Palaeomagnetism and magnetic fabric of the Roraima sandstone and basement rocks of the Santa Elena region, south eastern Venezuela
Palaeomagnetism and magnetic fabric of the Roraima sandstone and basement rocks of the Santa Elena region, south eastern Venezuela
A study of the palaeomagnetism and magnetic fabric of rocks from the Roraima Group and the Cuchivero Province of the Guayana shield of southeastern Venezuela has been carried out. A total of 232 samples (361 specimens) were collected from the Uairen, Cuquenan and Uaimapue sedimentary formations of the Roraima Group and 29 samples (38 specimens) from the Cuchivero Province. The characteristic magnetisations of each sample were analyzed by linear regression analysis of Zijderveld vector diagrams and/or vector average, using data obtained from incremental a.f. and thermal demagnetization. The eccentricity method of Engebretson and Beck (1978) has been applied to estimate, and aid interpretation of, the elongation direction of the palaeomagnetic data set for the Uairen formation. Rotations suggested by Bullard et al. (1965), and Onstott and Hargraves (1981) have been applied to the palaeomagnetic pole positions obtained from this study, in order to evaluate their possible significance in the context of published Precambrian continental reconstruction. Two components of the magnetization were generally isolated by incremental demagnetization in samples from the Cuchivero Province, the Uairen and the Uaimapue formations, while samples from the Cuquenan formation showed only a single component of magnetization. The more stable component from the Cichivero rocks yields a palaeomagnetic pole position which, when compared with the apparent polar wander curves of McElhinny and McWilliams (1977), and Graterol and Hailwood (1981), indicates that the magnetization was probably acquired during the Pretransamazonian orogenesis (2600-2100 m.y.). The less-stable component is believed to have been acquired during the low grade Nickorie metamorphic event (1300-1100 m.y.). The pole positions calculated from both the more-stable and less-stable components of the Uairen formation corresponds approximately with the 2000 m.y. point on the apparent polar wander path of Onstott and Hargraves (1981). This suggests that both components of magnetization may have been acquired at about this time. The single component of magnetization identified in samples from the Cuquenan formation suggests a possible age of magnetization of about 1900 m.y. The magnetic fabric results indicate a dominant east-southeasterly alignment in grain long axes in the sediments of the Uairen formation, which may be related to sediment transport in this direction. (D67494/86)
University of Southampton
Castillo Rodriguez, Jesus Horacio
1985
Castillo Rodriguez, Jesus Horacio
Castillo Rodriguez, Jesus Horacio
(1985)
Palaeomagnetism and magnetic fabric of the Roraima sandstone and basement rocks of the Santa Elena region, south eastern Venezuela.
University of Southampton, Doctoral Thesis.
Record type:
Thesis
(Doctoral)
Abstract
A study of the palaeomagnetism and magnetic fabric of rocks from the Roraima Group and the Cuchivero Province of the Guayana shield of southeastern Venezuela has been carried out. A total of 232 samples (361 specimens) were collected from the Uairen, Cuquenan and Uaimapue sedimentary formations of the Roraima Group and 29 samples (38 specimens) from the Cuchivero Province. The characteristic magnetisations of each sample were analyzed by linear regression analysis of Zijderveld vector diagrams and/or vector average, using data obtained from incremental a.f. and thermal demagnetization. The eccentricity method of Engebretson and Beck (1978) has been applied to estimate, and aid interpretation of, the elongation direction of the palaeomagnetic data set for the Uairen formation. Rotations suggested by Bullard et al. (1965), and Onstott and Hargraves (1981) have been applied to the palaeomagnetic pole positions obtained from this study, in order to evaluate their possible significance in the context of published Precambrian continental reconstruction. Two components of the magnetization were generally isolated by incremental demagnetization in samples from the Cuchivero Province, the Uairen and the Uaimapue formations, while samples from the Cuquenan formation showed only a single component of magnetization. The more stable component from the Cichivero rocks yields a palaeomagnetic pole position which, when compared with the apparent polar wander curves of McElhinny and McWilliams (1977), and Graterol and Hailwood (1981), indicates that the magnetization was probably acquired during the Pretransamazonian orogenesis (2600-2100 m.y.). The less-stable component is believed to have been acquired during the low grade Nickorie metamorphic event (1300-1100 m.y.). The pole positions calculated from both the more-stable and less-stable components of the Uairen formation corresponds approximately with the 2000 m.y. point on the apparent polar wander path of Onstott and Hargraves (1981). This suggests that both components of magnetization may have been acquired at about this time. The single component of magnetization identified in samples from the Cuquenan formation suggests a possible age of magnetization of about 1900 m.y. The magnetic fabric results indicate a dominant east-southeasterly alignment in grain long axes in the sediments of the Uairen formation, which may be related to sediment transport in this direction. (D67494/86)
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Published date: 1985
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Local EPrints ID: 461516
URI: http://eprints.soton.ac.uk/id/eprint/461516
PURE UUID: 81b5526d-aee0-4511-b87d-7b3a24511291
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Date deposited: 04 Jul 2022 18:48
Last modified: 04 Jul 2022 18:48
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Author:
Jesus Horacio Castillo Rodriguez
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