Timing of Magmatism following Initial Convergence at a Passive Margin, Southwestern U.S. Cordillera, and Ages of Lower Crustal Magma Sources

Initiation of the Cordilleran magmatic arc in the southwestern United States is marked by intrusion of granitic plutons, predominantly composed of alkali‐calcic Fe‐ and Sr‐enriched quartz monzodiorite and monzonite, that intruded Paleoproterozoic basement and its Paleozoic cratonal‐miogeoclinal cove...

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Bibliographic Details
Published in:The Journal of geology 2006-03, Vol.114 (2), p.231-245
Main Authors: Barth, Andrew P., Wooden, Joseph L.
Format: Article
Language:English
Subjects:
Convergence
Crystallization
Geological time
Granite
Magma
Magmatism
Melting
Mountains
Petrology
Plutons
Proterozoic eon
Quartz
Rocks
Weighted averages
Zirconium
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Summary:Initiation of the Cordilleran magmatic arc in the southwestern United States is marked by intrusion of granitic plutons, predominantly composed of alkali‐calcic Fe‐ and Sr‐enriched quartz monzodiorite and monzonite, that intruded Paleoproterozoic basement and its Paleozoic cratonal‐miogeoclinal cover. Three intrusive suites, recognized on the basis of differences in high field strength element and large ion lithophile element abundances, contain texturally complex but chronologically distinctive zircons. These zircons record heterogeneous but geochemically discrete mafic crustal magma sources, discrete Permo‐Triassic intrusion ages, and a prolonged postemplacement thermal history within the long‐lived Cordilleran arc, leading to episodic loss of radiogenic Pb. Distinctive lower crustal magma sources reflect lateral heterogeneity within the composite lithosphere of the Proterozoic craton. Limited interaction between derived magmas and middle and upper crustal rocks probably reflects the relatively cool thermal structure of the nascent Cordilleran continental margin magmatic arc.
ISSN:0022-1376
1537-5269
DOI:10.1086/499573