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.

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.

scholarly journals Two Dimensional Modeling of Basaltic Rocks Intrusion Based on The Local Magnetic Anomalies Data in Jatilawang District Banyumas Regency

2020 ◽  
Vol 10 (2) ◽  
pp. 171
Author(s):  
Sehah Sehah ◽  
Sukmaji Anom Raharjo ◽  
Urip Nurwijayanto Prabowo
Keyword(s):  
Magnetic Susceptibility ◽  
Magnetic Anomalies ◽  
Basaltic Rock ◽  
Research Area ◽  
Magnetic Data ◽  
Two Dimensional ◽  
Basaltic Rocks ◽  
Dimensional Modeling ◽  
Susceptibility Contrast ◽  
Lateral Length

Two dimensional modeling to basaltic rocks intrusion in Pekuncen and Karanglewas Villages Jatilawang District, Banyumas Regency, Central Java based on the local magnetic anomalies data has been carried out in March – June 2020. The amount of magnetic data obtained from the acquisition in the field was 239 data stretching in position of 109.107222° – 109.134944°E and 7.561361° – 7.577306°S, with the local magnetic anomalies values ranging of -2,961.11 – 1,516.31 nT. To model anomalous sources in the subsurface in two dimensions, then the local magnetic anomalies data is transformed into pseudogravity anomalies data, so that anomalous value can be obtained as -27.815 – 41.087 mGal. Based on the pseudogravity anomalous map, the basaltic rock intrusion is interpreted to be located in the eastern part of the research area, so modeling of anomalous sources is conducted in this area. The results of 2D-modeling to local magnetic anomalies data indicate the presence of anomalous object interpreted as basaltic rock intrusion with magnetic susceptibility contrast value of 0.0223 cgs, located at depth of 52.61 – 505.97 m and a lateral length of 1777.94 m. This rock intrudes sediment rock from the Halang Formation and is connected to other basaltic rock near the surface with magnetic susceptibility contrast value of 0.0165 cgs, located at depth of 1.94 – 80.90 m and lateral length of 751.83 m. The results of lithological interpretation are in accordance with the geological information of the research area.

SPECTRAL ANALYSIS OF GRAVITY AND MAGNETIC ANOMALIES DUE TO TWO‐DIMENSIONAL STRUCTURES

Geophysics ◽  
1975 ◽  
Vol 40 (6) ◽  
pp. 993-1013 ◽  
Author(s):  
B. K. Bhattacharyya ◽  
Lei‐Kuang Leu
Keyword(s):  
Linear Equations ◽  
Magnetic Anomalies ◽  
Dimensional Structure ◽  
Approximation Technique ◽  
System Of Equations ◽  
Two Dimensional ◽  
System Of Linear Equations ◽  
Unknown Parameters ◽  
Low Frequencies ◽  
Gravity And Magnetic

The expressions for the spectra of both gravity and magnetic anomalies due to a two‐dimensional structure consist of (except for a factor) sums of exponentials. The exponents of these exponentials are functions of frequency and the locations of the corners of the polygonal cross‐section of the structure. Two computationally feasible methods for determining the exponents from a given spectrum are described in this paper; they are essentially based on the generation of a system of linear equations. The unknown coefficients in this system of equations are functions of the corner locations. The first method requires expansion of the exponentials in the expressions for the spectra in the form of a series and works reliably when the amplitudes of low frequencies are analyzed. The unknown parameters are determined fairly accurately with this method by suitable combinations of the spectra of the observed anomaly and its moments. The second method utilizes an exponential approximation technique for producing the system of linear equations. If only the spectrum of the anomaly is used, the system of equations becomes ill‐conditioned in most cases resulting in grossly inaccurate solutions. However, particular combinations of the spectra of the anomaly and its first and second order moments are found to improve significantly the behavior of the system of equations and thus the quality of results. It has also been found that the mean values of corner locations can be calculated fairly accurately by taking the ratios of the spectra of the anomaly and its moments. Once the corner locations are found, computation of the density contrast in the case of a gravity anomaly and the magnetization contrast for a magnetic anomaly is straightforward.

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.

Modeling complexly magnetized two‐dimensional bodies of arbitrary shape

Geophysics ◽  
1993 ◽  
Vol 58 (5) ◽  
pp. 637-644 ◽  
Author(s):  
John Mariano ◽  
William J. Hinze
Keyword(s):  
Arbitrary Shape ◽  
Lake Superior ◽  
Volcanic Rocks ◽  
Three Dimensional ◽  
Magnetic Anomalies ◽  
Two Dimensional ◽  
Discrete Elements ◽  
Convenient Means ◽  
Equivalent Dipole ◽  
Forward Computation

A method has been devised for the forward computation of magnetic anomalies due to two‐dimensional (2-D) polygonal bodies with heterogeneously directed magnetization. The calculations are based on the equivalent line source approach wherein the source is subdivided into discrete elements that vary spatially in their magnetic properties. This equivalent dipole line method provides a fast and convenient means of representing and computing magnetic anomalies for bodies possessing complexly varying magnitude and direction of magnetization. The algorithm has been tested and applied to several generalized cases to verify the accuracy of the computation. The technique has also been used to model observed aeromagnetic anomalies associated with the structurally deformed, remanently magnetized Keweenawan volcanic rocks in eastern Lake Superior. This method is also easily adapted to the calculation of anomalies due to two and one‐half‐dimensional (2.5-D) and three‐dimensional (3-D) heterogeneously magnetized sources.

scholarly journals Gravity and magnetic susceptibility survey over the northern part of the supracrustal rocks in the Disko Bugt area, central West Greenland

1989 ◽  
Vol 145 ◽  
pp. 20-23
Author(s):  
L Thorning
Keyword(s):  
Magnetic Susceptibility ◽  
Geophysical Data ◽  
Aeromagnetic Survey ◽  
West Greenland ◽  
Gravity And Magnetic

As part of the Disko Bugt project (Kalsbeek, 1989) a survey of gravity and magnetic susceptibility was carried out over parts of the supracrustal rocks and the Atå granite/tonalite (fig. 1). The objective of the survey was to acquire new geophysical data that, together with the existing regional aeromagnetic survey in the area (Thorning, 1988), can be used to study the deeper structures related to the granite and the supracrustal belts in the area.

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