|
|||||
|
|
Petrogenesis and tectonic setting of the peralkaline Pine Canyon caldera, Trans-Pecos Texas, USA |
|
| Authors: | John Charles White S Christian Benker Minghua Ren Kevin M Urbanczyk Donald W Corrick |
| Institution: | aDepartment of Earth Sciences, Eastern Kentucky University, Richmond, KY 40475, USA bDepartment of Geological Sciences, University of Texas at El Paso, El Paso, TX 79968, USA cDepartment of Earth and Physical Sciences, Sul Ross State University, Alpine, TX 79832, USA dNational Park Service, Big Bend National Park, TX 79834, USA |
| Abstract: | The Pine Canyon caldera is a small (6–7 km diameter) ash-flow caldera that erupted peralkaline quartz trachyte, rhyolite, and high-silica rhyolite lavas and ash-flow tuffs about 33–32 Ma. The Pine Canyon caldera is located in Big Bend National Park, Texas, USA, in the southern part of the Trans-Pecos Magmatic Province (TPMP). The eruptive products of the Pine Canyon caldera are assigned to the South Rim Formation, which represents the silicic end member of a bimodal suite (with a “Daly Gap” between 57 and 62 wt.% SiO2); the mafic end member consists primarily of alkali basalt to mugearite lavas of the 34–30 Ma Bee Mountain Basalt. Approximately 60–70% crystallization of plagioclase, clinopyroxene, olivine, magnetite, and apatite from alkali basalt coupled with assimilation of shale wall rock (Ma/Mc = 0.3–0.4) produced the quartz trachyte magma. Variation within the quartz trachyte–rhyolite suite was the result of  70% fractional crystallization of an assemblage dominated by alkali feldspar with subordinate clinopyroxene, fayalite, ilmenite, and apatite. High-silica rhyolite is not cogenetic with the quartz trachyte–rhyolite suite, and can be best explained as the result of 5% partial melting of a mafic granulite in the deep crust under the fluxing influence of fluorine. Variation within the high-silica rhyolite is most likely due to fractional crystallization of alkali feldspar, quartz, magnetite, biotite, and monazite. Lavas and tuffs of the South Rim Formation form A-type rhyolite suites, and are broadly similar to rock series described in anorogenic settings both in terms of petrology and petrogenesis. The Pine Canyon caldera is interpreted to have developed in a post-orogenic tectonic setting, or an early stage of continental rifting, and represents the earliest evidence for continental extension in the TPMP. |
| Keywords: | Peralkaline Trachyte Rhyolite Petrogenesis Continental extension |
| 本文献已被 ScienceDirect 等数据库收录！ | |