Eastern margin of the Vaasa Migmatite Complex, Kauhava, western Finland: preliminary petrography and geochemistry of the diatexites

Mäkitie, Hannu

doi:10.17741/bgsf/73.1-2.003

Cited by 10 publications

(12 citation statements)

References 22 publications

(19 reference statements)

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“…Based on field work and petrological and geochemical observations of the VMC granitoids in the inner part and the surrounding migmatites and schists in the outer part, Mäkitie () suggested that the granitic rocks represent in situ melting of the adjacent sedimentary rocks. This is supported by the similar inherited U‐Pb ages, the initial Nd isotopic composition of the granitoids, and the surrounding metasediments (Kotilainen et al, ; Suikkanen et al, ).…”

Section: Geological and Geophysical Settingmentioning

confidence: 99%

The Vaasa Migmatitic Complex (Svecofennian Orogen, Finland): Buildup of a LP‐HT Dome During Nuna Assembly

et al. 2020

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Tectonic evolution of the Paleoproterozoic Vaasa migmatitic complex (VMC) in the central part of the Svecofennian accretionary orogen is deciphered using aeromagnetic and gravity maps, deep seismic and magnetotelluric profiles, and structural and metamorphic data. The VMC is a semicircular structure with migmatitic rim and granitic core composed of several subdomes. It evolved in three main tectonic events (D1-D3). The D1 event (ca. 1.89-1.88 Ga) corresponds to the stacking of supracrustal rocks and the formation of an inverted metamorphic gradient. Anatexis at LP-HT metamorphic conditions enabled the material to flow. The D2 event (ca. 1.88-1.87 Ga) corresponds to large-scale folding of the partially molten crust within an orocline. It is marked by folds with an E-W vertical axial planar foliation. The late D3 event resulted from mass redistribution owing to mechanical instabilities within the hinge of the orocline. It is marked by vertical shearing (ca. 1.87-1.85 Ga) in the marginal parts of the complex and along the granitoid subdomes. The seismic reflection profile (FIRE 3a) and magnetotelluric profiles (MT-PE and MT-B2) image large-scale D1 stacking structures within an accretionary prism. Near vertical breaks in crustal-scale reflectivity and conductivity models are interpreted as D3 shear zones. The VMC is an example of early mass and heat transfer within a collage of hot supracrustal rocks in an accretionary belt. Partial melting enhanced the flow of material, the production, and rise of magma as well as exhumation, marked by magmatic domes in the hinge of the orocline.

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Section: Geological and Geophysical Settingmentioning

confidence: 99%

The Vaasa Migmatitic Complex (Svecofennian Orogen, Finland): Buildup of a LP‐HT Dome During Nuna Assembly

et al. 2020

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“…The batholith, together with the surrounding metasediments, comprises the Vaasa complex. The boundary between the granitoids of the Vaasa batholith and the schists of the Bothnian Belt is gradual through metatexites and diatexites (Mäkitie et al, 2012) with no observed intrusive contacts (Mäkitie et al, 1999;Mäkitie, 2001;Lehtonen et al, 2005;Sipilä et al, 2008). In fact, the boundary area is texturally, mineralogically, and geochemically continuous (Mäkitie et al, 2012).…”

Section: Geologic Settingmentioning

confidence: 99%

“…In fact, the boundary area is texturally, mineralogically, and geochemically continuous (Mäkitie et al, 2012). This has led many workers to consider the granitoids of the Vaasa complex to represent in situ melting (e.g., Mäkitie, 2001;Sipilä et al, 2008;Mäkitie et al, 2012).…”

Section: Geologic Settingmentioning

confidence: 99%

“…There is no unanimous consensus on the origin of the Vaasa batholith. It has been interpreted as entirely diatexitic (Lahtinen et al 2005), proposed to represent a metamorphic core complex (Valtonen, 2011;Hölttä, 2013), and the result of in situ melting of the Bothnian Belt metasedimentary rocks (Mäkitie, 2001;Sipilä et al, 2008;Mäkitie et al, 2012). Mäkitie et al (2012) further suggested that the grainitoids of Vaasa batholith represent a 'magma layer', not accumulated melting products of migmatite protoliths.…”

Section: Introductionmentioning

confidence: 99%

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New monazite U-Pb age constraints on the evolution of the Paleoproterozoic Vaasa granitoid batholith, western Finland

Kotilainen¹,

Mänttäri²,

Kurhila³

et al. 2016

Bull Geol Soc Finland

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The Vaasa batholith, western Finland, is a large, peraluminous granitoid pluton that crystallized at 1.88-1.87 Ga during the culmination of the Svecofennian orogeny. The batholith has gradual contacts, through metatexites and diatexites, with the enveloping metasedimentary rocks of the Bothnian Belt. We present ID-TIMS U-Pb age data on monazite from granitoids and xenoliths of the Vaasa batholith and combine these with published U-Pb zircon ages in order to shed further light on the evolution of the Vaasa batholith. The apparent monazite ages for seven of the examined samples are 1870-1863 Ma, and 1855±3 Ma for one further sample from the southern part of the batholith. Combined with pre-existing data, the monazite ages of the granitoids are 9 to 18 Ma (face values) or 3 to 9 Ma (external errors considered) younger than the U-Pb zircon crystallization ages from respective samples. Our new data suggest slow cooling for the Vaasa batholith -the closure/saturation temperature of the monazite U-Pb system was probably reached in ~10 m.y. after the crystallization of magmatic zircon in the examined rocks.

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“…First, there are numerous examples of terranes preserving voluminous amounts of segregated former granitic liquids that apparently did not leave the deep-crustal environment as liquids (Percival, 1991;Jung et al, 2000;Makitie, 2001;Redler et al, 2013). If melt is readily extractable in small volumes, the large amounts of leucosome in some migmatities (metatexites and diatexites) would have to represent either partial melts arrested in a state of incomplete escape or liquids from a foreign source arrested in transit through a terrane undergoing high grade metamorphism, with or without partial melting.…”

Section: The Problem Of the Extractability Of Granitic Partial Meltmentioning

confidence: 99%

Dehydration melting and the relationship between granites and granulites

Aranovich

Makhluf

Manning

et al. 2014

Precambrian Research

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a b s t r a c tFor more than half a century, thought about granite genesis and crustal evolution has been guided by the concept of partial melting in the lower crust. In this model, granitic magmas produced at depth are lost to shallow levels, leaving behind a more mafic, volatile poor residue that is depleted in incompatible components (H 2 O, alkalis, and heat-producing elements). Although granite extraction must be the dominant process by which crust is modified over time, the preferred model of granite genesis triggered by metamorphic dehydration reactions (dehydration melting) does not adequately explain important aspects of granite formation. The temperatures required for voluminous granite production by dehydration melting need heat and mass input to the crust from mantle-derived mafic magmas. In addition, prediction of the H 2 O contents of granitic liquids by extrapolation from low-pressure experiments to deep-crustal pressures (P) and temperatures (T) implies that the H 2 O resident in hydrous minerals is insufficient to account for large granite volumes, such as anorogenic granite batholiths in continental interiors. To test this, we conducted new experiments on the H 2 O contents of simple granitic liquids at 10 kbar and 800-950• C. We confirm previous extrapolations from lower P and T indicating that a minimum of 3-4 wt% H 2 O is present at the studied P and T in a granitic liquid in equilibrium with quartz and feldspars. For large-scale melting, this is much more than could have been supplied by the H 2 O resident in biotite and amphibole by dehydration melting at these conditions, unless lower-crustal temperatures were higher than generally inferred. Another problem with the dehydration-melting model is that the crystal chemistry of the large-ion lithophile elements (LILE) does not favor their partitioning into granitic liquids; rather, U, Th, Rb and the rare earth elements (REE) would more likely be concentrated in the postulated mafic residues. Finally, observations of migmatite complexes reveal many features that can not be satisfied by a simple dehydration-melting model.We suggest that the volatile components CO 2 and Cl are important agents in deep-crustal metamorphism and anatexis. They induce crystallization and outgassing of basalt magmas at lower-crustal levels, where the combination of latent heat and liberated H 2 O may contribute to granite production, leading to larger melt fractions than for simple dehydration-melting models. Since the Cl and CO 2 are very insoluble in granite liquids, granite generation leads naturally to production or separation of a coexisting metamorphic fluid with low H 2 O activity. Such a fluid could coexist with granulite-facies assemblages and yet be capable of dehydration, alkali exchange and LILE extraction to explain many chemical processes of deep-crustal metamorphism not readily explainable by dehydration melting.

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Eastern margin of the Vaasa Migmatite Complex, Kauhava, western Finland: preliminary petrography and geochemistry of the diatexites

Cited by 10 publications

References 22 publications

The Vaasa Migmatitic Complex (Svecofennian Orogen, Finland): Buildup of a LP‐HT Dome During Nuna Assembly

The Vaasa Migmatitic Complex (Svecofennian Orogen, Finland): Buildup of a LP‐HT Dome During Nuna Assembly

New monazite U-Pb age constraints on the evolution of the Paleoproterozoic Vaasa granitoid batholith, western Finland

Dehydration melting and the relationship between granites and granulites

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