GEOLOGIC MAP OF A PORTION OF CAPE SAN MARTIN/ALDER PEAK/VILLA CREEK/BURRO MOUNTAIN 7.5' QUADRANGLES

The Nacimiento block is a fault bounded terrain located in the central coastal ranges of California. It is bounded to the northeast by the Sur- Nacimiento fault and to the southwest by San Gregorio/ Hosgri Fault. This block spans the Franciscan complex, recognized as one of the best examples of an accretionary prism subjected to low temperature-high pressure (LT-HP) metamorphism. Although published geological maps of this area are available, their scales are too small to fully describe stratigraphy and address the geometry of the Franciscan complex in the Nacimiento block.

In this contribution we propose a new detailed bedrock and structural maps of the Nacimiento block in the vicinity of Cape San Martin, California that feature the complex stratigraphy and geometry of the area. This new proposed geological and structural map highlight new evidence of a complex polyphase deformation unrecognized until now. One of the most significant results from this map is the presence of a 50-75 degrees counter clock-wise re-orientation of structures from the regional orientation. This structural re-orientation is spatially associated with a previously recognized thermal anomaly, in which bedrocks record peak temperatures up to 360 ^oC compared to the sub-200^oC regional background.

The structural maps presented here are used to determine if the thermal anomaly is either: (1) a post subduction high temperature metamorphic overprint or (2) differential uplift associated with a transpressive ridge.