Determining the origin of inclusions in garnet: Challenges and new diagnostic criteria

Griffiths, Thomas; Habler, Gerlinde; Abart, Rainer

doi:10.2475/11.2020.01

Cited by 8 publications

(51 citation statements)

References 70 publications

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“…The first hypothesis implies that magnetite and the potentially accompanying phases nucleated on the surface of the growing plagioclase. The newly forming magnetite and potentially accompanying phases thus would grow in contact with the plagioclase, at least along parts of their surfaces, allowing for the evolution of systematic CORs by topotaxy (Griffiths et al 2021).…”

Section: Discussionmentioning

confidence: 99%

“…The observed SORs and CORs are still compatible with oriented nucleation of magnetite and potentially accompanying phases on the surface of growing plagioclase (hypothesis 1) as well as with the precipitation from supersaturated plagioclase (hypothesis 2). It has been shown recently that specific SORs tend to be selected depending on the orientation of the growth facet, if needle-shaped micro-inclusions are formed by oriented nucleation on the surface of a growing crystal (Griffiths et al 2021). In the plagioclase under consideration, the SORs of the magnetite micro-inclusions always follow specific crystallographic directions, and differences in SOR between different domains in a plagioclase grain are only due to the effect of twinning.…”

Section: Pl(150)n-mt Micro-inclusionmentioning

confidence: 99%

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Formation pathways of oriented magnetite micro-inclusions in plagioclase from oceanic gabbro

Bian

Ageeva

Rečnik

et al. 2021

Contrib Mineral Petrol

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Plagioclase hosted needle- and lath-shaped magnetite micro-inclusions from oceanic gabbro dredged at the mid-Atlantic ridge at 13° 01–02′ N, 44° 52′ W were investigated to constrain their formation pathway. Their genesis is discussed in the light of petrography, mineral chemistry, and new data from transmission electron microscopy (TEM). The magnetite micro-inclusions show systematic crystallographic and shape orientation relationships with the plagioclase host. Direct TEM observation and selected area electron diffraction (SAED) confirm that the systematic orientation relations are due to the alignment of important oxygen layers between the magnetite micro-inclusions and the plagioclase host, a hypothesis made earlier based on electron backscatter diffraction data. Precipitation from Fe-bearing plagioclase, which became supersaturated with respect to magnetite due to interaction with a reducing fluid, is inferred to be the most likely formation pathway. This process probably occurred without the supply of Fe from an external source but required the out-diffusion of oxygen from the plagioclase to facilitate partial reduction of the ferric iron originally contained in the plagioclase. The magnetite micro-inclusions contain oriented lamellae of ilmenite, the abundance, shape and size of which indicate high-temperature exsolution from Ti-rich magnetite constraining the precipitation of the magnetite micro-inclusions to temperatures in excess of ~ 600 °C. This is above the Curie temperature of magnetite, and the magnetic signature of the magnetite-bearing plagioclase grains must, therefore, be considered as the thermoremanent magnetization.

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Section: Discussionmentioning

confidence: 99%

Section: Pl(150)n-mt Micro-inclusionmentioning

confidence: 99%

Formation pathways of oriented magnetite micro-inclusions in plagioclase from oceanic gabbro

Bian

Ageeva

Rečnik

et al. 2021

Contrib Mineral Petrol

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“…In total, 88% of rutiles have at least one of the investigated alignments <101> rutile //<100> garnet which accounts for 22% of the data (Table 2). This is a result of its widespread prevalence in sample HS00704 in the data of Griffiths et al (2020) but does not reflect a universal commonality; COR A* rutile constitutes 1% of the data of Griffiths et al (2016) and is absent from the data of Keller and Ague (2019). The most common rutile COR that is present in each dataset is the edge-to-edge matching COR A rutile : {100} rutile //{134} garnet + <103> rutile //<111> garnet , which accounts for 13% of the analysed data (Table 2).…”

Section: Rutilementioning

confidence: 99%

“…The rocks studied by Griffiths et al (2016Griffiths et al ( , 2020 are kyanite-bearing metapegmatites from near Wirtbartl in the Austrian Alps. The metapegmatites were subjected to Cretaceous eclogite facies metamorphism and crop out as pods in crystalline Alpine basement alongside eclogites (Rogowitz & Huet, 2021).…”

Section: Rock Samplesmentioning

confidence: 99%

“…We analysed EBSD data for 96 rutile LAMs with SPO parallel to <111> garnet in the Brimfield Schist samples (Keller & Ague, 2019), 250 rutile LAMs in the Wirtbartl garnet cores (Griffiths et al, 2016) and 184 rutile LAMs, 79% of which have SPO parallel to <111> garnet , in the Wirtbartl garnet rims (Griffiths et al, 2020). Rutile results are given in Table 2 and Figure 4.…”

Section: Rutilementioning

confidence: 99%

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Predicting and explaining crystallographic orientation relationships of exsolved precipitates in garnet using the edge‐to‐edge matching model

Keller

Ague

2022

Journal Metamorphic Geology

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Relative alignments of mineral exsolutions and their host crystals can be described by crystallographic orientation relationships (COR). Exsolved phases in garnet from high-grade metamorphic rocks and igneous rocks may have COR, but the complexity of COR distributions has thus far restricted their use to identifying exsolved phases. Classification of COR also remains mineral-specific, leaving doubt as to what information COR preserve. To test how COR may be standardized, we calculated mismatch of low-index crystallographic planes (d-value ratios) and crystallographic directions (rows of atoms) between precipitates and garnet and defined search criteria for structural alignments likely to be energetically favourable. We analysed published electron backscatter diffraction (EBSD) data for apatite, rutile, ilmenite, corundum, and quartz precipitates in garnet (n tot = 1,296) for the presence of these alignments. Our method predicts between 88% and 98% of observed alignments across the studied minerals and requires only calculations using unit cell parameters. We further show that each exsolved mineral forms COR predicted by the edgeto-edge matching model which was developed to describe unambiguous exsolution textures in alloys. Edge-to-edge matching aligns atoms at the hostprecipitate interface by parallelism or near-parallelism of crystallographic planes of similar spacing and parallelism of crystallographic directions (rows of atoms) of similar length on the edges of those planes. Edge-to-edge matches likely facilitate coherent to semi-coherent interfaces by lowering surface free energy and strain energy, stabilizing precipitates. These matches are defined by criteria applicable to all minerals, making them an ideal tool for classifying, discovering and interpreting COR of diverse precipitates in garnet. This approach may also predict COR in other geological mineral pairs (e.g., exsolved feldspars). We find that edge-to-edge matching may explain the stability of the needle-shaped morphologies commonly observed for exsolution textures in garnet. Edge-to-edge matching COR distributions can be tested as proxies of the state of the host rock at the time of exsolution to evaluate factors such as temperature, cooling rate, degree of undercooling, and/or strain. Patterns of edge-to-edge matching COR may be paired with

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Variations in orientation relationships between rutile inclusions and garnet host relate to magmatic growth zoning

Kohn,

Griffiths,

Alifirova

et al. 2024

Contrib Mineral Petrol

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Rutile inclusions in almandine-spessartine garnet from a peraluminous pegmatoid from the Moldanubian zone (Bohemian Massif, AT) show distinct changes in aspect ratio, shape preferred orientations (SPO) and crystallographic orientation relationships (COR) along the transition between microstructurally different growth zones in the garnet core and rim. For identification of the COR characteristics we pool specific CORs based on their common axial relationship into three COR groups: Group 103R/111G, Group 001R/111G and Group 001R/100G. The rutile inclusions in the garnet core domains are elongated along the four Grt$$\langle$$ ⟨ 111$$\rangle$$ ⟩ directions and are dominated by COR Group 103R/111G. The garnet rim zone additionally contains rutile needles elongated along Grt$$\langle$$ ⟨ 100$$\rangle$$ ⟩ . Here, Group 001R/111G and 001R/100G are more abundant than in the garnet core. Needle-shaped rutile in the rim shows a systematic correlation between SPOs and CORs as needles elongated parallel to Grt$$\langle$$ ⟨ 111$$\rangle$$ ⟩ are dominated by Group 103R/111G and 001R/111G, whereas those needles elongated parallel to Grt$$\langle$$ ⟨ 100$$\rangle$$ ⟩ exclusively pertain to CORs of 001R/100G. Furthermore, the frequency of each particular SPO in the garnet rim clearly depends on the local growth direction of the particular Grt{112} sector. Facet-specific variations in rutile SPO frequencies in different sectors and growth zones of garnet were observed even between equivalent directions, indicating that the microstructures and textures of rutile inclusions reflect varying parameters of garnet growth. The characteristic differences in COR groups of different garnet growth zones are referred to compositional changes in the bulk melt or compositional boundary layer, associated with magmatic fractional crystallisation.

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Determining the origin of inclusions in garnet: Challenges and new diagnostic criteria

Cited by 8 publications

References 70 publications

Formation pathways of oriented magnetite micro-inclusions in plagioclase from oceanic gabbro

Formation pathways of oriented magnetite micro-inclusions in plagioclase from oceanic gabbro

Predicting and explaining crystallographic orientation relationships of exsolved precipitates in garnet using the edge‐to‐edge matching model

Variations in orientation relationships between rutile inclusions and garnet host relate to magmatic growth zoning

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