The Niemcza diorites and moznodiorites (Sudetes, SW Poland): a record of changing geotectonic setting at ca. 340 Ma.
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Abstract:
Granites sensu lato in the Sudetes intruded in several episodes during the Variscan orogeny recording different stages of crust and mantle evolution. Correlating precise ages with geochemistry of the Variscan granites provides information on the evolution of these sources within the Variscan orogen. The Variscan intrusive rocks from the Niemcza Zone (Bohemian Massif, Sudetes, SW Poland) include undeformed dioritic to syenitic rocks and magmatically foliated granodiorites. In this study we analysed low SiO2 (48–53 wt.%) monzodioritic rocks from Przedborowa and Koźmice. The monzodiorites contain late-magmatic zircons with ages of 341.8 ± 1.9 Ma for Przedborowa and 335.6 ± 2.3 Ma for Koźmice, interpreted as emplacement ages of the dioritic magmas. Older Przedborowa rocks are lower in K, Mg, Rb and Ni than the Koźmice rocks and similar compositional trend is also observed in the Central Bohemian Plutonic Complex. The implication is that the mantle underlying the Niemcza Zone became more enriched from ca. 342 to ca. 336 Ma, probably following the collision of the Saxothuringian and Moldanubian/Lugian domains. The magmatism related to the collision occurred ca. 12 Ma later than that in the Central Bohemian Plutonic Complex, but was accompanied by a similar change in magma chemistry from high-K (Przedborowa) to shoshonitic (Koźmice, Kośmin enclaves) and probably to ultrapotassic (Wilków Wielki) Keywords:
Massif
Orogeny
Age and Geochemical Character of Granite and Syenite Plutons in the Grenville Province of Southeastern Ontario; Insights into Magmatism During the Ottawan Orogeny and Evidence of the Frontenac Intrusive Suite in the Sharbot Lake Domain
Orogeny
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The composite Sierra Bermeja Pluton (southern Iberian Massif): science, heritage and geoconservation
ABSTRACT The Sierra Bermeja Pluton (∼60 km2 surface area) exemplifies a type of controversial granites of the Iberian Massif (European Variscan Belt), the cordierite-bearing ‘Serie Mixta’ (mixed series) monzogranites. The pluton is included almost completely in the Cornalvo Natural Park (Badajoz, Spain), a relevant target area in Roman times. The geological mapping summarised in the presented map at 1:10,000 scale has revealed a complex intrusive assemblage. Three main cordierite-bearing monzogranite types that show local varieties constitute most of the massif. Monzogranite intrusions are younger towards the centre of the pluton and gave rise to outstanding mappable mingling/mixing zones in some areas. A NE–SW trending reduced dyke complex composed by vaugnerite series rocks, lamprophyres, aplites and quartz dykes, completes the lithological assemblage of the pluton. An inventory of Geologic Points of Interest to promote the geological knowledge of this remarkable protected area and its geoconservation is also presented.
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Assemblage (archaeology)
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Three-dimensional model of the upper and middle crust of the Korsun-Novomirgorod pluton and the Novoukrainka massif has been constructed applying the maps of anomalous magnetic field of a scale 1: 200 000, the data of gravity modeling and DSS. A specific feature of the Korsun-Novomirgorod pluton together with directly magnetized formations of gabbro-anorthosite complex is widely distributed rocks of this complex with inverse magnetization that is an evidence of their multiphase origin. It has been also revealed an asymmetry in distribution of magnetic formations of the pluton and of the deep structure of the Earth’s crust as to trans-regional separation zone of Kherson—Smolensk. According to the data of magnetic maps, magnetic model of the pluton has been supplemented by the distinguished semicircular structures that underline the individual character of development of each of the massifs in its limits and are considered as prototectonic faults related to multiphase formation of the pluton.The Novoukrainka massif is characterized by the development of rocks with different intensity, magnetized in direction of contemporary magnetic field. Formation of the massif is strongly related to large deep fault zones and trans-regional separation zone Kherson-Smolensk, which form an intersection knot at the base of the crust.Structural position of large dyke dolerite belts of the region has been analyzed showing that their formation occurred in the period between establishment of the Novoukrainka massif and the Korsun-Novomirgorod pluton.
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Anorthosite
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The Rhodopean massif during the Paleogene was an area of rich collision magmatism, mainly represented by bimodal volcanism. Its occurences could be connected to the global processes of interaction between the African Continent and the Euro-Asian Platform. An attempt has been made to outline and describe the magmatic centres using a series of regional geophysical maps, compiled by Bulgarian and Greek geophysicists .
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Paleogene
Bulgarian
Exploration geophysics
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The common association of mid-crustal migmatites with an upper-level granite pluton could indicate that the migmatites are a feeder zone for the pluton. If magma from a deeper level pervasively intrudes a high temperature metamorphic complex, most of the intruded magma would not freeze because of the prevailing temperature. The interaction between the magma and country rocks, which could include partial melting and crystallisation of the magma passing through, would modify magma to a more granitic composition, as found in the higher-level pluton.
Migmatite
Magma chamber
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Orogeny
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Field and geochronologic evidence indicate that large and broadly homogeneous plutons can accumulate incrementally over millions of years.This contradicts the common assumption that plutons form from large, mobile bodies of magma.Incremental assembly is consistent with seismic results from active volcanic areas which rarely locate masses that contain more than 10% melt.At such a low melt fraction, a material is incapable of bulk flow as a liquid and perhaps should not even be termed magma.Volumes with higher melt fractions may be present in these areas if they are small, and this is consistent with geologic evidence for plutons growing in small increments.The large melt volumes required for eruption of large ignimbrites are rare and ephemeral, and links between these and emplacement of most plutons are open to doubt.We suggest that plutons may commonly form incrementally without ever existing as a large magma body.If so, then many widely accepted magma ascent and emplacement processes (e.g., diapirism and stoping) may be uncommon in nature, and many aspects of the petrochemical evolution of magmatic systems (e.g., in situ crystal fractionation and magma mixing) need to be reconsidered.
Magma chamber
Caldera
Igneous differentiation
Dike
Silicic
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Zircons from durbachite and syenite samples, from Třebic and
Jihlava massifs, were dated. Whereas the durbachite contains
complex zircons and gives discordant U-Pb ages, the syenite
contains rounded zircons, yielding concordant age of 335 Ma.
Both rocks represent relics of the orogen-wide late Variscan
magmatism, along with rocks from other parts of the Variscan
belt in Europe.
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