The northbrae rhyolite of Berkeley (California, USA) constrains motion of the proto-Hayward Fault

Wesley G. Henschel, Eben B. Hodgin, John L. Grimsich, Nicholas L. Swanson-Hysell

Research output: Contribution to journalArticlepeer-review

Abstract

Right-lateral transform motion associated with the Pacific-North American plate boundary in the modern-day San Francisco Bay Area occurs across a series of sub-parallel fault zones. Much of this motion is accommodated east of the San Andreas Fault by the faults of the East Bay fault system. A major tool for reconstructing the spatial and temporal history of fault motion is the correlation of offset Neogene volcanic rocks. These Neogene volcanics within the California Coast Ranges formed in association with the slab gap that grew as the Mendocino Triple Junction migrated northward. Some of the volcanic centres have been variably offset by subsequent strike-slip faulting. A felsic volcanic unit exposed in Berkeley, CA, known as the Northbrae rhyolite has variably been interpreted to be one of these Neogene volcanic units or to be a Mesozoic volcanic unit associated with the Coast Range ophiolite. A new U-Pb zircon date of 11.10 (Formula presented.) 0.09 Ma confirms the Neogene volcanic interpretation. This date is indistinguishable from previously published Ar/Ar dates from the Burdell Mountain volcanics of the North Bay region as well as a new U-Pb zircon date of 11.07 (Formula presented.) 0.10 Ma. In addition to the indistinguishable ages, similarities in bulk lithology, zircon crystallization/dissolution textures, and zircon trace element geochemistry are consistent with these rhyolites being associated with the same volcanic centre. This correlation implies that 40 (Formula presented.) 5 km of right-lateral offset occurred to the west of the modern-day position of the Hayward-Rodgers Creek fault zone. This offset represents (Formula presented.) 20% of the total offset along the East Bay fault system. A proto-Hayward Fault with a different geometry than that of the present-day played a significant role in the evolution of the fault system. This result highlights the dynamic spatiotemporal variability of strike-slip faults along transform margins.

Original languageEnglish (US)
JournalInternational Geology Review
DOIs
StateAccepted/In press - 2024
Externally publishedYes

Bibliographical note

Publisher Copyright:
© 2024 Informa UK Limited, trading as Taylor & Francis Group.

Keywords

  • Burdell Mountain volcanics
  • East Bay fault system
  • fault offset
  • Hayward Fault
  • Mendocino Triple Junction
  • Neogene volcanic rocks
  • Northbrae rhyolite
  • Pacific-North American plate boundary
  • proto-Hayward Fault
  • Right-lateral transform motion
  • San Francisco Bay Area
  • slab gap volcanism
  • strike-slip faulting
  • transform margins
  • U-Pb zircon dating
  • zircon rare earth elements

Fingerprint

Dive into the research topics of 'The northbrae rhyolite of Berkeley (California, USA) constrains motion of the proto-Hayward Fault'. Together they form a unique fingerprint.

Cite this