Direct dating of paleomagnetic results from Precambrian sediments in the Amazon craton: Evidence for Grenvillian emplacement of exotic crust in SE Appalachians of North America

摘要

We apply a new diagenetic dating technique to determine the age of magnetization for Precambrian sedimentary rocks in the SW Amazon craton. Two new palcomagnetic poles are reported from the rocks of the Aguapei Gp.: red beds of the Fortuna Fm. (P-lat = 59.8 degrees N, P-lon = 155.9 degrees E, A(95)=9.5, K= 14, 18 sites, N 128/115, Q=5) and the reverse-polarity mudstones of the overlying Vale da Promissao Formation (P-lat=49.5 degrees N, P-lon = 89.3 degrees E, A(95) = 12.5, K=30, 6 sites, N=94/80, Q=4). The Fortuna Fm. magnetization is hosted by massive, interstitial hematite cement and constitutes a post-depositional remanence. The age of diagenesis of the red beds is well-constrained by the 1149 +/- 7 Ma U-Pb age of authigenic xenotime rims on detrital zircons determined by SHRIMP analysis. The magnetite-hosted remanence of the Vale da Promissao Fm. may be detrital in origin, but the age of deposition is poorly constrained. The reliable and precisely-dated Fortuna Fun. pateomagnetic pole fixes the paleogeographic position of the Amazon craton near the SE Appalachians portion of North America at 1.15 Ga. These data demonstrate a mobile Grenvillian link between these two cratons, and support the recent identification of Amazon crust in the Blue Ridge province region of North America.