Discovery of flat seismic reflections in the mantle beneath the young Juan de Fuca Plate

Abstract

Crustal properties of young oceanic lithosphere have been examined extensively, but the nature of the mantle lithosphere underneath remains elusive. Using a novel wide-angle seismic imaging technique, here we show the presence of two sub-horizontal reflections at ∼11 and ∼14.5 km below the seafloor over the 0.51-2.67 Ma old Juan de Fuca Plate. We find that the observed reflectors originate from 300-600-m-thick layers, with an ∼7-8% drop in P-wave velocity. They could be explained either by the presence of partially molten sills or frozen gabbroic sills. If partially molten, the shallower sill would define the base of a thin lithosphere with the constant thickness (11 km), requiring the presence of a mantle thermal anomaly extending up to 2.67 Ma. In contrast, if these reflections were frozen melt sills, they would imply the presence of thick young oceanic lithosphere (20-25 km), and extremely heterogeneous upper mantle.

Semibrittle seismic deformation in high-temperature mantle mylonite shear zone along the Romanche transform fault

“…The longitude is shown on the top for reference. Isotherms are calculated using a plate cooling model ( 53 , 54 ) and averaging both sides of the transforms (see Materials and Methods). The solid green line indicates the 800°C isotherm extracted from the thermal model by Ligi et al ( 3 ).…”

“…The temperature contours in Fig. 2B were calculated using a plate cooling model (52)(53)(54), with a lithospheric thickness of 106 km (8). We assumed the mantle potential temperature is 1350°C (54).…”

Discovery of distinct lithosphere-asthenosphere boundary and the Gutenberg discontinuity in the Atlantic Ocean

“…3 ). The flatness of the reflection and the mismatch with the isotherms could be due to the fact that the thermal models do not consider the effects of hydrothermal circulation that would affect the lithosphere at younger ages and flatten the isotherms ( 18 ). Beyond ~5 Ma, the LAB reflection starts dipping steeply until almost ~12 Ma with a slope of 2.5 km/Ma (fig.…”

“…We use a method to determine the amplitude of the mantle reflections ( 13 , 18 ) in which we compare the observed amplitude of the target reflection with a reference reflection. We took the seafloor as the reference reflection and picked the maximum positive amplitude within a ±0.2-s window.…”

Seismic Attenuation at the Equatorial Mid‐Atlantic Ridge Constrained by Local Rayleigh Wave Analysis From the PI‐LAB Experiment

“…A number of receiver functions (RFs) studies also find a strong, sharp discontinuity beneath the oceanic plates (Akuhara et al, 2021;Hannemann et al, 2017;Kawakatsu et al, 2009;Kumar & Kawakatsu, 2011;Mark et al, 2021;Reeves et al, 2015;Rychert & Shearer, 2011;Rychert et al, 2018aRychert et al, , 2018bRychert et al, , 2021Schmerr, 2012;Tonegawa et al, 2019;Zhang & Olugboji, 2021). Active source imaging find unexpected sharp discontinuities associated with channels (Mehouachi & Singh, 2018;Qin et al, 2020;Stern et al, 2015). Magnetotelluric imaging also finds a low resistivity channels that are also not explained by thermal models (Naif et al, 2013).…”