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New surveys of the Chesapeake Bay impact structure suggest melt pockets and target-structure effect

Anjana K. Shah, John Brozena, Peter Vogt, David Daniels and Jeffrey Plescia
New surveys of the Chesapeake Bay impact structure suggest melt pockets and target-structure effect
Geology (Boulder) (May 2005) 33 (5): 417-420

Abstract

We present high-resolution gravity and magnetic field survey results over the 85-km-diameter Chesapeake Bay impact structure. Whereas a continuous melt sheet is anticipated at a crater this size, shallow-source magnetic field anomalies of approximately 100 nT instead suggest that impact melt pooled in kilometer-scaled pockets surrounding the base of a central peak. A central anomaly of approximately 300 nT may represent additional melt or rock that underwent shock-induced remagnetization. Models predict that the total volume of the melt ranges from approximately 0.4 to 10 km (super 3) , a quantity that is several orders of magnitude smaller than expected for an impact structure this size. However, this volume is within predictions given a transient crater of diameter of 20-40 km for a target covered with water and sedimentary deposits such that melt fragments were widely dispersed at the time of impact. Gravity data delineate a gently sloping inner basin and a central peak via a contrast between crystalline and sedimentary rock. Both features are ovoid, oriented parallel to larger preimpact basement structures. Conceptual models suggest how lateral differences in rock strength due to these preimpact structures helped to shape the crater's morphology during transient-crater modification.


ISSN: 0091-7613
EISSN: 1943-2682
Coden: GLGYBA
Serial Title: Geology (Boulder)
Serial Volume: 33
Serial Issue: 5
Title: New surveys of the Chesapeake Bay impact structure suggest melt pockets and target-structure effect
Affiliation: U. S. Naval Research Laboratory, Washington, DC, United States
Pages: 417-420
Published: 200505
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 27
Accession Number: 2005-034362
Categories: Applied geophysics
Document Type: Serial
Bibliographic Level: Analytic
Annotation: With GSA Data Repository Item 2005074
Illustration Description: illus. incl. sects., sketch maps
N37°00'00" - N37°40'00", W76°40'00" - W75°30'00"
Secondary Affiliation: U. S. Geological Survey, USA, United StatesJohns Hopkins University, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 200519
Program Name: USGSOPNon-USGS publications with USGS authors
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