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Ophiolite and volcanic arc assemblages on the Vizcaíno Peninsula and Cedros Island region, Baja California Sur, Mexico: Mesozoic forearc lithosphere of the Cordilleran magmatic arc

GSA Special Papers
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Abstract

Mesozoic ophiolites in the Vizcaíno Peninsula and Cedros Island region of Baja California Sur are suprasubduction zone Cordilleran-type ophiolites structurally juxtaposed with underlying high pressure-temperature subduction complex assemblages. The region is divided into three separate tectonostratigraphic terranes, but here we recognize stratigraphic, intrusive, and petrologie links between these terranes and interpret the evolution of the entire region within the same Late Triassic to Early Cretaceous tectonic framework. Several phases of extension are recognized, including two major phases that resulted in development of distinct ophiolite assemblages. The Late Triassic Vizcaine Peninsula Ophiolite (221 ± 2 Ma) represents the earliest stage of this history and comprises a complete spreading center sequence with depleted upper mantle and mafie crustal rocks, including sheeted dike complex, Jurassic are magmatic rocks with low-Ti are tholelite and boninite geochemical affinities were intruded through and constructed on the Triassic ophiolite basement. Ultra-depleted are-ankaramites on Cedros Island may represent an initial phase of are rifting that was followed by major Middle Jurassic extension and production of the Cedros Island Ophiolite (173 ± 2 Ma). The Late Jurassic-Early Cretaceous Coloradito and Eugenia Formations contain mudflows and olistostrome blocks intercalated with are volcanogenic sediment and rift-related pillow lavas; these units record extension and/or transtension and provide the earliest definite evidence of are-continent interaction in the region.

Middle Jurassic to Early Cretaceous are plutonic rocks (ca. 165-135 Ma) were shallowly intruded into low greenschist-facies ophiolite and are volcanic basement. Plutonic rocks range in composition from gabbro to granodiorite, but tonalite dominates. These intrusions are typical I-type Cordilleran batholithic rocks with relatively primitive are geochemical affinities (initial Sr87/86Sr range from ~0.704 to 0.706), but they are distinctly calcic in nature, a feature common to the adjacent Cretaceous Peninsular Ranges batholith.

The Vizcaíno-Cedros region correlates to ophiolitic terranes of the western Sierra Klamath belt and Coast Ranges of California and Oregon that were constructed in part across the North American margin. Age, stratigraphic, and petrochemical data from the Vizcaíno-Cedros region support previously proposed forearc rifting models developed for the U.S. sector of the Cordilleran orogen that interpret the ophiolite assemblages as autochthonous or parautochthonous forearc lithosphere constructed outboard of the Mesozoic continental margin arc.

Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Ophiolite and volcanic arc assemblages on the Vizcaino Peninsula and Cedros Island region, Baja California Sur, Mexico: Mesozoic forearc lithosphere of the Cordilleran magmatic arc
Series title GSA Special Papers
Volume 374
Year Published 2003
Language English
Publisher Geological Society of America
Publisher location Boulder, CO
Contributing office(s) Geology, Minerals, Energy, and Geophysics Science Center
Description 29 p.
Larger Work Type Book
Larger Work Title Tectonic evolution of northwestern Mexico and the southwestern USA
First page 43
Last page 71
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