U-Pb LA-ICPMS geochronology of detrital zircon grains from low-grade metasedimentary rocks (Neoproterozoic ? Cambrian) of the Mojotoro Range, northwest Argentina (2010)

APARICIO GONZALEZ PAMELA; MARCIO PIMENTEL

Brasilia

Simposio; VII SSAGI South American Symposium on Isotope Geology; 2010

The Mojotoro Range is located in the southeastern section of the argentine EasternCordillera (Figure 1), with a complex anticline of N-S orientation, as a principal structuralfeature. The stratigraphic core of this anticline is a lower grade metamorphic complex,identified as ?Puncoviscana Formation s.l.? (Aceñolaza, 1988) or ?Puncoviscana Complex?(Zimmerman, 2005).The Puncoviscana Complex has been recently mapped in the Mojotoro Range (AparicioGonzález et. al, 2010) with the identification of three stratigraphic units: Chachapoyas, Altode la Sierra and Guachos Formations.Chachapoyas Formation (Aparicio González et al., 2010) crops out in the western flank ofthe range, and contains shales and greenish sands, of very fine grain, with a cleavage parallelto the axial plain. Sandy facies are thin and mainly composed of grain-supported quartzarenites. Clays mineralogy corresponds to illite and clorite. The unit is strongly folded andintruded by acid dikes, dated in 533 ± 2 Ma, so this formation is the older unit in the MojotoroRange.(Figure 1)The next unit is Alto de la Sierra Formation (Aparicio González et al., 2010), composed bylayers of purple and gray sands, with parallel bedding, shales and feldespatic wackes.Volcaniclastic material is recognized in thin sections, and clays mineralogy corresponds toillite and interlayer illite/smectite.(Figure 1)Finally, an heterolitic sequence of brown to greenish brown shally sands, with Nereitesichnofacies was recognized as Guachos Formation (Moya, 1998). Sandstones are mainlycomposed of quartz, with few volcaniclastic grains with felsitic texture. Shales are composedof illite, illite/chlorite and chlorite. The outcrops are folded and affected by a deformationevent, characteristic reflected also in thin sections.(Figure 1).The objective of this paper is to obtain similarities and differences between thesestratigraphic units, in order to get the stratigraphic relationship, through the use of U-Pb LAIiCPMSgeochronology of detrital zircons and sediment provenance