Guadalupe pluton-Mariposa Formation age relationships in the southern Sierran Foothills: Onset of Mesozoic subduction in northern California?

We report a new 153 +/- 2 Ma SIMS U-Pb date for zircons from the hypabyssal Guadalupe pluton which crosscuts and contact metamorphoses upper crustal Mariposa slates in the southern Sierra. A similar to 950 m thick section of dark metashales lies below sandstones from which clastic zircons were analyzed at 152 +/- 2 Ma. Assuming a compacted depositional rate of similar to 120 m/Myr, accumulation of Mariposa volcanogenic sediments, which overlie previously stranded Middle Jurassic and older ophiolite + chertargillite belts in the Sierran Foothills, began no later than similar to 160 Ma. Correlative Oxfordian-Kimmeridgian strata of the Galice Formation occupy a similar position in the Klamath Mountains. We speculate that the Late Jurassic was a time of transition from (1) a mid-Paleozoic-Middle Jurassic interval of mainly but not exclusively strike-slip and episodic docking of oceanic terranes; (2) to transpressive plate underflow, producing calcalkaline igneous arc rocks +/- outboard blueschists at similar to 170-150 Ma, whose erosion promoted accumulation of the Mariposa-Galice overlap strata; (3) continued transpressive underflow attending similar to 200 km left-lateral displacement of the Klamath salient relative to the Sierran arc at similar to 150-140 Ma and development of the apparent polar wander path cusps for North and South America; and (4) then nearly orthogonal mid and Late Cretaceous convergence commencing at similar to 125-120 Ma, during reversal in tangential motion of the Pacific plate. After similar to 120 Ma, nearly head-on subduction involving minor dextral transpression gave rise to voluminous continent-building juvenile and recycled magmas of the Sierran arc, providing the erosional debris to the Great Valley fore arc and Franciscan trench.