A geophysical interpretation of the onshore and offshore geology of the southern Avalon Terrane, Newfoundland

1987 ◽  
Vol 24 (1) ◽  
pp. 60-69 ◽  
Author(s):  
H. G. Miller
Keyword(s):  
Sedimentary Basin ◽  
Gravity Data ◽  
Volcanic Rocks ◽  
Geophysical Data ◽  
Magnetic Data ◽  
Ultramafic Rocks ◽  
Volcanic Island ◽  
Thrust Faulting ◽  
Geophysical Interpretation ◽  
Avalon Peninsula

This paper presents new land and underwater gravity data for the southern portion of the Avalon Terrane of Newfoundland. These gravity data are combined with existing airborne and marine magnetic data to produce a detailed geophysical interpretation of the geology of the southern Avalon Peninsula and the adjacent portions of Placentia and St. Mary's bays.Qualitative interpretation of the geophysical data in conjunction with the known geology reveals that the major faults previously mapped only on land and inferred beneath St. Mary's Bay can be traced offshore geophysically. In addition, the previously unknown offshore limits of a small sedimentary basin in the southeast part of the area can be delineated.Quantitative modelling demonstrates that (1) Precambrian mafic to ultramafic rocks underlie the whole area, (2) thrust faulting in the St. Mary's Peninsula and elsewhere has led to the juxtaposition of Bull Arm volcanic rocks over Harbour Main volcanic rocks, and (3) the evolution of the area may be explained by a combination of earlier volcanic island and extensional models.The mapping has also revealed the presence of previously unknown northwest–southeast lineations in the geophysical patterns, which may be related to the late wrench faulting.

A geophysical interpretation of the geology of Conception Bay, Newfoundland

1983 ◽  
Vol 20 (9) ◽  
pp. 1421-1433 ◽  
Author(s):  
H. G. Miller
Keyword(s):  
Magnetic Susceptibility ◽  
Volcanic Rocks ◽  
Magnetic Anomalies ◽  
Vertical Movement ◽  
Geophysical Data ◽  
Two Dimensional ◽  
Geophysical Interpretation ◽  
Gravity And Magnetic ◽  
Conception Bay ◽  
Avalon Peninsula

Geophysical data from Conception Bay and the adjacent peninsulas of the Avalon Peninsula, Newfoundland are presented and quantitatively interpreted using two-dimensional models to interpret the geology beneath the bay. The portion of the bay underlain by mafic volcanic rocks is determined and the maximum extent of the Cambro-Ordovician rocks containing the Wabana hematite deposit is delineated. All gravity and magnetic anomalies in the area are explained in terms of density and magnetic susceptibility variations confined to the upper 12 km of the crust. The geophysical models indicate that mafic volcanics underlie a significant portion of the study area and are more extensive than indicated by the surface outcrop on land. The models also indicate significant vertical movement on the Topsail Fault and on the extension of a fault passing out into the bay near Holyrood. The Cambro-Ordovician sediments are confined to the southern portion of the block bounded by these faults. The geophysical data are unable to detect the presence of the mafic volcanics east of the Topsail Fault in the study area.

Geophysical interpretation of the geology of the northeast Gander Terrane, Newfoundland

1988 ◽  
Vol 25 (8) ◽  
pp. 1161-1174 ◽  
Author(s):  
H. G. Miller
Keyword(s):  
Gravity Data ◽  
Geochemical Data ◽  
Ultramafic Rocks ◽  
Thrust Belt ◽  
Mafic Rocks ◽  
Geological Interpretation ◽  
The North ◽  
Geophysical Interpretation ◽  
Lateral Extent ◽  
North And South

New gravity data from the northeastern portion of the Gander Terrane of Newfoundland are analysed in association with existing gravity data. These are combined with the digitized and filtered aeromagnetic and geochemical data to produce an interpretation of the subsurface geology.Interpretation of these data suggests that there are two extensive areas underlain at depth by rocks similar to the Dunnage Terrane mafic and ultramafic rocks that outcrop at the Gander River ultrabasic belt. These regions of ultramafic and mafic rocks extend in two north–south belts throughout the study area, and both may have tongues continuing seaward beneath the Deadman's Bay pluton. The western belt, the Ocean Pond belt, probably consists of a series of granitic plutons underlain by mafic and ultramafic rocks. Geophysical modelling corroborates an earlier geological interpretation that the eastern belt, the Indian Bay Big Pond thrust belt, is a thrust sheet. The lateral extent of the thrust belt is accurately determined by new geophysical data. The presence of these two subsurface units composed of material similar to typical Dunnage Terrane rocks demonstrates that the Gander River ultrabasic belt is neither the most eastward extent of the Dunnage Terrane nor the sole thrust upon which Dunnage Terrane material was transported eastward. The two belts have associated diagnostic geochemical signatures and are bounded on the north and south by linear patterns in both the geophysical and geochemical patterns. The block defined by these geophysical and geochemical patterns is the same as that upon which the classic Gander Terrane was defined. The evidence presented in this paper suggests that this block may be allochthonous, which implies that the nature of the Gander Terrane may need to be reconsidered.

Offshore extensions of the Avalon Zone of Newfoundland

1985 ◽  
Vol 22 (8) ◽  
pp. 1163-1170 ◽  
Author(s):  
H. G. Miller ◽  
A. K. Goodacre ◽  
R. V. Cooper ◽  
D. Halliday
Keyword(s):  
Strong Correlation ◽  
Sedimentary Basin ◽  
Magnetic Data ◽  
Two Dimensional ◽  
Gravity And Magnetic ◽  
Magnetic Modelling ◽  
Dimensional Gravity ◽  
Gravity And Magnetic Data ◽  
Avalon Peninsula ◽  
Block Faulting

Gravity and magnetic data from the nearshore region of the Avalon Zone of Newfoundland provide evidence of the nature of a sedimentary basin immediately east of the Avalon Peninsula. The data also suggest a strong correlation between the arcuate magnetic patterns of the offshore portion of the Avalon Zone and the Precambrian mafic volcanics mapped onshore. The offshore basin is interpreted to have been formed by Precambrian block faulting and subsequently filled by sediments derived from surrounding paleotopographic highs. Two-dimensional gravity and magnetic modelling results suggest the presence of mafic material beneath the modelled 9+ km of sediment in the basin.

Potential-field signatures of buried Precambrian basement in the Western Canada Sedimentary Basin

2000 ◽  
Vol 37 (11) ◽  
pp. 1453-1471 ◽  
Author(s):  
M Pilkington ◽  
W F Miles ◽  
G M Ross ◽  
W R Roest
Keyword(s):  
Sedimentary Basin ◽  
Gravity Data ◽  
Magnetic Data ◽  
Western Canada ◽  
Precambrian Basement ◽  
Western Canada Sedimentary Basin ◽  
Magmatic Arc ◽  
Magnetic Source ◽  
Definition Of ◽  
Canada Sedimentary Basin

An internally consistent, levelled compilation of magnetic data is derived for Alberta and northeastern British Columbia. With Bouguer gravity data, this compilation is used to refine the definition of Precambrian basement domains within the Western Canada Sedimentary Basin. Magnetic data are draped at a constant distance above the mapped basement surface to reduce the effects of varying magnetic source depths. Automated interpretation methods that effectively map outlines of magnetic sources are used to characterize the internal structure of the domains and to aid in their delineation. The basement domain map thus derived differs from previous interpretations in the extension of domains further to the southwest, due mainly to the availability of new public-domain magnetic data and the more precise definition of domain boundaries, based on the magnetic source location maps. The Nahanni, Hottah, Chinchaga, Thorsby, Vulcan, and Kiskatinaw domains are weakly magnetic and characterized by magnetic sources that are paramagnetic, comprising low-susceptibility silicate minerals. All other domains are characterized by the presence of ferrimagnetic material, most likely magnetite, which has a sufficiently high susceptibility to produce measurable anomalies. The largest anomalies and magnetizations are found in the Fort Nelson, Fort Simpson, Buffalo Head, Talston, Ksituan, and Matzhiwin domains. Such large magnetizations are usually indicative of intermediate igneous rocks associated with magmatic arc environments. Moderate-amplitude anomalies and (or) magnetizations are characteristic of the Nova, Wabamun, Lacombe, Rimbey, Loverna, and Medicine Hat domains, suggesting the presence of ferrimagnetic basic and granitoid rocks. Within some of the moderately magnetic domains are areas of paramagnetic lithologies that produce no magnetic anomalies. The narrower regions of magnetic lows, such as the Thorsby, Kiskatinaw, and Vulcan domains, are interpreted as resulting from demagnetization effects accompanying collision. Since demagnetization zones are limited in areal extent, the wider, more extensive magnetic lows of the Chinchaga and Hottah domains likely result from a combination of boundary demagnetization and a lower bulk magnetization level of crustal lithologies present.

Geological significance of high-resolution magnetic data in the Quesnel terrane, Central British Columbia1This article is one of a series of papers published in this Special Issue on the theme of New insights in Cordilleran Intermontane geoscience: reducing exploration risk in the mountain pine beetle-affected area, British Columbia.2Geological Survey of Canada Contribution No. 20100225.

2011 ◽  
Vol 48 (6) ◽  
pp. 1065-1089 ◽  
Author(s):  
M.D. Thomas ◽  
M. Pilkington ◽  
R.G. Anderson
Keyword(s):  
British Columbia ◽  
High Resolution ◽  
Mountain Pine Beetle ◽  
Gravity Data ◽  
Sedimentary Cover ◽  
Volcanic Rocks ◽  
Geological Mapping ◽  
Magnetic Data ◽  
Structural Variations ◽  
High Resolution Data

The ability of airborne sensors to image the magnetic signatures of prospective Quesnel terrane rocks through ubiquitous Quaternary glacial sedimentary cover in central British Columbia helps target new areas for mineral exploration. Newly acquired high-resolution data provide new perspectives on the nature and probable areal distribution of many geological units, revealing detail and information unattainable by conventional geological mapping. In combination with gravity data, these magnetic data indicate the presence of a granitic intrusion and a development of Nicola Group volcanic rocks, both potential hosts for porphyry- and (or) vein-type mineralization, under younger Tertiary volcanic cover. At a finer scale, magnetic patterns and fabrics permit discrimination between volcanic rocks of the Tertiary Chilcotin and Kamloops groups, and detection of subtle compositional and (or) structural variations within the groups. Contacts between volcanic cover and basement rocks and between basement units are more accurately defined, significantly reducing locally the areal extent of volcanic cover and opening up more ground for exploration. The high resolution of features in images of magnetic vertical derivatives reveals the Naver pluton to be more complex than currently mapped, comprising several integral elements, one of which may be a large roof pendant. Internal subdivisions of the Thuya batholith are defined, and annular marginal phases are proposed within two large granodioritic intrusions. Several new intrusions are proposed within the extensive, mainly sedimentary Devonian–Triassic terrain northeast of Kamloops, internal composition variation is suggested for some larger mapped intrusions, and areas underlain by some intrusions are enlarged.

scholarly journals Potential-field modelling of the prospective Chibougamau area (northeastern Abitibi subprovince, Quebec, Canada) using geological, geophysical, and petrophysical constraints

2020 ◽  
pp. 1-16
Author(s):  
Amir Maleki ◽  
Richard Smith ◽  
Esmaeil Eshaghi ◽  
Lucie Mathieu ◽  
David Snyder ◽  
...  
Keyword(s):  
Potential Field ◽  
Gravity Data ◽  
Geophysical Data ◽  
Magnetic Data ◽  
Data Sets ◽  
Seismic Section ◽  
Potential Field Data ◽  
Abitibi Subprovince ◽  
Seismic Sections ◽  
Potential Field Modelling

This paper focusses on obtaining a better understanding of the subsurface geology of the Chibougamau area, in the northeast of the Abitibi greenstone belt (Superior craton), using geophysical data collected along a 128 km long traverse with a rough southwest–northeast orientation. We have constructed two-dimensional (2D) models of the study area that are consistent with newly collected gravity data and high-resolution magnetic data sets. The initial models were constrained at depth by an interpretation of a new seismic section and at surface by the bedrock geology and known geometry of lithological units. The attributes of the model were constrained using petrophysical measurements so that the final model is compatible with all available geological and geophysical data. The potential-field data modelling resolved the geometry of plutons and magnetic bodies that are transparent on seismic sections. The new model is consistent with the known structural geology, such as open folding, and provides an improvement in estimating the size, shape, and depth of the Barlow and Chibougamau plutons. The Chibougamau pluton is known to be associated with Cu–Au magmatic-hydrothermal mineralisation and, as the volume and geometry of intrusive bodies is paramount to the exploration of such mineralisation, the modelling presented here provides a scientific foundation to exploration models focused on such mineralisation.

Late Precambrian Rocks of Eastern Avalon Peninsula, Newfoundland — A Volcanic Island Complex

1971 ◽  
Vol 8 (8) ◽  
pp. 899-915 ◽  
Author(s):  
C. J. Hughes ◽  
W. D. Brückner
Keyword(s):  
Volcanic Rocks ◽  
Main Group ◽  
Volcanic Island ◽  
Precambrian Rocks ◽  
Crustal Movements ◽  
Late Precambrian ◽  
Isostatic Adjustment ◽  
Avalon Peninsula ◽  
Vertical Crustal Movements

A model of island volcanism is presented in which rocks are referred to (1) a "syn-volcanic" constructional phase represented by rocks of four penecontemporaneous facies—vent, alluvial, marine, and plutonic—whose interrelationships are discussed and (2) a "post-volcanic" destructional phase of erosion and sedimentation accompanied by isostatic adjustment resulting in the spreading of an apron of volcanic sediments around a slowly rising and eroding island core.The late Precambrian rocks of the eastern part of the Avalon Peninsula, southeasternmost Newfoundland, are shown to fit this model rather closely, both petrographically and in their distribution and field relationships. The Harbour Main Group of volcanic rocks, the Conception Group of marine volcanic sediments and tuffs, and the Holyrood Plutonic Series, dated at 574 ± 11 m.y., were all formed during the syn-volcanic constructional phase. Their apparently conflicting age relationships can be reconciled to the view that they are penecontemporaneous facies. The Cabot and Hodgewater Groups of marine and alluvial volcanic sediments were formed during the post-volcanic destructional phase. Apart from vertical crustal movements, only minor diastrophic deformation appears to have occurred during these two phases.This model of volcanic island environment may help in interpreting the geology of several other belts in eastern and central Newfoundland comprising late Precambrian and Paleozoic volcanic rocks and sediments.

Hockley Fault revisited: More geophysical data and new evidence on the fault location, Houston, Texas

Geophysics ◽  
2018 ◽  
Vol 83 (3) ◽  
pp. B133-B142 ◽  
Author(s):  
Mustafa Saribudak ◽  
Michal Ruder ◽  
Bob Van Nieuwenhuise
Keyword(s):  
Structural Damage ◽  
Fault Location ◽  
Gulf Coast ◽  
Gravity Data ◽  
Geophysical Data ◽  
Aerial Photographs ◽  
Unconsolidated Sediments ◽  
Magnetic Data ◽  
Harris County ◽  
Resistivity Data

Ongoing sediment deposition and related deformation in the Gulf of Mexico cause faulting in coastal areas. These faults are aseismic and underlie much of the Gulf Coast area including the city of Houston in Harris County, Texas. Considering that the average movement of these faults is approximately 8 cm per decade in Harris County, there is a great potential for structural damage to highways, utility infrastructure, and buildings that cross these features. Using integrated geophysical data, we have investigated the Hockley Fault, located in the northwest part of Harris County across Highway 290. Our magnetic, gravity, conductivity, and resistivity data displayed a fault anomaly whose location is consistent with the southern portion of the Hockley Fault mapped by previous researchers at precisely the same location. Gravity data indicate a significant fault signature that is coincident with the magnetic and conductivity data, with relatively positive gravity values observed in the downthrown section. Farther north across Highway 290, the resistivity data and the presence of fault scarps indicate that the Hockley Fault appears to be offset to the east, which has not been previously documented. The publicly available LiDAR data and historical aerial photographs of the study area support our geophysical findings. This important geohazard result impacts the mitigation plan for the Hockley Fault because it crosses and deforms Highway 290 in the study area. The nonunique model of the gravity and magnetic data indicates strong correlation of a lateral change in density and magnetic properties across the Hockley Fault. The gravity data differ from the expected signature. The high gravity observed on the downthrown side of the fault is probably caused by the compaction of unconsolidated sediments on the downthrown side. There is a narrow zone of relative negative magnetic anomalies adjacent to the fault on the downthrown side. The source of this magnetization could be due to the alteration of mineralogies by the introduction of fluids into the fault zone.

Airborne geophysical surveys in Greenland in 1998

1999 ◽  
pp. 34-38 ◽  
Author(s):  
Thorkild M. Rasmussen ◽  
Leif Thorning
Keyword(s):  
High Resolution ◽  
Geophysical Data ◽  
Digital Data ◽  
Geological Survey ◽  
Magnetic Data ◽  
Magnetic Survey ◽  
Original Series ◽  
Geophysical Surveys ◽  
The Government

NOTE: This article was published in a former series of GEUS Bulletin. Please use the original series name when citing this article, for example: Rasmussen, T. M., & Thorning, L. (1999). Airborne geophysical surveys in Greenland in 1998. Geology of Greenland Survey Bulletin, 183, 34-38. https://doi.org/10.34194/ggub.v183.5202 _______________ Airborne geophysical surveying in Greenland during 1998 consisted of a magnetic project referred to as ‘Aeromag 1998’ and a combined electromagnetic and magnetic project referred to as ‘AEM Greenland 1998’. The Government of Greenland financed both with administration managed by the Geological Survey of Denmark and Greenland (GEUS). With the completion of the two projects, approximately 305 000 line km of regional high-resolution magnetic data and approximately 75 000 line km of detailed multiparameter data (electromagnetic, magnetic and partly radiometric) are now available from government financed projects. Figure 1 shows the location of the surveyed areas with highresolution geophysical data together with the area selected for a magnetic survey in 1999. Completion of the two projects was marked by the release of data on 1 March, 1999. The data are included in the geoscientific databases at the Survey for public use; digital data and maps may be purchased from the Survey.

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