TY - JOUR
T1 - Butcher ridge igneous complex
T2 - A glassy layered silicic magma distribution center in the ferrar large igneous province, antarctica
AU - Nelson, Demian A.
AU - Cottle, John M.
AU - Schoene, Blair
N1 - Funding Information:
This material is based upon work supported by the National Science Foundation (NSF) Graduate Research Fellowship under grant no. 1650114, with support from NSF grant ANT-1043152 and NSF grant ANT-1443296. This research used samples and/or data provided by the Polar Rock Repository (PRR). The PRR is sponsored by the NSF Office of Polar Programs. We are grateful to Anne Grunow and the PRR for providing samples and assisting with sample selection. Special thanks go to G. Hagen-Peter and F. Horton for field assistance, and J. Lackey and R. Mills for analytical assistance. We thank two anonymous reviewers and the associate editor for their many suggestions that helped to improve and clarify this manuscript.
Publisher Copyright:
© 2019 Geological Society of America.
PY - 2020/5/1
Y1 - 2020/5/1
N2 - The Butcher Ridge igneous complex, Antarctica, is an-6000 km3 hypabyssal silicic intrusion containing rhythmically layered glassy rocks. Baddeleyite U-Pb geochronologic analysis on a sample of the Butcher Ridge igneous complex yielded an age of ca. 182.4 Ma, which confirms that it was emplaced synchronously with the Ferrar large igneous province. Rocks of the Butcher Ridge igneous complex vary from basaltic andesite to rhyolite, and so the inferred volume of the Butcher Ridge igneous complex makes it the most voluminous silicic component of the Ferrar large igneous province. Major-element, trace-element, and isotopic data combined with binary mixing, assimilation-fractional crystallization (AFC), and energy-constrained AFC models are consistent with formation of Butcher Ridge igneous complex silicic rocks by contamination of mafic Ferrar parental magma(s) with local Paleozoic plutonic basement rocks. Field and petrographic observations and evidence for alkali ion exchange suggest that the kilometer-long, meter-thick enigmatic rhythmic layering formed as a result of secondary hydration and devitrification of volcanic glass along parallel fracture networks. The regularity and scale of fracturing/layering imply a thermally driven process that occurred during shallow emplacement and supercooling of the intrusion in the upper crust. We suggest that layering observed in the Butcher Ridge igneous complex is analogous to that reported from terrestrial and Martian cryptodomes, and therefore it is an ideal locality at which to study layering processes in igneous bodies.
AB - The Butcher Ridge igneous complex, Antarctica, is an-6000 km3 hypabyssal silicic intrusion containing rhythmically layered glassy rocks. Baddeleyite U-Pb geochronologic analysis on a sample of the Butcher Ridge igneous complex yielded an age of ca. 182.4 Ma, which confirms that it was emplaced synchronously with the Ferrar large igneous province. Rocks of the Butcher Ridge igneous complex vary from basaltic andesite to rhyolite, and so the inferred volume of the Butcher Ridge igneous complex makes it the most voluminous silicic component of the Ferrar large igneous province. Major-element, trace-element, and isotopic data combined with binary mixing, assimilation-fractional crystallization (AFC), and energy-constrained AFC models are consistent with formation of Butcher Ridge igneous complex silicic rocks by contamination of mafic Ferrar parental magma(s) with local Paleozoic plutonic basement rocks. Field and petrographic observations and evidence for alkali ion exchange suggest that the kilometer-long, meter-thick enigmatic rhythmic layering formed as a result of secondary hydration and devitrification of volcanic glass along parallel fracture networks. The regularity and scale of fracturing/layering imply a thermally driven process that occurred during shallow emplacement and supercooling of the intrusion in the upper crust. We suggest that layering observed in the Butcher Ridge igneous complex is analogous to that reported from terrestrial and Martian cryptodomes, and therefore it is an ideal locality at which to study layering processes in igneous bodies.
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U2 - 10.1130/B35340.1
DO - 10.1130/B35340.1
M3 - Article
AN - SCOPUS:85090084967
SN - 0016-7606
VL - 132
SP - 1201
EP - 1216
JO - Bulletin of the Geological Society of America
JF - Bulletin of the Geological Society of America
IS - 5-6
ER -