scholarly journals Southern Chile crustal structure from teleseismic receiver functions: Responses to ridge subduction and terrane assembly of Patagonia

Geosphere ◽  
2019 ◽  
Vol 16 (1) ◽  
pp. 378-391 ◽  
Author(s):  
E.E. Rodriguez ◽  
R.M. Russo
Keyword(s):  
Crustal Structure ◽  
Triple Junction ◽  
Oceanic Lithosphere ◽  
Receiver Functions ◽  
Moho Depth ◽  
The South ◽  
Ridge Subduction ◽  
The North ◽  
Tectonic Processes ◽  
Chile Triple Junction

Abstract Continental crustal structure is the product of those processes that operate typically during a long tectonic history. For the Patagonia composite terrane, these tectonic processes include its early Paleozoic accretion to the South America portion of Gondwana, Triassic rifting of Gondwana, and overriding of Pacific Basin oceanic lithosphere since the Mesozoic. To assess the crustal structure and glean insight into how these tectonic processes affected Patagonia, we combined data from two temporary seismic networks situated inboard of the Chile triple junction, with a combined total of 80 broadband seismic stations. Events suitable for analysis yielded 995 teleseismic receiver functions. We estimated crustal thicknesses using two methods, the H-k stacking method and common conversion point stacking. Crustal thicknesses vary between 30 and 55 km. The South American Moho lies at 28–35 km depth in forearc regions that have experienced ridge subduction, in contrast to crustal thicknesses ranging from 34 to 55 km beneath regions north of the Chile triple junction. Inboard, the prevailing Moho depth of ∼35 km shallows to ∼30 km along an E-W trend between 46.5°S and 47°S; we relate this structure to Paleozoic thrust emplacement of the Proterozoic Deseado Massif terrane above the thicker crust of the North Patagonian/Somún Cura terrane along a major south-dipping fault.

scholarly journals The crustal structure of the Northeast Greenland continental shelf across the extension of the West Jan Mayen Fracture Zone

2020 ◽  
Author(s):  
Thomas Funck ◽  
Andreas Skifter Madsen ◽  
Christian Berndt ◽  
Anke Dannowski ◽  
Dieter Franke ◽  
...  
Keyword(s):  
Continental Margin ◽  
Crustal Structure ◽  
Fracture Zone ◽  
Seismic Refraction ◽  
Moho Depth ◽  
Gravity Modeling ◽  
The South ◽  
The West ◽  
The North ◽  
Lower Crustal

<p>Between August and October 2017, the German research vessel Maria S. Merian acquired geophysical data along the Northeast Greenland continental margin during its cruise MSM-67. This included seismic reflection and wide-angle/refraction data as well as potential field data. In comparison to the conjugate mid-Norwegian margins, the Northeast Greenland continental margin is less well studied. Hence, one of the key objectives of the expedition was to improve the understanding of the opening of the Northeast Atlantic Ocean and the evolution of the conjugate margin pair. One particular goal of the experiment was the mapping of the lateral extent of magmatism associated with the opening and how this relates to margin segmentation.</p><p>Seismic refraction line BGR17-2R2 runs on the shelf and parallel to the coast of NE Greenland. It crosses the landward extension of the West Jan Mayen Fracture Zone that separates the seafloor spreading along the Mohn’s Ridge in the north from the Kolbeinsey Ridge in the south. A total of 29 ocean bottom seismometers (OBS) equipped with a hydrophone and three-component geophones were deployed along the 235-km-long line. The seismic source was a G-gun array with a total volume of 4840 cubic inches (79.3 L) fired every 60 s. In the central and northern part of the line, two older seismic refraction profiles are crossed (lines AWI2003-500 and 400, respectively), which run perpendicular to the margin and can be used for lateral correlation of the crustal structure.</p><p>For the initial analysis, a velocity model was developed by forward and inverse modeling of travel times using the program RAYINVR. Later, a travel time tomography was carried out employing the code Tomo2D and performing a Monte Carlo analysis with 100 inversions from which an average model was calculated. The models show a 1-to 3-km-thick sedimentary column with velocities ranging from 1.6 to 4.0 km/s. In the central and northern part, a 1-km-thick layer with velocities around 4.6 km/s is underlying the sediments and is interpreted to consist of volcanic material. Below and extending along the entire length of the line, velocities of 5.6 km/s are observed in a layer that is ~2 km thick. The crystalline basement has a depth around 5 km with higher velocities in the north (6.5 km/s) than in the south (6.3 km/s). High lower crustal velocities (>7.2 km/s) are observed along the entire line and either indicate magmatic underplating or lower crustal sill intrusions. The Moho depth is seismically constrained along the central part of the line where it is 30 km. Gravity modeling suggest a depth of 35 and 27 km at the southern and northern limit of the profile, respectively. Within the zone of the landward extension of the West Jan Mayen Fracture Zone, a decrease in mid-crustal velocities by 0.2 km/s is observed. Slightly to the north of the fracture zone, a 50-km-wide zone with increased mid-and lower crustal velocities may indicate an igneous center in an area where the upper volcanic layer is shallowest.</p>

New seismic, magnetic, and gravity constraints on the crustal structure of the Lincoln Sea continent–ocean transition

1994 ◽  
Vol 31 (6) ◽  
pp. 905-918 ◽  
Author(s):  
D. A. Forsyth ◽  
M. Argyle ◽  
A. Okulitch ◽  
H. P. Trettin
Keyword(s):  
Crustal Structure ◽  
Velocity Structure ◽  
Seismic Survey ◽  
Moho Depth ◽  
Gravity Gradient ◽  
Volcanic Complex ◽  
Lomonosov Ridge ◽  
The North ◽  
Shelf Slope ◽  
Volcanic Margin

A new seismic model of Canada's northeasternmost margin indicates a complex continent to ocean transition with similarities to both volcanic and nonvolcanic margins. The crustal structure beneath the Lincoln Sea includes: (i) a continental shelf with a uniform 3 km thick cover (velocity = 1.8–3.6 km/s) overlying at least 6 km of synrift(?) basinal strata (velocity = 4.3–4.9 km/s) that terminate near the base of the slope; (ii) a thick unit of oceanic layer 2-type velocity (5.4–5.8 km/s) overlying a velocity structure resembling a volcanic margin; (iii) a high-velocity lower crust (> 7.4 km/s) resembling North Atlantic volcanic margins or the Alpha Ridge but different from the Lomonosov Ridge near the North Pole; (iv) a change in velocity structure 15–25 km seaward of the shelf–slope break that coincides with a distinct short-wavelength, high-amplitude magnetic anomaly and the centre of a steep gravity gradient; and (v) a suggested Moho depth of 23 km beneath the Lincoln Sea margin along 63°W.The velocity structure beneath the Lincoln Sea is transitional from thinned continental crust beneath the shelf to a structure with oceanic affinities to the north. Typical, 10 km thick oceanic crust is not apparent beneath the northern Lincoln Sea. The upper crustal structure resembles a rifted, nonvolcanic margin such as the Goban Spur, while the high lower crustal velocity resembles a volcanic margin like the Hatton Bank or an oceanic complex like the Alpha Ridge. North of the seismic survey, the enigmatic Lincoln Sea plateau may be an intruded Lomonosov Ridge segment or a volcanic complex similar to the Alpha Ridge or the Morris Jesup Plateau.

Magmatic–tectonic effects of high thermal regime at the site of active ridge subduction: the Chile Triple Junction model

2000 ◽  
Vol 326 (3-4) ◽  
pp. 255-268 ◽  
Author(s):  
Yves Lagabrielle ◽  
Christèle Guivel ◽  
René C. Maury ◽  
Jacques Bourgois ◽  
Serge Fourcade ◽  
...  
Keyword(s):  
Thermal Regime ◽  
Triple Junction ◽  
Ridge Subduction ◽  
Chile Triple Junction

Linking collision, slab break-off and subduction polarity reversal in the evolution of the Central Indian Tectonic Zone

2020 ◽  
Vol 157 (2) ◽  
pp. 340-350
Author(s):  
Tanzil Deshmukh ◽  
N. Prabhakar
Keyword(s):  
Polarity Reversal ◽  
The South ◽  
Tectonic Zone ◽  
The North ◽  
Tectonic Processes ◽  
South Indian ◽  
Indian Craton ◽  
Directed System ◽  
Central Indian Tectonic Zone ◽  
Collisional Regime

AbstractThe Central Indian Tectonic Zone demarcates the zone of amalgamation between the North Indian Craton and the South Indian Craton. Presently, the major controversies in the existing tectonic models of the Central Indian Tectonic Zone revolve around the direction of subduction and the precise timing of accretion between the North Indian Craton and the South Indian Craton. A new model for the tectonic evolution of the Central Indian Tectonic Zone is postulated in this contribution, based on recent geological and geophysical evidence, combined with previously documented tectonic configurations. The present study employs the slab break-off hypothesis and subsequent polarity reversal to explain the tectonic processes involved in the evolution of the Central Indian Tectonic Zone. We propose that the subduction initiated (c. 2.5 Ga) in a S-directed system producing island-arc sequences on the South Indian Craton. The southward subduction regime culminated with slab break-off underneath the South Indian Craton between c. 1.65 Ga and 1.55 Ga, which subsequently induced subduction polarity reversal and set the course for N-directed subduction (<1.55 Ga). The final closure along the Central Indian Tectonic Zone is governed by the collisional regime during the Sausar Orogeny (1.0–0.9 Ga).

Thermal regime around the Chile Triple Junction based on JAMSTEC MR18-06 cruise 'EPIC'

2020 ◽  
Author(s):  
Masataka Kinoshita ◽  
Ryo Anma ◽  
Yuka Yokoyama ◽  
Kosuke Ohta ◽  
Yusuke Yokoyama ◽  
...  
Keyword(s):  
Heat Flow ◽  
Sedimentation Rate ◽  
Thermal Regime ◽  
Triple Junction ◽  
Accretionary Prism ◽  
Age Dating ◽  
Spreading Center ◽  
Ridge Axis ◽  
Ridge Subduction ◽  
Chile Triple Junction

&lt;p&gt;&lt;span&gt;The Chile triple junction (CTJ) is a unique place where a spreading center of mid-ocean ridge is subducting near the Taitao peninsula. Around CTJ, presence of high heat flow on the continental slope and near-trench young granitic rocks on the Taitao peninsula suggests the thermal and petrological impact of subducting ridge on the continental side. The tectonic history of the southeast Pacific since early Cenozoic to the present suggests that ridge subduction continuously occurred along the Chile trench, which migrated northward.&lt;/span&gt;&lt;/p&gt;&lt;p&gt;&lt;span&gt;In January 2019, the MR18-06 cruise Leg 2 was conducted at CTJ, as a part of 'EPIC' expedition by using R.V Mirai of JAMSTEC. During the leg, we completed 4 SCS lines, 6 piston coring with heat flow measurements, 2 dredges, and underway geophysics observations, as well as deployment of 13 OBSs. Coring/heatflow sites were located across the ridge axis, HP5 on the seaward plateau of axial graben, HP1/HP2/HP6 on the axis, and HP3/HP7 on the forearc slope near the trench axis. The primary object of heat flow measurement at CTJ is to better constrain the thermal regime around CTJ by adding new data right above CTJ. The key question is whether CTJ is thermally dominated by ridge activity (magmatic, tectonic, and/or hydrothermal) or by subduction initiation (tectonic thickening, accretion, and/or erosion). The ultimate goal is to model the temperature at the plate interface from the heat flow and other data, and to infer how the thermal regime at CTJ contributes the seismogenic behavior at the M~9 megathrust zone. &lt;/span&gt;&lt;/p&gt;&lt;p&gt;&lt;span&gt;Onboard and post-cruise measurements include; bulk density, porosity, Vp, resistivity, CT imags, iTracks element scan, age dating, etc. Core saples seaward of ridge axis (HP5) has few turbidites with higher density (~2 g/cc) and low sedimentation rate (SR; 0.2 m/ky), whereas cores on the axis the density are turbidite dominant with lower (1.6~1.8 g/cc) and very high SR (1~3 m/ky). The accretionary prism (landward of trench) cores have the density of 1.6~1.7 g/cc and SR=0.5~1 m/ky. They suggest that the turbidite covers only the axial graben. &lt;/span&gt;&lt;/p&gt;&lt;p&gt;&lt;span&gt;Heat flow in the axial graben range 140-210 mW/m^2, which is lower than on the seaward plateau (370 mW/m^2). This apparent controversy may be due to lower magmatic activity and/or high sedimentation rate on the axis. The lower spreading rate (2.6 cm/yr one side) and the rapid convergent rate at the trench (7.2 cm/yr) may suppress sufficient magma supply or hydrothermal circulation. Heat flow on the accretionary prism (230 mW/m^2) is higher than borehole or BSR-derived heat flow (~&lt;100 mW/m^2). It is suggestive of fluid upwelling along the decollement as proposed in the previous study. Some numerical thermal models will be presented to show the effect of ridge subduction. &lt;/span&gt;&lt;/p&gt;

scholarly journals Petrogenesis of the ridge subduction-related granitoids from the Taitao Peninsula, Chile Triple Junction Area

2013 ◽  
Vol 47 (2) ◽  
pp. 167-183 ◽  
Author(s):  
YOSHIAKI KON ◽  
TSUYOSHI KOMIYA ◽  
RYO ANMA ◽  
TAKAFUMI HIRATA ◽  
TAKAZO SHIBUYA ◽  
...  
Keyword(s):  
Triple Junction ◽  
Junction Area ◽  
Ridge Subduction ◽  
Chile Triple Junction

An assessment of the megathrust earthquake potential of the Cascadia subduction zone

1988 ◽  
Vol 25 (6) ◽  
pp. 844-852 ◽  
Author(s):  
Garry C. Rogers
Keyword(s):  
United States ◽  
Subduction Zone ◽  
Subduction Zones ◽  
Oceanic Lithosphere ◽  
The United States ◽  
Cascadia Subduction Zone ◽  
The South ◽  
The North ◽  
The Pacific ◽  
Juan De Fuca

The active tectonic setting of the southwest coast of Canada and the Pacific northwest coast of the United states is dominated by the Cascadia subduction zone. The zone can be divided into four segments where oceanic lithosphere is converging independently with the North American plate: the Winona and the Explorer segments in the north, the larger Juan de Fuca segment that extends into both Canada and the United States, and the Gorda segment in the south. The oceanic lithosphere entering the Cascadia subduction zone in all segments is extremely young, less than 10 Ma. Of the other six zones around the Pacific where young (< 20 Ma) lithosphere is being subducted, five have had major thrust earthquakes (megathrust events) on the subduction interface in historic time. An estimation based on potential area of rupture gives maximum possible earthquake magnitudes along the Cascadia subducting margin of 8.2 for the Winona segment, 8.5 for the Explorer segment, 9.1 for the Juan de Fuca segment, and 8.3 for the South Gorda segment. Repeat times for maximum earthquakes, based on the ratios of seismic slip to total slip observed in other subduction zones, are predicted to be up to several hundred years for each segment, well beyond recorded history of the west coast, which began about 1800. Thus the lack of historical seismicity information provides a few constraints on the assessment of the seismic potential of the subduction zone.

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