High Unblocking Temperature Component Research Articles

Florida as an exotic terrane: Paleomagnetic and geochronologic investigation of lower Paleozoic rocks from the subsurface of Florida

New geophysical and geochronological data are presented for a lower Paleozoic subsurface (794–827 m depth) sedimentary core recovered from Alachua County, northern Florida. Paleomagnetic data from samples taken at various depths along the core indicate that a high unblocking temperature component is isolated during thermal demagnetization between 400 and 600 °C. The mean inclination of this component is 65°, yielding a paleolatitude of 49°. Previous paleogeographic reconstructions for the early Paleozoic of North America place Florida at a significantly lower paleolatitude (∼28°), whereas our data are consistent with a Gondwanian fit (∼50°–60°). U/Pb isotopic systematics of zircons separated from core samples yield five dates ranging from ca. 1650 to 1800 Ma. Because there are no known source rocks of this antiquity in southeastern North America, the most probable provenance for these detrital zircons is either Africa or South America. These two new lines of geologic data provide strong evidence confirming previous suggestions that Florida was part of Gondwana during the early Paleozoic and that its current configuration is that of an exotic terrane sutured to North America during the fragmentation of Pangea.

Paleomagnetism of the Upper Devonian Catskill Formation from the southern limb of the Pennsylvania Salient: Possible evidence of oroclinal rotation

Multiple components of magnetization were isolated in the natural remanent magnetization of samples of the Upper Devonian Catskill Formation red beds taken from the southern limb of the Pennsylvania Salient. The dominant, thermally distributed component (SF), previously thought to predate folding, is demonstrably synfolding in origin. The mean direction for SF based on data from the current study and a previous study is Declination/Inclination = 161.6°/7.9°, a95 = 3.9° (pole position 127.3°E, 43.1°N, A95 = 3.1°, N = 14 sites). Although the remagnetization is clearly synfolding in most areas, the relative ages of folding and remagnetization vary locally. A subordinate high unblocking temperature component (HT) has a mean tilt corrected direction of 160°/36°, a95 = 16° (pole position 123.5°E, 26.1°N, A95 = 15.4°, n = 7 samples). Comparison of HT with the prefolding magnetization isolated in the northern limb of the salient suggests that the paleolatitude of this part of North America was about 16°S and that part of the curvature of the salient was acquired during orogenesis.