Sheeting and dyking emplacement of the Gunnison annular complex,SW Colorado |
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Institution: | 1. Laboratory for Ion Beam Physics, ETH Zürich, Switzerland;2. CNR - National Research Council, Institute of Geosciences and Earth Resources, Padova, Italy;3. Geological Survey of Austria, Vienna, Austria;1. Netherlands Centre for Luminescence Dating, Soil Geography and Landscape group, Wageningen University, 6700 AA Wageningen, The Netherlands;2. Coastal Engineering, Civil Engineering and Geosciences, Delft University of Technology, 2600 AA Delft, The Netherlands;3. Faculty of Applied Sciences, Delft University of Technology, Mekelweg 15, 2629 JB Delft, The Netherlands;1. Department of Land Administration and Surveying, Dilla University, P.O. Box 419, Dilla, Ethiopia;2. Department of Remote Sensing, Entoto Observatory and Research Center, Ethiopian Space Science and Technology Institute (ESSTI), Addis Ababa, Ethiopia;3. Department of Information Engineering and Computer Science, University of Trento, Italy;1. Laboratory for Ion Beam Physics, ETH Zürich, Switzerland;2. CNR - National research Council, Institute of Geosciences and Earth Resources, Padova, Italy;3. Geological Survey of Austria, Vienna, Austria |
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Abstract: | Emplacement of the Proterozoic Gunnison annular complex, Colorado, involved brittle failure and both subhorizontal sheeting and steeply-dipping dyking. The annular complex consists of a central diorite body (1730 Ma), surrounded by a ring of metamorphosed supracrustal rocks, in turn ringed by tonalite and granodiorite (1721 Ma). The older central diorite was emplaced as sills parallel to bedding, prior to regional deformation of the Gunnison volcanic arc, ~1730–1710 m.y. ago. This central body was deformed during regional shortening, into an upright bowl with inward-dipping walls. The surrounding country rocks were folded and locally transposed against the central body, forming an arcuate foliation, conforming roughly to the shape of the body. This foliation and bedding acted as mechanical planes of weakness, which localized the syn-deformational emplacement of the outer ring intrusions, as multiple magma sheets parallel to steeply dipping bedding and foliation. Portions of the outer rings were also injected along concentric, inward-dipping, shear fractures generated under high magma pressure, a process similar to cone sheet emplacement in volcanic ring-dyke complexes. Multiple mechanisms were therefore involved in the emplacement of this sheeted annular plutonic complex, which otherwise superficially resembles a subvolcanic ring-dyke complex. |
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