Geology and geophysics of Proterozoic basement rocks in the eastern midcontinent of the United States
- Univ. of Pittsburgh, PA (United States)
Upper crustal Proterozoic rocks of the eastern midcontinent of the U.S. are part of the transcontinental Proterozoic province, a 3,000 km-long belt of anorogenic igneous rocks that extends from western Ohio to southern California. Regional magnetic and gravity anomaly maps reveal a variety of prominent anomalies and gradients that reflect major basement or intrabasement structures. Widespread are pronounced (10--20 km diameter), high-amplitude (600--700 gamma) circular to elliptical positive magnetic anomalies that are associated with magnetite-series granites and coeval rhyolites. Also present (in Indiana) are a series of ring-shaped magnetic anomalies that have a diameter of about 50 km and form circular to elliptical patterns of narrow positive anomalies bordered by negative anomalies and ringing a central minimum. Modeling of the anomalies suggests that they may be ring dike complexes associated with calderas. Two prominent circular gravity lows associated with large granitic batholiths have also been identified. The larger of these, the Wisconsin gravity minimum, has a diameter of about 250 km and an amplitude of about [minus]65 mgals and is associated with the Wolf River batholith. The second gravity low has a diameter of about 75 km and an amplitude of about [minus]25 mgals and is in east-central Kentucky. Several major rift zones are present in the eastern midcontinent. The most prominent of these is the New Madrid rift complex, a failed-arm structure that extends into the craton beneath the Mississippi embayment. Also present are linear arrays of positive magnetic and gravity anomalies that are associated with basaltic rift zones. These include the mid-Michigan rift and the Ft. Wayne rift, as well as with possible rifts associated with the mid-Tennessee and Louisville positive anomalies.
- OSTI ID:
- 5707421
- Report Number(s):
- CONF-921058-; CODEN: GAAPBC
- Journal Information:
- Geological Society of America, Abstracts with Programs; (United States), Vol. 24:7; Conference: 1992 annual meeting of the Geological Society of America (GSA), Cincinnati, OH (United States), 26-29 Oct 1992; ISSN 0016-7592
- Country of Publication:
- United States
- Language:
- English
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