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

Abstract

The 16 N segment of the East Pacific Rise is the most overinflated and shallowest of this fastspreading ridge, in relation with an important magma flux due to the proximity of the Mathematician hotspot. Here, we analyze the detailed morphology of the axial dome and of the Axial Summit Trough (AST), the lava morphology, and the geometry of fissures and faults, in regard to the attributes of the magma chamber beneath and of the nearby hotspot. The data used are 1 m resolution bathymetry combined with seafloor photos and videos. At the dome summit, the AST is highly segmented by 10 third-order and fourth-order discontinuities over a distance of 30 km. Often, two contiguous and synchronous ASTs coexist. Such a configuration implies a wide (1100 m minimum) zone of diking. The existence of contiguous ASTs, their mobility, their general en echelon arrangement accommodating the bow shape of the axial dome toward the hotspot, plus the existence of a second magma lens under the western half of the summit plateau, clearly reflect the influence of the hotspot on the organization of the spreading system. The different ASTs exhibit contrasted widths and depths. We suggest that narrow ASTs reflect an intense volcanic activity that produces eruptions covering the tectonic features and partially filling the ASTs. AST widening and deepening would indicate a decrease in volcanic activity but with continued dike intrusions at the origin of abundant sets of fissures and faults that are not masked by volcanic deposits.

Detailed Analysis of Near Tectonic Features Along the East Pacific Rise at 16°N, Near the Mathematician Hot Spot

“…We present a detailed tectonic analysis of the 16°N segment of the EPR using near‐bottom microbathymetry, photographs, videos, and direct visual observations made from a submersible. These detailed analyses extend the morphological descriptions presented by Le Saout et al (). These new data allow us to evaluate the small‐scale interactions between volcanic and tectonic processes near ASTs, the nucleation and evolution of faulting patterns, and the distribution of tectonic strain in the context of an unusual spreading segment influenced by a hot spot.…”

“…Between 15°36′N and 15°53′N, based on data from Macdonald et al () and Carbotte et al (), and on high‐resolution bathymetry and videos (the same used in our present study), Le Saout et al () identified six 4–9.5 km long third‐order spreading segments referred as subsegments (Figure ). These subsegments are characterized by 10 distinct well‐defined ASTs of variable depth (1 to 40 m) and width (10 to 1,000 m).…”

“…It is the broadest and shallowest segment of the entire northern EPR with an unusually prominent along‐axial‐ridge, up to 15 km wide at its base and up 750 m high with respect to the adjacent abyssal hills (e.g., Baker et al, ; Carbotte et al, ; Carlut et al, ; Le Saout et al, ; Scheirer & Macdonald, ; Weiland & Macdonald, ). This morphology has been attributed to the influence of a hot spot (e.g., Carbotte et al, ; Carlut et al, ; Scheirer & Macdonald, ; Weiland & Macdonald, ), named “Mathematician hot spot” (Le Saout et al, ; Mougel et al, , ). A relationship between these features is supported by (1) the presence of the Mudskipper volcanic seamount ridge, located less than 5 km away from the ridge axis, on the western flank of the 16°N axial rise (e.g., Baker et al, ; Carlut et al, ; Macdonald et al, ; Weiland & Macdonald, ); (2) the location of the shallowest part of the dome, at 2,200 m depth, near the projected intersection of the Mudskipper volcanic chain with the ridge axis (15°42′N); (3) a geochemical anomaly identified in the axis‐lavas that indicates a mixing between a MORB and a more enriched and heterogeneous source associated with the hot spot magmatism (Mougel et al, , ); and (4) the presence of extinct spreading axes east of the ridge axis, indicating at least two westward jumps of 7 and 9 km in the direction of the hot spot at 150 and 300 kyr (e.g., Carbotte et al, ; Shah & Buck, ; Weiland & Macdonald, ).…”

“…The subsegments are defined by discontinuities at 15°37′N, 15°41′N, 15°45.5′N, 15°48′N, and 15°51′N, and these discontinuities are either lateral offsets (by 200–600 m), abrupt variations of the geometry of the ASTs (width and depth), or changes in the trend (by up to 5°) of the ASTs. Morphological discontinuities also often correlate with discontinuities of the axial melt lens (Le Saout et al, ).…”

Geology of the Alarcon Rise, Southern Gulf of California

“…It still falls far short of the estimated 11 km off axis advance of the 220 km 2 flow at 8°S (Macdonald et al, ). As Escartin et al () and Le Saout et al () note, the advance of off‐axis flows is stopped when they reach a fault too tall to overtop. The flows mapped on AR3 extend 3.5 km to the scarp at the base of the next older abyssal hill to the west, where the crustal age is inferred to be about 190 ka.…”