Upper Mantle Seismic Anisotropy as a Constraint for Mantle Flow and Continental Dynamics of the North American Plate

Abstract Active plate boundaries in the Caribbean form a complex tectonic environment that includes transform and subduction zones. The Caribbean-North American plate boundary is one such active margin, where subduction transitions from arc- to oblique-type off the northeast coast of Puerto Rico. Understanding mantle flow in this region will not only help determine the nature of tectonic activity and mantle dynamics that control these margins, but will also aid our understanding of the fate of subducting lithosphere. The existence of tears, windows, and gaps in subducting slabs has been proposed at various locations around the world but few have been confirmed. Since mantle flow and crustal deformation are believed to produce seismic anisotropy in the asthenosphere and lithosphere, searching for changes in, for example, SKS splitting parameters can help identify locations at which subducting slabs have been disrupted. Several lines of evidence support the notion of a slab tear within the subducting North American plate at this transition zone, including the counter-clockwise rotation of the Puerto Rico microplate over the past ~10 Ma, clusters of small seismic events, and trench collapse initiating ~3.3 m.y. Here we present results from a detailed investigation of seismic anisotropy from 28 stations across six networks in the Northeast Caribbean that support the hypothesis of a significant slab gap in the vicinity of the U.S. and British Virgin islands. A regional synthesis of our results reveals fast shear wave polarizations that are generally oriented parallel to the plate boundary with intermediate to high SH-SV delay times. For example, polarization directions are oriented roughly NE-SW along the bulk of the Lesser Antilles, E-W along the Puerto Rico trench and the northern Lesser Antilles, and NW-SE beneath Hispaniola. Beneath the U.S. and British Virgin Islands, however, the fast polarization direction differs markedly from the regional pattern, becoming almost perpendicular to the plate boundary. Stations on Anegada, British Virgin islands and St. Croix, U.S. Virgin islands show a fast polarization direction that is oriented nearly NNE-SSW and smaller delay times than surrounding stations. These results suggest that mantle flow is redirected NE-SW at this location through a gap in the subducted lithosphere of the North American plate.

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Breakouts in Alberta and stress in the North American plate

Canadian Journal of Earth Sciences ◽

10.1139/e83-130 ◽

1983 ◽

Vol 20 (9) ◽

pp. 1445-1455 ◽

Cited By ~ 19

Author(s):

C. K. Fordjor ◽

J. S. Bell ◽

D. I. Gough

Keyword(s):

United States ◽

North American ◽

Horizontal Stress ◽

The United States ◽

Oil Wells ◽

North American Plate ◽

Mantle Flow ◽

Orientation Data ◽

The North ◽

Canadian Basin

The paper reports a detailed statistical study of breakout azimuths in 48 oil wells widely distributed in the Alberta sedimentary basin, bringing the number of oil wells contributing azimuths to 94 for the western Canadian basin. The azimuths show significant regional variation between the northern, central, and southern parts of the basin. Twenty-one wells, in which breakouts cover depth ranges greater than 600 m, were used to investigate regression of breakout azimuths on depth. Ten wells give positive regression coefficients, 11 are negative, and no coefficient is significant at 95% confidence level. If the dominant northwest–southeast orientation of the long axes of breakouts gives the orientation of the lesser horizontal principal stress Sh, following the hypothesis of Bell and Gough, the inferred stress orientations indicate that throughout the whole basin the direction of the maximum horizontal stress SH is northeast–southwest. Stress measurements, by strain-relief techniques in a mine and from hydraulic fracture in wells, support the stress orientation given by the breakouts. The insignificant regression of breakout azimuths on depth supports the view that the orientation data represent stress in the lithosphere rather than in the sediments only. Directions of the lesser horizontal compression Sh, from Zoback and Zoback in the United States and from breakout studies in western Canada, are combined to suggest that the Mid-Continent stress province of North America may include the western Canadian basin and the Canadian Shield as well as the central United States. Coherent stress with the observed orientation, over the continent east of the Rocky Mountains, would result from northeastward basal drag on the North American plate, as Zoback and Zoback have pointed out. Basal drag to the northeast could arise either if the plate were sliding southwestward over a passive asthenosphere, as suggested by Zoback and Zoback, or if northeastward mantle flow were driving the asthenosphere and the plate northeastward.

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The North American upper mantle: Density, composition, and evolution

Journal of Geophysical Research Atmospheres ◽

10.1029/2010jb000866 ◽

2010 ◽

Vol 115 (B12) ◽

Cited By ~ 81

Author(s):

Walter D. Mooney ◽

Mikhail K. Kaban

Keyword(s):

North American ◽

Upper Mantle ◽

The North

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The Upper Mantle Flow Beneath the North China Platform

Mechanics Problems in Geodynamics Part II ◽

10.1007/978-3-0348-9200-1_12 ◽

1996 ◽

pp. 649-659

Author(s):

Rong-Shan Fu ◽

Jian-Hua Huang ◽

Zhe-Xun Wei

Keyword(s):

Upper Mantle ◽

North China ◽

Mantle Flow ◽

North China Platform ◽

The North

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Supplemental Material: Seismic anisotropy in southern Costa Rica confirms upper mantle flow from the Pacific to the Caribbean

10.1130/geol.s.12773969 ◽

2020 ◽

Author(s):

Vadim Levin ◽

et al.

Keyword(s):

Data Analysis ◽

Costa Rica ◽

Upper Mantle ◽

Seismic Anisotropy ◽

Data Sources ◽

Mantle Flow ◽

Analysis Methodology ◽

The Pacific ◽

Wave Splitting ◽

The Caribbean

Data sources, details of data analysis methodology, and additional diagrams and maps of shear wave splitting measurements.<br>

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Electromagnetic images of the Trans-Hudson orogen: the North American Central Plains anomaly revealed

Canadian Journal of Earth Sciences ◽

10.1139/e05-018 ◽

2005 ◽

Vol 42 (4) ◽

pp. 457-478 ◽

Cited By ~ 47

Author(s):

Alan G Jones ◽

Juanjo Ledo ◽

Ian J Ferguson

Keyword(s):

Electrical Properties ◽

North American ◽

Upper Mantle ◽

Lithospheric Mantle ◽

Three Dimensional ◽

Conductivity Anomaly ◽

Central Plains ◽

Slave Craton ◽

The North ◽

Kimberlite Field

Magnetotelluric studies of the Trans-Hudson orogen over the last two decades, prompted by the discovery of a significant conductivity anomaly beneath the North American Central Plains (NACP), from over 300 sites yield an extensive database for interrogation and enable three-dimensional information to be obtained about the geometry of the orogen from southern North Dakota to northern Saskatchewan. The NACP anomaly is remarkable in its continuity along strike, testimony to along-strike similarity of orogenic processes. Where bedrock is exposed, the anomaly can be associated with sulphides that were metamorphosed during subduction and compression and penetratively emplaced deep within the crust of the internides of the orogen to the boundary of the Hearne margin. A new result from this compilation is the discovery of an anomaly within the upper mantle beginning at depths of ~80100 km. This lithospheric mantle conductor has electrical properties similar to those for the central Slave craton mantle conductor, which lies directly beneath the major diamond-producing Lac de Gras kimberlite field. While the Saskatchewan mantle conductor does not directly underlie the Fort à la Corne kimberlite, which is associated with the Sask craton, the spatial correspondence is close.

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