Reactivation of ancient Antarctic rift zones by intraplate seismicity

We use both seismology and geobarometry to investigate the movement of melt through the volcanic crust of Iceland. We have captured melt in the act of moving within or through a series of sills ranging from the upper mantle to the shallow crust by the clusters of small earthquakes it produces as it forces its way upward. The melt is injected not just beneath the central volcanoes, but also at discrete locations along the rift zones and above the centre of the underlying mantle plume. We suggest that the high strain rates required to produce seismicity at depths of 10–25 km in a normally ductile part of the Icelandic crust are linked to the exsolution of carbon dioxide from the basaltic melts. The seismicity and geobarometry provide complementary information on the way that the melt moves through the crust, stalling and fractionating, and often freezing in one or more melt lenses on its way upwards: the seismicity shows what is happening instantaneously today, while the geobarometry gives constraints averaged over longer time scales on the depths of residence in the crust of melts prior to their eruption. This article is part of the Theo Murphy meeting issue ‘Magma reservoir architecture and dynamics'.

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Dense GPS derived deformation and rotation of intraplate blocks in Central Europe - comparison to seismicity and volcanism

10.5194/egusphere-egu21-1096 ◽

2021 ◽

Author(s):

Zhiguo Deng ◽

Torsten Dahm

Keyword(s):

High Precision ◽

Velocity Fields ◽

Shear Stresses ◽

Intraplate Seismicity ◽

Strain Rates ◽

Horizontal Shear ◽

Regional Patterns ◽

Quaternary Volcanism ◽

Intraplate Deformation ◽

Horizontal Strain

Intraplate deformation is often small but can nowdays be resolved from high precision GNSS velocity fields derived from decade-long time series and high precision network or point wise &#160;solutions if uncertainties are smaller than ~0.2 mm/a.If local effects are discarded, dense velocity fields may resolve regional patterns of intraplate deformation and motion, which are related to the bending of lithospheric plates, to mantle upwelling, the diffuse or zoned deformation along structural weaknesses or faults, and the rotation of rigid blocks within a plate.&#160;We derive for the first time, dense high precision network solutions at 323 GNSS stations in Germany and adjacent areas and resolve regions experiencing uplift with velocities of up to ~2 mm/a, rotational relative motions with angular velocities of ~0.7&#177;0.3 mas/a, and horizontal shear along an extended, &#160;NS trending zone with strain rates in the range of 10-8 1/a.&#160;We integrate European dense velocity solutions into our dataset to discuss the geodynamic context to European microplate motions, the Alpine collision, the structure of the European mantle, Quaternary volcanism and historical seismicity.&#160;Unexpectedly, the zones of high horizontal strain rates only partly correlate to seismicity. Such a non-correlation between ongoing horizontal strain and seismicity has been recognized before. We discuss possible reasons for the absence of intraplate seismicity in regions experiencing recent strain, including the stress shadow effects if the strain buildup is reducing shear stresses from plate tectonics. The combination of GNSS derived dense velocity fields with time dependent seismicity models may change our current understanding of intraplate seismicity and impact the assessment of intraplate seismic hazard in future.&#160;

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Tabular Icebergs: Implication from Geophysical Studies of Ice Shelves

Annals of Glaciology ◽

10.3189/s0260305500016967 ◽

1980 ◽

Vol 1 ◽

pp. 55-55

Author(s):

Sion Shabtaie ◽

Charles R. Bentley

Keyword(s):

Mass Balance ◽

Sea Water ◽

Ice Thickness ◽

Ice Shelf ◽

Frictional Drag ◽

Ice Shelves ◽

Ross Ice Shelf ◽

Rift Zones ◽

Different Characteristics ◽

Ice Water

Recent geophysical and glaciological investigations of the Ross Ice Shelf have revealed many complexities in the ice shelf that can be important factors in iceberg structure. The presence of rift zones, surface and bottom crevasses, corrugations, ridges and troughs, and other features could substantially modify the hydraulics of iceberg towing and lead to disintegration of the berg in the course of transport.The relationships between the elevation above sea-level and total ice thickness for three ice shelves (Ross, Brunt, and McMurdo) are given; from them, expressions for the thickness/freeboard ratios of tabular icebergs calved from these ice shelves are obtained. The relationships obtained from the measured values of surface elevation and ice thickness are in agreement with models derived assuming hydrostatic equilibrium.Areas of brine infiltration into the Ross Ice Shelf have been mapped. Examples of radar profiles in these zones are shown. Absorption from the brine layers results in a poor or absent bottom echo. It is probable that little saline ice exists at the bottom of the Ross Ice Shelf front due to a rapid bottom melting near the ice front, and that the thickness of the saline ice at the bottom of icebergs calving from the Ross Ice Shelf is no more than a few meters, if there is any at all.We have observed many rift zones on the ice shelf by airborne radar techniques, and at one site the bottom and surface topographies of (buried) rift zones have been delineated. These rift zones play an obvious role in iceberg formation and may also affect the dynamics of iceberg transport. Bottom crevasses with different shapes, sizes, and spacings are abundant in ice shelves; probably some are filled with saline ice and others with unfrozen sea-water. Existence of these bottom crevasses could lead to a rapid disintegration of icebergs in the course of transport, as well as increasing the frictional drag at the ice-water boundary.Radar profiles of the ice-shelf barrier at four sites in flow bands of very different characteristics are shown. In some places rifting upstream from the barrier shows regular spacings, suggesting a periodic calving. Differential bottom melting near the barrier causes the icebergs to have an uneven surface and bottom (i.e. dome-shaped).Electrical resistivity soundings on the ice shelf can be applied to estimate the temperature-depth function, and from that the basal mass-balance rate. With some modifications, the technique may also be applied to estimating the basal mass-balance rates of tabular icebergs.

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Seismites within Ordovician–Silurian carbonates and clastics of Southern Ontario, Canada and implications for intraplate seismicity

Sedimentary Geology ◽

10.1016/j.sedgeo.2014.12.004 ◽

2015 ◽

Vol 316 ◽

pp. 80-95 ◽

Cited By ~ 10

Author(s):

K. Wallace ◽

N. Eyles

Keyword(s):

Intraplate Seismicity ◽

Southern Ontario

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Tabular Icebergs: Implications from Geophysical Studies of Ice Shelves

Journal of Glaciology ◽

10.3189/s0022143000005037 ◽

1982 ◽

Vol 28 (100) ◽

pp. 413-430 ◽

Cited By ~ 6

Author(s):

Sion Shabtaie ◽

Charles R. Bentley

Keyword(s):

Mass Balance ◽

Sea Water ◽

Ice Thickness ◽

Ice Shelf ◽

Frictional Drag ◽

Ice Shelves ◽

Ross Ice Shelf ◽

Rift Zones ◽

Different Characteristics ◽

Ice Water

AbstractRecent geophysical and glaciological investigations of the Ross Ice Shelf have revealed many complexities in the ice shelf that can be important factors in iceberg structure. The presence of rift zones, surface and bottom crevasses, corrugations, ridge/troughs, and other features could substantially modify the hydraulics of iceberg towing and lead to disintegration in the course of transport.The relationships between the elevation above sea-level and total ice thickness for three ice shelves (Ross, Brunt, and McMurdo) are given; from them, expressions for the thickness/freeboard ratios of tabular icebergs calved from these ice shelves are obtained. The relationships obtained from the measured values of surface elevation and ice thickness are in agreement with models derived assuming hydrostatic equilibrium.Areas of brine infiltration into the Ross Ice Shelf have been mapped. Examples of radar profiles in these zones are shown. Absorption from the brine layers results in a poor or absent bottom echo. It is probable that little saline ice exists at the bottom of the Ross Ice Shelf front due to a rapid bottom melting near the ice front, and that the thickness of the saline ice at the bottom of icebergs calving from the Ross Ice Shelf is no more than a few meters, if there is any at all.We have observed many rift zones on the ice shelf by airborne radar techniques, and at one site the bottom and surface topographies of (buried) rift zones have been delineated. These rift zones play an obvious role in iceberg formation and may also affect the dynamics of iceberg transport. Bottom crevasses with different shapes, sizes, and spacings are abundant in ice shelves; probably some are filled with saline ice and others with unfrozen sea-water. Existence of these bottom crevasses could lead to a rapid disintegration of icebergs in the course of transport, as well as increasing the frictional drag at the ice-water boundary.Radar profiles of the ice shelf front at four sites in flow bands of very different characteristics are shown. In some places rifting up-stream from the front shows regular spacings, suggesting a periodic calving. Differential bottom melting near the front causes the icebergs to have an uneven surface and bottom (i.e. dome shaped).Electrical resistivity soundings on the ice shelf can be applied to estimate the temperature-depth function, and from that the basal mass-balance rate. With some modifications, the technique may also be applied to estimating the basal mass balance rates of tabular icebergs.

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Prospectivity of the Triassic successions of the North West Shelf of Australia: New insights from a regional integrated geoscience study

The Leading Edge ◽

10.1190/tle40030172.1 ◽

2021 ◽

Vol 40 (3) ◽

pp. 172-177

Author(s):

Jarrad Grahame ◽

Victoria Cole

Keyword(s):

Evaluation Tool ◽

System Perspective ◽

Sea Levels ◽

North West ◽

Petroleum Systems ◽

The North ◽

Study Results ◽

Half Graben ◽

Rift Zones ◽

Rising Sea Levels

The North West Shelf (NWS) of Australia is a prolific hydrocarbon province hosting significant volumes of hydrocarbons, primarily derived from Jurassic and Cretaceous targets. A new regional, integrated geoscience study has been undertaken to develop insights into the paleogeography and petroleum systems of Late Permian to Triassic successions, which have been underexplored historically in favor of Jurassic to Cretaceous targets. Within the NWS study area, graben and half-graben depocenters developed in response to intracratonic rifting that preceded later fragmentation and northward rifting of small continental blocks. This, coupled with contemporaneous cycles of rising sea levels, brought about the development of large embayments and shallow, epeiric seas between the Australian continental landmass and outlying continental fragments in the early stages of divergence. Key elements of the study results discussed herein include the study methodology, the paleogeographic and gross depositional environment mapping, and the reservoir and source kitchen modeling. The study results highlight the presence of depocenters that developed within oblique rift zones due to regional Permo-Triassic strike-slip tectonics that bear compelling similarities to modern-day analogues. These intracratonic rift zones are well-known and prominent tectonic features resulting from mantle upwelling and weakening of overlying lithospheric crust, initiating the development of divergent intraplate depocenters. The comprehensive analysis of these depocenters from a paleogeographic and petroleum system perspective provides a basin evaluation tool for Triassic prospectivity.

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Crustal structure of the southeast flank of Kilauea Volcano, Hawaii, from seismic refraction measurements

Bulletin of the Seismological Society of America ◽

10.1785/bssa0700041149 ◽

1980 ◽

Vol 70 (4) ◽

pp. 1149-1159

Author(s):

John J. Zucca ◽

David P. Hill

Keyword(s):

Oceanic Crust ◽

Crustal Structure ◽

Seismic Refraction ◽

Kilauea Volcano ◽

Geological Survey ◽

Pn Velocity ◽

Kīlauea Volcano ◽

Volcanic Pile ◽

Rift Zones ◽

The U.S

abstract In November 1976, the U.S. Geological Survey, in conjunction with the Hawaii Institute of Geophysics, established a 100-km-long seismic refraction line normal to the southeast coast of Hawaii across the submarine flank of Kilauea Volcano. Interpretation of the data suggests that the oceanic crust dips about 2° toward the island underneath the volcanic pile. The unreversed Pn velocity is 7.9 km/ sec with crustal velocities varying strongly along the profile. Profiles across the rift zones of Kilauea suggest that the velocity in the rifts is higher than the velocity in the surrounding extrusive rocks and that the velocity in the southwest rift (∼6.5 km/sec) is lower than the velocity in the east rift (∼7.0 km/sec). The rift boundaries seem to dip away from the rift such that a large part of the volcanic pile is composed of the higher velocity core of riftzone rock.

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