Crustal models of the eastern Superior Province, Quebec, derived from new gravity data

2000 ◽  
Vol 37 (2-3) ◽  
pp. 385-397 ◽  
Author(s):  
Hamid Telmat ◽  
Jean-Claude Mareschal ◽  
Clément Gariépy ◽  
Jean David ◽  
Caroline N Antonuk
Keyword(s):  
Gravity Data ◽  
Seismic Profile ◽  
Density Variation ◽  
Crustal Thickening ◽  
Superior Province ◽  
Seismic Line ◽  
Seismic Reflection Data ◽  
The North ◽  
Reflection Data ◽  
Field Evidence

New gravity data were collected in the Nemiscau and La Grande subprovinces of the Superior Province. This ~350 km gravity profile follows the Matagami-Radisson road and extends northward the gravity transect along the ~260 km long Lithoprobe seismic line 48, across the northern Abitibi and Opatica subprovinces. For the Abitibi-Opatica segment, the interpretation is consistent with the Lithoprobe seismic profile. It calls for crustal thickening near the boundary between the Abitibi and Opatica belts, where the Moho is ~5 km deeper than in the Abitibi subprovince and ~8 km deeper than in the northern Opatica subprovince. The gravity model complements the seismic reflection data and provides information on the uppermost supracrustal sequences poorly imaged in the seismic profile. Most of the intrusive rocks in the Opatica Belt appear as thin (<5 km) bodies. Across the Nemiscau and La Grande subprovinces, the Bouguer anomalies are of short wavelengths and their sources lie in the upper crust. The crustal thickness is constant from the northern Opatica Belt throughout the southern part of the Nemiscau subprovince. Density measurements indicate that the upper crustal density is higher in the Nemiscau and La Grande subprovinces than in the Abitibi and Opatica belts. There is some crustal thickening beneath the La Grande subprovince, and a gravity high at the northern end of the subprovince is related to the occurrence of mafic supracrustal sequences. The gravity anomaly signature associated with the lateral density variation and field evidence indicate that the main tectonic boundaries dip to the north.

Structural and stratigraphic architecture of Australia's frontier onshore sedimentary basins: the Arckaringa, Officer, Amadeus, and Georgina basins

2011 ◽  
Vol 51 (2) ◽  
pp. 703
Author(s):  
Lidena Carr ◽  
Russell Korsch ◽  
Wolfgang Preiss ◽  
Sandra Menpes ◽  
Josef Holzschuh ◽  
...  
Keyword(s):  
Sedimentary Basins ◽  
Petroleum Exploration ◽  
Seismic Line ◽  
Seismic Reflection Data ◽  
Petroleum Potential ◽  
Northern Margin ◽  
The North ◽  
Reflection Data ◽  
Southern Margin ◽  
Seismic Lines

The Onshore Energy Security Program—funded by the Australian Government and conducted by Geoscience Australia—has acquired deep seismic reflection data in conjunction with state and territory geological surveys, across several frontier sedimentary basins to stimulate petroleum exploration in onshore Australia. Here, we present data from two seismic lines collected in SA and NT. Seismic line 08GA-OM1 crossed the Arckaringa and Officer basins in SA and the southern-most Amadeus Basin in NT. Seismic line 09GA-GA1 crossed the northeastern part of the Amadeus Basin and the complete width of the southern Georgina Basin in NT. Structural and sequence stratigraphic interpretations of the seismic lines will be presented here, followed by an assessment of the petroleum potential of the basins. Seismic line 08GA-OM1 also crosses the Neoproterozoic to Devonian eastern Officer Basin. The basin is structurally complex in this area, being dominated by south-directed thrust faults and fault-related folds—providing potential for underthrust petroleum plays. The northern margin of the basin is overthrust to the south by the Mesoproterozoic Musgrave Province. To the north, the Moorilyanna Trough of the Officer Basin is a major depocentre of up to 7,000 m deep. Both seismic lines cross parts of the eastern Amadeus Basin. Seismic line 08GA-OM1 shows that the southern margin of the basin is overthrust to the north by the Musgrave Province with the main movement during the Petermann Orogeny. In the northeast, seismic line 09GA-GA1 crosses two parts of the basin separated by the Paleoproteroozic to Mesoproterozoic Casey Inlier (part of the Arunta Region). The northern margin of the basin is imaged seismically as a southward-verging, thinned-skinned thrust belt, showing considerable structural thickening of the stratigraphic succession. Seismic line 09GA-GA1 was positioned to cross that part of the southern Georgina Basin that was considered previously to be in the oil window. Here, the basin has a complex southern margin, with Neoproterozoic stratigraphy being thrust interleaved with basement rocks of the Arunta Region. The main part of the basin, containing a Neoproterozoic to Devonian succession, is asymmetric, thinning to the north where it overlies the Paleoproterozoic Davenport Province. The well, Phillip–2, drilled adjacent to the seismic line, intersected basement at a depth of 1,489 m, and has been used to map the stratigraphic sequences across the basin.

Plumbing and architecture of a crustal mineralizing system in the Archean Superior Province, Canada

2021 ◽  
Author(s):  
Eric Roots ◽  
Graham Hill ◽  
Ben M. Frieman ◽  
James A. Craven ◽  
Richard S. Smith ◽  
...  
Keyword(s):  
Upper Mantle ◽  
Spatial Association ◽  
Three Dimensional ◽  
3D Models ◽  
Superior Province ◽  
Seismic Reflection Data ◽  
Reflection Data ◽  
Abitibi Subprovince ◽  
Lower Crustal

&lt;p&gt;The role of melts and magmatic/metamorphic fluids in mineralization processes is well established. However, the role of crustal architecture in defining source and sink zones in the middle to lower crust remains enigmatic. Integration of three dimensional magnetotelluric (MT) modelling and seismic reflection data across the Archean Abitibi greenstone belt of the Superior Province, Canada, reveals a &amp;#8216;whole-of-crust&amp;#8217; mineralizing system and highlights the controls by crustal architecture on metallogenetic processes. Electrically conductive conduits in an otherwise resistive upper crust are coincident with truncations and offsets of seismic reflections that are mostly interpreted as major brittle-ductile fault zones. The spatial association between these features and low resistivity zones imaged in the 3D models suggest that these zones acted as pathways through which fluids and melts ascended toward the surface. At mid-crustal levels, these &amp;#8216;conduit&amp;#8217; zones connect to ~50 km long, north-south striking conductors, and are inferred to represent graphite and/or sulphide deposited from cooling fluids. At upper mantle to lower crustal depths, east-west trending conductive zones dominate and display shallow dips. The upper mantle features are broadly coincident with the surface traces of the major deformation zones with which a large proportion of the gold endowment is associated. We suggest that these deep conductors represent interconnected graphitic zones perhaps augmented by sulphides that are relicts from metamorphic fluid and melt emplacement associated primarily with the later stages of regional deformation. &amp;#160;Thus, from the combined MT and seismic data, we develop a crustal-scale architectural model that is consistent with existing geological and deformational models, providing constraints on the sources for and signatures of fluid and magma emplacement that resulted in widespread metallogenesis in the Abitibi Subprovince.&lt;/p&gt;

The gravity field over the Ungava Bay region from satellite altimetry and new land-based data: implications for the geology of the area

1999 ◽  
Vol 36 (1) ◽  
pp. 75-89 ◽  
Author(s):  
Hamid Telmat ◽  
Jean-Claude Mareschal ◽  
Clément Gariépy
Keyword(s):  
Satellite Altimetry ◽  
Gravity Data ◽  
Gravity Anomalies ◽  
Gravity Models ◽  
Crustal Thickening ◽  
Seismic Line ◽  
Crustal Thinning ◽  
Gravity Measurements ◽  
George River ◽  
Superior Craton

Gravity data were obtained along two transects on the southern coast of Ungava Bay, which provide continuous gravity coverage between Leaf Bay and George River. The transects and the derived gravity profiles extend from the Superior craton to the Rae Province across the New Quebec Orogen (NQO). Interpretation of the transect along the southwestern coast of Ungava Bay suggests crustal thickening beneath the NQO and crustal thinning beneath the Kuujjuaq Terrane, east of the NQO. Two alternative interpretations are proposed for the transect along the southeastern coast of the bay. The first model shows crustal thickening beneath the George River Shear Zone (GRSZ) and two shallow bodies correlated with the northern extensions of the GRSZ and the De Pas batholith. The second model shows constant crustal thickness and bodies more deeply rooted than in the first model. The gravity models are consistent with the easterly dipping reflections imaged along a Lithoprobe seismic line crossing Ungava Bay and suggest westward thrusting of the Rae Province over the NQO. Because no gravity data have been collected in Ungava Bay, satellite altimetry data have been used as a means to fill the gap in data collected at sea. The satellite-derived gravity data and standard Bouguer gravity data were combined in a composite map for the Ungava Bay region. The new land-based gravity measurements were used to verify and calibrate the satellite data and to ensure that offshore gravity anomalies merge with those determined by the land surveys in a reasonable fashion. Three parallel east-west gravity profiles were extracted: across Ungava Bay (59.9°N), on the southern shore of the bay (58.5°N), and onshore ~200 km south of Ungava Bay (57.1°N). The gravity signature of some major structures, such as the GRSZ, can be identified on each profile.

scholarly journals Hydraulic fracturing in thick shale basins: problems in identifying faults in the Bowland and Weald Basins, UK

2016 ◽  
Author(s):  
David K. Smythe
Keyword(s):  
Hydraulic Fracturing ◽  
Seismic Reflection ◽  
Upper Jurassic ◽  
Normal Faults ◽  
Regulatory Regime ◽  
Seismic Line ◽  
Seismic Reflection Data ◽  
Reflection Data ◽  
Unconventional Resource ◽  
The Uk

Abstract. North American shale basins differ from their European counterparts in that the latter are one to two orders of magnitude smaller in area, but correspondingly thicker, and are cut or bounded by normal faults penetrating from the shale to the surface. There is thus an inherent risk of groundwater resource contamination via these faults during or after unconventional resource appraisal and development. US shale exploration experience cannot simply be transferred to the UK. The Bowland Basin, with 1900 m of Lower Carboniferous shale, is in the vanguard of UK shale gas development. A vertical appraisal well to test the shale by hydraulic fracturing (fracking), the first such in the UK, triggered earthquakes. Re-interpretation of the 3D seismic reflection data, and independently the well casing deformation data, both show that the well was drilled through the earthquake fault, and did not avoid it, as concluded by the exploration operator. Faulting in this thick shale is evidently difficult to recognise. The Weald Basin is a shallower Upper Jurassic unconventional oil play with stratigraphic similarities to the Bakken play of the Williston Basin, USA. Two Weald licensees have drilled, or have applied to drill, horizontal appraisal wells based on inadequate 2D seismic reflection data coverage. I show, using the data from the one horizontal well drilled to date, that one operator failed identify two small but significant through-going normal faults. The other operator portrayed a seismic line as an example of fault-free structure, but faulting had been smeared out by reprocessing. The case histories presented show that: (1) UK shale exploration to date is characterised by a low degree of technical competence, and (2) regulation, which is divided between four separate authorities, is not up to the task. If UK shale is to be exploited safely: (1) more sophisticated seismic imaging methods need to be developed and applied to both basins, to identify faults in shale with throws as small as 4–5 m, and (2) the current lax and inadequate regulatory regime must be overhauled, unified, and tightened up.

scholarly journals Oligocene-Miocene extension led to mantle exhumation in the central Ligurian Basin, Western Alpine Domain

2019 ◽  
Author(s):  
Anke Dannowski ◽  
Heidrun Kopp ◽  
Ingo Grevemeyer ◽  
Dietrich Lange ◽  
Martin Thowart ◽  
...  
Keyword(s):  
Gravity Data ◽  
Sedimentary Cover ◽  
Seafloor Spreading ◽  
Wide Angle ◽  
The South ◽  
Seismic Line ◽  
Acoustic Basement ◽  
North West ◽  
The North ◽  
Ligurian Basin

Abstract. The Ligurian Basin is located in the Mediterranean Sea to the north-west of Corsica at the transition from the western Alpine orogen to the Apennine system and was generated by the south-eastward trench retreat of the Apennines-Calabrian subduction zone. Late Oligocene to Miocene rifting caused continental extension and subsidence, leading to the opening of the basin. Yet, it still remains enigmatic if rifting caused continental break-up and seafloor spreading. To reveal its lithospheric architecture, we acquired a state of the art seismic refraction and wide-angle reflection profile in the Ligurian Basin. The seismic line was recorded in the framework of SPP2017 4D-MB, the German component of the European AlpArray initiative, and trends in a NE-SW direction at the centre of the Ligurian Basin, roughly parallel to the French coastline. The seismic data recorded on the newly developed GEOLOG recorder, designed at GEOMAR, are dominated by sedimentary refractions and show mantle Pn arrivals at offsets of up to 70 km and a very prominent wide-angle Moho reflection. The main features share several characteristics (i.e. offset range, continuity) generally associated with continental settings rather than documenting oceanic crust emplaced by seafloor spreading. Seismic tomography results are augmented by gravity data and yield a 7.5–8 km thick sedimentary cover which is directly underlain by serpentinised mantle material at the south-western end of the profile. The acoustic basement at the north-eastern termination is interpreted to be continental crust, thickening towards the NE. Our study reveals that the oceanic domain does not extend as far north as previously assumed and that extension led to extreme continental thinning and exhumation of sub-continental mantle which eventually became serpentinised.

The Lithoprobe Abitibi-Grenville transect: two billion years of crust formation and recycling in the Precambrian Shield of Canada

2000 ◽  
Vol 37 (2-3) ◽  
pp. 459-476 ◽  
Author(s):  
John Ludden ◽  
Andrew Hynes
Keyword(s):  
Cross Sections ◽  
High Pressures ◽  
Significant Proportion ◽  
Superior Province ◽  
Crust Formation ◽  
Entire Cross Section ◽  
Grenville Province ◽  
Seismic Reflection Data ◽  
Precambrian Shield ◽  
Reflection Data

We summarize the results of Lithoprobe studies in the Neoarchean southeastern Superior Province and the Mesoproterozoic Grenville Province, in the southeastern Precambrian Shield of Canada, through two composite cross-sections based on seismic reflection data, which define dramatically different styles of crust formation and tectonic accretion in the Neoarchean and Mesoproterozoic. In the Neoarchean, the structures at the surface are steep, with discontinuous and flatter structures at depth, much of the crust appears to be juvenile, and the predominant process of crustal growth is inferred to have been subduction-accretion of primitive crust in a prograding arc system. In the Mesoproterozoic, surface structures are shallow and the seismic character of the crust is continuous over the entire cross-section. Archean parautochthonous rocks and reworked Archean crust comprise a very significant proportion of the preserved crust in the Mesoproterozoic and provided the backstop to the Grenvillian orogeny, resulting in the exhumation of crustal rocks formed at high pressures. Preservation of Neoarchean crust, including a thickened lithosphere in the Superior Province, in contrast to its general destruction in younger orogens, may well relate to a unique thermal regime at this time on Earth.

EXTENDED ARRAYS FOR MARINE SEISMIC ACQUISITION

Geophysics ◽  
1978 ◽  
Vol 43 (1) ◽  
pp. 3-22 ◽  
Author(s):  
J. H. Lofthouse ◽  
G. T. Bennett
Keyword(s):  
Data Quality ◽  
Data Acquisition ◽  
Signal Amplitude ◽  
Eastern Canada ◽  
Seismic Reflection Data ◽  
The North ◽  
Reflection Data ◽  
Formed Part ◽  
Marine Seismic ◽  
Receiver Arrays

In‐line arrays for both source and receiver have been implemented for marine seismic reflection data acquisition. The in‐line array dimensions (variable within limits) are considerably greater than any previously used system of which we are aware. The arrays were designed to attenuate extremely strong sea‐bottom multiples during the data acquisition phase. The source comprised 25 airguns arranged in five identical in‐line subarrays. Each subarray produced a signal of better than 6 barmeters acoustic intensity with a primary‐to‐bubble ratio of approximately 4.4 from guns totaling 297 cu in. When this source was delivered in 1973, it constituted the most powerful production airgun source for which we had seen calibration measurements. Receiver arrays were implemented by a “weighting‐mixing” box (which formed part of the DFS IV instrument), the input to which comprised 53 channels of data each from a 50 m live section in the streamer cable. Processing techniques which are complementary to the field procedures have been developed. Comparisons with “conventional” data (and such data processed to simulate field arrays) show significant improvements in “data quality” from the new field techniques, that is, the new data are easier to interpret geologically because interfering multiples have been attenuated relative to desired energy. Whilst the large outgoing signal amplitude will have made some contribution to the data quality, the major improvement is believed to result from the use of arrays in the recording phase. This system, first used for production in August 1973, was subsequently used successfully during recording of 17,000 km of offshore seismic data from Eastern Canada, the North Sea, and the Mediterranean.

Variable unroofing in the western Superior Province - metamorphic evidence and possible origin

2006 ◽  
Vol 43 (7) ◽  
pp. 805-819 ◽  
Author(s):  
Andrew Hynes ◽  
Zixin Song
Keyword(s):  
Superior Province ◽  
Surface Distribution ◽  
Seismic Line ◽  
The North ◽  
Metavolcanic Rocks ◽  
Limited Support ◽  
Greenstone Belts ◽  
Rotation Motion ◽  
East West ◽  
Broad Region

Western Superior Lithoprobe seismic-reflection line 1 exhibits a broad region of northward-dipping reflectors in the Uchi subprovince, which gives way to southward-dipping reflectors farther north in the Berens River sub province. Mafic metavolcanic rocks across the region of northward-dipping reflectors exhibit a decline in metamorphic pressure, from pressures of 6 kbar (1 kbar = 100 MPa) in the south to only 2 kbar 80 km to the north. This indicates that the southern edge of the Uchi subprovince has undergone significantly more unroofing than regions farther north. The differential unroofing is not consistent with a doubly vergent thrusting origin for the northward- and southward-dipping reflector pattern. It could result from a crustal-scale synform, of which the region of northward-dipping reflectors would make up the southern limb. Metamorphic pressures from samples off the seismic line, however, provide only limited support for a regional synform, and suggest that much of the pressure variation may result from deformation associated with motion on late faults that are widespread in the western Superior Province. These faults occur in a WNW-striking set with dextral offsets and an ENE-striking set with sinistral offsets. They could result from north–south compression and east–west extension, provided the faults have rotated towards the east–west direction during deformation. Regional tilting and (or) jostling of crustal blocks is attributed to deformation associated with the fault rotation. Motion on the faults and the associated deformation of intervening fault blocks may be important contributors to the present crustal architecture of the western Superior Province, including the surface distribution and form of the greenstone belts.

Structural variation along the Devil's Mountain fault zone, northwestern Washington

2006 ◽  
Vol 43 (4) ◽  
pp. 433-446 ◽  
Author(s):  
Nathan Hayward ◽  
Mladen R Nedimović ◽  
Matthew Cleary ◽  
Andrew J Calvert
Keyword(s):  
Fault Zone ◽  
Structural Variation ◽  
Puget Sound ◽  
Seismic Reflection Data ◽  
Juan De Fuca Plate ◽  
The North ◽  
Reflection Data ◽  
Juan De Fuca ◽  
Main Fault ◽  
Juan De Fuca Strait

The eastern Juan de Fuca Strait is subject to long-term, north–south-oriented shortening. The observed deformation is interpreted to result from the northward motion of the Oregon block, which is being driven north by oblique subduction of the oceanic Juan de Fuca plate. Seismic data, acquired during the Seismic Hazards Investigation in Puget Sound survey are used, with coincident first-arrival tomographic velocities, to interpret structural variation along the Devil's Mountain fault zone in the eastern Juan de Fuca Strait. The Primary fault of the Devil's Mountain fault zone developed at the northern boundary of the Everett basin, during north–south-oriented Tertiary compression. Interpretation of seismic reflection data suggests that, based on their similar geometry including the large magnitude of pre-Tertiary basement offset, the Primary fault of the Devil's Mountain fault west of ~122.95°W and the Utsalady Point fault represent the main fault of the Tertiary Devil's Mountain fault zone. The Tertiary Primary fault west of ~122.95°W was probably kinematically linked to faults to the east (Utsalady Point, Devil's Mountain, and another to the south), by an oblique north–northeast-trending transfer zone or ramp. Left-lateral transpression controlled the Quaternary evolution of the Devil's Mountain fault zone. Quaternary Primary fault offsets are smaller to the east of ~122.95°W, suggesting that stress here was in part accommodated by the prevalent oblique compressional structures to the north. Holocene deformation has focussed on the Devil's Mountain, Utsalady Point, and Strawberry Point faults to the east of ~122.8° but has not affected the Utsalady Point fault to the west of ~122.8°W.

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