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Abstract Faults on microcontinents record the dynamic evolution of plate boundaries. However, most microcontinents are submarine and difficult to study. Here, we show that the southern part of the Isla Ángel de la Guarda (IAG) microcontinent, in the northern Gulf of California rift, is densely faulted by a late Quaternary‐active normal fault zone. To characterize the onshore kinematics of this Almeja fault zone, we integrated remote fault mapping using high‐resolution satellite‐ and drone‐based topography with neotectonic field‐mapping. We produced 13 luminescence ages from sediment deposits offset or impounded by faults to constrain the timing of fault offsets. We found that north‐striking normal faults in the Almeja fault zone continue offshore to the south and likely into the nascent North Salsipuedes basin southwest of IAG. Late Pleistocene and Holocene luminescence ages indicate that the most recent onshore fault activity occurred in the last ∼50 kyr. These observations suggest that the North Salsipuedes basin is kinematically linked with and continues onshore as the active Almeja fault zone. We suggest that fragmentation of the evolving IAG microcontinent may not yet be complete and that the Pacific‐North America plate boundary is either not fully localized onto the Ballenas transform fault and Lower Delfin pull‐apart basin or is in the initial stage of a plate boundary reorganization.
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Slip History, Tectonic Evolution, and Fault Zone Structure Along the Southern Alpine Fault, New Zealand
The study of active fault zones is fundamental to understanding both long‐term tectonics and short‐term earthquake behavior. Here, we integrate lidar‐enabled geomorphic‐geologic mapping and petrochronological analysis to reveal the slip‐history, tectonic evolution, and structure of the southern Alpine Fault in New Zealand. New petrographic, zircon U‐Pb and zircon trace‐element data from fault‐displaced basement units provides constraint on ∼70–90 km of right‐lateral displacement on the presently active strand of the southern Alpine Fault, which we infer is of Plio‐Quaternary age. This incremental displacement has accumulated while the offshore part of the fault has evolved within a distributed zone of plate boundary deformation. We hypothesize that pre‐existing faults in the continental crust of the Pacific Plate have been exploited as components of this distributed plate boundary system. Along the onshore southern Alpine Fault, detailed mapping of active fault traces reveals complexity in geomorphic fault expression. Our analysis suggests that the major geomorphic features of the southern Alpine Fault correspond to penetrative fault zone structures. We emphasize the region immediately south of the central‐southern section boundary, where a major extensional stepover and restraining bend are located along‐strike of each other. We infer that this geometry may reflect segmentation of the Alpine Fault between two distinct fault segments. The ends of these proposed segments meet near where several Holocene earthquake ruptures have terminated. Our new constraints on the evolution and structure of the southern Alpine Fault help contribute to improved characterization of the greatest onshore source of earthquake hazard in New Zealand.
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- Award ID(s):
- 1901827
- PAR ID:
- 10576906
- Publisher / Repository:
- AGU
- Date Published:
- Journal Name:
- Geochemistry, Geophysics, Geosystems
- Volume:
- 25
- Issue:
- 11
- ISSN:
- 1525-2027
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1029/2024GC011839
