Development of three-dimensional basement structure in Taiwan deduced from past plate motion: Consistency with the present seismicity

The Santa Maria Basin in southern California is a lowland bounded on the south by the Santa Ynez River fault and on the northeast by the Little Pine‐Foxen Canyon‐Santa Maria River faults. It contains Neogene sedimentary rocks which rest unconformably on a basement of Cretaceous and older clastic rocks. Analysis of over 4 000 gravity stations obtained from the Defense Mapping Agency suggests that the Bouguer anomaly contains a short‐wavelength component arising from a variable‐density contrast between the basin’s Neogene units and the Cretaceous basement. A three‐dimensional inversion of the short‐wavelength component (constrained by wells drilled to basement) yields a structure model of the basement and the average density of the overlying sediments, assuming that the basement does not contain large‐scale density variations. The density anomalies modeled in the Neogene sediments, showing higher densities in the basin troughs, can be related to diagenetic changes in the silica facies of the Monterey and Sisquoc formations. The basement structure model shows the basin as composed of parallel ridges and troughs, trending west‐northwest and bounded by steep slopes interpreted as fault scarps. The basin is bounded on the west by a north‐south trending slope which may also represent a fault scarp.

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Opening and closure of Iranian back-arc basins: A seismic tomography view

10.5194/egusphere-egu21-5209 ◽

2021 ◽

Author(s):

Nalan Lom ◽

Abdul Qayyum ◽

Derya Gürer ◽

Douwe G. van der Meer ◽

Wim Spakman ◽

...

Keyword(s):

Seismic Tomography ◽

Subduction Zones ◽

Three Dimensional ◽

Plate Motion ◽

Limited Information ◽

Three Dimensional Model ◽

Slab Geometry ◽

Novel Approach ◽

Sanandaj Sirjan Zone ◽

Back Arc

Iran is a mosaic of continental blocks that are surrounded by Tethyan oceanic relics. Remnants of these oceanic rock assemblages are exposed around the Central Iranian Microcontinent (CIM), discretely along the Sanandaj-Sirjan Zone and in Jaz-Murian. The ophiolite belts surrounding the CIM are mainly assumed to represent narrow back-arc basins that opened in Cretaceous and closed before the Eocene. Although these ophiolites are exposed as small pieces on continental crust today, they represent oceans wide enough to form supra-subduction ophiolites and arc-related magmatic rocks which suggest that their palaeogeographic width was at least some hundreds of kilometers. Current models for the palaeogeographic dimension, opening and closure of these basins are highly schematic. They usually seem plausible in two-dimensional reconstructions, however a single three-dimensional model explaining whole Iran and its surrounding regions has not been fully accomplished.&#160; This is mostly because while the geological record provides constraints on the origin and ages of the subducted ocean floor, it provides limited information about onset and cessation of the subduction and almost no constraints on the dimension of these oceans and the subduction zones that consumed them.In this study, we follow a novel approach in estimating the dimension and evolution of these back-arc basin by using seismic tomography. Seismic tomography has revealed that we can image and trace subducted lithosphere relics. Imaged mantle structure is now being used to link sinking slabs with sutures and to define shape of a slab. Systematic comparison of regions where the timing of subduction is reasonably well constrained by geological data showed that slabs sink gradually through the mantle at rates more or less the same. This perspective enabled us to study slab shape as a function of absolute trench motion. While mantle stationary trenches tend to create steep slabs or slab walls, the flat-lying segments are formed where the overlying trenches are mobile relative to the mantle, normal facing during roll-back, overturned during slab advance. &#160;Under the assumption of vertical sinking after break-off, it is also possible to locate the palaeo-trenches. &#160;When combined with absolute plate motion reconstructions, tomographically determined volume and size of the subducted lithosphere can also be used to estimate the size/width of the prehistoric oceans. To this end, we build on and further develop concepts that relate absolute trench motion during subduction to modern slab geometry to evaluate the possible range of dimensions associated with opening and closure of the Iranian back-arc basins.

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Reconciling seismic structures and Late Cretaceous kimberlite magmatism in northern Alberta, Canada

Geology ◽

10.1130/g47163.1 ◽

2020 ◽

Vol 48 (9) ◽

pp. 872-876

Author(s):

Yunfeng Chen ◽

Yu Jeffrey Gu ◽

Larry M. Heaman ◽

Lei Wu ◽

Erdinc Saygin ◽

...

Keyword(s):

Late Cretaceous ◽

Source Region ◽

Three Dimensional ◽

Plate Motion ◽

Mountain Lake ◽

Low Velocity ◽

Age Progression ◽

Plate Reconstructions ◽

Competing Models ◽

Northern Alberta

Abstract The Late Cretaceous kimberlites in northern Alberta, Canada, intruded into the Paleoproterozoic crust and represent a nonconventional setting for the discovery of diamonds. Here, we examined the origin of kimberlite magmatism using a multidisciplinary approach. A new teleseismic survey reveals a low-velocity (−1%) corridor that connects two deep-rooted (>200 km) quasi-cylindrical anomalies underneath the Birch Mountains and Mountain Lake kimberlite fields. The radiometric data, including a new U-Pb perovskite age of 90.3 ± 2.6 Ma for the Mountain Lake intrusion, indicate a northeast-trending age progression in kimberlite magmatism, consistent with the (local) plate motion rate of North America constrained by global plate reconstructions. Taken together, these observations favor a deep stationary (relative to the lower mantle) source region for kimberlitic melt generation. Two competing models, mantle plume and slab subduction, can satisfy kinematic constraints and explain the exhumation of ultradeep diamonds. The plume hypothesis is less favorable due to the apparent age discrepancy between the oldest kimberlites (ca. 90 Ma) and the plume event (ca. 110 Ma). Alternatively, magma generation may have been facilitated by decompression of hydrous phases (e.g., wadsleyite and ringwoodite) within the mantle transition zone in response to thermal perturbations by a cold slab. The three-dimensional lithospheric structures largely controlled melt migration and intrusion processes during the Late Cretaceous kimberlite magmatism in northern Alberta.

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The three-dimensional geometries of segmented normal faults

10.5194/egusphere-egu2020-19706 ◽

2020 ◽

Author(s):

John Walsh ◽

Vincent Roche ◽

Giovanni Camanni ◽

Conrad Childs ◽

Tom Manzocchi ◽

...

Keyword(s):

Full Range ◽

Three Dimensional ◽

Normal Faults ◽

Basement Structure ◽

Mechanical Heterogeneity ◽

Fault Surface ◽

Mechanical Stratigraphy ◽

Data Resolution ◽

3D Geometry ◽

Quantitative Basis

Normal faults are often complex three dimensional structures comprising multiple sub-parallel segments separated by intervening relay zones. In this study we outline geometrical characterisations capturing this 3D complexity and providing a semi-quantitative basis for the comparison of faults and for defining the factors controlling their geometrical evolution.Individual relay zones can be assigned to one of four types according to their form (i.e. whether the bounding segments are unconnected in 3D or merge into a single surface) and their orientation (i.e. whether they are slip-parallel or slip-perpendicular). From the detailed analysis of 84 fault arrays mapped from 3D seismic reflection surveys (including 63 from our mapping of 8 different study areas and 21 derived from the literature), we show that the 3D geometry of fault arrays can be quantitatively defined on the basis of the relative numbers of these types of relay zones.Detailed mapping of fault zones indicates that whilst they can individually contain all four types of relay zone, their relative proportions varies between different study areas. Differences in the proportions of relay zone types are attributed to two primary controls, the mechanical heterogeneity of the faulted sequence and the presence of basement structure. For example, relay zones with an upward bifurcating geometry are prevalent in faults that reactivate deeper structures, whereas the formation of laterally bifurcating relays is promoted by heterogeneous mechanical stratigraphy.&#160;Fault arrays in the literature generally do not contain the full range of possible relay zone type but tend to comprise either all bifurcating relay zones or all unconnected relay zones. These end-member fault geometries have led to contrasting conceptual models for the growth of faults. The mapping conducted here suggests that the proportion of bifurcating relay zones increases as data resolution increases and that fault surface bifurcation is ubiquitous. Models for the geometrical evolution of fault arrays must account for the full range of relay zone geometries that appears to be a characteristic of all faults.

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Reduced ice mass loss and three-dimensional viscoelastic deformation in northern Antarctic Peninsula inferred from GPS

Geophysical Journal International ◽

10.1093/gji/ggaa229 ◽

2020 ◽

Vol 222 (2) ◽

pp. 1013-1022 ◽

Cited By ~ 1

Author(s):

Nahidul Hoque Samrat ◽

Matt A King ◽

Christopher Watson ◽

Andrew Hooper ◽

Xianyao Chen ◽

...

Keyword(s):

Mass Loss ◽

Antarctic Peninsula ◽

Upper Mantle ◽

Three Dimensional ◽

Plate Motion ◽

Viscoelastic Deformation ◽

Lithospheric Thickness ◽

Isostatic Adjustment ◽

Wide Range ◽

Uplift Rates

SUMMARY We consider the viscoelastic rheology of the solid Earth under the Antarctic Peninsula due to ice mass loss that commenced after the breakup of the Larsen-B ice shelf. We extend the previous analysis of nearby continuous GPS time-series to include five additional years and the additional consideration of the horizontal components of deformation. They show strong uplift from ∼2002 to 2011 followed by reduced uplift rates to 2018. Modelling the GPS-derived uplift as a viscoelastic response to ongoing regional ice unloading from a new ice model confirms earlier estimates of low upper-mantle viscosities of ∼0.3–3 × 1018 Pa s in this region but allows a wide range of elastic lithosphere thickness. The observed and modelled north coordinate component shows little nonlinear variation due to the location of ice mass change to the east of the GPS sites. However, comparison of the observed and modelled east coordinate component constrains the upper-mantle viscosity to be less than ∼9 × 1018 Pa s, consistent with the viscosity range suggested by the uplift rates alone and providing important, largely independent, confirmation of that result. Our horizontal analysis showed only marginal sensitivity to modelled lithospheric thickness. The results for the horizontal components are sensitive to the adopted plate rotation model, with the estimate based on ITRF2014 suggesting that the sum of residual plate motion and pre-2002 glacial isostatic adjustment is likely less than ∼±0.5 mm yr−1 in the east component.

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Tectonic plates in 3D mantle convection model with stress- history-dependent rheology

10.21203/rs.3.rs-18967/v2 ◽

2020 ◽

Author(s):

Takehiro Miyagoshi ◽

Masanori Kameyama ◽

Masaki Ogawa

Keyword(s):

Mantle Convection ◽

Plate Tectonics ◽

Three Dimensional ◽

Vertical Component ◽

Plate Motion ◽

Stress History ◽

Tectonic Plates ◽

Convection Model ◽

Narrow Plate ◽

Narrow Bands

Abstract Plate tectonics is a key feature of the dynamics of the Earth’s mantle. By taking into account the stress-history-dependent rheology of mantle materials, we succeeded in realistically producing tectonic plates in our numerical model of mantle convection in a three-dimensional rectangular box. The calculated lithosphere is separated into several pieces (tectonic plates) that rigidly move. Deformation of the lithosphere caused by the relative motion of adjacent plates is concentrated in narrow bands (plate margins) where the viscosity is substantially reduced. The plate margins develop when the stress exceeds a threshold and the lithosphere is ruptured. Once formed, the plate margins persist, even after the stress is reduced below the threshold, allowing the plates to stably move over geologic time. The vertical component of vorticity takes a large value in the narrow plate margins. Secondary convection occurs beneath old tectonic plates as two-dimensional rolls with their axes aligned to the direction of plate motion. The surface heat ﬂow decreases with increasing distance from divergent plate margins (ridges) in their vicinity in the way the cooling half-space model predicts, but it tends towards a constant value away from ridges as observed for the Earth because of the heat transport by the secondary convection.

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Tectonic plates in 3D mantle convection model with stress- history-dependent rheology

10.21203/rs.3.rs-18967/v1 ◽

2020 ◽

Author(s):

Takehiro Miyagoshi ◽

Masanori Kameyama ◽

Masaki Ogawa

Keyword(s):

Mantle Convection ◽

Plate Tectonics ◽

Three Dimensional ◽

Vertical Component ◽

Plate Motion ◽

Stress History ◽

Tectonic Plates ◽

Convection Model ◽

Narrow Plate ◽

Narrow Bands

Abstract Plate tectonics is a key feature of the dynamics of the Earth’s mantle. By taking into account the stress-history-dependent rheology of mantle materials, we succeeded in realistically producing tectonic plates in our numerical model of mantle convection in a three-dimensional rectangular box. The calculated lithosphere is separated into several pieces (tectonic plates) that rigidly move. Deformation of the lithosphere caused by the relative motion of adjacent plates is concentrated in narrow bands (plate margins) where the viscosity is substantially reduced. The plate margins develop when the stress exceeds a threshold and the lithosphere is ruptured. Once formed, the plate margins persist, even after the stress is reduced below the threshold, allowing the plates to stably move over geologic time. The vertical component of vorticity takes a large value in the narrow plate margins. Secondary convection occurs beneath old tectonic plates as two-dimensional rolls with their axes aligned to the direction of plate motion. The surface heat ﬂow decreases with increasing distance from divergent plate margins (ridges) in their vicinity in the way the cooling half-space model predicts, but it tends towards a constant value away from ridges as observed for the Earth because of the heat transport by the secondary convection.

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Three-Dimensional Surface Deformation Characteristics Based on Time Series InSAR and GPS Technologies in Beijing, China

Remote Sensing ◽

10.3390/rs13193964 ◽

2021 ◽

Vol 13 (19) ◽

pp. 3964

Author(s):

Kunchao Lei ◽

Fengshan Ma ◽

Beibei Chen ◽

Yong Luo ◽

Wenjun Cui ◽

...

Keyword(s):

Land Subsidence ◽

Surface Deformation ◽

Three Dimensional ◽

Horizontal Deformation ◽

Movement Rate ◽

Horizontal Movement ◽

Basement Structure ◽

Beijing Plain ◽

3D Surface ◽

3D Deformation

Excessive exploitation of the groundwater has resulted in obvious three-dimensional (3D) deformation features on the surface of the Beijing Plain. This paper, by combining Interferometric Synthetic Aperture Radar (InSAR) and Global Positioning System (GPS) technologies, has obtained time-series information of the 3D surface deformation in the Beijing Plain, analyzing its spatial distribution characteristics. On this basis, the relationship between different controlling factors with the 3D deformation of the surface has been analyzed as well. The following results are obtained: (1) From 2013 to 2018, the land subsidence, which generally showed the trend of slowing down, was mainly concentrated in the eastern, northern, and southern regions of Beijing Plain, with multiple subsidence centers. (2) Under the International Terrestrial Reference Frame 2005 (ITRF2005), the horizontal direction of all GPS points in the plain is basically the same, with the dominant movement direction being NE112.5°~NE113.8°. Under the Eurasian reference frame, the horizontal movement rate of GPS points significantly decreases. The movement rate and direction of each point are not characteristic of overall trend activity. (3) The distribution and extent of the 3D surface deformation in the Beijing Plain are controlled by the basement structure. Part of the subsided area corresponds to a Quaternary depression formed at the junction of active faults disrupting the area. Similarly, the distribution of horizontal deformation in the E-W and N-S directions of the plain is controlled by the regional basement structure comprising major faults bounding horizontal deformation. (4) Groundwater exploitation is the main cause of the 3D surface deformation in the Beijing Plain. The groundwater funnels of the second and third confined aquifer are in suitable agreement with the land subsidence. The horizontal movement in the Beijing Plain is either directed toward the center of the groundwater or the land subsidence funnel, and the deformation is directed from areas with higher to areas with lower groundwater levels.

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Determination of tectonic velocities of some continuously operating reference stations (CORS) in Vietnam 2016-2018 by using precise point positioning

Vietnam Journal of Earth Sciences ◽

10.15625/0866-7187/15571 ◽

2020 ◽

Vol 43 (1) ◽

pp. 1-12

Author(s):

Nguyen Ngoc Lau ◽

Richard Coleman ◽

Ha Minh Hoa

Keyword(s):

Precise Point Positioning ◽

Accurate Determination ◽

Three Dimensional ◽

Plate Motion ◽

Tectonic Plate ◽

North East ◽

The North ◽

Positioning Technique ◽

Point Positioning

Determining the speed of tectonic plate displacement helps us to better understand tectonic activities of the area, and is a prerequisite to help forecast earthquakes. The determination of tectonic plate displacement by GNSS technology in Vietnam has been conducted since the 2000s, mainly using the relative positioning technique. The increasing accuracy of precise point positioning technique, and the number of CORS in Vietnam, will facilitate the accurate determination of tectonic velocities. Based on the GNSS data of some CORSs in Vietnam from 2016-2018, we have determined accurately their three-dimensional coordinates using a precise point positioning technique. After modeling periodic variations on the time series, we calculated the tectonic movement rate of 7 Vietnamese stations and 3 other stations in the region. Through analysis and comparison with other geology/plate motion models and GPS results, we conclude that this result is reliable. The velocity of tectonic motion in the North, East and Up components of Ha Noi, Da Nang and Ho Chi Minh City are respectively (-13.1, +32.8, -1.3), (-9.9, +31.0, +2.6) and (-10.3, +26.9, +2.7) mm/year.

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3-D Gravity Basement Structure Around Mashiki, Kumamoto, Japan

Journal of Disaster Research ◽

10.20965/jdr.2018.p0193 ◽

2018 ◽

Vol 13 (1) ◽

pp. 193-198

Author(s):

Shun Araki ◽

Tatsuya Noguchi ◽

Masao Komazawa ◽

Shoya Arimura ◽

Mitsuhiro Tamura ◽

...

Keyword(s):

Seismic Wave ◽

Bouguer Anomaly ◽

Three Dimensional ◽

Target Area ◽

Density Structure ◽

2016 Kumamoto Earthquake ◽

Dimensional Model ◽

Three Dimensional Model ◽

Basement Structure ◽

The One

Gravity survey has been carried out around central part of Mashiki, Kumamoto, Japan, where was severely damaged by 2016 Kumamoto earthquake. Dense observations were performed at more than 450 sites around the central part of Mashiki. The observation sites satisfy enough density to discuss density structure shallower than 500-meter depth around the target area. After applying some corrections to the observed data, Bouguer anomaly is obtained and three dimensional model of gravity basement is estimated. As a result, a graben runs parallel to the Akitsukawa River and some isolated small basins are found inside of the graben. The central part of Mashiki is located immediately above of the one of such the small basins. We also analyze focusing and defocusing effects of ray of seismic wave under very simple assumptions and it is found that the central part of Mashiki locates close to a focusing area.

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