Wolf–Darwin lineament and plume–ridge interaction in northern Galápagos

Abstract

[1] The Wolf-Darwin Lineament (WDL), located in the northwestern sector of the Galápagos Archipelago, lies between the focus of the Galápagos hot spot and the Galápagos Spreading Center. Consequently, most researchers have attributed its origin to the interaction between the plume and the adjacent ridge. We propose that the WDL is caused only partially by the plume-ridge interaction, and instead that it is primarily the result of tensional stresses emanating from the inside corner of the transform fault at 91°W. An additional factor that amplifies the tension in this region is the oblique orientation of the major transform fault with respect to the Nazca plate's spreading direction. This setting creates a transtensional zone whereby strain is partitioned into strike-slip motion along the transform and extension throughout the inside corner of the ridge-transform system. The area under tension is magmatic owing to the overlapping effects of the ridge and the Galápagos plume. The extensional model predicts no age-progressive volcanism, which is supported by observed age relationships. The WDL volcanoes define two distinct chemical groups: lavas erupted south of Wolf Island have compositions similar to those produced along the GSC west of 93°W, while those from the northern WDL resemble GSC lavas from the segment directly north of the lineament. This geographic distribution implies that the WDL is supplied by the same type of plume-affected mantle as the segment of the GSC that produced the lithosphere underlying the volcanoes. The observed WDL geochemical gradients are consistent with the extension model; the region under tension simply taps hybrid products of mixing at the margins of the subridge convection system and the periphery of the plume. Essentially, the stress field around the transform fault, normally not observable in a typical midocean ridge setting, is illuminated by the presence of melt from the adjacent hot spot.Components: 8821 words, 8 figures.

Mantle flow and multistage melting beneath the Galápagos hotspot revealed by seismic imaging

“…The GSC has a half-spreading rate of 28 mm yr −1 in a north-south direction 10 , a direction approximately perpendicular to the motion of the Nazca plate over the hotspot. In addition to the volcanoes that lie on the main hotspot trace, five islands and dozens of seamounts lie between the central archipelago and the GSC, and their origin 1 has been attributed to the flow of plume material towards the spreading centre 11,13,14 .…”

Patterns in Galápagos Magmatism Arising from the Upper Mantle Dynamics of Plume‐Ridge Interaction

“…The lithosphere also thins more rapidly to the N-NE, and this allows for more rapid upslope flow and melting along its base. The localized area of high magma production predicted by Model 1 implies that magma need not migrate laterally very far to feed the active Galápagos Islands as well as the numerous volcanoes and volcanic lineaments between the main islands and the GSC [e.g., Harpp and Geist, 2002;Sinton et al, 2003;Mittelstaedt et al, 2012]. The total volume flux of magma that is assumed to erupt off of the GSC and presumably as off-axis volcanism is 4.5-5.3 × 10 5 km 3 / Myr, for ξ = 0.5-1.0, respectively.…”

“…ability in mantle temperatures, compositions, melting conditions, and magmatic fluxes associated with plumeridge interaction [e.g., Harpp and White, 2001;Detrick et al, 2002;Harpp and Geist, 2002;Hooft et al, 2003;Schilling et al, 2003;Christie et al, 2005;Villagomez et al, 2007;Mittelstaedt et al, 2012]. However, what this variability indicates about the rheology of the upper mantle and the dynamical processes by which heat and mass transfer from the hotspot center toward and along the ridge axis are not well-understood.…”

A 1.5 Ma record of plume-ridge interaction at the Western Galápagos Spreading Center (91°40′–92°00′W)

“…All samples are situated within 8 km of the center profile line, except DR69 and DR72, which are located 17 and 23 km east of the profile line respectively. The profile was collected north of the spreading center to avoid overprinting by younger volcanism as is evident from the numerous volcanic edifices between the Galápagos Platform and the WGSC, largely clustered along the lineaments described above (Harpp and Geist, 2002;Sinton et al 2003;Mittelstaedt et al, 2012). A further advantage of the sampled profile is that there is no evidence for ridge jumps or overlapping spreading centers along the 50 km profile.…”

“…At the Western GSC (WGSC), possible surface expressions of plume transport towards the GSC are several arcuate chains of volcanic seamounts and islands (up to ~1.8 Ma old) in the western inside corner of the 91°W transform of which the most widely known is the Wolf-Darwin Lineament (Morgan, 1978;White et al, 1993;Sinton et al, 1996;Harpp and Geist, 2002;Mittelstaedt et al, 2012). These arcuate volcanic chains radiate from Pinta Island northwestwards until they intersect the WGSC at 91°00'W, 91°16'W, 91°47'W and 92°10'W (Sinton et al, 2003).…”