Magmatic infiltration and melting in the lower crust and upper mantle beneath the Cima volcanic field, California

1996 ◽  
Vol 123 (4) ◽  
pp. 358-374 ◽  
Author(s):  
H. G. Wilshire ◽  
Anne V. McGuire
Keyword(s):  
Upper Mantle ◽  
Lower Crust ◽  
Volcanic Field ◽  
Crust And Upper Mantle ◽  
Cima Volcanic Field

scholarly journals Constraints on the rheology of lower crust in a strike-slip plate boundary: Evidence from the San Quintin xenoliths, Baja California, Mexico

2017 ◽  
Author(s):  
Thomas van der Werf ◽  
Vasileios Chatzaras ◽  
Leo M. Kriegsman ◽  
Andreas Kronenberg ◽  
Basil Tikoff ◽  
...  
Keyword(s):  
Upper Mantle ◽  
Lower Crust ◽  
Baja California ◽  
Volcanic Field ◽  
Strike Slip ◽  
Mafic Granulite ◽  
Dislocation Creep ◽  
Diffusion Creep ◽  
Plate Boundaries ◽  
Crust And Upper Mantle

Abstract. The rheology of lower crust and its time-dependent behavior in active strike-slip plate boundaries remain poorly understood. To address this issue, we analyzed a suite of mafic granulite and lherzolite xenoliths from the Holocene San Quintin volcanic field, of northern Baja California, Mexico. The San Quintin volcanic field is located 20 km east of the Baja California shear zone, which accommodates the relative movement between the Pacific plate and Baja California microplate. Combining microstructural observations, geothermometry and phase equilibria modeling we constrain that crystal-plastic deformation took place at temperatures of 750–900 °C and pressures of 400–580 MPa, corresponding to 15–22 km depth. A hot crustal geothermal gradient of 40 °C/km is required to explain the estimated deformation conditions. Infrared spectroscopy shows that plagioclase in the mafic granulites is dry. Microstructural evidence suggests that the mafic granulite and peridotite xenoliths were dominantly deforming by processes transitional between dislocation creep and diffusion creep. Recrystallized grain size paleopiezometry yields similar differential stresses in both the uppermost lower crust and upper mantle. Using dry-plagioclase and dry-olivine flow laws we demonstrate that the viscosity of the lower crust and upper mantle is low (2.2 × 1018 – 1.4 × 1020 Pa s). Comparing the viscosity structure of the lithosphere constrained from the San Quintin xenoliths with results from post-seismic relaxation studies from western US, we suggest that lower crust is stronger during transient deformation (e.g., post-seismic relaxation period) while the upper mantle is stronger during long-term deformation (e.g., interseismic period).

scholarly journals Lithospheric dynamics in the vicinity of the Tengchong volcanic field (southeastern margin of Tibet): an investigation using P receiver functions

2020 ◽  
Vol 224 (2) ◽  
pp. 1326-1343
Author(s):  
Hengchu Peng ◽  
José Badal ◽  
Jiafu Hu ◽  
Haiyan Yang ◽  
Benyu Liu
Keyword(s):  
Upper Mantle ◽  
Lower Crust ◽  
Volcanic Field ◽  
Receiver Functions ◽  
Indian Plate ◽  
Fast Wave ◽  
Low Velocity ◽  
Crust And Upper Mantle ◽  
Velocity Anomaly ◽  
Lateral Extrusion

SUMMARY Tengchong volcanic field (TVF) in the northern Indochina block lies in a critical area for understanding complex regional dynamics associated with continent–continent convergence between the Indian and Eurasian plates, including northeastward compression generated by subduction of the Indian Plate beneath the Burma Arc, and southeastward lateral extrusion of the crust from below central Tibet. We gathered 3408 pairs of P receiver functions with different frequencies and calculated the splitting parameters of the Moho-converted Pms phase. An anisotropic H-κ stacking algorithm was used to determine crustal thickness and Vp/Vs ratios. We also inverted for the detailed S-velocity structure of the crust and upper mantle using a two-step inversion technique. Finally, we mapped the topography of the lithosphere–asthenosphere boundary. Results show fast-wave polarization directions with a dominant NE–SW orientation and delay times varying between 0.19 and 1.22 s, with a mean of 0.48 ± 0.07 s. The crustal Vp/Vs ratio varies from 1.68 to 1.90 and shows a maximum value below the central part of the TVF, where there is relatively thin crust (∼35–39 km) and a pronounced low-velocity anomaly in the middle–lower crust. The depth of the lithosphere–asthenosphere boundary ranges from 53 to 85 km: it is relatively deep (∼70–85 km) in the vicinity of the TVF and relatively shallow in the south of the study area. In the absence of low shear wave velocity in the upper mantle below the TVF, we propose that the low-velocity anomaly in the lower crust beneath the TVF derives from the upper mantle below the neighbouring Baoshan block.

scholarly journals Constraints on the rheology of the lower crust in a strike-slip plate boundary: evidence from the San Quintín xenoliths, Baja California, Mexico

Solid Earth ◽  
2017 ◽  
Vol 8 (6) ◽  
pp. 1211-1239 ◽  
Author(s):  
Thomas van der Werf ◽  
Vasileios Chatzaras ◽  
Leo Marcel Kriegsman ◽  
Andreas Kronenberg ◽  
Basil Tikoff ◽  
...  
Keyword(s):  
Grain Size ◽  
Upper Mantle ◽  
Lower Crust ◽  
Baja California ◽  
Plate Boundary ◽  
Volcanic Field ◽  
Strike Slip ◽  
Low Viscosity ◽  
The Pacific ◽  
Flow Laws

Abstract. The rheology of lower crust and its transient behavior in active strike-slip plate boundaries remain poorly understood. To address this issue, we analyzed a suite of granulite and lherzolite xenoliths from the upper Pleistocene–Holocene San Quintín volcanic field of northern Baja California, Mexico. The San Quintín volcanic field is located 20 km east of the Baja California shear zone, which accommodates the relative movement between the Pacific plate and Baja California microplate. The development of a strong foliation in both the mafic granulites and lherzolites, suggests that a lithospheric-scale shear zone exists beneath the San Quintín volcanic field. Combining microstructural observations, geothermometry, and phase equilibria modeling, we estimated that crystal-plastic deformation took place at temperatures of 750–890 °C and pressures of 400–560 MPa, corresponding to 15–22 km depth. A hot crustal geotherm of 40 ° C km−1 is required to explain the estimated deformation conditions. Infrared spectroscopy shows that plagioclase in the mafic granulites is relatively dry. Microstructures are interpreted to show that deformation in both the uppermost lower crust and upper mantle was accommodated by a combination of dislocation creep and grain-size-sensitive creep. Recrystallized grain size paleopiezometry yields low differential stresses of 12–33 and 17 MPa for plagioclase and olivine, respectively. The lower range of stresses (12–17 MPa) in the mafic granulite and lherzolite xenoliths is interpreted to be associated with transient deformation under decreasing stress conditions, following an event of stress increase. Using flow laws for dry plagioclase, we estimated a low viscosity of 1.1–1.3×1020 Pa ⋅ s for the high temperature conditions (890 °C) in the lower crust. Significantly lower viscosities in the range of 1016–1019 Pa ⋅ s, were estimated using flow laws for wet plagioclase. The shallow upper mantle has a low viscosity of 5.7×1019 Pa ⋅ s, which indicates the lack of an upper-mantle lid beneath northern Baja California. Our data show that during post-seismic transients, the upper mantle and the lower crust in the Pacific–Baja California plate boundary are characterized by similar and low differential stress. Transient viscosity of the lower crust is similar to the viscosity of the upper mantle.

Distributed deformation in the lower crust and upper mantle beneath a continental strike-slip fault zone: Marlborough fault system, South Island, New Zealand

Geology ◽  
2004 ◽  
Vol 32 (10) ◽  
pp. 837 ◽  
Author(s):  
Charles K. Wilson ◽  
Craig H. Jones ◽  
Peter Molnar ◽  
Anne F. Sheehan ◽  
Oliver S. Boyd
Keyword(s):  
New Zealand ◽  
Fault Zone ◽  
Upper Mantle ◽  
Lower Crust ◽  
Strike Slip ◽  
Strike Slip Fault ◽  
Fault System ◽  
Crust And Upper Mantle

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>

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