MULTI-DETRITAL MINERAL GEOCHRONOLOGY OF SEDIMENTARY ROCKS FROM ORDOVICIAN TO DEVONIAN FOREDEEPS IN THE NEWFOUNDLAND APPALACHIANS

Provenance studies using U-Pb geochronology and trace elements on multiple detrital minerals can yield more unique provenance interpreations over solely detrital zircon-based studies. We here present preliminary zircon, rutile and apatite U-Pb and trace element provenance data from several foredeeps in the Newfoundland Appalachians to better understand the tectonic evolution involved in terrane accretion.

Four samples were dated from the Devonian(?) Fortune belt on the western margin of the Avalonia near its contact with Ganderia. The belt mainly comprises three formations of sandstone and conglomerate separated by unconformities. The two lowest formations are cut by ca. 376 Ma granite dikes. Apatite from two sandstone samples yielded dominant age peaks at ca. 440 and ca. 495 Ma, respectively, and rutile from the former a single age peak at ca. 460 Ma. Rutile from another sandstone has major age peaks at ca. 650 Ma and 730 Ma, and that from a conglomerate ca. 460 Ma and 610 Ma. Rutile also has minor peaks at ca. 1000 Ma and 1200 Ma. These data suggest a mainly Ganderian provenance with some Avalonian contribution.

Blocks and matrix sandstone was collected from the Lower Ordovician Dunnage Mélange near the main Iapetus suture zone (Beothuk line). Apatite yielded two major age peaks at ca. 570 Ma and 650 Ma, and two minor peaks at ca. 910 Ma and 1800 Ma. Rutile has a major age peak at ca. 1100 Ma and three subordinate peaks at ca. 680 Ma, 1900 Ma and 2200 Ma. The ages are consistent with a Ganderian provenance.

Apatite from a large sandstone block in the Companion Mélange of the Humber Arm allochthon yielded a major peak at ca. 980 Ma, and three subordinate peaks at ca. 1780 Ma, 2710 Ma and 3010 Ma, whereas rutile gave two major peaks at 1070 Ma and 1730 Ma. All ages are indicative of a Laurentian provenance. Apatite from red beds of the Upper Ordovician Misty Point Formation yielded a single age peak at ca. 468 Ma. Their trace element compositions indicate a mainly high-grade metamorphic origin suggesting a Taconic source. Metamorphic rutile from the same sample yielded major peaks at ca. 540 Ma, 1035 Ma, 1120 Ma and 1685 Ma, and a minor peak at ca. 1970 Ma. The Proterozoic dates indicate a Laurentian provenance, but the provenance of the ca. 540 Ma rutile is uncertain and may be exotic.