Distributed Deformation in an Oceanic Transform System: Applying Statistical Tools to Structural and Paleomagnetic Data Near the Husavik-Flatey Fault, Northern Iceland

摘要

The right-lateral Husavik-Flatey fault is part of the Tjornes Fracture Zone, which links the offshore and onshore rift axes in northern Iceland. There has been debate about whether rocks near this fault have accommodated distributed off-fault deformation, which is testable using paleomagnetic data. Recent studies from Flateyjarskagi show clockwise declination deflections that are largest near the fault. We augment these data with new structural and paleomagnetic measurements from 106 lava flows across three peninsulas-Flateyjarskagi, Trollaskagi, and Tjornes-also finding clockwise deflections that vary with distance from the fault. To test whether the deflections could be caused by off-fault deformation, we combine our measurements with other regional data sets, applying several statistical tools including regressions of structural or paleomagnetic directions versus fault-normal distance. To evaluate the significance and uncertainties of the regressions, we use permutation tests and bootstrapping. For Flateyjarskagi, our analysis suggests that lavas and dikes were deformed together; the regression results predict 4 degrees-6 degrees of rotation per kilometer about a steep, but not vertical, axis. Rocks on Trollaskagi hint at similar spatial patterns with fault distance, but the data quality precludes a full analysis. Rocks on Tjornes show no spatial patterns, but they preserve a temporal history, where rotation seems to have ceased after deposition of the Pliocene-age Tjornes beds. Using constraints from our statistical analyses, geochronology, and comparisons with the transform system in southern Iceland, we propose several modifications to models for the evolution of axial rift zones in northern Iceland.