High K Calc-Alkaline Granitoids of Ca. 1 Ga. TDM Along the Limit Peal Massif/Sergipano Fold Belt, Ne Brazil and Their Geotectonic Significance.

Abstract

The Pernambuco -Alagoas Massif is located in the Southern Domain of the Borborema Province. Sm/Nd isotopic data show the existence of 15 Brasiliano granitic intrusions (ca. 0.6 Ga) with Sm/Nd T DM ages ranging from 0.9 Ga to 1.2 Ga. They can be divided into two groups: Group 1 includes metaluminous diorites, monzogranites, and granodiorites showing SiO 2 contents between 60 and 68 wt.%, Na 2 O + K 2 O ~8 wt.%, high LILE/HFSE ratios, and spiderdiagrams characterized by troughs at Nb, Sr and Ti. Group 2 comprises peraluminous leucosyenogranites and leuco-monzogranites. They have high SiO 2 (70 -75 wt.%), and spidergrams and LILE contents similar to those of Group 1. Both groups show volcanic arc signatures and εNd(t) at 0.6 Ga from +3.0 to -1.7. Granitoids from both groups were generated from sources with similar Sm/Nd signatures. Brasiliano granitoids showing such young Nd isotopic signatures have not been recorded in other domains of the BP. Geochemical and isotopic data suggest mafic underplating during the late Mesoproterozoic or early Neoproterozoic in the Southern Domain of the Borborema Province. The volcanic arc and Nd signatures suggest that the mafic magma may have been a mixture from a subducting oceanic slab (~1.0 Ga?) and older lithospheric mantle. The mafic magmas differentiated to yield a zoned lower crust, explaining the geochemical differences among the granitoid magmas subsequently derived from it. T DM values < 1.0 Ga require later addition of younger juvenile material to the 1.0 Ga lower crust.

Proterozoic history of the Borborema province (NE Brazil): Correlations with neighboring cratons and Pan‐African belts and implications for the evolution of western Gondwana

“…For reasons discussed in previous sections, it is unlikely that a large ocean developed during the Cariris Velhos event. However, T DM ages between 1.9 and 1.4 Ga for Cariris Velhos plutonic rocks [ Van Schmus et al , 1995; Brito Neves et al , 2001b] and the presence of Brasiliano plutons with T DM ages around 1 Ga at the northern border of the Sergipano belt [ Da Silva Filho et al , 2000] indicate accretion of some juvenile material to the continental lithosphere during this event, suggesting either formation of oceanic crust or underplating of mafic magmas during active rifting.…”

“…Occurrence of the Cariris Velhos event in the southern domain is suggested by Sm‐Nd data from Brasiliano granitoids. In this region some plutons yielded T DM model ages between 1.5 and 1.0 Ga, which may either result from mixed sources with Paleoproterozoic and Brasiliano ages or from juvenile sources of Cariris Velhos age [ Da Silva Filho et al , 2000, 2002]. It has been proposed that the Cariris Velhos event represents a true orogeny [ Brito Neves et al , 1995; Santos , 1995; Santos and Medeiros , 1999; Brito Neves et al , 2000, 2001b].…”

Lu-Hf Isotopic Data of the Mb&#233;-Sassa-Mbersi Tonalite (Central Cameroon Domain): Indicator of ca. 1.0 Ga Juvenile Tonian Magmatism in the Region

“…Although some authors have interpreted the Tonian episode as failed attempts of dislocation of the Atlantica Paleoproterozoic continent (Renné et al, 1990; Journal of Geoscience and Environment Protection Schobbenhaus, 1996;Uhlein et al, 1998;Alvarenga et al, 2000;Tack et al, 2001), the T DM ages obtained by Da Silva Filho et al (2000) in the northern edge of the Sergipano belt were interpreted as an accretion of some juvenile material to the continental lithosphere and suggesting either formation of oceanic crust or underplating of mafic magmas during active rifting. The local occurrence of C-type eclogites near the Pernambuco shear zone (PSZ) in the central domain of the Borborema province (Beurlen et al, 1992) and obduction of ultramafic rocks with pillow basalts in the Araguaia belt (Alvarenga et al, 2000) are in favour with existence of an oceanic crust form around the early and middle Neproterozoic.…”

“…The various studies carried out show that Tonian magmatism takes place between 1000 and 850 Ma in Brazil and Africa (Santos, 1995;Vicat & Pouclet 1995;Vicat et al, 1997Vicat et al, , 2001Van Schmus et al, 1999Da Silva Filho et al, 2000;Brito Neves et al, 2001;Tack et al, 2001;Kozuch, 2003;Neves, 2003;Santos et al, 2010;Guimarães et al, 2012). This magmatism which is materialized in the outcrops by volcano-sedimentary formations associated with meta-mafic and felsic volcanic and plutonic rocks, orthogneisses and dolerite dykes show continental tholeiite and alkaline signature (Souza & Moura 1995;Vicat et al, 2001;Neves, 2003;Guimarães et al, 2012;Viana & Battilani 2014).…”