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Quantifying rates of "rifting while drifting" in the southern Gulf of California; the role of the southern Baja California Microplate and its eastern boundary zone

Paul J. Umhoefer, C. Plattner and R. Malservisi
Quantifying rates of "rifting while drifting" in the southern Gulf of California; the role of the southern Baja California Microplate and its eastern boundary zone
Lithosphere (February 2020) 12 (1): 122-132

Abstract

The southern Baja California (Mexico) microplate has been rapidly moving away from the North America plate since ca. 12 Ma. This relative motion toward the northwest developed an oblique-divergent plate boundary that formed the Gulf of California. The rift-drift hypothesis postulates that when a continent ruptures and seafloor spreading commences, rifting on the plate margins ceases, and the margins start to drift, subside, and accumulate postrift sediments, eventually becoming a passive margin. In contrast to this hypothesis, the southern part of the Baja California microplate (BCM), and in particular its actively deforming eastern boundary zone, has continued significant rifting for millions of years after seafloor spreading initiated within the southern Gulf of California at 6-2.5 Ma. This is a process we call "rifting-while-drifting." Global positioning system (GPS)-based data collected from 1998 to 2011 show relative motion across the eastern boundary zone up to approximately 2-3.2 mm/yr with respect to a stable BCM. Furthermore, the velocity directions are compatible with normal faulting across the eastern boundary zone nearly perpendicular to the trend of the plate boundary at the latitude of La Paz and therefore a highly strain partitioned domain. North of 25 degrees N latitude up to the Loreto area, there is a domain with no strain partitioning, and northwest-directed transtensional deformation dominates. From long-term geologic and paleoseismology studies, late Quaternary faulting rates are equal to or less than the GPS-derived rates, while geologic rates older than 1-2 Ma are commonly much higher. We suggest that the "rifting-while-drifting" process may be caused by the large topographic relief across the BCM margin, which created a significant gradient in gravitational potential energy that helps in driving continued relatively slow faulting. The relief was inherited from the much faster faulting of the BCM eastern boundary zone before plate motions largely localized along the modern transform-spreading centers in the axis of the Gulf of California. The low sediment flux from the small drainages and arid climate on the southern Baja California Peninsula result in the maintenance of underfilled to starved basins, and the relatively slow late Quaternary active faulting promotes continued topographic relief over millions of years.


ISSN: 1941-8264
EISSN: 1947-4253
Serial Title: Lithosphere
Serial Volume: 12
Serial Issue: 1
Title: Quantifying rates of "rifting while drifting" in the southern Gulf of California; the role of the southern Baja California Microplate and its eastern boundary zone
Affiliation: Northern Arizona University, School of Earth and Sustainability, Flagstaff, AZ, United States
Pages: 122-132
Published: 202002
Text Language: English
Publisher: Geological Society of America, Boulder, CO, United States
References: 60
Accession Number: 2020-039333
Categories: Seismology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 3 tables, geol. sketch maps
N22°40'00" - N26°30'00", W113°30'00" - W111°30'00"
N26°00'00" - N31°30'00", W116°30'00" - W111°04'60"
Secondary Affiliation: Ludwig-Maximilians-Universitaet Muenchen, DEU, GermanyUniversity of South Florida, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2020, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 2020
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