Geophysical framework and the Appalachian-Caledonide connection

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Abstract
Summary: Gravity and magnetic data from the Appalachian-Caledonide area demonstrate the overall continuity of the orogen while identifying its segmentation into areas of contrasting structural style. The extension of this segmentation into ‘drift’-covered areas (e.g. the southern U.S.A.) and offshore areas (e.g. around Newfoundland and the British Isles) provides an orogen-wide framework into which structural detail established at outcrop can be accommodated. Linear gravity and magnetic anomalies often reflect contrasts within the Precambrian basement that have controlled tectonic events to the present. Such basement structure has been investigated by deep seismic profiling, which has also identified large-scale thrusting throughout the Appalachians and the Caledonides with some thrusts even extending into the upper mantle. Speculation to greater depths based on conductivity and P-wave travel-time residuals suggests that traces of the early Palaeozoic collision zone may still exist in the lower crust and upper mantle beneath the northern Appalachians. The loading imposed by thrust sheets during that collision produced foreland basins in the eastern USA whose form and sedimentary record indicate the magnitude and duration of thrusting. Palaeomagnetic results suggest transcurrent movement in Devonian-Carboniferous time, but the early Palaeozoic collisional choreography has not yet been uniquely defined.