Chapter 20: Magma mixing and mingling between synplutonic mafic dikes and granite in the Idaho-Bitterroot batholith

Foster, David A.; Hyndman, Donald W.

doi:10.1130/mem174-p347

Cited by 34 publications

(14 citation statements)

References 21 publications

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“…Important differences between the three suites occur in their HREE contents and the size of their Eu anomalies. Rocks of the Idaho Batholith tend to be relatively depleted in HREE, with steeply sloping patterns and variable but generally high La/Yb (Figs 6, 7; see also Shuster & Bickford 1985;Foster & Hyndman 1990). The more fractionated samples (i.e.…”

Section: Rare-earth Elementsmentioning

confidence: 96%

Granites and rhyolites from the northwestern U.S.A.: temporal variation in magmatic processes and relations to tectonic setting

Norman¹,

Leeman²,

Mertzman³

1992

Geological Society of America Special Papers

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Cretaceous and Cainozoic granites and rhyolites in the northwestern U.S.A. provide a record of silicic magmatism related to diverse tectonic settings and large-scale variations in crustal structure. The Late Cretaceous Idaho Batholith is a tonalitic to granitic Cordilleran batholith that was produced during plate convergence. Rocks of the batholith tend to be sodic (Na 2 0>K 2 0), with fractionated HREE, negligible Eu anomalies, and high Sr contents, suggesting their generation from relatively mafic sources at a depth sufficient to stabilise garnet. In contrast, Neogene rhyolites of the Snake River Plain, which erupted in an extensional environment, are potassic (K 2 0>Na 2 0), with unfractionated HREE patterns, negative Eu anomalies, and low Sr contents, suggesting a shallower, more feldspathic source with abundant plagioclase. Eocene age volcanic and plutonic rocks have compositions transitional between those of the Cretaceous batholith and the Neogene rhyolites. These data are consistent with a progressively shallowing locus of silicic magma generation as the tectonic regime changed from convergence to extension.

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Section: Rare-earth Elementsmentioning

confidence: 96%

Granites and rhyolites from the northwestern U.S.A.: temporal variation in magmatic processes and relations to tectonic setting

Norman¹,

Leeman²,

Mertzman³

1992

Geological Society of America Special Papers

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“…Contacts between the two units are lobate and cuspate, typical of mingled magmas ( Fig. 14A; Yoder, 1973;Wiebe, 1980;Frost and Mahood, 1987;Foster and Hyndman, 1990). Some monzodiorite dikes have been brecciated and are intruded by small veins of Lincoln granite, suggesting that the granite remained above its solidus after the monzodiorite cooled sufficiently to behave brittlely.…”

Section: Interaction Between Monzodiorite and Lincoln Granitementioning

confidence: 94%

An overview of the petrology and geochemistry of the Sherman batholith, southeastern Wyoming: Identifying multiple sources of Mesoproterozoic magmatism

Edwards

Frost²

2000

Rocky Mountain Geology

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The 1.43-Ga Sherman batholith of southeastern Wyoming and northeastern Colorado is a texturally and geochemically heterogeneous intrusion that comprises rocks derived from at least four different sources. The coarse-grained, metaluminous, biotite-hornblende Sherman Granite is volumetrically the most significant unit in the batholith. It has geochemical characteristics at the extreme end of A-type suites with high Fe# > 88, high q0 wt. % (generally > 5%), molar Na/K generally c 1, and high abundances of incompatible elements. The source for the Sherman Granite is constrained to be a Fe-rich, low oxygen fugacity source mafic material by initial isotopic ratios (E,~ = -0.8-1.1 and initial 87Sr/86Sr = 0.7024-0.7126), low oxygen fugacity (-0.1 to -0.5 log units below the fayalite-magnetite-quartz buffer reaction) and water activity ( NO. 7), comparisons to experimental melt compositions, and mineralogical and geochemical similarities to monzonitic intrusions from the Laramie anorthosite complex (LAC). The medium-grained, peraluminous Lincoln granite, which is volumetrically subordinate to the Sherman Granite, has less extreme A-type geochemical characteristics. Initial isotopic ratios (ENd ---1 and initial 87Sr/86Sr = 0.7189 and 0.7238), comparisons to experimental melt compositions, and geochemical similarities to intrusions from the peraluminous Silver Plume suite favor a parental magma for the Lincoln granite derived from intermediate to felsic crustal rocks from the Colorado province, which forms the basement to the Sherman batholith. A suite of mineralogically heterogeneous biotite-hornblende porphyritic quartz monzonites and granites has geochemical characteristics that also fit the A-type classification but are less extreme than that for the Sherman Granite, with distinctly lower Fe# ( c 88) and molar Na/K (generally > 1). Field and geochemical observations are consistent with many of the porphyritic granites having formed by mixing between granitic and monzodioritic magmas and highlight the importance of magma mixing in the formation of the batholith. Mafic rocks are present in the batholith in minor quantities and include gabbro, ferrodiorite, and monzonite in addition to monzodiorite. All of the mafic rocks are geochemically and mineralogically similar to rocks from the adjacent LAC, and the gabbro presumably is derived from a mantle source similar to that for gabbroic rocks from the LAC. Geochemically distinct sodic granodiorite, which occurs in minor quantities in the batholith, represents a distinct unit likely derived from partially melted metabasalt.The rocks of the Sherman batholith record the evolution of Mesoproterozoic lithosphere in five ways: 1) gabbro records asthenospheric input of heat and mass(?) into the juvenile, Paleoproterozoic lithosphere; 2) peraluminous granite records partial melting of the Paleoproterozoic lithosphere in response to the influx of asthenospheric melts; 3) hybrid porRocky Mountain Geology, u. 35, no. I , p . 113-137, 17 figs., July, 2000 113 B. R. EDWARDS AND C. D. FROS...

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“…Due to the residual tumultuous force, some of these globules could have been deformed and rimmed as observed in the field. In the late stages of mixing, as the temperature diminished, the injecting mafic magma would have contracted, and rounded and ovoidal pillows with sharp to gradational boundaries were formed and dispersed in the hybrid zones (Noblelt and Staub, 1990;Foster and Hyndman, 1990;Blundy and Sparks, 1992).…”

Section: Hybridization Processmentioning

confidence: 99%

Synplutonic mafic injections into crystallizing granite pluton from Gurgunta area, northern part of Eastern Dharwar Craton: Implications for magma chamber processes

et al. 2009

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In this paper we document widespread coeval felsic-mafic magma interaction and progressive hybridization near Gurgunta in the northern part of Eastern Dharwar Craton (EDC) where mafic magma pulses have injected into a 2.5 Ga granite pluton. The pluton contains voluminous pink porphyritic facies with minor equigranular grey facies. The mafic body shows compositional variation from diorite to meladiorite with hornblende as the chief mafic mineral with lesser clinopyroxene and biotite. The observed variation on binary diagrams suggests that granite was evolved by fractional crystallization. Chemical characteristics such as higher Al 2 O 3 and moderate to high CaO, Mg#, Ni, Cr, Co and V are interpreted by slab-melting. Mafic bodies show lower SiO 2 , Na 2 O and K 2 O; but higher CaO, Mg#, FeO, Cr, Ni and V; higher LREE with moderate to higher HREE which suggest their derivation from mantle. A major active shear zone has played an important role at the time of synplutonic mafic injection and hybridization process.Field evidences suggest that the synplutonic mafic body has injected into the crystallizing felsic magma chamber in successive stages. The first stage injection has resulted in extensive mixing and hybridization due to the liquidus state of resident felsic magma to which hot mafic magma was injected. However, progressive mixing produced heterogeneity as the xenocrysts started mechanically dispersed into hybrid magma. The second stage injection, after a time gap, encountered colder and viscous hybrid magma in the magma chamber, which inhibited free injection. As a consequence, the mafic magma spread into magma chamber as flows, producing massive mafic bodies. However, with the continued mafic pulses and the heat gradient, the viscosity contrasts of mafic magma and felsic magma were again lowered resulting in second stage mixing. This episode was followed by mingling when the granite was almost crystallized, but still viscous enough to accommodate lamellar and ribbon like mafic penetrations to produce mingling. The successive mixing and mingling processes account for the observed heterogeneity in the granite pluton.

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Chapter 20: Magma mixing and mingling between synplutonic mafic dikes and granite in the Idaho-Bitterroot batholith

Cited by 34 publications

References 21 publications

Granites and rhyolites from the northwestern U.S.A.: temporal variation in magmatic processes and relations to tectonic setting

Granites and rhyolites from the northwestern U.S.A.: temporal variation in magmatic processes and relations to tectonic setting

An overview of the petrology and geochemistry of the Sherman batholith, southeastern Wyoming: Identifying multiple sources of Mesoproterozoic magmatism

Synplutonic mafic injections into crystallizing granite pluton from Gurgunta area, northern part of Eastern Dharwar Craton: Implications for magma chamber processes

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