Waning magmatic activity along the Southern Explorer Ridge revealed through fault restoration of rift topography

Abstract

[1] We combine high-resolution bathymetry acquired using the Autonomous Underwater Vehicle ABE with digital seafloor imagery collected using the remotely operated vehicle ROPOS across the axial valley of the Southern Explorer Ridge (SER) to infer the recent volcanic and tectonic processes. The SER is an intermediate spreading ridge located in the northeast Pacific. It hosts the Magic Mountain hydrothermal vent. We reconstruct the unfaulted seafloor terrain at SER based on calculations of the vertical displacement field and fault parameters. The vertical changes between the initial and the restored topographies reflect the integrated effects of volcanism and tectonism on relief-forming processes over the last 11,000-14,000 years. The restored topography indicates that the axial morphology evolved from a smooth constructional dome >500 m in diameter, to a fault-bounded graben,~500 m wide and 30-70 m deep. This evolution has been accompanied by changes in eruptive rate, with deposition of voluminous lobate and sheet flows when the SER had a domed morphology, and limited-extent low-effusion rate pillow eruptions during graben development. Most of the faults shaping the present axial valley postdate the construction of the dome. Our study supports a model of cyclic volcanism at the SER with periods of effusive eruptions flooding the axial rift, centered on the broad plateau at the summit of the ridge, followed by a decrease in eruptive activity and a subsequent dominance of tectonic processes, with minor low-effusion rate eruptions confined to the axial graben. The asymmetric shape of the axial graben supports an increasing role of extensional processes, with a component of simple shear in the spreading processes.Components: 9,800 words, 8 figures.

Segmentation and eruptive activity along the East Pacific Rise at 16°N, in relation with the nearby Mathematician hotspot

“…Phases T1 and T2 are therefore considered as ''magmatic'' phases, and T3 and T4 as ''tectonic'' phases. This model is similar to the one proposed by Cormier et al [2003] on the EPR (17 S) and Deschamps et al [2013] for the intermediate-spreading Explorer ridge.…”

Seafloor incubation experiments at deep-sea hydrothermal vents reveal distinct biogeographic signatures of autotrophic communities

“…MGCs were incubated at four vent sites in the SE caldera of Axial Seamount, over a distance of 3 km from north to south: Milky vent (marker N2), Marker 33 vent, Cloud Vent (markers N4 and N6), and Marker 113 vent ( Figure S3 , Supporting Information ). The location for these markers has been fully described (Glazer and Rouxel 2009 , Opatkiewicz et al 2009 , Deschamps et al 2013 , Fullerton et al 2017 ).…”

Microplate Evolution in the Queen Charlotte Triple Junction & Explorer Region: New Insights From Microseismicity

“…Michael et al, 1989). Alternatively, Deschamps et al (2013) suggest that current spreading is occurring tectonically, with waxing and waning in tectonic-volcanic cycles lasting over 11,000-14,000 years due to a discontinuous magmatic source (possibly intermittent episodes of magmatism from the deep mantle suggested by P. J. Michael et al (1989)).…”