An improved velocity model for the crust and upper mantle along the central mobile belt of the Newfoundland Appalachian orogen and its offshore extension

1998 ◽  
Vol 35 (11) ◽  
pp. 1238-1251 ◽  
Author(s):  
Deping Chian ◽  
François Marillier ◽  
Jeremy Hall ◽  
Garry Quinlan
Keyword(s):  
Upper Mantle ◽  
Lower Crust ◽  
Velocity Structure ◽  
Sedimentary Basins ◽  
Velocity Model ◽  
Mobile Belt ◽  
Wide Angle ◽  
Crust And Upper Mantle ◽  
Angle Data ◽  
Appalachian Orogen

New modelling of wide-angle reflection-refraction data of the Canadian Lithoprobe East profile 91-1 along the central mobile belt of the Newfoundland Appalachian orogen reveals new features of the upper mantle, and establishes links in the crust and upper mantle between existing land and marine wide-angle data sets by combining onshore-offshore recordings. The revised model provides detailed velocity structure in the 30-34 km thick crust and the top 30 km of upper mantle. The lower crust is characterized by a velocity of 6.6-6.8 km/s onshore, increasing by 0.2 km/s to the northeast offshore beneath the sedimentary basins. This seaward increase in velocity may be caused by intrusion of about 4 km of basic rocks into the lower crust during the extension that formed the overlying Carboniferous basins. The Moho is found at 34 km depth onshore, rising to 30 km offshore to the northeast with a local minimum of 27 km. The data confirm the absence of deep crustal roots under the central mobile belt of Newfoundland. Our long-range (up to 450 km offset) wide-angle data define a bulk velocity of 8.1-8.3 km/s within the upper 20 km of mantle. The data also contain strong reflective phases that can be correlated with two prominent mantle reflectors. The upper reflector is found at 50 km depth under central Newfoundland, rising abruptly towards the northeast where it reaches a minimum depth of 36 km. This reflector is associated with a thin layer (1-2 km) unlikely to coincide with a discontinuity with a large cross-boundary change in velocity. The lower reflector at 55-65 km depths is much stronger, and may have similar origins to reflections observed below the Appalachians in the Canadian Maritimes which are associated with a velocity increase to 8.5 km/s. Our data are insufficient for discriminating among various interpretations for the origins of these mantle reflectors.

Crust and upper mantle velocity structure of the Intermontane belt, southern Canadian Cordillera

1992 ◽  
Vol 29 (7) ◽  
pp. 1530-1548 ◽  
Author(s):  
B. C. Zelt ◽  
R. M. Ellis ◽  
R. M. Clowes ◽  
E. R. Kanasewich ◽  
I. Asudeh ◽  
...  
Keyword(s):  
Upper Mantle ◽  
Lower Crust ◽  
Velocity Structure ◽  
P Wave ◽  
Seismic Reflection Profile ◽  
Wide Angle ◽  
Low Velocity ◽  
Crust And Upper Mantle ◽  
Middle Crust ◽  
Refraction Data

As part of the Lithoprobe Southern Cordillera transect, seismic refraction data were recorded along a 330 km long strike profile in the Intermontane belt. An iterative combination of two-dimensional traveltime inversion and amplitude forward modelling was used to interpret crust and upper mantle P-wave velocity structure. This region is characterized by (i) a thin near-surface layer with large variations in velocity between 2.8 and 5.4 km/s, and low-velocity regions that correlate well with surface expressions of Tertiary sedimentary and volcanic rocks; (ii) an upper and middle crust with low average velocity gradient, possibly a weak low-velocity zone, and lateral velocity variations between 6.0 and 6.4 km/s; (iii) a distinctive lower crust characterized by significantly higher average velocities relative to midcrustal values beginning at 23 km depth, approximately 8 km thick with average velocities of 6.5 and 6.7 km/s at top and base; (iv) a depth to Moho, as defined by wide-angle reflections, that averages 33 km with variations up to 2 km; and (v) a Moho transition zone of depth extent 1–3 km, below which lies the upper mantle with velocities decreasing from 7.9 km/s in the south to 7.7 km/s in the north. Where the refraction line obliquely crosses a Lithoprobe deep seismic-reflection profile, good agreement is obtained between the interpreted reflection section and the derived velocity structure model. In particular, depths to wide-angle reflectors in the upper crust agree with depths to prominent reflection events, and Moho depths agree within 1 km. From this comparison, the upper and middle crust probably comprise the upper part of the Quesnellia terrane. The lower crust from the refraction interpretation does not show the division into two components, parautochthonous and cratonic North America, that is inferred from the reflection data, indicating that their physical properties are not significantly different within the resolution of the refraction data. Based on these interpretations, the lower lithosphere of Quesnellia is absent and presumably was recycled in the mantle. At a depth of ~ 16 km below the Moho, an upper mantle reflector may represent the base of the present lithosphere.

Crust-mantle velocity structure in Shanxi rift, Central North China Craton

2020 ◽  
Author(s):  
Yan Cai ◽  
Jianping Wu
Keyword(s):  
Upper Mantle ◽  
High Velocity ◽  
North China Craton ◽  
Lower Crust ◽  
North China ◽  
Velocity Structure ◽  
Low Velocity ◽  
Crust And Upper Mantle ◽  
The North ◽  
Shanxi Rift

<p>North China Craton is the oldest craton in the world. It contains the eastern, central and western part. Shanxi rift and Taihang mountain contribute the central part. With strong tectonic deformation and intense seismic activity, its crust-mantle deformation and deep structure have always been highly concerned. In recent years, China Earthquake Administration has deployed a dense temporary seismic array in North China. With the permanent and temporary stations, we obtained the crust-mantle S-wave velocity structure in the central North China Craton by using the joint inversion of receiver function and surface wave dispersion. The results show that the crustal thickness is thick in the north of the Shanxi rift (42km) and thin in the south (35km). Datong basin, located in the north of the rift, exhibits large-scale low-velocity anomalies in the middle-lower crust and upper mantle; the Taiyuan basin and Linfen basin, located in the central part, have high velocities in the lower crust and upper mantle; the Yuncheng basin, in the southern part, has low velocities in the lower crust and upper mantle velocities, but has a high-velocity layer below 80 km. We speculate that an upwelling channel beneath the west of the Datong basin caused the low velocity anomalies there. In the central part of the Shanxi rift, magmatic bottom intrusion occurred before the tension rifting, so that the heated lithosphere has enough time to cool down to form high velocity. Its current lithosphere with high temperature may indicate the future deformation and damage. There may be a hot lithospheric uplift in the south of the Shanxi rift, heating the crust and the lithospheric mantle. The high-velocity layer in its upper mantle suggests that the bottom of the lithosphere after the intrusion of the magma began to cool down.</p>

Crustal velocity structure in the southern Coast Belt, British Columbia

1993 ◽  
Vol 30 (12) ◽  
pp. 2389-2403 ◽  
Author(s):  
D. M. O'Leary ◽  
R. M. Clowes ◽  
R. M. Ellis
Keyword(s):  
Upper Mantle ◽  
Velocity Structure ◽  
Seismic Refraction ◽  
Velocity Model ◽  
Structural Features ◽  
P Wave ◽  
Crust And Upper Mantle ◽  
Near Surface ◽  
Collision Zone ◽  
Refraction Data

We applied an iterative combination of two-dimensional traveltime inversion and amplitude forward modelling to seismic refraction data along a 350 km along-strike profile in the Coast Belt of the southern Canadian Cordillera to determine crust and upper mantle P-wave velocity structure. The crustal model features a thin (0.5–3.0 km) near-surface layer with an average velocity of 4.4 km/s, and upper-, middle-, and lower-crustal strata which are each approximately 10 km thick and have velocities ranging from 6.2 to 6.7 km/s. The Moho appears as a 2 km thick transitional layer with an average depth of 35 km and overlies an upper mantle with a poorly constrained velocity of over 8 km/s. Other interpretations indicate that this profile lies within a collision zone between the Insular superterrane and the ancient North American margin and propose two collision-zone models: (i) crustal delamination, whereby the Insular superterrane was displaced along east-vergent faults over the terranes below; and (ii) crustal wedging, in which interfingering of Insular rocks occurs throughout the crust. The latter model involves thick layers of Insular material beneath the Coast Belt profile, but crustal velocities indicate predominantly non-Insular material, thereby favoring the crustal delamination model. Comparisons of the velocity model with data from the proximate reflection lines show that the top of the Moho transition zone corresponds with the reflection Moho. Comparisons with other studies suggest that likely sources for intracrustal wide-angle reflections observed in the refraction data are structural features, lithological contrasts, and transition zones surrounding a region of layered porosity in the crust.

Quaternary sodic and potassic intraplate volcanism in northeast China controlled by the underlying heterogeneous lithospheric structures

Geology ◽  
2021 ◽  
Author(s):  
Xingli Fan ◽  
Qi-Fu Chen ◽  
Yinshuang Ai ◽  
Ling Chen ◽  
Mingming Jiang ◽  
...  
Keyword(s):  
Upper Mantle ◽  
Lithospheric Mantle ◽  
Northeast China ◽  
Velocity Structure ◽  
Seismic Velocity ◽  
Subcontinental Lithospheric Mantle ◽  
Seismic Velocities ◽  
S Wave ◽  
Crust And Upper Mantle ◽  
Potassic Volcanism

The origin and mantle dynamics of the Quaternary intraplate sodic and potassic volcanism in northeast China have long been intensely debated. We present a high-resolution, three-dimensional (3-D) crust and upper-mantle S-wave velocity (Vs) model of northeast China by combining ambient noise and earthquake two-plane wave tomography based on unprecedented regional dense seismic arrays. Our seismic images highlight a strong correlation between the basalt geochemistry and upper-mantle seismic velocity structure: Sodic volcanoes are all characterized by prominent low seismic velocities in the uppermost mantle, while potassic volcanoes still possess a normal but thin upper-mantle “lid” depicted by high seismic velocities. Combined with previous petrological and geochemical research findings, we propose that the rarely erupted Quaternary potassic volcanism in northeast China results from the interaction between asthenospheric low-degree melts and the overlying subcontinental lithospheric mantle. In contrast, the more widespread Quaternary sodic volcanism in this region is predominantly sourced from the upwelling asthenosphere without significant overprinting from the subcontinental lithospheric mantle.

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