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San Jacinto Intrusive Complex: 2. Geochemistry

Hill, R. I. and Chappell, B. W. and Silver, L. T. (1988) San Jacinto Intrusive Complex: 2. Geochemistry. Journal of Geophysical Research B, 93 (B9). pp. 10349-10372. ISSN 0148-0227. doi:10.1029/JB093iB09p10349.

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Rocks from three large (>100^2 km) tonalitic intrusions exposed in the San Jacinto Mountains of southern California show a restricted compositional range of between 63 and 68 wt % SiO_2 for all but volumetrically minor felsic differentiates (with Si0_2≈70 wt %). All rocks with less than 65.5 wt % SiO_2 show linear element-element covariation. Felsic differentiates have characteristics (higher SiO_2, K_2O, Rb, Ba, U; higher and variable rare earth elements) consistent with derivation by in situ fractionation; rocks with between 65.5 and 70 wt % SiO_2 have intermediate characteristics and are interpreted as derived from liquids formed by mixing “primitive” liquids with fractionated liquids within an intermittently recharged, continuously solidifying magma chamber. Mafic inclusions extend the compositional trends of the mafic tonalites to 55 wt % SiO_2. The chemical variations of both inclusions and more mafic tonalites are interpreted as resulting from processes acting before injection of their parental liquids into the observed crustal magma chambers. Effects of chamber processes are minor for all but the most felsic rocks. The major effect of recharge is to buffer the thermal and chemical properties of liquids within the magma chambers, yielding large volumes of relatively homogeneous tonalite. For those elements where the bulk distribution coefficient is between about 0.5 and 2, concurrent recharge and solidification produces rocks that closely approximate the composition of the added liquids. Estimated Rayleigh numbers for these liquids are high (>10^(10)), implying convection throughout much of the solidification history of each chamber. Existence of trace element variations within analyzed rocks imply that convection was not totally efficient at homogenizing the various batches of liquid added to each chamber.

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Additional Information:© 1988 American Geophysical Union. Received November 26, 1984; revised March 3, 1986; accepted March 4, 1986. This work was conducted as part of a Ph.D. project supervised by L.T.S. Funding was provided by a Conoco Fellowship, by the Division of Geological and Planetary Sciences, California Institute of Technology, and by the Australian Research Grants Committee. This work has benefited from discussion with many people, but particularly Dave Walker, Steve Sparks, Alex McBirney, Wes Hildreth and Mike Dungan. Dungan pointed out the need for a model that explained the similarity of (inferred) liquid and solid Na/(Na+Ca) and Mg(Mg/Fe) ("Dungan's Dilemna"). Journal reviews by Calvin Barnes and Lawford Anderson led to significant improvements in clarity. Division of Geological and Planetary Sciences, California Institute of Technology, contribution 4161. Paper number 4B5361.
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Conoco FellowshipUNSPECIFIED
Caltech Division of Geological and Planetary SciencesUNSPECIFIED
Australian Research Grants CommitteeUNSPECIFIED
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Caltech Division of Geological and Planetary Sciences4161
Issue or Number:B9
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Official Citation:Hill, R. I., B. W. Chappell, and L. T. Silver (1988), San Jacinto Intrusive Complex: 2. Geochemistry, J. Geophys. Res., 93(B9), 10349–10372, doi:10.1029/JB093iB09p10349.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:44269
Deposited By: Ruth Sustaita
Deposited On:12 Mar 2014 16:24
Last Modified:10 Nov 2021 16:49

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