Ropy flow structures; a neglected indicator of magma-flow direction in sills and dikes

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doi: 10.1130/0091-7613(2002)030<0715:RFSANI>2.0.CO;2
Authors:Liss, Dirk; Hutton, Donald H. W.; Owens, William H.
Author Affiliations:Primary:
University of Birmingham, Department of Earth Sciences, Birmingham, United Kingdom
Volume Title:Geology (Boulder)
Source:Geology (Boulder), 30(8), p.715-718. Publisher: Geological Society of America (GSA), Boulder, CO, United States. ISSN: 0091-7613
Publication Date:2002
Note:In English. 25 refs.; illus., incl. sketch map
Summary:Ropy flow structures that form in dikes and sills are very similar to ropy lava structures (pahoehoe), but are of intrusive origin. They are unusual among magma-flow indicators in that they provide a frozen record of the magma flow. Our observations suggest that they occur in large vesicles, which form as a result of local repeated pressure drops during propagation and emplacement of the magma. Adiabatic gas expansion causes a ductile rim to form around a vesicle; this rim is then sheared by the underlying flow. Anisotropy of magnetic susceptibility data from the contact zones confirm the flow data from the ropy flow structures, but the results from deeper within the body, both locally and regionally, yield different, yet consistent flow orientations. This discrepancy suggests that a distinction can be made between the magma flow close to the contact and the deeper regional flow patterns in sills and dikes.
Subjects:Carboniferous; Diabase; Dikes; Emplacement; Flow mechanism; Igneous rocks; Intrusions; Magmas; Magnetic susceptibility; Outcrops; Paleomagnetism; Paleozoic; Permian; Plutonic rocks; Sills; Textures; Vesicular texture; Durham England; England; Europe; Great Britain; Northumberland England; United Kingdom; Western Europe; Harkess Rock; Holy Island; Ropy flow structures; Tyne and Wear England; Whin Sill
Coordinates:N543000 N553500 W0012000 W0024000
Abstract Numbers:03M/976
Record ID:2002079343
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
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