Paleoproterozoic metamorphosed calc-alkaline dikes of the southwestern Rio de la Plata craton, Tandilia belt of Argentina, record a prograde high-pressure, medium-temperature evolution

Two metamorphosed talc-alkaline dikes, a metadacite and metarhyolite, and their country-rock from El Quebracho hill in the Tandilia belt (TB), Rio de la Plata craton, were studied in detail. Both dikes contain chemically zoned garnet porhyroblasts with the following compositions: Alm(35)GrosAnd(36.5)Pyr(0.5)Spes(28) (core), Alm(41)GrosAnd(41)Pyr(1)Spes(17) (rim) in the metadacite; Alm(37)GrosAnd(38)Pyr(0)Spes(25)(core), Alm(50.8)GrosAnd(32)Pyr(0.2)SPes(17 )(rim) in the metarhyolite. We calculated P-T pseudosections in the system Na-K-Ca-Fe-Mn-Mg-Al-Si-Ti-H-O and contoured them for chemical and modal parameters of interest with the PERPLE_X computer software to model these metamorphosed dikes. Molar fractions in garnet and mineral assemblages signalize a prograde metamorphic evolution along an apparent geothermal gradient of similar to 14 degrees Ckm(-1). Syn-kinematic growth of garnet at a NE-SW compressional D-1 event during burial to depths of similar to 43 km at around 600 degrees C trapped titanite, epidote, and quartz (S-i) at crustal depths of 35-40 km at 535-540 degrees C. Afterwards, the rocks were exhumed in a continuously lasting compressional regime with S-1 formation delineated by mafic minerals in the metadacite (Ca-amphibole + biotite) and metarhyolite (biotite). Biotite with Mg# contents of similar to 0.2 in the metadacite and Ca-rich plagioclase in both dikes point to exhumation accompanied by cooling. Local mylonitization (D2) with the development of an S-m - foliation occurred between 600-500 degrees C, prior to the late post-kinematic blastesis of muscovite (Si similar to 3.15 pfu) in the metarhyolite. LA-ICP-MS U-Th-Pb dating of zircon and its trace-element signature indicate intrusion ages of 2130 +/- 10 Ma (MSWD = 4.9) for the metarhyolite and 2205 +/- 7 Ma (MSWD = 1.4) for the country-rock (metagranodiorite). Based on the regional background, the metamorphic overprint is hypothesized to have taken place still in the Paleoproterozoic.