scholarly journals Crustal accretion at a sedimented spreading center in the Andaman Sea

Geology ◽  
2016 ◽  
Vol 44 (5) ◽  
pp. 351-354 ◽  
Author(s):  
Aurélie Jourdain ◽  
Satish C. Singh ◽  
Javier Escartin ◽  
Yann Klinger ◽  
K.A. Kamesh Raju ◽  
...  
Keyword(s):  
Andaman Sea ◽  
Spreading Center ◽  
Crustal Accretion

scholarly journals Assessing the impact of sedimentation on fault spacing at the Andaman Sea spreading center

Geology ◽  
2020 ◽  
Author(s):  
Clément de Sagazan ◽  
Jean-Arthur Olive
Keyword(s):  
Active Faults ◽  
Spreading Rate ◽  
Andaman Sea ◽  
Spreading Center ◽  
Normal Faults ◽  
Mid Ocean Ridge ◽  
Plate Separation ◽  
Slow Spreading ◽  
Ocean Ridge ◽  
The Impact

The stabilizing effect of surface processes on strain localization, albeit predicted by several decades of geodynamic modeling, remains difficult to document in real tectonic settings. Here we assess whether intense sedimentation can explain the longevity of the normal faults bounding the Andaman Sea spreading center (ASSC). The structure of the ASSC is analogous to a slow-spreading mid-ocean ridge (MOR), with symmetric, evenly spaced axis-facing faults. The average spacing of faults with throws ≥100 m (8.8 km) is however large compared to unsedimented MORs of commensurate spreading rate, suggesting that sedimentation helps focus tectonic strain onto a smaller number of longer-lived faults. We test this idea by simulating a MOR with a specified fraction of magmatic plate separation (M), subjected to a sedimentation rate (s) ranging from 0 to 1 mm/yr. We find that for a given M ≥ 0.7, increasing s increases fault lifespan by ~50%, and the effect plateaus for s > 0.5 mm/yr. Sedimentation prolongs slip on active faults by leveling seafloor relief and raising the threshold for breaking new faults. The effect is more pronounced for faults with a slower throw rate, which is favored by a greater M. These results suggest that sedimentation-enhanced fault lifespan is a viable explanation for the large spacing of ASSC faults if magmatic input is sufficiently robust. By contrast, longer-lived faults that form under low M are not strongly influenced by sedimentation.

Rock and paleomagnetic evidence for the existence and nature of a Cayman Trough spreading center

1978 ◽  
Vol 15 (12) ◽  
pp. 1930-1940 ◽  
Author(s):  
M. J. Clark ◽  
J. M. Hall ◽  
J. W. Peirce
Keyword(s):  
Central Valley ◽  
Spreading Center ◽  
Small Scale ◽  
Low Temperature Oxidation ◽  
Crustal Accretion ◽  
Temperature Oxidation ◽  
Magnetic Parameters ◽  
Mid Atlantic Ridge ◽  
Curie Temperatures

Rock and paleomagnetic measurements have been made on a set of 54 basalts dredged from 17 stations located within the central valley of the Cayman Trough. Seventeen of the samples could be oriented with respect to the in situ vertical by the use of lava cooling ledges and stalactites.Peak remanent intensities in the Cayman Trough are lower than peak Mid-Atlantic Ridge values by a factor of 2 or 3 even after allowance is made for the latitudinal variation in geomagnetic field intensity. This difference is likely to be the result of the combined effects of relatively low saturation magnetization and more advanced low temperature oxidation of titanomagnetite in the Cayman Trough basalts.Five young, reversely magnetized basalts, similar to those found on the Mid-Atlantic Ridge, occur in the Cayman Trough sample set.Plots of the magnetic parameters of the pillow basalts with distance from the axis of the trough show broad highs or lows associated with the axis. Our interpretation is that crustal formation in the central valley has occurred recently, but it has either been rather diffuse or is now much disturbed tectonically on a small scale in comparison with the Mid-Atlantic Ridge. Analysis of the distribution of Curie temperatures suggests that crustal accretion has been slow (0.1–0.4 cm year−1 half-rate) and may have ceased in the area studied at about 0.6 Ma BP.

scholarly journals Supplemental Material: Assessing the impact of sedimentation on fault spacing at the Andaman Sea spreading center

2020 ◽  
Author(s):  
Clément de Sagazan ◽  
Jean-Arthur Olive
Keyword(s):  
Source Code ◽  
Andaman Sea ◽  
Spreading Center ◽  
Visualization Tools ◽  
The Impact

Supplemental text, supplemental Figures S1–S3, Tables S1 and S2, source code (in a .zip file), visualization tools, and videos.<br>

scholarly journals Supplemental Material: Assessing the impact of sedimentation on fault spacing at the Andaman Sea spreading center

2020 ◽  
Author(s):  
Clément de Sagazan ◽  
Jean-Arthur Olive
Keyword(s):  
Source Code ◽  
Andaman Sea ◽  
Spreading Center ◽  
Visualization Tools ◽  
The Impact

Supplemental text, supplemental Figures S1–S3, Tables S1 and S2, source code (in a .zip file), visualization tools, and videos.<br>

Fault spacing enhanced by sedimentation at the Andaman Sea spreading center

2020 ◽  
Author(s):  
Clement de Sagazan ◽  
Jean-Arthur Olive
Keyword(s):  
Sedimentation Rate ◽  
Strain Localization ◽  
Andaman Sea ◽  
Spreading Center ◽  
Normal Faults ◽  
Plate Boundaries ◽  
Spreading Ridge ◽  
Seismic Reflection Data ◽  
Wide Range ◽  
The Impact

&lt;p&gt;Tectonic models commonly predict that erosion and sedimentation enhance strain localization onto a few major faults at subaerial plate boundaries such as orogens and continental rifts. By contrast, the influence of &amp;#8220;seafloor-shaping processes&amp;#8221; on the tectonic makeup of submarine plate boundaries has received far less attention. Submarine plate boundaries are however subjected to a wide range of sedimentation rates, and as such constitute excellent natural laboratories to investigate the influence of sediment deposition on seafloor shaping tectonics. Here we assess the impact of sedimentation on fault development at the Andaman Sea spreading center (ASSC), by comparing it to unsedimented mid-ocean ridges (MORs) of commensurate spreading rate (38 mm/yr).&lt;/p&gt;&lt;p&gt;Seafloor spreading has been occurring for the last ~4 Myrs along the ASSC, which is located at the center of a pull-apart basin in the back-arc domain of the Sumatra subduction. Recent bathymetric and seismic reflection data show that fault-induced topography at the ASSC is buried under a sedimentary layer of thickness up to 1.5&amp;#8211;2 km. This massive sedimentary input is largely provided by the Irawaddy river, and amounts to an average deposition rate of ~0.5 mm/yr over the last 4 Myrs. The structure of the ASSC is analogous to an intermediate- / slow-spreading MOR, with symmetric, evenly spaced axis-facing normal faults. The characteristic spacing of these faults is however unusually large (8.8 km) and their dips are unusually shallow (~30&amp;#186;) compared to typical MORs.&lt;/p&gt;&lt;p&gt;We use numerical modeling to assess whether sedimentation can explain the unusual longevity of ASSC normal faults. We use the FLAC method to model a spreading ridge subjected to a sedimentation rate ranging from 0 to 1 mm/yr. In our models, a fraction &lt;em&gt;M &lt;/em&gt;of plate separation (between 0.6 and 0.8) is taken up by magma injection. This allows the sequential growth of regularly-spaced, axis-facing faults. In the absence of sedimentation, fault lifespan and spacing decrease with increasing &lt;em&gt;M&lt;/em&gt;. We find that, for a given &lt;em&gt;M&lt;/em&gt; of 0.7 or above, increasing the sedimentation rate increases fault lifespan by as much as ~50%, and the effect plateaus for rates &gt; 0.5 mm/yr. By contrast, we cannot resolve any significant effect of sedimentation on fault lifespan for &lt;em&gt;M &lt;/em&gt;&lt; 0.7. The effect of sedimentation is more pronounced on fault spacing, with rates as fast as 1 mm/yr nearly suppressing the decrease in spacing with increasing &lt;em&gt;M&lt;/em&gt;.&lt;/p&gt;&lt;p&gt;We propose that sedimentation prolongs slip on active faults by leveling seafloor relief and raising the threshold for breaking new faults. The effect is more pronounced for faults with a slower throw rate, which is favored by a greater &lt;em&gt;M&lt;/em&gt; fraction. Our simulations show that enhancement of fault lifespan by sediment blanketing is a viable explanation for the anomalously high spacing of normal faults at the ASSC. This could therefore constitute the first field evidence of topographic reworking promoting strain localization at a major plate boundary, a mechanism predicted by over two decades of geodynamic modeling.&lt;/p&gt;

scholarly journals Diffuse spreading, a newly recognized mode of crustal accretion in the southern Mariana Trough backarc basin

Geosphere ◽  
2021 ◽  
Author(s):  
Jonathan D. Sleeper ◽  
Fernando Martinez ◽  
Patricia Fryer ◽  
Robert J. Stern ◽  
Katherine A. Kelley ◽  
...  
Keyword(s):  
Plate Tectonics ◽  
Volcanic Rocks ◽  
High Water ◽  
Threshold Effect ◽  
Philippine Sea Plate ◽  
Spreading Center ◽  
Normal Extension ◽  
Crustal Accretion ◽  
Side Scan Sonar ◽  
Diffuse Spreading

South of the latitude of Guam, the Mariana Trough exhibits both trench-parallel and trench-normal extension. In this study, we examined the locus of trench-normal extension separating the Philippine Sea plate from the broadly deforming Mariana platelet. Along this boundary, we identified three distinct modes of extension and described their distinguishing characteristics using deep- and shallow-towed side-scan sonar and ship multibeam data along with regional geophysical, geochemical, and seismicity data. In the west, the Southwest Mariana Rift is an active tectonic rift exhibiting abundant strong earthquakes up to mb 6.7 and limited evidence of volcanism. In the east, the Malaguana-Gadao Ridge is a seafloor spreading center producing few and weak earthquakes less than mb 5. Between these zones, there is an ~20–40-km-wide and ~120-km-long area of high acoustic backscatter characterized by closely spaced volcano- tectonic ridges and small volcanic cones with distributed intermediate-strength seismicity up to mb 5.7. Fresh-looking volcanic rocks with high water contents and strong arc chemical affinities have been recovered from the high-backscatter zone. We interpret this morphologically and geophysically distinct zone as undergoing diffuse spreading, a distributed form of magmatic crustal accretion where new crust forms within a broad zone tens of kilometers across rather than along a narrow spreading axis. Diffuse spreading appears to be a rheological threshold effect enabled by slow opening rates and a high slab-fluid flux that facilitate the formation of a broad zone of weak hydrous lithosphere, within which new crust is accreted. Our findings describe a poorly understood process in plate tectonics, and observations of similar terrains in other backarc basins suggest that this process is not unique to the Mariana Trough.

GAS HYDRATE SATURATION ESTIMATED FROM ACOUSTIC IMPEDANCE IN THE ANDAMAN SEA, INDIA

2014 ◽  
Vol 33 (2) ◽  
pp. 163-168
Author(s):  
Xiujuan WANG ◽  
Jiliang WANG ◽  
Wei LI ◽  
Nittala Satyavani ◽  
Kalachand Sain
Keyword(s):  
Gas Hydrate ◽  
Acoustic Impedance ◽  
Andaman Sea ◽  
Hydrate Saturation
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