SHRIMP U-Pb and U-Pb Laser Ablation Geochronological on Zircons from Monte Santo Alkaline Intrusive Suite, Westhern Araguaia Belt, Tocantins State, Brazil

Abstract

The Monte Santo Alkaline Intrusive Suite (MSAIS) is an association syenite foid, nepheline syenite and syenite, which are intruded in metapelites of the Rio do Coco meta-volcanic-sedimentary Sequence, presenting abundant pegmathoid veins cutting all of them. The ages obtained by Shrimp (1051 ± 22 Ma, 1048 ± 11 Ma) are very close those younger age obtained by U-Pb laser ablation (1056 ± 21), beeing interpreted as crystallization age. These dating reveal also that MSAIS rocks were affected by common succession of younger events below 550 Ma ago, responsible by the later rocky bodies of varying composition occurring in the region, including the alkaline pegmatites hosted in the nepheline syenite of the MSAIS.

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

“…The time between 1.0 Ga and 651 Ma fits well into the estimated period for the formation of the old long-lived orogenic belts (1000 -600 Ma) to which the Central African Orogenic belt belongs (Kröner, 1975;Bayer & Lesquer, 1978;Drake, 1980;Chikhaoui et al, 1980;Lesquer et al, 1981;Regan & Marsh, 1982;Nzenti et al, 1984;Poidevin, 1985;Caby, 1987;Barbey et al, 1990;Fernandez et al, 1992;Penaye et al, 1993). Similar age (1011 ± 86 Ma, 1051 ± 22 Ma, 1048 ± 11 Ma and 1056 ± 21) is obtained on zircons from alkaline syenitic gneisses by Pb/Pb and U/Pb method on zircon and interpreted as evidence of the beginning of the rifting process in the Araguaia Group in Brazil (Souza & Moura 1995;Viana & Battilani 2014).…”

“…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). In the Central Cameroon Domain in Central African Orogenic Belt (Figure 2(a) and Figure 2(b)), the tonian ages are mentioned in the biotite-muscovite granitoids (~926 Ma) and amphibole-biotite gneiss (~889 Ma) respectively in the Ngaoundere cliff and Meiganga area (Tchameni et al, 2006;Ganwa et al, 2011).…”

“…Excluding continental rifting stages between 1.8 and 1.5 Ga mark by ubiquitous taphrogenesis, this continent remained unaffected for about 1 Ga (Neves, 2003). But, around 1 Ga at the early Neoproterozoic (Tonian), this portion of the crust is witness of an important magmatic event in Borborema province and Araguaia Group correlates with important rifting episodes in central-western Africa and anorogenic magmatism in the São Francisco, Congo, and Amazonian cratons (Vicat & Pouclet 1995;Souza & Moura 1995;Vicat et al, 1997Vicat et al, , 2001Neves, 2003;Guimarães et al, 2012;Viana & Battilani 2014).…”

Petrogenesis of a nepheline syenite from parts of the Chotanagpur Granite Gneissic Complex: implications for Neoproterozoic crustal extension in the East Indian Shield

“…However, in addition to older DARCs, the SCLM beneath the >950 Ma crust of the CGGC could also have received contributions from other sources (e.g. from fluid derived from the subducted oceanic crust (Castillo, 2016) or a mixture of HIMU and (Eby et al 1998;Upadhyay & Raith, 2006;Upadhyay et al 2006a,b,c;Casquet et al 2008;Nude et al 2009;Obeid & Lalonde, 2013;Viana & Battilani, 2014;Cheng et al 2018).…”