Petrogenesis of the early Cretaceous Valle Chico igneous complex (SE Uruguay): Relationships with Paraná-Etendeka magmatism

• Published in: Lithos
• Main Authors: LUSTRINO, Michele, MELLUSO L., BROTZU P., GOMES G. B., MORBIDELLI L., MUZIO R., RUBERTI E., TASSINARI C. C. G.
• Other Authors: Lustrino, Michele, Melluso, L., Brotzu, P., Gomes, G. B., Morbidelli, L., Muzio, R., Ruberti, E., Tassinari, C. C. G.
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: -Amsterdam Netherlands: Elsevier BV -Oslo : Universitetsforlaget 2005
• Subjects: Uruguay; Cretaceou; CFB; Paranà; granitoid; South Atlantic Ocean
• Online Access: http://hdl.handle.net/11573/37650; https://doi.org/10.1016/j.lithos.2004.07.004; http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=PARTNER_APP&SrcAuth=LinksAMR&KeyUT=000229717600008&DestLinkType=FullRecord&DestApp=ALL_WOS&UsrCustomerID=0c7ff228ccbaaa74236f48834a34396a; http://www.scopus.com/inward/record.url?eid=2-s2.0-19044393445&partnerID=65&md5=1cb408adbfb57d1e1d5058ef7d39c4cf

The early Cretaceous (~130 Ma) igneous complex of Valle Chico (SE Uruguay) is made up of felsic plutonic and subordinate volcanic rocks and dykes cropping out over an area of about 250 km2. This complex is strictly linked with the formation of the Parana ́–Etendeka Igneous Province and the first stages of the South Atlantic Ocean rifting. The plutonic rocks range from quartz-monzonite to syenite, quartz-syenite and granite. The volcanic rocks and the dykes range from quartz-latite to trachyte and rhyolite; no substantial differences in term of chemical composition have been found between plutonic and volcanic rocks. Only a sample of basaltic composition (with tholeiitic affinity) has been sampled associated with the felsic rocks. The Agpaitic Index of the Valle Chico felsic rocks range from 0.72 to 1.34, with the peralkaline terms confined in the most evolved samples (SiO2N65 wt.%). Initial 87Sr/86Sr(130) of the felsic rocks range from 0.7046 to 0.7201, but the range of 87Sr/86Sr of low-Rb/Sr samples cluster at 0.7083; 143Nd/144Nd(130) ratios range from 0.5121 (syenite) to 0.5117 (granite). The tholeiitic basalt show more depleted isotopic compositions (87Sr/86Sr(130)=0.7061; 143Nd/144Nd(130)=0.5122), and plots in the field of other early Cretaceous low-Ti basaltic rocks of SE Uruguay. The radiogenic Sr and unradiogenic Nd of the Valle Chico felsic rocks require involvement of lower crustal material in their genesis either as melt contaminant or as protolith (crustal anatexis). In particular, most of the Valle Chico (VC) felsic rocks define a near-vertical array in Sr–Nd isotopic spaces, pointing toward classical EMI-type composition; this feature is considered to reflect a lower crust involvement as observed for other mafic and felsic rocks of the Parana ́–Etendeka Igneous Province. Decompression melting of the lower crust related to Gondwana continental rifting before the opening of the South Atlantic Ocean or the presence of thermal anomalies related to the Tristan plume may have induced the lower crust to ...