Info

Well-determined rock age and a presumption that the magnetization is the same age Sufficient number of samples (N > 24), k (or K) > 10, and a95 (or A95) < 16° Adequate demagnetization that demonstrably includes vector subtraction information Field tests that constrain the age of magnetization Structural control and tectonic coherence with craton or block involved Documented evidence of the presence of reversals

No resemblance to paleomagnetic poles of younger age (by more than a period)

"After Van der Voo (1990a).

assured that the magnetic components are isolated as much as possible. Field tests may not always be possible as required by (No. 4), but if such tests are positive they satisfy this criterion. The area studied should clearly belong to the craton or tectonic block involved (No. 5). For orogenic belts, results from intrusives with ages older than the last tectonic phase, or results from thrust sheets that may have been rotated, will generally not satisfy this criterion. The presence of reversals (No. 6) is a powerful test that enough time has elapsed for secular variation to be averaged. Antipodal reversals also preclude any systematic bias caused by an overprint. There should be no suspicion of remagnetization (No. 7), a criterion satisfied when a pole position does not resemble results from rocks of much younger age. A pole position based on a remagnetization is only viable if the age of remagnetization is constrained by independent means.

Few results satisfy all seven criteria; however, Van der Voo (1990a) suggests that a data set satisfying on average most of the criteria (Q > 4) can be described as more robust than one with Q- 2.

6.2.3 The Global Paleomagnetic Database (GPMDB)

The Paleomagnetism Working Group of the International Association of Geomagnetism and Aeronomy, IAGA, has established various databases in paleomagnetism. The most important of these from the perspective of this book is the Global Paleomagnetic Database, GPMDB, which contains details of all

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