Skip to Main Content
Skip Nav Destination
GEOREF RECORD

Evolution of a Middle Jurassic back-arc basin, Cedros Island, Baja California; evidence from a marine volcaniclastic apron

Cathy J. Busby-Spera
Evolution of a Middle Jurassic back-arc basin, Cedros Island, Baja California; evidence from a marine volcaniclastic apron
Geological Society of America Bulletin (February 1988) 100 (2): 218-233

Abstract

A rifted arc-ophiolite assemblage and over-lying volcaniclastic rocks, all of late Middle Jurassic age, represent a fragment of the frontal-arc margin of a back-arc basin, now exposed on Cedros Island in Baja California (Mexico). Ophiolite generation was immediately followed by progradation of a deep- marine volcaniclastic apron (Gran Cannon Formation) contemporaneous with the growth of island-arc volcanoes. This back-arc apron shows relatively simple, uniform sedimentation patterns that may be recognizable in other back-arc basins isolated from terrigenous sediment influx.The progradational back-arc apron sequence includes, from base to top, (1) the tuff lithofacies-thin-bedded, well-sorted, laterally continuous tuffs that thicken into basement paleo-lows. These were deposited from dilute sediment gravity flows generated by eruptions from a deeply submerged, nascent arc. (2) the lapilli tuff-tuff breccia lithofacies-medium- to very thick-bedded lapilli tuffs and tuff breccias. These were deposited from debris flows on proximal parts of the apron, and high-density turbidites were deposited on more distal parts. This lithofacies records increasing generation and resedimentation of scoriaceous and hyaloclastic debris as the summits of the arc volcanoes grew nearer to sea level. (3) the primary volcanic lithofacies-monolithologic dacite pyroclastic flows were produced during the eruption of differentiated magmas, which climaxed the growth of the island arc. Basalt lava flows were fed from fissures that extended down the apron within the back-arc basin.Pyroclastic rocks of the back-arc apron were blanketed with silty basinal turbidites (epiclastic facies) that record abrupt cessation of volcanism and erosion of the arc within about 10 m.y. of ophiolite generation, reflecting the temporal episodicity of back-arc basins.It is predicted from this study that the frontal-arc side of back-arc spreading centers is preferentially preserved in the geologic record relative to the center of the basin. It is suggested that the "hot" frontal-arc side of the basin is prone to intra-plate volcanism but is unaffected by faulting subsequent to basin initiation. Several factors lead to slumps occurring more frequently on the arc flank of back-arc basins than in any other tectonic setting, except perhaps intra-arc marine basins.


ISSN: 0016-7606
EISSN: 1943-2674
Coden: BUGMAF
Serial Title: Geological Society of America Bulletin
Serial Volume: 100
Serial Issue: 2
Title: Evolution of a Middle Jurassic back-arc basin, Cedros Island, Baja California; evidence from a marine volcaniclastic apron
Affiliation: Univ. Calif., Dep. Geol. Sci., Santa Barbara, CA, United States
Pages: 218-233
Published: 198802
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 52
Accession Number: 1988-015615
Categories: StratigraphySedimentary petrologySolid-earth geophysics
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. sects., geol. sketch map
N23°00'00" - N32°30'00", W117°00'00" - W109°00'00"
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2019, American Geosciences Institute.
Update Code: 1988
Close Modal

or Create an Account

Close Modal
Close Modal