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Title:
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Time scales of pluton construction at differing crustal levels;examples from the Mount Stuart and Tenpeak Intrusions, north Cascades,Washington
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Reference Number:
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7437
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ISSN:
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0016-7606
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Publication Year:
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2006
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Publisher:
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Geological Society of America (GSA), Boulder, CO, United States (USA)
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GeoREF Number:
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2006-091383 (View Original Data File)
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Authors:
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Matzel, Jennifer E P; Bowring, Samuel A; Miller, Robert B
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Descriptors:
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absolute age; batholiths; Cascade Range; Cenozoic; Chiwaukum Schist;continental crust; crust; dates; emplacement; granodiorites; igneousrocks; Ingalls Complex; intrusions; island arcs; Jurassic;lithostratigraphy; magma chambers; magmas; magmatism; Mesozoic;models; Mount Stuart; Napeequa Complex; Nason Ridge Gneiss; Neogene;nesosilicates; orthosilicates; P-T conditions; Pliocene; plutonicrocks; processes; silicates; Swakane Gneiss; Tenpeak Pluton; Tertiary;U/Pb; United States; Washington; zircon; zircon group
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Source:
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Geological Society of America Bulletin, vol.118, no.11-12,pp.1412-1430, Dec 2006
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Abstract:
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Deciphering the magmatic history of continental magmatic arcs, ingeneral, and the growth history of individual intrusions, inparticular, is key to understanding the complex history of magmageneration, segregation, and transport that define the dynamics ofcrustal growth. We utilize high precision U-Pb geochronology toresolve a detailed magmatic history from two composite intrusions, the2-4 kbar Mount Stuart Batholith and the 7-10 kbar Tenpeak Pluton,emplaced in the Cretaceous North Cascades Arc. This temporal frameworkprovides a way to evaluate models of pluton growth that explain commonfeatures of intrusions such as concentric compositional zoning andinternal magmatic contacts. U-Pb zircon crystallization ages wereobtained from 12 samples of the Mount Stuart Batholith and 8 samplesof the Tenpeak Intrusion, representing the range of compositionaldiversity and geographical extent. These dates indicate that the MountStuart Batholith was constructed over a approximately 5.5 m.y. timeperiod that was punctuated by four intervals of high magma flux. Thedurations of the high-flux periods are short (a few hundred thousandyears) relative to the duration of the batholith. The consistentpattern of magmatic fabrics and the lack of distinct contacts in thebatholith may be explained by the juxtaposition of melt-rich and mushzones with subtle contacts between mineralogically and texturallysimilar tonalite and time-transgressive magma fabrics.In contrast, theTenpeak Intrusion was constructed over a approximately 2.6 m.y. timeperiod, with magma influx distributed throughout the intrusive historyand texturally distinct magma bodies. The Tenpeak Intrusion lacksdistinct age domains, which suggests that any magma reservoir wassmaller in size and potentially more ephemeral. Although the distinctage domains and discrete compositional and textural phases indicatethat pluton growth occurred incrementally, neither pluton bearsresemblance to a purely end-member incremental growth model whereby apluton is constructed from hundreds to thousands of discrete magmapulses that have little, if any, interaction. In particular, ages fromthe youngest domain of the Mount Stuart Batholith indicate that amelt-rich magma reservoir of > or =520 km (super 3) existed over a170 + or - 90 k.y. time span.
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Notes:
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With GSA Repository Item 2006220
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Copyright:
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GeoRef, Copyright 2007, American Geological Institute. Referenceincludes data supplied by the Geological Society of America, Boulder,CO, United States
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