ACCRETION AND TRANSLATION OF THE MARA TERRANE: INSIGHTS FROM U/PB CHARACTERIZATION OF SIERRA DE MAZ AND RAMADITAS

The MARA terrane was accreted to and displaced along the Pampean margin of western Gondwana along the Valle Fertil Fault Zone (VFFZ) between 515-400 Ma. The VFFZ projects northward to the Sierra de Maz (SdM) region where relationships between the Famatina arc on the Pampean margin and accreted material are poorly constrained. SdM is underlain by Mesoproterozoic-Neoproterozoic igneous and metamorphic units of the MARA terrane, a western clastic assemblage with a simple metamorphic history and an eastern granulite facies metamorphic assemblage exposed in Ramaditas. Relations on the eastern boundary are less clear.

U/Pb data from the MARA terrane define magmatic ages of tonalite orthogneiss between 1221 ± 10 and 1276 ± 13 Ma; intrusive granitic bodies yield ages of 1090 ± 11, 827 ± 32, and 845 ± 9 Ma. Timing of deformation is constrained by metamorphic rims on zircon, syn-deformational titanite, and deformed leucosomes and granitic bodies that cross-cut the orthogneiss; these yield ages ranging 399 ± 9 to 433 ± 9 and ca. 1050 and . MARA terrane orthogneiss units in southern SdM yield protolith ages of 1217 ± 13 and 1237 ± 23 Ma and metamorphic ages of 1047 ± 13 and 1063 ± 17 Ma. Deformed and cross-cutting leucosomes were emplaced at 462 ± 19 and 425 ± 9 Ma, respectively. A felsic intrusion in the western clastic assemblage yields an age of 469 ± 7 Ma. Detrital zircon data places the maximum depositional age of paragneiss in Ramaditas at ca. 460 Ma. Deformed leucosomes yield ages of 445 ± 5 to 455 ± 3 Ma and undeformed granites yield ages of 418 ± 4 and 420 ± 5 Ma.

The U/Pb data suggest that Proterozoic basement units of SdM have separate metamorphic and protolith histories and were juxtaposed between 420-460 Ma. Paleozoic units in Ramaditas are interpreted to have formed as part of the Famatina arc, placing the northern trace of VFFZ between Ramaditas and SdM. Metamorphic assemblages and kinematic indicators suggest this took place at amphibolite conditions in a sinistral transpressional regime. The magmatic and metamorphic history is similar to that observed west of the VFFZ to the south in Las Chacras and Pie de Palo, suggesting that SdM records a complex late Ordovician to early Devonian history of convergence and translation of the MARA terrane along the Pampean margin.