Crustal velocity structure of the Lucky Strike segment of the Mid‐Atlantic Ridge at 37°N from seismic refraction measurements

Abstract

[1] We estimate the seismic structure of the slow spreading Lucky Strike segment of the Mid-Atlantic Ridge, located approximately 300 km south of the Azores platform, using seismic reflection and seismic refraction data acquired in June 2005 as a part of the Seismic Study for Monitoring of the Mid-Atlantic Ridge (SISMOMAR) survey. The threedimensional velocity model shows an upper crustal low-velocity anomaly running parallel to the ridge axis, which is limited by the median valley bounding faults. The velocity models also show a low-velocity anomaly underlying the axial melt lens reflector located at the segment center below the Lucky Strike volcano. This lower crustal low-velocity region can be explained by elevated temperatures and possibly small amounts of melt. The lower crustal low-velocity anomaly and the axial melt lens reflector constrain the geometry of the magma chamber responsible for the construction of the Lucky Strike volcano. The presence of this magma chamber and thick crust at the segment center are consistent with a focused melt supply to the segment center.

Tracking stress and hydrothermal activity along the Eastern Lau Spreading Center using seismic anisotropy

“…Activesource seismic studies are not usually designed with the intent to measure three-dimensional variations in anisotropy, but the results thus far are encouraging. Several studies have examined one-dimensional depth-dependent anisotropy in oceanic crust, including measurements along mid-ocean ridge crests (Caress et al, 1992;MacDonald et al, 1994;Sohn et al, 1997;Barclay et al, 1998;Dunn and Toomey, 2001;Barclay and Wilcock, 2004;Tong et al, 2004;Seher et al, 2010), in older oceanic crust (>1 Ma) (Stephen, 1981(Stephen, , 1985White and Whitmarsh, 1984;Shearer and Orcutt, 1986;Detrick et al, 1998), and in back-arc basins (Hirata et al, 1992). Few prior studies have attempted to extract lateral variations in crustal anisotropy at a spreading center (e.g., Sohn et al, 1997;Dunn and Toomey, 2001;Weekly et al, 2014).…”

Constraints from melt inclusions on depths of magma residence at intermediate magma supply along the Galápagos Spreading Center

“…Only one of the analyzed melt inclusions contained a vapor bubble, although the sample set contained additional melt inclusions with bubbles. This vapor bubble was exposed, measured, and corrected for following the procedure described by Shaw et al (2010) (Table S3), wherein the ideal gas law is used to calculate the volatile content of a bubble with known volume at the pressure inferred from the dissolved volatile content of the melt inclusion itself.…”

“…After crushing and sieving selvage glass from the exterior of each sample, olivine crystals with fully enclosed glassy melt inclusions were hand-picked for analysis. Melt inclusions were exposed following methods described by Shaw et al (2010). Prior to exposing melt inclusions, they were visually inspected for the presence of vapor bubbles using a binocular microscope.…”

“…Circles, locations of samples used in this study; colors are those used for melt inclusions from each sample in Figs. 3-6. melt inclusions can preserve the pressures at which the melt inclusions were trapped, provided that the magma is volatile-saturated at the time of melt inclusion entrapment (Saal et al, 2002;Shaw et al, 2010;Wanless and Shaw, 2012).…”

Inversion of ocean-bottom seismometer (OBS) waveforms for oceanic crust structure: a synthetic study

“…Researchers attempted to invert waveform data obtained from ocean reflection experiment for elastic parameters of oceanic crust (Igel et al 1996;Mendes et al 1990) and crust and upper-mantle velocity structure from surface waves (Cara and Lévêque 1987;Debayle and Lévêque 1997). In recent years, ocean-bottom seismometer (OBS) techniques have provided increasing amount of seismic data to study the oceanic crust of localized areas, such as north-eastern Japan (Takahashi et al 2004), Lucky Strike segment (Seher et al 2010), Southwest Indian Ridge (Li et al 2015) and north-eastern South China Sea (Zhao et al 2010). Full-waveform inversion has been applied to OBS data to improve the resolution of oceanic crust structure (Jian et al 2014;Operto et al 2006;Borisov and Singh 2015).…”