Andrea Fabbrizzi, Jillian M. Maloney, Boe Derosier, Bradley Keith
The Outer California Borderland (OCB) is an active transform plate boundary offshore Southern California, where the relationship between faulting and submarine mass transport deposits (MTDs) remains poorly understood. Onshore paleoseismic data provide high-resolution earthquake records, whereas marine geophysical data capture longer-term histories. Offshore fault systems pose hazards to infrastructure and dense coastal populations, particularly when linked to submarine landslides. We present new high-resolution geophysical data set (cruise SR2303), including bathymetric and CHIRP sub-bottom data integrated with legacy seismic reflection data and chronostratigraphic constraints from ODP Site 1012 to examine Quaternary MTD recurrence and tectonic controls in the Cortes Basin, OCB. Bathymetry shows deformational features, including slide scarps and previously unmapped fault segments with evidence of Holocene activity. CHIRP profiles reveal 10 stacked MTDs in the East Cortes Basin and 8 in the West Cortes Basin, spanning ∼752 ka with an average recurrence of ∼83.6 ± 1 ka. Acoustic imaging shows 7 MTD intervals coinciding with fault offset increments and fault growth suggesting earthquake-triggered mass wasting. A strong association between MTD occurrences and sea-level extremes also supports glacio-eustatic contribution to slope failure. Stratigraphic correlations suggest quasi-synchronous MTDs across the eastern and western areas, likely triggered by larger eathquakes in the Quaternary. Although the identified MTDs occur relatively far from the Southern California coast, they still pose a potential tsunamigenic hazard requiring further assessment. Moreover, if linked to earthquakes along major strike-slip faults, for example, the Ferrelo fault, the MTDs may provide valuable proxies to constrain rupture scenarios and fault connectivity within the understudied OCB.
{"title":"Interplay Between Tectonics and Submarine Mass Transport Deposits in Cortes Basin: New High-Resolution Geophysics in the Outer California Borderland","authors":"Andrea Fabbrizzi, Jillian M. Maloney, Boe Derosier, Bradley Keith","doi":"10.1029/2025jb032100","DOIUrl":"https://doi.org/10.1029/2025jb032100","url":null,"abstract":"The Outer California Borderland (OCB) is an active transform plate boundary offshore Southern California, where the relationship between faulting and submarine mass transport deposits (MTDs) remains poorly understood. Onshore paleoseismic data provide high-resolution earthquake records, whereas marine geophysical data capture longer-term histories. Offshore fault systems pose hazards to infrastructure and dense coastal populations, particularly when linked to submarine landslides. We present new high-resolution geophysical data set (cruise SR2303), including bathymetric and CHIRP sub-bottom data integrated with legacy seismic reflection data and chronostratigraphic constraints from ODP Site 1012 to examine Quaternary MTD recurrence and tectonic controls in the Cortes Basin, OCB. Bathymetry shows deformational features, including slide scarps and previously unmapped fault segments with evidence of Holocene activity. CHIRP profiles reveal 10 stacked MTDs in the East Cortes Basin and 8 in the West Cortes Basin, spanning ∼752 ka with an average recurrence of ∼83.6 ± 1 ka. Acoustic imaging shows 7 MTD intervals coinciding with fault offset increments and fault growth suggesting earthquake-triggered mass wasting. A strong association between MTD occurrences and sea-level extremes also supports glacio-eustatic contribution to slope failure. Stratigraphic correlations suggest quasi-synchronous MTDs across the eastern and western areas, likely triggered by larger eathquakes in the Quaternary. Although the identified MTDs occur relatively far from the Southern California coast, they still pose a potential tsunamigenic hazard requiring further assessment. Moreover, if linked to earthquakes along major strike-slip faults, for example, the Ferrelo fault, the MTDs may provide valuable proxies to constrain rupture scenarios and fault connectivity within the understudied OCB.","PeriodicalId":15864,"journal":{"name":"Journal of Geophysical Research: Solid Earth","volume":"18 1","pages":""},"PeriodicalIF":3.9,"publicationDate":"2026-02-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146129278","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The Late Cretaceous Oman ophiolite includes a series of volcanic rocks generated during the transition from spreading ridge to protoarc associated with subduction initiation. We analyzed major and trace elements and Sr, Nd, and Pb isotope compositions of lavas and dikes of the protoarc stage, especially boninites. We also analyzed amphibolites and metacherts of the metamorphic sole, as subducted slab materials. Furthermore, we examined trace element patterns reconstructed based on analyses of whole rocks and relict clinopyroxene phenocrysts from volcanic rocks of both axial and protoarc stages. The compositions of protoarc tholeiites, which represent the first and most voluminous magmas generated in the protoarc stage, are consistent with flux melting of residual depleted mantle, metasomatized by aqueous fluids liberated from the amphibolite-facies slab. On the other hand, the successively produced calc-alkaline, low-Si boninites show distinctly radiogenic Sr, Nd, and Pb isotope ratios, spoon-shaped rare earth patterns, and low Nb/Ta ratios, which require addition of amphibolite slab fluids formed at higher temperatures as well as small amounts of mafic-sedimentary hybrid slab melt to the residual highly depleted mantle. Although axial lavas lack enrichment in fluid-mobile elements except for K, later off-ridge lavas exhibit clear K, Sr, and Pb enrichments, suggesting decompression melting of fluid-metasomatized mantle associated with subduction initiation near the dying spreading ridge. The resultant hot subduction zone is favorable for mantle wedge melting to generate tholeiitic and boninitic magmas in the protoarc stage.
{"title":"Slab-Mantle Interaction During Subduction Initiation: Constraints From Trace Element and Sr-Nd-Pb Isotope Systematics of Boninite and Other Magmas and Metamorphic Sole in the Oman Ophiolite","authors":"Tsuyoshi Ishikawa, Kazuya Nagaishi, Kyoko Kanayama, Keitaro Kitamura, Shigeyuki Wakaki, Yuki Kusano, Susumu Umino","doi":"10.1029/2025JB032926","DOIUrl":"10.1029/2025JB032926","url":null,"abstract":"<p>The Late Cretaceous Oman ophiolite includes a series of volcanic rocks generated during the transition from spreading ridge to protoarc associated with subduction initiation. We analyzed major and trace elements and Sr, Nd, and Pb isotope compositions of lavas and dikes of the protoarc stage, especially boninites. We also analyzed amphibolites and metacherts of the metamorphic sole, as subducted slab materials. Furthermore, we examined trace element patterns reconstructed based on analyses of whole rocks and relict clinopyroxene phenocrysts from volcanic rocks of both axial and protoarc stages. The compositions of protoarc tholeiites, which represent the first and most voluminous magmas generated in the protoarc stage, are consistent with flux melting of residual depleted mantle, metasomatized by aqueous fluids liberated from the amphibolite-facies slab. On the other hand, the successively produced calc-alkaline, low-Si boninites show distinctly radiogenic Sr, Nd, and Pb isotope ratios, spoon-shaped rare earth patterns, and low Nb/Ta ratios, which require addition of amphibolite slab fluids formed at higher temperatures as well as small amounts of mafic-sedimentary hybrid slab melt to the residual highly depleted mantle. Although axial lavas lack enrichment in fluid-mobile elements except for K, later off-ridge lavas exhibit clear K, Sr, and Pb enrichments, suggesting decompression melting of fluid-metasomatized mantle associated with subduction initiation near the dying spreading ridge. The resultant hot subduction zone is favorable for mantle wedge melting to generate tholeiitic and boninitic magmas in the protoarc stage.</p>","PeriodicalId":15864,"journal":{"name":"Journal of Geophysical Research: Solid Earth","volume":"131 2","pages":""},"PeriodicalIF":4.1,"publicationDate":"2026-02-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2025JB032926","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146115581","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
D. A. Jivanjee Medina, S. Kaboli, B. M. Patterson, P. C. Burnley
We present a suite of 13 uniaxial deformation experiments on fine grained polycrystalline α-quartz conducted in a D-DIA apparatus monitored with in situ synchrotron x-rays. Experimental temperatures range from 25°C to 1199°C with pressures between 1.4 and 3.2 GPa, and strain rates between 3.4 × 10−6 s−1 and 1.8 × 10−5 s−1. Powder diffraction data from the (