Problems in palaeomagnetic synthesis illustrated by results from Permo-Triassic dolerites in Guyana |
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| Authors: | RB Hargraves |
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| Institution: | Department of Geological and Geophysical Sciences, Princeton University, Princeton, NJ 08540 U.S.A. |
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| Abstract: | Relatively consistent palaeomagnetic results have been obtained after alternating field demagnetization of samples from seven of eight dolerite dykes (ten sites) intruding the basement shield in Guyana. Results from five of these dykes (seven sites, 33 samples) give an average site-pole at 63°S, 138°W, k = 24.6, α95 = 12.4°. Despite KAr ages ranging from 262 to 675 m.y., the good grouping suggests that these dykes are generally contemporaneous, and they are judged to be Permo-Triassic. The remaining two dykes have distinct, apparently Precambrian, magnetizations.Comparison of these Permo-Triassic data with other studies of reputedly similar age rocks from elsewhere in South America, show a significant scatter, the cause of which cannot be uniquely determined. This problem is commonly encountered in general palaeomagnetic synthesis, and to alleviate it, the analysis of all site-poles from a single continent for a substantial time segment is recommended.A polar-wander swath should result, the dimensions and pattern of which are theoretically a function primarily of secular variation and continental drift. Such a plot of site-poles gives appropriate weight to all useful palaeomagnetic data; it can be readily updated as new results are added to the data reservoir. |
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