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Published 2000 | public
Book Section - Chapter

Relation of the Puertecitos Volcanic Province, Baja California, Mexico, to development of the plate boundary in the Gulf of California

Abstract

The Puertecitos Volcanic Province is a late Miocene and Pliocene ignimbrite field covering an area of ~2600 km^2, with an estimated erupted volume of at least 500 km^3. It is unique on the Baja California Peninsula in terms of both its volume and age. It lies at a 35° bend in the edge of the Gulf of California rift system, at a location where the character of the Gulf extensional province, in terms of topography, style of faulting, and paleomagnetic rotations, changes dramatically along strike. This chapter presents a speculative model linking the along-strike structural variations of the extensional province at this location, and the two major episodes of volcanism in the Puertecitos Volcanic Province ca. 6 Ma and 3 Ma, to events in the evolution of the spreading and transform system nearby in the Gulf of California. Two fracture zone systems project northwestward into the Puertecitos Volcanic Province. The Guaymas transform fault system passes through the Ballenas Channel and is aligned with the southern boundary of the volcanic province; the Tiburón fracture zone (between Isla Tiburón and Isla Angel de la Guarda) projects into the northcentral part of the province. The Tiburón fracture zone was important during the early evolution of the Gulf of California. The Guaymas transform fault system was much shorter during the early evolution of the Gulf of California was only active near the Puertecitos Volcanic Province after 2 Ma. The Tiburón fracture zone may have been connected to a west-northwest-trending zone of deformation on land, the Matomi accommodation zone. Regional field evidence suggests that this accommoda: tion zone was active in late Miocene time and may have localized most of the vents for the voluminous ca. 6 Ma volcanism of the northern Puerteci tos Volcanic Province. An episode of 3.3-2.7 Ma volcanism in the extending region is related to a Pliocene jump of one Gulf of California spreading center from the Tiburón basin into this area (which is now the lower Delfin basin). Continental extension, growth faulting, and basin formation in Pliocene time in the southern part of the Puertecitos Volcanic Province probably preceded this spreading center jump by 1 to 2 m.y. The temporal and spatial aspects of extension in this model may explain the structural transition seen in the Puertecitos region. North of the Puertecitos Volcanic Province, the San Pedro Martir fault and basin and range topography partly reflect pre-6 Ma extension. Regions to the south, from Puertecitos southward to Gonzaga Bay, may have been unaffected by extension at this time. The pre-Pliocene rift margin probably passed through the northeast part of the province and southeastward into the Gulf of California, east of Isla Angel de la Guarda. When major deformation began to affect the main part of the volcanic province, the motion in the sector from Puertecitos to Gonzaga Bay may have been primarily transform in nature, producing a very different structural style from that inherited from the earlier transtensional history in the region north of the Matomi accommodation zone.

Additional Information

© 2000 Geological Society of America. Manuscript accepted by the Society August 31, 1998. This research was supported by National Science Foundation grant EAR-9296102. Gary Axen and Paul Umhoefer provided helpful comments on an earlier version of this paper. Division of Geological and Planetary Sciences, California Institute of Technology. Contribution 5632.

Additional details

Created:
August 19, 2023
Modified:
January 13, 2024