Mesozoic Cordilleran arc magmatism along the western margins of North and South America shows similar patterns of episodic activity, but differences in tectonic setting, in composition, and in peak magnitudes of magma fluxes. The development of iron oxide(-copper-gold) (‘IOCG’) mineralization accompanies the pulse of arc magmatism in North and South America, but is most prolific during the early to middle Mesozoic pre-orogenic phases of the Cordillera. The focus of this work is to better understand the episodic nature of Cordilleran magmatism, controls to magma sources and compositions, and controls to Cordilleran IOCG mineralization. The objectives of this study are accomplished by focusing on two regions of the Cordillera that experienced similar early-middle Mesozoic tectonic settings, but display very different magmatic fluxes, compositions, and development of IOCG systems. The Coastal Batholith of northern Chile was investigated for the timing, composition, and fluxes of magmatism at three scales of observation including 1:1M scale between ~18°S to 34°S, 1:100K scale between 26°S to 28°S, and 1:20K scale along a transect at ~27.5°S where new major elemental, trace elemental, and Nd, Sr, and O isotope data were acquired. From the western United States magmatic fluxes and compositions were compiled from the literature, as were characteristics of Jurassic IOCG occurrences in the central Mojave Desert, California. Geologic framework analysis at 1:250K scale and new 1:5K scale mapping of the hydrothermal features associated with Jurassic IOCG occurrences were conducted in the central Mojave Desert, California. Results from northern Chile reveal that the Coastal Batholith formed in a dominantly extensional setting, had episodic magma fluxes that were dominantly mafic (dioritic-quartz dioritic) during peak output, and has uniformly depleted mantle-like Nd and Sr isotopes regardless of magma composition. Published compilations from coeval arcs of North America indicate that they display the opposite relationships to Chile between tectonic setting, magmatic fluxes, and magmatic compositions. Results from mapping in the southern Palen Mountains, California, and synthesis of composite exposures across the central Mojave Desert, California demonstrates that IOCG systems in this region are vertically zoned and genetically related Jurassic intrusions ranging from diorite/gabbro to granite in composition. The mineralized occurrences have intermediate depth (1–4 km), cores of magnetite±hematite mineralization with sparse Fe(-Cu) sulfides, and zone upward to acid-altered tops and downward to Fe-depleted, metal-poor, Na±Ca-altered roots. These patterns resemble those observed in IOCG systems throughout the Cordillera of the Americas.
| Identifer | oai:union.ndltd.org:arizona.edu/oai:arizona.openrepository.com:10150/319881 |
| Date | January 2014 |
| Creators | Girardi, James Daniel |
| Contributors | Barton, Mark D., Patchett, P. Jonathan, Zandt, George, Haxel, Gordon, Seedorff, C. Eric |
| Publisher | The University of Arizona. |
| Source Sets | University of Arizona |
| Language | en_US |
| Detected Language | English |
| Type | text, Electronic Dissertation |
| Rights | Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author. |
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