Abstract

Diverse oceanic rocks exposed in west-central Baja California (Mexico) are assigned to three shallowly dipping tectonic units. The lower plate is a subduction complex consisting of regionally metamorphosed blueschists and divided into structurally and petrologically distinct subterranes. The upper plate consists of Triassic-Lower Cretaceous are rocks and overlapping mid-Cretaceous turbidites. A fault-bounded serpentinite-matrix melange between lower and upper plate rocks contains blueschist, eclogite, amphibolite, and variably serpentinized mafic and ultramafic blocks. Lower plate blueschists were metamorphosed in the late Early Cretaceous and uplifted along shallowly dipping normal faults during conditions of steady-state subduction. Exotic blocks of blueschist, eclogite, and amphibolite are derived from a cryptic terrane or terranes, record varied P-T-t histories, and were uplifted via tectonic emplacement or diapiric rise of serpentinite along the normal faults.

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