THE INFLUENCE OF TECTONIC CONTROLS ON PLUTONISM AND VOLCANISM: COMPARING THE CRETACEOUS SIERRA NEVADA BATHOLITH AND THE ACTIVE EL SALVADOR VOLCANIC ARC

The Late Cretaceous Sierra Nevada batholith, USA, and the modern El Salvador volcanic arc, Central America, are two systems at different crustal levels (plutonic and volcanic) which exhibit similar geometries, kinematics, and voluminous magmatism. Emplacement of the Sierra Nevada batholith between 92-85 Ma (Late Cretaceous) has been explained by the P-shear model, which indicates simultaneous movement of en echelon strike-slip fault segments. This geometry of the faults results in large-scale pull apart structures (dilational jogs) occur between ~60 km long strike-slip segments. Late-stage silicic plutons with miarolitic cavities occur along these strike-slip shear zones. Similarly, the modern El Salvador volcanic arc also exhibits en echelon strike-slip fault segments at the same scale observed in the Sierra Nevada batholith. Extensional deformation and magmatism occurs in pull apart regions along the El Salvador fault system, with the occurrence of normal fault arrays in young (<100 ka) volcanic deposits and the intrusion of large andesitic-basaltic volcanic centers. Major silicic magmatism occurs exclusively along the strike-slip faults.

The transcurrent motion recorded by the strike-slip segments is likely not the result of oblique convergence in either of these settings. In the active El Salvador fault system, the angle of subduction is nearly orthogonal to the magmatic arc. The strike-slip tectonism results from the eastward escape of the Caribbean plate (backarc) with respect to the forearc. Transcurrent motion in the Late Cretaceous Sierra Nevada arc likely resulted from the oblique collision of the Insular superterrane. Thus, in both of these systems, knowledge of the tectonic setting is critical to understanding localization of tectonic strain and subsequent controls on plutonism and volcanism.