Las Matras Block, Central Argentina (37°S - 67°W): The southernmost Cuyania terrane and its relationship with the Famatinian orogeny

SATO, A.M.; TICKYJ, H.; LLAMBÍAS, E.J.; BASEI, M.A.S.; GONZÁLEZ, P.D.

GONDWANA RESEARCH

International Association for Gondwana Research

Lugar: Trivandrum; Año: 2004 vol. 7 p. 1077 - 1087

1342-937X

The Las Matras Block, Central Argentina, belongs to the southernmost part of the Cuyania terrane, accreted to the southwestern margin of Gondwana during Early to Mid Ordovician (Famatinian orogeny). The Grenvillian age rocks are represented by the tonalitic to trondhjemitic Las Matras pluton. For this pluton we obtained a new U-Pb conventional zircon age of 1244 ± 42 Ma, that confirms the previous Sm-Nd and Rb-Sr isochron ages. The EPMA mineral data, like the composition of Na-rich feldspars, agree with the tonalitic–trondhjemitic character of the pluton, and constrain its shallow crustal emplacement level to 1.30 – 1.96 Kb. This shallow level together with the undeformed character of the pluton are the distinct features of this southernmost basement. The regional comparison indicates that the igneous-metamorphic evolution of the whole Granvillian-age basement rocks of the Cuyania terrane occurred through more than 200 million years, with ages older than 1200 Ma up to those close to 1000 Ma. The shallowest crustal level found in Las Matras suggests a southward shallowing of this basement. The deformation and metamorphism associated with the collisional Famatinian orogeny affected both the Cuyania terrane and the border of Gondwana. This Gondwana border was also the locus of the related arc magmatism. The compressive effects of the collision were stronger in the northern regions and decreased toward the south. Even though the Famatinian metamorphism and magmatism are well documented further south within the Patagonia region, the southern continuity of the Cuyania terrane remains uncertain.