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Book Chapter

Temporal and spatial variations in the southern Patagonian batholith; Constraints on magmatic arc development

By
Robert M. Bruce
Robert M. Bruce
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Eric P. Nelson
Eric P. Nelson
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Stephen G. Weaver
Stephen G. Weaver
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Daniel R. Lux
Daniel R. Lux
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Published:
January 01, 1991

The plutonic record of the southern Patagonian batholith extends from 165 to 11 Ma, with a peak between 120 to 70 Ma that coincides with the Cretaceous global maximum in sea-floor spreading and the climax of the Andean orogeny. A spectrum of lithologies from gabbro to granite was intruded throughout the history of the batholith. Most plutons crystallized at middle crustal depths. At a local scale, 5,000 to 10,000 km2, plutonism appears episodic and diachronous with adjacent areas, exhibits a gradual change from gabbro to granite over tens of millions of years, and is accompanied by a decrease in initial Sr. Therefore the lithologic progression must result from enduring processes that span the life of many individual magma batches and can not result from a progressive increase in crustal contamination. Plutons generally intrude older plutons near the central axis of the batholith rather than country rocks on the margins. This magmatic inflation of the arc isolates young plutons from the radiogenic country rocks in a manner that becomes increasingly effective over time. It also suggests that the state of stress within the magmatic arc was neutral to extensional, at least during periods of pluton emplacement. This interpretation is supported by a general lack of deformed plutons in the batholith.

The gradual change in lithology, the generally undeformed nature of the batholith, and the stable position of axial intrusion suggest that the arc developed in a relatively stable tectonic setting. This contrasts strongly with the complex tectonic history of the foreland region. The batholith is exposed at mesozonal levels, whereas the foreland region is exposed at epizonal levels. Thus, not only does the tectonic record vary laterally across Andean orogens, but can vary depending on the crustal level examined.

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Contents

GSA Special Papers

Andean Magmatism and Its Tectonic Setting

Russell S. Harmon
Russell S. Harmon
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Carlos W. Rapela
Carlos W. Rapela
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Geological Society of America
Volume
265
ISBN print:
9780813722658
Publication date:
January 01, 1991

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