Strain partitioning in highly oblique rift settings: Inferences from the southwestern margin of the Gulf of California (Baja California Sur, Mexico)
Por:
Bonini, Marco, Cerca, Mariano, Moratti, Giovanna, Lopez-Martinez, Margarita, Corti, Giacomo, Gracia-Marroquin, Diego
Publicada:
1 dic 2019
Ahead of Print:
1 dic 2019
Resumen:
This study aims to analyze the modalities of strain accommodation within
a highly oblique rift, taking the Gulf of California as a prototype.
Rifting in the Gulf of California is accomplished by intra-Gulf
strike-slip (transform) faults, and mostly dip-slip displacement on the
rift-margin faults. We have collected fault-slip data and samples for
radiometric dating at selected sites in southeastern Baja California,
which is host to the southwestern margin of the rift. We have identified
three styles of faulting, particularly (1) WSW-dipping normal faults,
(2) E-ENE-dipping normal faults, and (3) steep NNE-NE-trending
left-lateral faults. The E-ENE-dipping normal faults define the western
margin of the Gulf of California rift and are most likely coeval (late
Miocene to recent) with both the similar to NNE-NE-trending left-lateral
faults and some of the WSW-dipping faults. Fault-slip data have often
been collected on potentially active Gulf of California rift-margin
faults, which invariably display dominant dip-slip kinematics (generally
with minor dextral component). Distribution of extension directions
determined from stress inversion of brittle fault kinematic data
indicates a peak of 080 degrees-090 degrees, which is strikingly similar
to the orientations of T axes from earthquake focal mechanisms of both
rift-margin normal/faults and intra-Gulf strike-slip faults. These
findings suggest that this stretching may have been occurring throughout
the protracted rift history. Furthermore, highly oblique rifts do not
show across-rift variations in the orientation of local extension, which
is instead typical of continental rifts with lower obliquity.
Plain Language Summary Divergent movement between tectonic plates
extends continental crust that progressively thins and subsides
generating tectonic depressions called continental rifts. With
increasing extension, continental rifts can eventually break through the
continental lithosphere and become the locus of creation of new ocean
crust. With sufficient tectonic subsidence, a rift can be invaded by
ocean water at some point during the rifting process. The displacement
vector between the diverging plates may range from orthogonal to
oblique, relative to the orientation of the boundary between the plates.
The Gulf of California exemplifies a highly oblique continental rift
produced by the displacement of Baja California Peninsula with respect
to mainland Mexico. Ongoing rifting in the Gulf of California produces
intense seismicity, and one long pending question is how deformation is
accommodated within highly oblique continental rifts, particularly
whether the style of deformation changes from the rift margins toward
the rift interior. Analysis of faults exposed along the southwestern
rift margin (southeastern Baja California), and its comparison with
characteristics of historical seismicity generated by the long
strike-slip faults underwater in the Gulf of California shed new light
on the kinematics of high obliquity continental rifts and improves our
understanding of the ongoing deformation of our planet.
Filiaciones:
Bonini, Marco:
CNR, Consiglio Nazionale delle Ricerche, Istituto di Geoscienze e Georisorse, Florence, Italy
CNR, Ist Geosci & Georisorse, Florence, Italy
Cerca, Mariano:
Laboratorio de Mecánica de Geosistemas, Centro de Geociencias, Universidad Nacional Autónoma de México, Juriquilla, Mexico
Univ Nacl Autonoma Mexico, Lab Mecan Geosistemas, Ctr Geociencias, Juriquilla, Mexico
Univ Nacl Autonoma Mexico, Ctr Geociencias, Lab Mecan Geosistemas, Juriquilla, Mexico
Moratti, Giovanna:
CNR, Consiglio Nazionale delle Ricerche, Istituto di Geoscienze e Georisorse, Florence, Italy
CNR, Ist Geosci & Georisorse, Florence, Italy
Lopez-Martinez, Margarita:
Departamento de Geología, Centro de Investigación Científica y de Educación Superior de Ensenada Baja California, Ensenada, Mexico
Ctr Invest Cient & Educ Super Ensenada Baja Calif, Dept Geol, Ensenada, Baja California, Mexico
Ctr Invest Cient & Educ Super Ensenada Baja Cali, Dept Geol, Ensenada, Baja California, Mexico
Corti, Giacomo:
CNR, Consiglio Nazionale delle Ricerche, Istituto di Geoscienze e Georisorse, Florence, Italy
CNR, Ist Geosci & Georisorse, Florence, Italy
Gracia-Marroquin, Diego:
Laboratorio de Mecánica de Geosistemas, Centro de Geociencias, Universidad Nacional Autónoma de México, Juriquilla, Mexico
Univ Nacl Autonoma Mexico, Lab Mecan Geosistemas, Ctr Geociencias, Juriquilla, Mexico
Univ Nacl Autonoma Mexico, Ctr Geociencias, Lab Mecan Geosistemas, Juriquilla, Mexico
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