Gulf of California - Eastern California - Walker Lane:Two major transtensional belts in the
Pacific - North America plate boundary
Paul Umhoefer, Northern Arizona University
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Linking MARGINS and EarthScope;
lead into discussion…
SIMILARITIES IN BOTH BELTS:• Major part of plate boundary {but 90-95% vs 20-25% of r.p.m.}• Active since 14-12 Ma• Formed between batholiths & calderas
edge PC crust; on arc• Western edge of Basin & Range
• Transtensional (throughout history?)• Strain partitioning - across plate boundary & within belts {margin vs center of belts}
• Localization of strain over time
DIFFERENCES • stages of development
• rates of motion across belts• different total offsets (opening)
• pre-rift crust (Mojave)
NATURE OF PRE-RIFTED CRUST:
Do older batholith/caldera beltscontrol location-processes of belts?Laramide (Mojave only) effects?Did mid-Tertiary caldera beltseffect rifting process?
Thermal state of crust?
WEST EDGE OF BASIN & RANGE:
Do differences in previous extensioneffect rifting processes?
OVERALL STRAIN RATES:
Is there a threshold for fundamentallydifferent behavior related to strainrates?
Science objectives:
• how previous crustal structure effects oblique rifting
• New crust and nature of lower crust in N Gulf of Cal & Salton
• Kinematic/opening budget across belts = strain rates through time
• age/nature of oldest rift basins and especially marine initiation
• failed rifts and jumping of rift centers (really strain localization)
• obliquity and style of rifting (LANFs)
• formation of strike-slip and transform faults
• strain partitioning and fault mechanics
• role of mantle lithosphere??
MARGINS funding in Salton trough - NW Mexico onshore:
None?
• A few NSF-Tectonics grants recently• Many studies of neotectonics
• Fair number of proposals• NO proposals for large passive-active seismic transects ala
Lizarralde PESCADOR in southern Gulf of California{Fuis et al study - late 1970s}
• Northern Gulf of Cal will remain a hole for seismic, except CORTEZ
Can we merge MARGINS & EarthScope?? {& Continental Dynamics & Core??}1) {USGS - new projects…}2) Salton trough - Mojave ECSZ as link between belts
3) Comparative studies S to N
4) Different stages of rifting S to N
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Lizarralde et al 2003 EwingPESCADERO cruise
CORTEZ cruise
PESCADEROcruise
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