Polygenetic tonalite-trondhjemite-granodiorite (TTG) magmatism in the Smartville Complex, Northern California with a note on LILE depletion in plagiogranites

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doi: 10.1007/BF01226562
Authors:Beard, J. S.
Author Affiliations:Primary:
Virginia Museum of Natural History, Martinsville, VA, United States
Volume Title:Mineralogy and Petrology
Source:Mineralogy and Petrology, 64(1-4), p.15-45. Publisher: Springer-Verlag, Vienna, Austria. ISSN: 0930-0708
Publication Date:1998
Note:In English with German summary. 42 refs.; illus., incl. 6 tables, geol. sketch maps
Summary:TTG occur in dykes, plugs and tabular to equant plutons within the intrusive core of the Smartville complex, a late Jurassic rifted arc. A high-K group consisting of calc-alkaline tonalite to granodiorite is enriched in LILE and Th and depleted in Na, Y and HREE with respect to a more tholeiitic and trondhjemitic low-K group. Within the high-K group, Th, LIL, La, and La/Lu show a regional southwards increase from biotite tonalite plutons in the north to granodiorite intrusions in the south. These regional chemical variations parallel regional chemical variations in older metavolcanic rocks and massive metadiabase that form the bulk of the basement into which the Smartville TTG were intruded. The characteristics of most high-K group rocks are consistent with an origin by low-P partial melting of arc basement rocks. Some high-K rocks are strongly depleted in Y and HREE, suggestive of melting in the garnet stability field. Thus, the basement probed by the high K-group may be vertically, as well as laterally extensive. Within the low-K group of largely tholeiitic tonalite to trondhjemite intrusions Y, Ga and Na increase to the west towards the Smartville sheeted dyke complex. The westernmost intrusives have the chemical characteristics of ocean ridge granites. The low-K group is best modeled by crystal fractionation of coeval, basaltic and andesitic magmas, although crustal assimilation appears to be important in one of the intrusions. Like most oceanic tonalites, the low-K group rocks are over-depleted in LIL elements which appears to be an intrinsic property of the low-K intrusives, unrelated to post-magmatic hydrothermal effects. It is suggested that LIL elements are lost because they evolve a vapour phase prior to their fixing by crystallization of phases such as biotite. [H.E.]
Subsections:Igneous rocks
Subjects:Chemical composition; Depletion; Diorites; Enrichment; Genesis; Granodiorites; Igneous rocks; Jurassic; Lithophile elements; Magmas; Magmatic associations; Mesozoic; Petrology; Plagiogranite; Plutonic rocks; Smartville Complex; Tonalite; Trondhjemite; California; Northern California; Pacific Coast; United States
Abstract Numbers:99M/3979
Record ID:2017035184
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom, Reference includes data from Geoline, Bundesanstalt fur Geowissenschaften und Rohstoffe
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