Two lithospheric profiles across southern California derived from gravity and seismic data

Romanyuk, T. V.; Mooney, Walter D.; Detweiler, S.

doi:10.1016/j.jog.2006.09.011

Cited by 13 publications

(15 citation statements)

References 86 publications

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“…The offset of the Moho at this locality may connect to thrusting along the Palos Verdes fault (see Figure ) and if so, then the mantle communication between the Moho and the surface is weaker here than along the NIFZ, based on the strength of the R/Ra ratio in the two areas (Figure ). Another study, based on gravity and seismic data, concludes the NIFZ is the southwest boundary between a thick section of ultramafic lower crust on the north and a thin section of oceanic crust to the south [see Romanyuk et al ., , Figure 8]. The abrupt lateral change in lithospheric material in the deep crust adjacent to the NIFZ is consistent with a deep‐seated conduit to the Moho along the NIFZ and the preservation of a paleo‐subduction boundary.…”

Section: Discussionmentioning

confidence: 99%

Mantle helium along the Newport‐Inglewood fault zone, Los Angeles basin, California: A leaking paleo‐subduction zone

Boles

Garven

Camacho

2015

Geochem Geophys Geosyst

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Mantle helium is a significant component of the helium gas from deep oil wells along the Newport-Inglewood fault zone (NIFZ) in the Los Angeles (LA) basin. Helium isotope ratios are as high as 5.3 Ra (Ra 5 3 He/ 4 He ratio of air) indicating 66% mantle contribution (assuming R/Ra 5 8 for mantle), and most values are higher than 1.0 Ra. Other samples from basin margin faults and from within the basin have much lower values (R/Ra < 1.0). The 3 He enrichment inversely correlates with CO 2 , a potential magmatic carrier gas. The d 13 C of the CO 2 in the 3 He rich samples is between 0 and 210&, suggesting a mantle influence.The strong mantle helium signal along the NIFZ is surprising considering that the fault is currently in a transpressional rather than extensional stress regime, lacks either recent magma emplacement or high geothermal gradients, and is modeled as truncated by a proposed major, potentially seismically active, d ecollement beneath the LA basin. Our results demonstrate that the NIFZ is a deep-seated fault directly or indirectly connected with the mantle. Based on a 1-D model, we calculate a maximum Darcy flow rate q 2.2 cm/yr and a fault permeability k 6 3 10 217 m 2 (60 microdarcys), but the flow rates are too low to create a geothermal anomaly. The mantle leakage may be a result of the NIFZ being a former Mesozoic subduction zone in spite of being located 70 km west of the current plate boundary at the San Andreas fault.

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Section: Discussionmentioning

confidence: 99%

Mantle helium along the Newport‐Inglewood fault zone, Los Angeles basin, California: A leaking paleo‐subduction zone

Boles

Garven

Camacho

2015

Geochem Geophys Geosyst

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“…Our alternate gravity model of the continental slope of southern QCS is that of an abandoned transform fault (Figure 12). Shear zones of this width have been mapped across transform plate boundaries (e.g., line 88‐03, Figure 5) and typically have lower seismic velocities and by implication lower densities [ Stern and McBride , 1998; Wilson et al , 2004; Romanyuk et al , 2007]. Gravity interpretations are of course nonunique; calculating a successful alternate simply shows that previous models of this margin as a subduction zone cannot be used as definitive proof of tectonic interactions.…”

Section: Interpretation and Discussionmentioning

confidence: 99%

Pacific‐North America plate boundary reorganization in response to a change in relative plate motion: Offshore Canada

Rohr¹,

Tryon

2010

Geochem Geophys Geosyst

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[1] The transition from subduction in Cascadia to the transform Queen Charlotte fault along western Canada is often drawn as a subduction zone, yet recent studies of GPS and earthquake data from northern Vancouver Island are not consistent with that model. In this paper we synthesize seismic reflection and gravity interpretations with microseismicity data in order to test models of (1) microplate subduction and (2) reorganization of the preexisting strike-slip plate boundary. We focus on the critical region of outer Queen Charlotte Sound and the adjacent offshore. On much of the continental shelf, several million years of subsidence above thin crust are a counterindicator for subduction. An undated episode of compression uplifted the southernmost shelf, but subsidence patterns offshore show that recent subduction is unlikely to be responsible. Previously unremarked near-vertical faults and a mix of extensional and compressional faults offshore indicate that strike-slip faulting has been a significant mode of deformation. Seismicity in the last 18 years is dominantly strike-slip and shows large amounts of moment release on the Revere-Dellwood fault and its overlap with the Queen Charlotte fault. The relative plate motion between the Pacific and North American plates rotated clockwise ∼6 Ma and appears to have triggered formation of an evolving array of structures. We suggest that the paleo-Queen Charlotte fault which had defined this continental margin retreated northward as offshore distributed shear and the newly formed Revere Dellwood fault propagated to the northwest.

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“…There is some support for a density origin of the HVB from detailed 2D gravity and isostatic modeling by Romanyuk et al (2007), although the gravity expression of this deep body is weak. Biasi (2009) has interpreted the origins of high-velocity mantle anomalies in California, concluding, based on volumetric arguments, that they do not have local sources (they are too big), but are possibly downwelled lithospheric roots of the Sierra Nevada and Peninsular Ranges batholiths.…”

Section: Appendix Cmentioning

confidence: 99%

A New Perspective on the Geometry of the San Andreas Fault in Southern California and Its Relationship to Lithospheric Structure

Fuis¹,

Scheirer²,

Langenheim³

et al. 2012

Bulletin of the Seismological Society of America

128

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Two lithospheric profiles across southern California derived from gravity and seismic data

Cited by 13 publications

References 86 publications

Mantle helium along the Newport‐Inglewood fault zone, Los Angeles basin, California: A leaking paleo‐subduction zone

Mantle helium along the Newport‐Inglewood fault zone, Los Angeles basin, California: A leaking paleo‐subduction zone

Pacific‐North America plate boundary reorganization in response to a change in relative plate motion: Offshore Canada

A New Perspective on the Geometry of the San Andreas Fault in Southern California and Its Relationship to Lithospheric Structure

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