Burial and exhumation of the Long Range Inlier and its surroundings, western Newfoundland: results of an apatite fission-track study

Abstract

The Long Range Inlier, a steep-sided plateau underlain mainly by Grenvillian gneisses, is the most prominent topographic feature of western Newfoundland. Apatite fission-track analysis of 31 samples from the Long Range Inlier and its surroundings yielded measured apparent ages of 343–152 Ma. Age versus elevation plots, track-length distributions, and model thermal histories indicate that the region experienced slow cooling in the late Paleozoic, with apparent exhumation rates of 7–9 m∙Ma−1 and cooling rates of 0.08–0.28 °C∙Ma−1. Model thermal histories suggest that the present upper surface of the Long Range plateau cooled below ~120 °C in Ordovician times. The thermal histories are compatible with, but do not require, some exhumation of the Long Range Inlier along Acadian thrust faults. Results from Early Carboniferous sedimentary rocks of the Deer Lake Basin are similar to Long Range Inlier data from similar elevations, implying that at some time between ~350 and 300 Ma, the entire region was buried to depths sufficient to induce total annealing (T > 120 °C) in these samples. Closure ages determined from model thermal histories indicate that regional cooling to temperatures below ~120 °C began before 300 Ma. The Carboniferous sedimentary cover was largely removed by Jurassic time, perhaps in response to lowering of regional base level by rifting associated with the opening of the Atlantic Ocean.

Zircon fission‐track ages from Newfoundland—A proxy for high geothermal gradients and exhumation before opening of the Central Atlantic Ocean

“…Zircon fission‐track (ZFT) ages of Appalachian metamorphic rocks in Nova Scotia (Willner et al., ) revealed ages up to 150 Ma younger than the overlying Lower Carboniferous sedimentary cover of the late Palaeozoic Maritimes Basin. These data indicate a period of cooling before opening of the Atlantic Ocean, supporting similar conclusions drawn from several apatite fission‐track (AFT) studies in Atlantic Canada (e.g., Hendriks, Jamieson, Willett, & Zentilli, ; Ryan, ; Ryan & Zentilli, ). Additionally, the typical ~200 to 240°C closure temperatures of ZFT ages (e.g., Reiners & Brandon, ) provide a higher minimum estimate of late Palaeozoic sedimentary burial than AFT ages with closure temperatures of ~100°C.…”

“…However, the former extent and thickness of such cover remain to be poorly constrained. Estimates are restricted to interpretation of AFT results from the north‐western part of the island (Hendriks et al., ). We present new ZFT ages from basement rocks in central Newfoundland to constrain more fully the extent and depth of maximum temperatures reached during late Palaeozoic burial, as well as to date more precisely the timing of removal of this cover.…”

Detrital monazite geochronology, Upper Jurassic–Lower Cretaceous of the Scotian Basin: significance for tracking first-cycle sources

“…The Gulf of St Lawrence and adjacent land areas host the thick terrestrial sedimentary rocks of the Maritimes Basin, of late Devonian to early Permian age. Most of the contacts between major rock types in the Appalachians are steep, and apatite fission track data suggest no more than 1 km of denudation since the Jurassic (Hendriks et al 1993;Grist & Zentilli 2003). Taken together, this implies that the modern distribution of rock types (Fig.…”

Varietal heavy mineral analysis of sediment provenance, Lower Cretaceous Scotian Basin, eastern Canada

“…The Gulf of St Lawrence and adjacent land areas host the thick Maritimes Basin of late Devonian to early Permian age. Most of the contacts between major rock types in the Appalachians are steep, and apatite fission track data suggest no more than 1 km of denudation since the Jurassic (Hendriks et al, 1993;Grist and Zentilli, 2003), suggesting that the modern distribution of rock types (Fig. 1) is a reasonable proxy for Early Cretaceous sources of detrital sediment.…”