Abstract
The Arenópolis volcano-sedimentary sequence is located in the southern part of the Goiás Magmatic Arc and includes a ca. 900 Ma calc-alkaline arc sequence made of volcanic rocks ranging in composition from basalts to rhyolites, metamorphosed under greenschist to amphibolite facies. Small calc-alkaline gabbro to granite sub-volcanic bodies are also recognized. The Morro do Baú intrusion is the largest of these intrusions, and is made of gabbros and diorites. Zircon grains separated from one gabbro sample and analyzed by SHRIMP I yielded the mean 206Pb/238U age of 890 +/- 8 Ma, indicating that the intrusion is roughly coeval or only slightly younger than the Arenópolis volcanics. Contrary to the metavolcanics, which are juvenile, the Nd isotopic composition of the Morro do Baú gabbro indicates strong contamination with archean sialic material (T DM of 2.8 Ga and EpsilonNd(T) of -9.7), represented in the area by an allochthonous sliver of archean/paleoproterozoic gneisses (Ribeirão gneiss) which are the country-rocks for the gabbro/dioritic intrusion. The emplacement age of ca. 890 Ma represents a minimum age limit for the tectonic accretion of the gneiss sliver to the younger rocks of the Arenópolis sequence. The data suggest that this happened early in the evolution of the Goiás Magmatic Arc, between ca. 920 and 890 Ma.
Highlights
IntroductionPIMENTEL, MARIA HELENA B.M. HOLLANDA and RICHARD ARMSTRONG grained amphibolites
The Arenópolis volcano-sedimentary sequence is one of the supracrustal associations comprising the southern part of the Goiás Magmatic Arc
In this study we present U-Pb SHRIMP zircon age and the Sm-Nd isotopic characteristic of the Morro do Baú intrusion and discuss their significance for the tectonic evolution of the Arenópolis volcano-sedimentary sequence and the age of accretion to the Ribeirão gneiss to the younger terrains
Summary
PIMENTEL, MARIA HELENA B.M. HOLLANDA and RICHARD ARMSTRONG grained amphibolites. This intrusion is exposed within the Ribeirão gneisses and is probably intrusive into them, clear cross-cutting relationships are not observed due to poor exposure conditions. The Ribeirão gneiss represents a fault-bounded slice of older rocks (Archean Nd isotopic signature and Paleoproterozoic Rb-Sr and Pb-Pb isochrons) tectonically emplaced, probably during the Neoproterozoic, in between the younger supracrustals of the Arenópolis sequence. It has Archean TDM model ages but the Sm-Nd isotopic system has been severely disturbed during a ca. It has Archean TDM model ages but the Sm-Nd isotopic system has been severely disturbed during a ca. 800 Ma event, as indicated by the Sm-Nd whole-rock isochron (Pimentel 1992)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
