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Distribution and U-Pb isotope ages of some lineated plutons, northwestern Mexico

Anderson, T. H. and Silver, L. T. and Salas, G. A. (1980) Distribution and U-Pb isotope ages of some lineated plutons, northwestern Mexico. In: Cordilleran Metamorphic Core Complexes. GSA Memoirs. No.153. Geological Society of America , Boulder, CO, pp. 269-283. ISBN 9780813711539.

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Characteristically lineated and foliated rocks of middle to late Mesozoic(?) age crop out in ranges in north-central Sonora throughout an area of 15,000 km2, between lat 31° 307′N and 30° 30′N. The terrane consists predominantly of layered sedimentary, volcanic, and volcaniclastic units, commonly metamorphosed to greenschist facies. Associated plutons, which are unambiguously intrusive, consist mainly of biotite- or biotite-muscovite–bearing granite. The layered suite and intrusive rocks are distinguished by subhorizontal, penetrative lineation, commonly defined by smeared mineral grains, which consistently trend northeast. Foliation is also predominantly low dipping. South of lat 30° 30′N, sporadic occurrences of lineated granitic and metamorphic rocks suggest the existence of this deformational fabric at least to Sierra Mazatan, which lies east of Hermosillo near lat 29°00′N. Cogenetic suites of zircon from one undeformed and three deformed plutons yield U-Pb ages from 75 to 55 m.y. These intrusive bodies are elements of a widespread, time-transgressive, late Mesozoic magmatic suite. They are not known to be affected by folds and faults commonly related to the Laramide orogeny. The apparent ages of the plutons are interpreted to be crystallization ages and therefore indicate that lineation and foliation formed, at least locally, later than 55 m.y. ago. Outcrops of distinctively deformed rocks appear to crudely define a north-trending belt. Rocks outside of this general zone are composed of sedimentary, volcanic, and volcaniclastic rocks of Precambrian and Mesozoic age which locally have been strongly folded and metamorphosed to greenschist or higher facies. However, postdeformational pegmatites and intrusive rocks indicate pre-Tertiary minimum ages for related episodes of deformation and metamorphism.

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Additional Information:© 1980 Geological Society of America. Our investigations have benefited from logistical support at times from the Instituto de Geología, Universidad Nacional Autónoma de México; Universidad de Sonora; and Consejo de Recursos Naturales no Renovables. Conversations with Jaime Roldan Q., Claude Rangin, George H. Davis, Peter Coney, and Doug Shakel have contributed to our perspective of regional geology. Mineral separations by O. Shields and Jamie Alvarez; microscope work by F. Corona; and ever friendly, helpful contributions of chemistry and mass spectrometry by Gerri Silver and Maria Pearson are most kindly acknowledged. This work was supported by NSF Grants GA-15989 and EAR 74-00155 A01 (formerly GA-40858) awarded to California Institute of Technology and EAR 76-84167 awarded to the University of Arizona.
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NSFEAR 74-00155 A01
NSFEAR 76-84167
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Caltech Division of Geological and Planetary Sciences3208
Series Name:GSA Memoirs
Issue or Number:153
Record Number:CaltechAUTHORS:20220729-413253000
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Official Citation:T. H. Anderson, L. T. Silver, G. A. Salas, 1980. "Distribution and U-Pb isotope ages of some lineated plutons, northwestern Mexico", Cordilleran Metamorphic Core Complexes, Max D. Crittenden, Jr., Peter J. Coney, George H. Davis; DOI: 10.1130/mem153-p269
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:115950
Deposited By: Tony Diaz
Deposited On:29 Jul 2022 16:16
Last Modified:29 Jul 2022 16:16

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