Gravity analysis of the offset between crustal structure and topography in the Liupan Shan, northeast Tibetan Plateau

AbstractDense gravity/GPS measurements collected around the southwest margin of the Ordos Block in 2014 and 2017 were used to obtain three gravity anomaly profiles across the Liupan Shan Mountains. The Liupan Shan is located in a Bouguer gravity anomaly (BGA) transitional zone; however, low BGAs to the west do not correspond to the topography of the Liupan Shan in that region, with a maximum offset of approximately 34 km. This offset is also found in inverted crustal density structures whereby the interface between the upper and lower crust is notably concave to the west of the Liupan Shan. Flexural analysis indicates that the effective elastic thickness is 5 km and the uplift is caused by oblique subduction of surface materials. According to this uplift mechanism, the offset suggests that Liupan Shan migrated eastward following partial isostatic compensation. Therefore, we suggest that Liupan Shan has experienced an uplift–compensation–uplift tectonic process.

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Crustal density structure of the Antarctic continent from constrained 3-D gravity inversion

10.5194/egusphere-egu2020-4427 ◽

2020 ◽

Author(s):

Fei Ji ◽

Qiao Zhang

Keyword(s):

Gravity Inversion ◽

Inversion Method ◽

Rift System ◽

Low Density ◽

Density Structure ◽

West Antarctica ◽

The West ◽

Antarctic Continent ◽

Crustal Density ◽

The Antarctic

Crustal density is a fundamental physical parameter that helps to reveal its composition and structure, and is also significantly related to the tectonic evolution and geodynamics. Based on the latest Bouguer gravity anomalies and the constrains of 3-D shear velocity model and surface heat flow data, the 3-D gravity inversion method, incorporating deep weight function, has been used to obtain the refined density structure over the Antarctic continent. Our results show that the density anomalies changes from -0.25 g/cm3 to 0.20 g/cm3. Due to the multi-phase extensional tectonics in Mesozoic and Cenozoic, the low density anomalies dominates in the West Antarctica, while the East Antarctica is characterized by high values of density anomalies. By comparing with the variations of effective elastic thickness, the inverted density structure correlates well with the lithospheric integrated strength. According to the mechanical strength and inverted density structure in the West Antarctic Rift System (WARS), our analysis found that except for the local area affected by the Cenozoic extension and magmatic activity, the crustal thermal structure in the WARS tends to be normal under the effect of heat dissipation. Finally, the low density anomalies features in West Antarctica extend to beneath the Transantarcitc Mountains (TAMs), however, we hypothesize that a single rift mechanism seems not be used to explain the entire TAMs range.

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An analysis of the crust–mantle boundary in Hudson Bay from gravity and seismic observations

Canadian Journal of Earth Sciences ◽

10.1139/e68-127 ◽

1968 ◽

Vol 5 (5) ◽

pp. 1297-1303 ◽

Cited By ~ 4

Author(s):

J. R. Weber ◽

A. K. Goodacre

Keyword(s):

Gravity Anomaly ◽

Gravity Anomalies ◽

Gravitational Effect ◽

Compressional Wave ◽

Seismic Survey ◽

Hudson Bay ◽

Mantle Boundary ◽

Crustal Velocity ◽

Velocity Variations ◽

Crustal Density

A study of the results of the gravity and seismic surveys in Hudson Bay in 1965 has shown that the gravitational effect of a two-layer model based on the seismically determined depths has no correlation with the observed gravity anomalies. On the profile from Churchill to Povungnituk the gravity and seismic observations can be reconciled by postulating lateral variations of the acoustic compressional wave velocity within the crust. A crustal model has been calculated—using the same time-terms and the same mean crustal velocity—whose gravitational effect fits the observed gravity. The velocity varies from 6.15 to 6.56 km/s and the postulated depths are almost entirely within the confidence limits of the original model.In order to test the hypothesis, the postulated velocity variations have been compared with the lower refractor velocities of the shallow seismic survey, based on the assumption that the crustal velocities ought to be systematically higher than the crystalline surface velocities and that there may be a correlation between variations in crustal and surface velocities. The test is inconclusive because bottom refractor velocities are higher than crustal velocities in two areas where volcanic flows and high-velocity sediments may be present.The case of linearly related velocity (V) and density (ρ) variations has been analyzed and it is shown that the gravitational effect of the crust–mantle boundary undulations may be completely masked or even overbalanced by density changes in the crust if [Formula: see text]. The crust can be characterized by having dominant velocity variations (in which case the gravity anomaly reflects the undulations of the crust–mantle boundary) or dominant density variations (in which case the gravity anomaly inversely reflects the crust–mantle boundary undulations) depending on the relationship between average crustal density and average crustal velocity.

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Positive gravity anomaly over the Sydney basin

Exploration Geophysics ◽

10.1071/eg989191 ◽

1989 ◽

Vol 20 (2) ◽

pp. 191 ◽

Cited By ~ 6

Author(s):

I.R. Qureshi

Keyword(s):

Gravity Anomaly ◽

Sedimentary Rocks ◽

Cubic Splines ◽

The Body ◽

Western Boundary ◽

Positive Density ◽

Crustal Extension ◽

Isostatic Compensation ◽

Basement Fault ◽

Wide Zone

A prominent positive gravity anomaly overlies the Macdonald trough in the Sydney basin. Allowing for isostatic compensation and the effect of sedimentary rocks, the anomaly is determined to have an amplitude of 440 GU (mms-2) and a width of 60 km. The anomaly is smoothed using cubic splines, FFT and IFFT. It is interpreted by a large mafic body of density 2.9 g cm-3 underlying the basin to a depth of 13.5 km. A 12 km wide zone with a small positive density contrast underlies the body within the lower crust.The steep western boundary of the body represents a major basement fault underlying the Lapstone monocline and Kurrajong Fault System.The anomaly is a member of the Meandarra Gravity Ridge which marks a zone of crustal extension within which dominant nature of intrusion is mafic in character.

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The lithospheric effective elastic thickness and its tectonic implications in the Ordos Block and adjacent areas

Geological Journal ◽

10.1002/gj.4335 ◽

2021 ◽

Author(s):

Qing Chen ◽

Franz Neubauer ◽

Yunpeng Dong ◽

Xianfeng Tan ◽

Hao Chen

Keyword(s):

Ordos Block ◽

Tectonic Implications ◽

Effective Elastic Thickness

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Defining a mid-Holocene earthquake through speleoseismological and independent data: implications for the outer Central Apennines (Italy) seismotectonic framework

Solid Earth ◽

10.5194/se-8-161-2017 ◽

2017 ◽

Vol 8 (1) ◽

pp. 161-176 ◽

Cited By ~ 6

Author(s):

Alessandra Di Domenica ◽

Alberto Pizzi

Keyword(s):

Normal Fault ◽

Transitional Zone ◽

Quantitative Modeling ◽

Normal Faults ◽

Independent Data ◽

The West ◽

Central Apennines ◽

Strong Earthquakes ◽

Surrounding Areas ◽

Karst Conduit

Abstract. A speleoseismological study has been conducted in the Cavallone Cave, located in the easternmost carbonate sector of the Central Apennines (Maiella Massif), in a seismically active region interposed between the post-orogenic extensional domain, to the west, and the contractional one, to the east. The occurrence of active silent normal faults, to the west, close to blind thrusts, to the east, raises critical questions about the seismic hazard for this transitional zone. Large collapses of cave ceilings, fractures, broken speleothems with new re-growing stalagmites on their top, preferential orientation of fallen stalagmites and the absence of thin and long concretions have been observed in many portions of the karst conduit. This may indicate that the cave suffered sudden deformation events likely linked to the occurrence of past strong earthquakes. Radiocarbon dating and, above all, the robust correspondence with other coeval on-fault and off-fault geological data collected in surrounding areas outside the cave, provide important constraints for the individuation of a mid-Holocene paleoearthquake around 4.6–4.8 kyr BP. On the basis of the available paleoseismological data, possible seismogenic sources can be identified with the Sulmona normal fault and other active normal fault segments along its southern prosecution, which recorded synchronous strong paleoevents. Although the correlation between speleotectonic observations and quantitative modeling is disputed, studies on possible effects of earthquake on karstic landforms and features, when corroborated by independent data collected outside caves, can provide a useful contribution in discovering past earthquakes.

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Geodynamic pattern of the West Bohemia region based on permanent GPS measurements

Studia Geophysica et Geodaetica ◽

10.1007/s11200-009-0021-y ◽

2009 ◽

Vol 53 (3) ◽

pp. 329-341 ◽

Cited By ~ 13

Author(s):

Vladimir Schenk ◽

Zdeňka Schenkova ◽

Zuzana Jechumtálová

Keyword(s):

Gps Measurements ◽

The West ◽

West Bohemia

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Geogenetic patterns in mouse lemurs (genus Microcebus) reveal the ghosts of Madagascar's forests past

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1601081113 ◽

2016 ◽

Vol 113 (29) ◽

pp. 8049-8056 ◽

Cited By ~ 48

Author(s):

Anne D. Yoder ◽

C. Ryan Campbell ◽

Marina B. Blanco ◽

Mario dos Reis ◽

Jörg U. Ganzhorn ◽

...

Keyword(s):

Population Genetic ◽

Anthropogenic Activities ◽

Transitional Zone ◽

The West ◽

Central Highland ◽

Genetic Patterns ◽

Mouse Lemurs ◽

Closed Canopy ◽

Central Highlands ◽

Original Vegetation

Phylogeographic analysis can be described as the study of the geological and climatological processes that have produced contemporary geographic distributions of populations and species. Here, we attempt to understand how the dynamic process of landscape change on Madagascar has shaped the distribution of a targeted clade of mouse lemurs (genus Microcebus) and, conversely, how phylogenetic and population genetic patterns in these small primates can reciprocally advance our understanding of Madagascar's prehuman environment. The degree to which human activity has impacted the natural plant communities of Madagascar is of critical and enduring interest. Today, the eastern rainforests are separated from the dry deciduous forests of the west by a large expanse of presumed anthropogenic grassland savanna, dominated by the Family Poaceae, that blankets most of the Central Highlands. Although there is firm consensus that anthropogenic activities have transformed the original vegetation through agricultural and pastoral practices, the degree to which closed-canopy forest extended from the east to the west remains debated. Phylogenetic and population genetic patterns in a five-species clade of mouse lemurs suggest that longitudinal dispersal across the island was readily achieved throughout the Pleistocene, apparently ending at ∼55 ka. By examining patterns of both inter- and intraspecific genetic diversity in mouse lemur species found in the eastern, western, and Central Highland zones, we conclude that the natural environment of the Central Highlands would have been mosaic, consisting of a matrix of wooded savanna that formed a transitional zone between the extremes of humid eastern and dry western forest types.

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The Pontiac problem, Quebec–Ontario, in the light of gravity data

Canadian Journal of Earth Sciences ◽

10.1139/e87-181 ◽

1987 ◽

Vol 24 (9) ◽

pp. 1916-1919 ◽

Cited By ~ 8

Author(s):

J. Kalliokoski

Keyword(s):

Gravity Anomaly ◽

Greenstone Belt ◽

Gravity Data ◽

Volcanic Rocks ◽

Sedimentary Rocks ◽

Iron Formation ◽

Bouguer Gravity ◽

The West ◽

Abitibi Greenstone Belt ◽

Uplifted Block

A belt of Archean quartzose metasedimentary gneisses with minor mafic volcanic rocks (the Pontiac Group) lies south of the Blake River and older Archean mafic volcanic rocks of the Abitibi Greenstone Belt, and is separated from them by the Larder Lake – Cadillac Break. To the west of the Pontiac Group, on strike, is the Archean Larder Lake Group of turbidite conglomerate, argillite, limestone, and iron formation with abundant mafic flows and intrusions. These strata also lie south of the Larder Lake – Cadillac Break and south of the Blake River and older Archean mafic volcanic rocks. The western contact between the Pontiac and Larder Lake groups is covered by a narrow north–south strip of Proterozoic Cobalt sedimentary rocks. On the basis of gravity work that compares the Bouguer gravity anomaly gradient across the Cadillac Break with that across the west margin of the Pontiac Group, it is proposed that the Larder Lake and Pontiac groups are separated by a north–south fault and that the Pontiac Group represents a lithologically distinct uplifted block. The Pontiac block may be an Archean terrane.

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