Abstract

We present a general model for the structural and stratigraphic evolution of extensional oceanic arcs, combining published data from modern oceanic arcs with our outcrop data from a Cretaceous oceanic arc in Baja California. Thirty lithofacies building blocks are assembled into architectural models for two phases of evolution. Phase I is characterized by intermediate to silicic explosive and effusive volcanism, culminating in caldera-forming silicic ignimbrite eruptions. This represents an extensional island arc, with the onset of arc rifting being recorded in the climactic caldera-forming eruptions. Phase II is characterized by mafic effusive and hydroclastic rocks and widespread dike swarms, and it records rifting of the arc. The cycle of arc extension followed by arc rifting reflects the episodicity of rifting in arc-backarc systems, which appears to recur on 10–15 m.y. time scales.

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