Mesozic blueschists and mélanges of Cedros Island (Baja California, Mexico): a consequence of nappe emplacement or subduction?

Details Mesozic blueschists and mélanges of Cedros Island (Baja California, Mexico): a consequence of nappe emplacement or subduction? Mesozic blueschists and mélanges of Cedros Island (Baja California, Mexico): a consequence of nappe emplacement or subduction?

Jun 1982

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1982e%26psl..59..119k&link_type=abstract

Earth and Planetary Science Letters, Volume 59, Issue 1, p. 119-138.

Computer Science

7

Scientific paper

Cedros Island and the adjacent Vizcaino peninsula are characterized by the major overthrust of a volcanic-plutonic terrane of middle to late Jurassic age (San Andres-Cedros volcanic arc), and associated late Triassic ophiolites, on top of blueschist units metamorphosed mainly in early Cretaceous time, and mélange terranes. P/T metamorphic conditions for the blueschist units are 5-6 kbar and 200-235°C. Recrystallizations are located both in foliated rocks (dynamic metamorphism), and in undeformed protoliths (``in situ'' static metamorphism). A relatively later high-pressure/low-temperature fissural static metamorphism was observed cutting through previously metamorphosed rocks. The blueschists are tectonically intermixed with, or present as blocks in, the unmetamorphosed mélanges, testifying to superimposed thrust events. Development of the complex relationship between these metamorphosed and unmetamorphosed Franciscan-type rocks is not interpreted here as resulting of a simple subduction episode, but as the result of an advancing nappe induced by interarc collision in mid-Cretaceous time along the continental margin of Baja California. The supposed original thickness of the allochthon present upon the blueschist rocks 18-20 km thick) is apparently sufficient to consider these metamophic rocks as formed in the shear zone at the base of the nappe, at the first stage of its development. However, the alternative formation of these blueschists in a subduction zone, just before collision, cannot be disregarded.

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