GEOLOGY OF THE SOUTHERN AMAZON CRATON IN SOUTHWESTERN MATO GROSSO, BRAZIL: A REVIEW

JAYME ALFREDO DEXHEIMER LEITE, GÉRSON SOUZA SAES

Resumo


The southern Amazon Craton in Mato Grosso, is reviewed in light of more recent geological, petrological, structural and geochronological data. Jaurú and Rio Alegre terranes, the Santa Helena Granite Complex and the Aguapeí Belt are the major tectonic units of the area. The Jaurú terrain consists of MORB suite and arc basalts with minor chert and felsic volcanics, calc-alkaline tonalites, orthogneisses, and migmatites of ca. 1.78 Ga. Two well-marked granitic events occurred in this terrain between 1.55 to 1.48 Ga (the Cachoeirinha magmatic arc) and close to 1.0 Ga (the Guapé Intrusive Suite). The Rio Alegre terrain consists of mafic volcanics and ultramafic intrusives with minor chert and tonalite intrusions and its minimum age is given 1.55 Ga tonalites. The Santa Helena Granite Complex (1.45 Ga) is a NW-trending, A-type, hornblende-biotite syenogranite batholith with abundant xenoliths of older rocks and emplaced between the Rio Alegre and Jauru terranes. The Aguapeí Belt is a narrow NW-trending zone that follows the limits between the Rio Alegre terrain and the Santa Helena Complex. It consists of low-grade, folded shallow marine to fluvial sediments. The Jaurú Terrain is interpreted as representing an island arc and the Rio Alegre as ophiolite, both with an age between 1.9 Ga and 1.55 Ga. The Cachoeirinha magmatic arc of ca. 1.55 Ga is likely to result from the amalgamation of these two terranes. The suture between the Rio Alegre and Jaurú terranes was intruded by the Santa Helena Granite Complex at about 1.45 Ga. The youngest events (1.2 Ga to 1.0 Ga) are represented in the Aguapeí Belt, by extensional reactivation, intracontinental rifting, sedimentation, deformation, and low-grade metamorphism, and are correlated to the Sunsas Orogeny of eastern Bolivia.

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