From forearc to transform : sedimentary record of changing tectonic setting in the central California and eastern Zealandia continental margins

Convergent continental margins are complex settings that characteristically juxtapose exhumed rocks adjacent to rapidly subsiding basins. Moreover, major transform margins can obscure paleogeographic relationships through lateral translation along strike-slip faults. While these structural and stratigraphic complexities are integrated over time as plate boundaries transition between these settings, careful analysis of allogenic signals preserved in associated sedimentary basins can be used to decipher local and regional tectonic history. This dissertation uses the detrital provenance record to investigate plate deformation and resulting sedimentation patterns during the initiation of two major transform margins. The first part of this dissertation focuses on the sedimentary strata of central California that was deposited during the late stages of Farallon subduction and following development of the San Andreas strike-slip system. Chapter 1 integrates new detrital zircon U-Pb geochronology from the Mount Diablo region with previously established sedimentologic relationships to document how sandstone composition varied in response to changing tectonic environments and paleogeography over the past 100 million years. These provenance trends reveal reorganization and expansion of continental drainage during the transition to flat-slab subduction of the Farallon plate, the subsequent onset of volcanism and southwestward migration of the paleodrainage divide during slab roll-back, and ultimately the cessation of convergent margin tectonics due to the initiation of the San Andreas transform system. Chapter 2 revises the long-term slip history of the San Andreas fault by comparing the provenance of hypothesized offset features in the La Honda and San Joaquin basins. Spatial relationships are best resolved by restoring ~360 km of displacement on the San Andreas fault since early Miocene time. Disparity in this slip magnitude with the coeval ~315 km displacement of the Pinnacles--Neenach volcanic center is due to 45 km of net intraplate deformation along the margin. This new constraint removes the need for controversial Paleogene slip on the San Andreas or precursor faults and rectifies previous discrepancies between global plate rotations and estimates of total displacement across the continental transform margin. The second part of this dissertation addresses the development of the Hikurangi subduction zone and adjacent Alpine strike-slip fault of Zealandia. Chapter 3 assembles a comprehensive new dataset of detrital zircon U-Pb ages for samples of Cretaceous and Cenozoic sediments along a 700 km latitudinal extent of New Zealand's East Coast Basin. A mixture modeling approach was employed to interpret the detrital zircon U-Pb age distributions of basin samples in terms of Zealandia's principle igneous and metasedimentary source regions. These results were integrated with existing geologic, thermochronology, and paleoenvironmental data to develop hypotheses regarding sediment routing to Zealandia's East Coast basin from Early Cretaceous to Pliocene time. Modeling results reveal systematic changes in extraregional and local sediment sources that correlate closely with evolving tectonic conditions over the past 120 million years. Overall, the study illustrates the power of large databases of detrital zircon U-Pb provenance data and interpretative tools such as mixture modeling for deciphering sediment dispersal in dynamic tectonic settings

Keywords: Geological and Environmental Sciences.
Advisor: Graham S. A. (Stephan Alan)
Grove Marty
Lowe Donald R.