Changing characteristics of deformation, sedimentation, and magmatism as a result of island arc-continent collision.

摘要

Studies of the collision zone between the Cretaceous Alisitos island arc, which accreted to North America between 115 and 100 Ma, and the continental margin in the Peninsular Ranges batholith (PRB), Baja California provide a means of evaluating the temporal evolution of (1) paleo-displacement fields and gradients within the arc and continental margin; (2) geochemical changes in the magmatic system; and (3) sedimentary basins in the collision zone and source changes for sediments in these basins.; The paleo-displacement field in the Sierra Calamajue is characterized by a SW-vergent fold-thrust belt that records collision-related contraction, but also preserves evidence for Paleozoic deformation along the southern margin of North America. Comparison between the Sierra Calamajue and the collision zone in the Sierra San Pedro Martir (SSPM) and near San Vicente shows that paleo-displacements inferred from structural characteristics change along strike due to (1) changes in tectonic setting from sinistral transpression in the north to normal convergence along the eastern margin of the arc; (2) the pre-existing geometry of the continental margin, including a promontory of miogeoclinal strata east of the SSPM; and (3) rheologic changes caused by the transition from Paleozoic shallow to deep-water deposits at 30.5°N latitude and southward decrease of Cretaceous sedimentary deposits.; Bulk shortening (including finite strain) estimates in the collision zone support arc-perpendicular shortening of >60% and crustal thickening (up to 10 km) that is greatest along the east side of the arc. Geochemical analyses, which suggest magma generation at depth >40 km after 110 Ma (a significant increase in depth from 30 to 35 km or less prior to collision), further support crustal thickening.; Provenance links between Paleozoic and early Mesozoic units in the PRB and North America are established using detrital zircons. The data are also used to distinguish marine basins. Basin deposits north and east of the Alisitos arc are dominated by arc detritus between 117 and 110 Ma, whereas deposits farther east received input from arc and cratonal sources. By ∼110 Ma syn-collisional sediments in the Alisitos arc show links to cratonally-derived sources suggesting close proximity between the arc and North America.