Triassic magmatism and tectonic setting of the eastern Tianshan, NW China: Constraints from the Weiya intrusive complex
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Keywords:
Hornblende
Geochronology
Diorite
A small layered and differentiated diorite pluton in Cape Breton Island contains abundant layers and pillow-like inclusions of hornblende gabbro. The diorite is characterized by cryptic layering, lamination, and sporadic mineral layering. Compositional variation (diorite to adamellite) was controlled largely by gravitative settling and accumulation of plagioclase, hornblende, magnetite, biotite, and quartz at appropriate levels of the intrusion. Hornblende gabbro layers and inclusions have sharp, generally chilled margins and are conformable with layering and lamination in the diorite. Many of the layers have forms resembling pahoehoe lava flows. Hornblende gabbro also occurs as a large homogeneous pipe and as pillow-like inclusions within several small pipes of re-mobilized diorite cumulates. These small composite pipes have fed inclusion-rich layers in the diorite. Bodies of hornblende gabbro often carry rounded, apparently stretched inclusions of diorite. Field relations indicate that basic magma was injected through pipelike bodies into a chamber of actively fractionating dioritic magma. There, the basic magma flowed out onto diorite cumulate-liquid interfaces and solidified as "flows" and "pillows" of hornblende gabbro. These flows can be termed "intramagmatic." Deposition of major cumulus minerals from the dioritic magma continued on top of the gabbroic bodies. Beneath the solidifying gabbro, the diorite cumulates contained a large amount of interstitial liquid. Because of higher solidus temperatures, the gabbroic layers solidified well before the underlying diorite cumulates. Some gabbroic layers have been fractured, allowing upward injection by these cumulates. Mixing and reaction between diorite and gabbro are quite restricted. Gabbro inclusions above the thickest layers show the greatest effects of assimilation by diorite. Extensive crystallization of intercumulus liquid in the diorites led to the formation of a separate vapor phase which concentrated, rose into, and reacted with overlying gabbro layers forming "flame" structures.
Diorite
Hornblende
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It is shown that post-island-arc intrusive magmatism of the West-Magnitogorsk Zone embraced the time from Late Devonian to Late Carbon. The new systematization scheme for all variety of intrusive formations is proposed based on the new geological-geochemical data and evolutionary-genetic reconstructions. It presents four discrete intrusive series: 1) gabbro-norite-diorite, 2) gabbro-diorite-granite, 3) peridotite-gabbro-diorite-granite, 4) lamprophyre-dolerite. Each series is characterized by original properties of the body’s morphology and rocks petrography, mineralogy and geochemistry.
Diorite
Norite
Devonian
Island arc
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It is shown that post-island-arc intrusive magmatism of the West-Magnitogorsk Zone embraced the time from Late Devonian to Late Carbon. The new systematization scheme for all variety of intrusive formations is proposed based on the new geological-geochemical data and evolutionary-genetic reconstructions. It presents four discrete intrusive series: 1) gabbro-norite-diorite, 2) gabbro-diorite-granite, 3) peridotite-gabbro-diorite-granite, 4) lamprophyre-dolerite. Each series is characterized by original properties of the body’s morphology and rocks petrography, mineralogy and geochemistry.
Diorite
Norite
Devonian
Anorthosite
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Diorite
Massif
Dike
Fractional crystallization (geology)
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Hornblende gabbro-lamprophyre-diorite Complex in Guwoonri, Hwacheon distributes in a zonal pattern, where the diorite distributed along the margin of the Complex encompasses the hornblende gabbro body in the central part of the Complex, and lamprophyre intruded in vein along the boundary between diorite and hornblende gabbro. The hornblende gabbro in the central part of the Complex also shows a zonal distribution pattern, where hornblende gabbro containing subspherical amphibole phenocrysts as a major mafic mineral(Sag) surrounds hornblende gabbro with prismatic amphiboles as a principal mafic mineral(Pag). The zonal distributions observed in hornblende gabbro-lamprophyre-diorite Complex in Guwoonri resulted from two different geological processes. The zonal distribution among diorite, lamprophyre, and hornblende gabbro was due to intrusions of three distinct magmas derived from different degree of partial melting of a common source rock, whereas the zonal distribution shown within the hornblende gabbro body occupying the central part of the Complex resulted from an inward fractional crystallization of a single magma. Geochemical characteristics and mineral mode of hornblende gabbro, lamprophyre, and diorite indicate that these rocks formed from hydrous mafic to intermediate magma derived from partial melting of enriched mantle, which has been caused by infiltration of volatiles including water into mantle in plate margin.
Hornblende
Diorite
Amphibole
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Diorite
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The Journal of the Japanese Association of Mineralogists Petrologists and Economic Geologists (1983)
K-Ar dating on hornblende from biotite-hornblende quartz diorite in northeastern part of the Kanto Mountains was carried out. The age of the quartz diorite is 251±8 Ma. The result, together with geological facts, supports the idea that island arc composed of granitic plutons was present between the Sanbagawa and the Ryoke metamorphic belts.
Diorite
Hornblende
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The Journal of the Japanese Association of Mineralogists Petrologists and Economic Geologists (1963)
Hornblende gabbro, diorite and gabbro-diorite occur in the sheared zone of biotite gneiss and basic hornblende plagioclase rocks. Careful observations on the occurrence of these rocks and the comparison of the component minerals between the coarse igneous textured rocks and the country metamorphic rocks have revealed that the basification and the acidification of plagioclase occur more intensively in igneous textured rocks than in metamorphic rocks, and moreover quality of the country metamorphic rocks provide for that of gabbro and diorite and the regulation is not vice versa. Consequentry, these igneous textured rocks in these districts are the metablastic rock originated from the country rocks, from which it is produced by metamorphic differentiation.
Diorite
Hornblende
Country rock
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