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Title:
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Magmatic lobes as snapshots of magma chamber growth and evolution in large, composite batholiths: An example from the Tuolumne intrusion, Sierra Nevada, California
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Reference Number:
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9084
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ISSN:
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0016-7606
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Publication Year:
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2010
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GeoREF Number:
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2010-098069 (View Original Data File)
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Authors:
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Memeti, Valbone; Paterson, Scott; Matzel, Jennifer; Mundil, Roland; Okaya, David
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Descriptors:
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Age distribution Ages Biotite Cathodoluminescence Chambers Compositions Contacts Continuous Contrasts Cores Cross Sections Crystallization Crystals Dikes Direction Forming Fractionation Fractions Grades Grain sizes Granite Gray Scale Growth Horizontal Indexes Intrusion Lakes Lobes Location Magma Magma chambers Mapping Materials Military Personnel Minerals Modeling Models Moving Occurrences Plots Plutons Potential Pulses Recycling Relationships Rock Shades Sheets Sliding Small Solidus Square Texture Thermal Two-Dimensional Vertical Zircon Zones Zoning
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Source:
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Bulletin of the Geological Society of America. Vol. 122, no. 11-12, pp. 1912-1931. Nov 2010.
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Abstract:
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Precise chemical abrasion-thermal ionization mass spectrometry (CA-TIMS) U-Pb zircon ages in combination with detailed field mapping, super(40)Ar/ super(39)Ar thermochronology, and finite difference thermal modeling in the magmatic lobes of the Tuolumne batholith characterize these 10-60 km super(2) bodies as shorter-lived, simpler magmatic systems that represent increments of batholith growth. Lobes provide shorter-term records of internal and external processes that are potentially obliterated in the main body of long-lived, composite batholiths. Zircon ages complemented by thermal modeling indicate that lobe-sized magma chambers were present between 60.2 and 1 m.y., representing only a small fraction of the total duration of melt presence in the main body. During these shorter intervals, a concentric pattern of normal compositional zoning formed during inward crystallization and widespread zircon recycling in the lobes. Lobes largely evolved as individual magma bodies that did not interact significantly with the main, more complex magma chamber(s). Antecrystic zircons and the range of autocrysts, used to track the extent of interconnected melt, record only a limited range of ages and have contrasting zircon populations to those found in the same units in the main batholith. We consider lobes to either be single batches formed during continuous magma flow or multiple, quickly coalescing pulses that in either case formed separate magma chambers that failed to amalgamate with other compositionally distinct pulses such as those occurring in the central batholith. Zircon age comparisons between all four lobes and the main body imply that growth of the Tuolumne intrusion was not stationary, but that the locus of magmatism shifted both inward and northwestward.
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Copyright:
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GeoRef, Copyright 2010, American Geological Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States | Reference includes data supplied by the Geological Society of America, Boulder, CO, USA, United States
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