|کد مقاله||کد نشریه||سال انتشار||مقاله انگلیسی||ترجمه فارسی||نسخه تمام متن|
|4724609||1639723||2007||20 صفحه PDF||سفارش دهید||دانلود رایگان|
The style of tectonic processes on the young Earth is a topic of intense debate. Palaeomagnetism provides the only robust tests with which to settle theoretical disputes based on the rock record that infer large scale horizontal motions between palaeocontinents. A possible apparent polar wander path (APWP) of the Kaapvaal Craton shows significant distances between adjacent palaeomagnetic poles that can be interpreted as evidence for such horizontal displacements during the Archaean-Palaeoproterozoic. There are, however, substantial uncertainties build into this APWP. Currently, the published APWP for the Kaapvaal Craton comprises eight palaeopoles between 3.0 and 1.9 Ga, including several between 2.8 and 2.7 Ma that indicate possible horizontal motions exceeding 6500 km. The aim of this contribution is to increase the pole density within this interval and in doing so to test the robustness of the Kaapvaal APWP within this time frame. More than 250 samples of basalt, diamictite and dolerite of the Neoarchaean Pongola (ca. 2.95–2.85 Ga) and Ventersdorp (ca. 2.71–2.70 Ga) Supergroups of the Kaapvaal Craton were sampled both at the surface and in an underground mine. Thermal demagnetisation revealed two magnetic components. A high temperature component is present in three Pongola formations and in two Ventersdorp formations; these may be recorders of the primary natural remanent magnetisation. Because of lack of precise geochronology and positive field tests, this magnetisation can only be constrained to be older than ca. 2.05 Ga. A medium temperature overprint in many samples probably records remagnetisation at ca. 180 Ma, during the emplacement of basalts and dolerites of the Mesozoic Karoo Large Igneous Province. This remagnetisation appears to have affected a vast area of the Kaapvaal Craton. Our new palaeopoles, together with those published previously, demonstrate that the Neoarchaean APWP of the Kaapvaal Craton remains poorly defined. Direct comparisons between the APWP of the Kaapvaal Craton with APWPs of other Archaean cratons to determine relative motions between Archaean continents, therefore, need more reliable data.
Journal: Precambrian Research - Volume 153, Issues 1–2, 10 February 2007, Pages 96–115