):  
Granulite Facies ◽  
Variscan Orogeny ◽  
Granulite Facies Metamorphism ◽  
Magmatic Arc ◽  
Nw Iberia ◽  
Facies Metamorphism ◽  
Minimum Age ◽  
Arc Setting ◽  
Depositional Age ◽  
Devonian Age

Abstract. The Sobrado unit, within the upper part of the Órdenes complex (NW Iberia) represents an allochthonous tectonic slice of exhumed high grade metamorphic rocks formed during a complex sequence of orogenic processes in the middle to lower crust. In order to constrain those processes, U-Pb geochronology and REE analyses of accessory minerals in migmatitic paragneisses (monazite, zircon), and mylonitic amphibolites (titanite) were conducted using LASS-ICP-MS. The youngest metamorphic zircon age obtained co-incides with a Middle Devonian concordia monazite age (~ 385 Ma) and is interpreted to represent the minimum age of the Sobrado high-P granulite-facies metamorphism that occurred during the early stages of the Variscan Orogeny. Metamorphic titanites from the mylonitic amphibolites yield a Late Devonian age (~ 365 Ma), and track the progressive exhumation of the Sobrado unit. In zircon, cathodoluminescence images and REE analyses allow two aliquots with different origins in the paragneiss to be distinguished. An Early Ordovician age (~ 490 Ma) was obtained for metamorphic zircons, employing the TuffZirc algorithm, although with a large analytical dispersion. This age is considered to mark the onset of granulite-facies metamorphism in the Sobrado unit under intermediate-P conditions, and related to intrusive magmatism and coeval burial in a magmatic arc setting. A maximum depositional age for the Sobrado unit is established in the late Cambrian (~ 503 Ma). The zircon dataset also record several inherited populations. The youngest cogenetic set of zircons yield a crystallization age from TuffZirc algorithm of ~ 530 Ma and are thought to be related to the peri-Gondwana magmatic arc. The additional presence of inherited zircons older than ~ 530 Ma is interpreted as suggesting a West African Craton provenance.

A Discussion on global tectonics in Proterozoic times - Late Proterozoic cratonization in southwest Saudi Arabia

1976 ◽  
Vol 280 (1298) ◽  
pp. 517-527 ◽  
Keyword(s):  
Saudi Arabia ◽  
Volcanic Rocks ◽  
Sedimentary Rocks ◽  
Granulite Facies ◽  
Greenschist Facies ◽  
Arabian Shield ◽  
Granulite Facies Metamorphism ◽  
Quartz Monzonite ◽  
Facies Metamorphism ◽  
Global Tectonics

Early cratonal development of the Arabian Shield of southwestern Saudi Arabia began with the deposition of calcic to calc-alkalic, basaltic to dacitic volcanic rocks, and immature sedimentary rocks that subsequently were moderately deformed, metamorphosed, and intruded about 960 Ma ago by dioritic batholiths of mantle derivation (87Sr/86Sr = 0.7029). A thick sequence of calc-alkalic andesitic to rhyodacitic volcanic rocks and volcanoclastic wackes was deposited unconformably on this neocraton. Regional greenschistfacies metamorphism, intensive deformation along north-trending structures, and intrusion of mantle-derived (87Sr/86Sr = 0.7028) dioritic to granodioritic batholiths occurred about 800 Ma. Granodiorite was emplaced as injection gneiss about 785 Ma (87Sr/86Sr = 0.7028- 0.7035) in localized areas of gneiss doming and amphibolite to granulite facies metamorphism. Deposition of clastic and volcanic rocks overlapped in time and followed orogeny at 785 Ma. These deposits, together with the older rocks, were deformed, metamorphosed to greenschist facies, and intruded by calc-alkalic plutons (87Sr/86Sr = 0.7035) between 600 and 650 Ma. Late cratonal development between 570 and 550 Ma involved moderate pulses of volcanism, deformation, metamorphism to greenschist facies, and intrusion of quartz monzonite and granite. Cratonization appears to have evolved in an intraoceanic, island-arc environment of comagmatic volcanism and intrusion.

scholarly journals Mapping in the Fiskefjord area, southern West Greenland

1982 ◽  
Vol 110 ◽  
pp. 55-57
Author(s):  
A.A Garde ◽  
V.R McGregor
Keyword(s):  
Granulite Facies ◽  
Amphibolite Facies ◽  
Isotopic Age ◽  
Supracrustal Rock ◽  
Granulite Facies Metamorphism ◽  
West Greenland ◽  
Facies Metamorphism ◽  
Geological Work ◽  
Age Determinations

Previous geological work on the 1:100000 map sheet 64 V.l N (fig. 15) includes published maps of smaller areas by Berthelsen (1960, 1962) and Lauerma (1964), mapping by Kryolitselskabet Øresund A/S (Bridgwater et al., 1976) and mapping by GGU geologists for the 1:500000 map sheet Frederikshåb Isblink - Søndre Strømfjord (Allaart et al., 1977, 1978). The Amltsoq and Niik gneisses and Malene supracrustal rock units south and east of Godthåbsfjord have not so far been correlated with rocks in the Fiskefjord area. Godthåbsfjord separates the granulite facies gneisses in Nordlandet from amphibolite facies Nûk gneisses on Sadelø and Bjørneøen; the granulite facies metamorphism occurred at about 2850 m.y. (Black et al., 1973), while no published isotopic age determinations from the Fiskefjord area itself are available.

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