Middle Miocene to early Pliocene oblique extension in the southern Gulf of California

摘要: A multichannel seismic (MCS) experiment spanning 600 km across the Alarcon Rise and its conjugate rifted margins in southern Gulf of California (western North America) provides insight into spatial temporal evolution extension between Baja mainland (Mexico). Stratigraphic analysis multiple rift basins within spreading corridor indicates an initial stage oblique starting ca. 14–12 Ma. This phase was characterized by formation several large center gulf on southeast margin with negligible synrift sedimentation. second extension, likely synchronous large-scale basin opening central northern California, began 8–5 Ma smaller half-grabens distributed that contain both postrift deposits. key feature imaged MCS data is a highly reflective, ropey layer at top basement, interpreted to be either volcanic rocks from 25–12 Comondu Group, and/or early rifting are 11 9 Ma, or younger. extensively faulted, suggesting it predates episode extension. Upper crustal appears equally margins, forming symmetrical continental rift. Two styles observed; older (estimated as 14–11 using sedimentation rates) show extensive basement faulting. In contrast, younger (likely post–6 Ma) asymmetrical deposits thickening basin-bounding faults. The northeast-southwest geomorphic expression Tamayo bank trough other features additional evidence northwest-southeast 12 These new constraints, when combined thickness profile obtained entire corridor, suggest significant started well before 6 contrast earlier models.