Tectonic significance of a Miocene dike swarm and its post-emplacement vertical and meridional collapse, Lake Mead area, Nevada, Arizona
- Geological Survey, Denver, CO (United States). Denver Federal Center
Major upper-crustal extension accompanied the dike-on-dike emplacement process that formed the north part of the Miocene-age Wilson Ridge pluton in the northern Black Mountains of northwestern Arizona and adjacent Nevada. Complex patterns of shallow-axis tilting and steep-axis bending of dikes and strata are interpreted as reflecting contrasting styles of accommodation for extension that accompanied and followed the large-magnitude extension represented by the pluton. These events occurred along the south-southeast projection of the Miocene-age northern Nevada rift and perhaps represent a continuation of that feature. Thousands of dikes of intermediate to mafic composition were initially steep and elongate normal to an extension axis oriented 077. Continued extension, as magma supply diminished, produced areally variable, mostly post-emplacement structures resulting mainly from horizontal-axis tilting and associated faulting south of Lake Mead and vertical-axis bending north of Lake Mead. South of the lake pre-intrusive strata and the dikes are steeply tilted away from and downfaulted toward the axis of the pluton, thereby forming structurally raised shoulders and a zone of central vertical collapse analogous to larger scale rifts worldwide. North of the lake pre-intrusive strata and dikes are only slightly tilted, but the steep dikes are spectacularly folded in plain view. These steep-axis folds were initially interpreted as drag features associated with the adjacent Hamblin Bay fault. On the basis of their areally variable vergence and other structural relations, they are now interpreted as resulting from a meridional collapse of the pluton. This horizontal collapse accommodate extension that occurred during the magma-starved phase of protracted deformation, as did the vertical collapse south of the lake.
- OSTI ID:
- 5423390
- Report Number(s):
- CONF-9305259-; CODEN: GAAPBC
- Journal Information:
- Geological Society of America, Abstracts with Programs; (United States), Vol. 25:5; Conference: 89. annual meeting of the Cordilleran Section and the 46th annual meeting of the Rocky Mountain Section of the Geological Society of America (GSA), Reno, NV (United States), 19-21 May 1993; ISSN 0016-7592
- Country of Publication:
- United States
- Language:
- English
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