Hydroacoustic monitoring of seismicity at the slow-spreading Mid-Atlantic Ridge

2002 ◽  
Vol 29 (11) ◽  
Author(s):  
Deborah K. Smith
Keyword(s):  
Mid Atlantic Ridge ◽  
Slow Spreading

scholarly journals Quantifying tectonic strain and magmatic accretion at a slow spreading ridge segment, Mid-Atlantic Ridge, 29°N

1999 ◽  
Vol 104 (B5) ◽  
pp. 10421-10437 ◽  
Author(s):  
J. Escartín ◽  
P. A. Cowie ◽  
R. C. Searle ◽  
S. Allerton ◽  
N. C. Mitchell ◽  
...  
Keyword(s):  
Spreading Ridge ◽  
Mid Atlantic Ridge ◽  
Slow Spreading

scholarly journals Young volcanism and related hydrothermal activity at 5°S on the slow-spreading southern Mid-Atlantic Ridge

2007 ◽  
Vol 8 (11) ◽  
pp. n/a-n/a ◽  
Author(s):  
K. M. Haase ◽  
S. Petersen ◽  
A. Koschinsky ◽  
R. Seifert ◽  
C. W. Devey ◽  
...  
Keyword(s):  
Hydrothermal Activity ◽  
Mid Atlantic Ridge ◽  
Slow Spreading

Hydrothermal activity on a 105-year scale at a slow-spreading ridge, TAG hydrothermal field, Mid-Atlantic Ridge 26°N

1995 ◽  
Vol 100 (B9) ◽  
pp. 17855-17862 ◽  
Author(s):  
Claude Lalou ◽  
Jean-Louis Reyss ◽  
Evelyne Brichet ◽  
Peter A. Rona ◽  
Geoffrey Thompson
Keyword(s):  
Hydrothermal Activity ◽  
Hydrothermal Field ◽  
Spreading Ridge ◽  
Mid Atlantic Ridge ◽  
Slow Spreading ◽  
Tag Hydrothermal Field

scholarly journals Microseismicity constrains on the lithospheric structure at the ridge-transform intersection at the Romanche Transform Fault and Mid-Atlantic Ridge

2020 ◽  
Author(s):  
Zhiteng Yu ◽  
Satish C. Singh ◽  
Emma Gregory ◽  
Wayne Crawford ◽  
Marcia Maia ◽  
...  
Keyword(s):  
Thermal Structure ◽  
P Wave ◽  
Seismogenic Zone ◽  
Depth Range ◽  
Thermal Variation ◽  
Transform Fault ◽  
Pull Apart Basin ◽  
Mid Atlantic Ridge ◽  
Southern Border ◽  
Slow Spreading

<p>The Romanche Transform Fault (TF) in the equatorial Atlantic Ocean is the largest oceanic transform fault on Earth, offsetting the slow-spreading (2 cm/ yr) Mid-Atlantic Ridge (MAR) by 900-km and producing a maximum age contrast at the Ridge-Transform Intersection (RTI) of 45 Myr. This offset could cause a large thermal variation in the lithosphere around the RTI, but it is not known how this thermal variation would manifest itself. Here we present a ~21-day-long micro-earthquake study using a temporary deployment of 19 ocean-bottom seismometers (OBSs) during the 2019 SMARTIES cruise. 1363 earthquakes were detected on at least three OBSs and 622 could be located, of which 351 have high location accuracy (mean semi-major-axis of 3.9 km).</p><p>Linear (HYPOSAT) and non-linear (NonLinLoc) location algorithms reveal a similar earthquake distribution. Two event groups cluster at depths of 1) 0 km to ~18 km and 2) ~20 km to 30 km. Along the Romanche TF, micro-earthquakes are located beneath the southern border of the 30 km wide transform valley; no events are observed beneath the central or northern sections of the valley. These events' depths increase rapidly and linearly from a few km at the RTI to 30 km at 40 km along the transform fault, indicating a rapid increase in the thickness of the seismogenic zone (and lithosphere) along the transform fault. The presence of earthquakes on the southern border of the transform fault, which is younger and hence warmer, suggests that these events, and hence the seismogenic zone, follow an isotherm separating the brittle-ductile boundary. The absence of seismicity beneath the centre and northern boundary of the transform fault could be due to a much colder lithosphere and hence deeper ductile-brittle boundary.  </p><p>An aseismic gap exists beneath the pull-apart basin observed on bathymetry data. Beneath the RTI, earthquakes mainly occur in the 0-18 km depth range. Eight well-constrained focal mechanisms, derived from P-wave polarities, suggest that strike-slip faulting dominates along the transform fault. Normal faults are also observed, which may be attributed to an active detachment fault or pull-apart basin formation.</p><p>From the RTI to the tip of the southern MAR segment, micro-earthquakes show an undulating focal depth distribution from north to south. They can be summarized into three clustering groups: the RTI, the 16.6°W group, and the 16.2°W group. Micro-earthquakes beneath the MAR are mainly located in the axial valley. Events in the 16.6°W group mainly occur in the mantle at depths of 12-20 km, whereas those in the 16.2°W group are located at shallow depths of 2-12 km, which is similar to that observed along other slow-spreading Mid-Ocean Ridges. This evidence indicates that there are significant variations in the along-axis thermal structure of the lithosphere along the rift axis.</p><p>ZY acknowledges the China Postdoctoral Science Foundation (2019M652041, BX20180080); DB acknowledges funding PRIN2017KY5ZX8.</p>

scholarly journals THE ORIGIN AND STRUCTURE OF THE LOWER CRUST OF OCEANS AND BACK-ARC SEAS: EVIDENCE FROM THE MARKOV DEEP (MID-ATLANTIC RIDGE) AND THE VOIKAR OPHIOLITE ASSOCIATION (POLAR URALS)

2019 ◽  
Vol 10 (1) ◽  
pp. 101-121
Author(s):  
E. V. Sharkov
Keyword(s):  
Lithospheric Mantle ◽  
Lower Crust ◽  
Structural Element ◽  
Polar Urals ◽  
Magma Sources ◽  
Mid Atlantic Ridge ◽  
Tectonic Development ◽  
Slow Spreading ◽  
Back Arc ◽  
Markov Deep

The Markov Deep (the axial part of the slow-spreading Mid-Atlantic Ridge, 6°N, Sierra Leone oceanic core complex) and the Paleozoic Voikar ophiolite association (Polar Urals) formed in the back-arc sea conditions. In both cases, the lower crust of a close structure was formed on the basements composed ofdepleted peridotites of the ancient lithospheric mantle. The available data show that the composition of the lower crust of the oceans and back-arc seas is dominated by layeredmafic-ultramafic intrusions originating from the MORB melts, and suggest a similar asthenospheric source of magmas. Sills and dykes formed from other magma sources represent the second structural element of the lower oceanic crust: in case of the ocean, mainly ferrogabbroids originating from specific melts with the OIB involvement, and, in case of the back-sea sea, gabbro-norites of the supra-subduction calc-alkaline series. In both cases, the upper crust originates frombasaltic flows that occurred later and are associated with new episodes in the tectonic development. According to [Sharkov,2012], the development of slow-spreading ridges takes place in discrete impulses and non-simultaneously along their entire length. Furthermore, oceanic core complexes (OCC) in their axial parts are the ridge segments, where spreading is resumed. At the OCC stage, newly formed basalt melts move upwards from the magma generation zone into fractures (dykes) through the lithospheric mantle, and the thickness of the lower crust is built up by sills. As spreading develops in this area, the crust becomes thicker from below due to underplating in form of large layered intrusions. The newly formed restites, in their turn, cause an increase in the lithospheric mantle thickness from below. Apparently, the lower crust formed in the back-arc seas according to a similar scenario, although complicated by the processes taking place in the subduction zone.

Evidence for accumulated melt beneath the slow-spreading Mid-Atlantic Ridge

1999 ◽  
pp. 17-38 ◽  
Author(s):  
M. C. Sinha ◽  
D. A. Navin ◽  
L. M. MacGregor ◽  
S. Constable ◽  
C. Peirce ◽  
...  
Keyword(s):  
Mid Atlantic Ridge ◽  
Slow Spreading
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