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Cerro Pedreira is a syenitic alkaline complex located on the Paraguay River of north-western Paraguay, belonging to the Alto Paraguay Igneous Province. The complex is a semi-circular stock of ~1 km2 standing at around 20-30 m above the landscape, associated with 1-2 m thick NE-SW trending dykes. Main stock lithologies consist mostly of syenite, with scarce nepheline syenite present. Accessory phases include apatite, zircon, and titanite, with the notable absence of eudialyte which is found in abundance at the nearby Cerro Siete Cabezas complex. Nepheline, when present, is usually altered to cancrinite. Occasional xenoliths of basanite are found, suggesting its presence at depth, as none is found outcropping. Dyke rock types include alkali rhyolite and quartz trachyte, with a xenolith of cumulatic amphibole plagioclase, opaques, biotite, and apatite present in one occurrence. Dykes compositionally range from peralkaline to metaluminous. Geochemical data, including whole rock major and trace element, mineral chemical, and Sr-Nd isotope analysis, can be found in Comin-Chiaramonti and Gomes (2005).
COMIN-CHIARAMONTI, P., GOMES, C.B., CENSI, P., GASPARON, M. & VELÁZQUEZ. 2005. Alkaline complexes from the Alto Paraguay Province at the border of Brazil (Mato Grosso do Sul state) and Paraguay. In: Comin-Chiaramonti, P. & Gomes, C.B. (eds) Mesozoic to Cenozoic alkaline magmatism in the Brazilian Platform. Editora Universidade de São Paulo, São Paulo, 71-89. VELÁZQUEZ, V.F., GOMES, C.B., LAURENZI, M., TEXEIRA, W. & COMIN-CHIARAMONTI, P., 1996. Contribution to the geochronology of the Permo-Triassic alkaline magmatism from the Alto Paraguay Province. Revista Brasileira de Geociências 26, pp 90-103