Metasomatic Textures in Granites

Rong, Jiashu; Wang, Fenggang

doi:10.1007/978-981-10-0666-1

Cited by 9 publications

(4 citation statements)

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“…The origin of granite has been discussed for dozens of years and is considered a puzzling topic in geology, and the investigation of mineral texture is exactly one of the keys to this significant issue. In addition to the snowball texture, other mineral textures of granite, such as myrmekitic texture, perthitic texture and graphic texture, have also attracted great attention due to their implications for revealing mechanisms of diagenesis and/or metamorphism [93]. The fractal characterization resulted from the proposed framework contributes to interpreting evolving behaviors of the complex textures in a quantitative manner, which would enrich the thoughts of mineralogical study and facilitate the research progress on granite genesis.…”

Section: Fractal Results Of Snowball Texture and Their Implication Fo...mentioning

confidence: 99%

Fractal-Based Pattern Quantification of Mineral Grains: A Case Study of Yichun Rare-Metal Granite

Liu,

Sun,

et al. 2024

Fractal Fract

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The quantification of the irregular morphology and distribution pattern of mineral grains is an essential but challenging task in ore-related mineralogical research, allowing for tracing the footprints of pattern-forming geological processes that are crucial to understanding mineralization and/or diagenetic systems. In this study, a large model, namely, the Segmenting Anything Model (SAM), was employed to automatically segment and annotate quartz, lepidolite and albite grains derived from Yichun rare-metal granite (YCRMG), based on which a series of fractal and multifractal methods, including box-counting calculation, perimeter–area analysis and multifractal spectra, were implemented. The results indicate that the mineral grains from YCRMG show great scaling invariance within the range of 1.04~52,300 μm. The automatic annotation of mineral grains from photomicrographs yields accurate fractal dimensions with an error of only 0.6% and thus can be utilized for efficient fractal-based grain quantification. The resultant fractal dimensions display a distinct distribution pattern in the diagram of box-counting fractal dimension (Db) versus perimeter–area fractal dimension (DPA), in which lepidolites are sandwiched between greater-valued quartz and lower-valued albites. Snowball-textured albites, i.e., concentrically arranged albite laths in quartz and K-feldspar, exhibit characteristic Db values ranging from 1.6 to 1.7, which coincide with the fractal indices derived from the fractal growth model. The zonal albites exhibit a strictly increasing trend regarding the values of fractal and multifractal exponents from core to rim, forming a featured “fractal-index banding” in the radar diagram. This pattern suggests that the snowball texture gradually evolved from rim to core, thus leading to greater fractal indices of outer zones, which represent higher complexity and maturity of the evolving system, which supports a metasomatic origin of the snowball texture. Our study demonstrates that fractal analyses with the aid of a large model are effective and efficient in characterizing and understanding complex patterns of mineral grains.

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Section: Fractal Results Of Snowball Texture and Their Implication Fo...mentioning

confidence: 99%

Fractal-Based Pattern Quantification of Mineral Grains: A Case Study of Yichun Rare-Metal Granite

Liu,

Sun,

et al. 2024

Fractal Fract

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“…Distinguishing a replacive metasomatic structure from epitaxial overgrowth in cases where parent and product phases have similar structure is difficult, because they occur with the same crystallographic orientation (Rong and Wang 2016). The morphology and distribution patterns characteristic of epitaxial growth of albite on microcline are expected to be evenly distributed in the rock mass, whereas the albite replacive structure (albitization) will be patchy (Rong and Wang 2016). The latter is in line with our observations of perthite crystals in the studied kakortokite, and therefore, supports a replacive process.…”

Section: Discussionmentioning

confidence: 99%

Perthite in nepheline syenite from the kakortokite unit in the Ilímaussaq Complex, south Greenland

Schønwandt,

Barnes,

Ulrich

2023

J. Geosci.

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Petrographic investigations of white kakortokite (nepheline syenite) reveal two structurally different types of perthite grains, herein called type A and B. Type A is more common and consists of an intimate intergrowth of microcline and albite. Microcline in type A perthites consists of two irregular penetrative individuals which appear as elongated pointed bodies parallel to (010) intergrown with polysynthetic twinned albite, which occurs as serrated bodies elongated parallel to (010). In type B perthites, K-feldspar (microcline) shows tiled structure and albite appears as microcrystalline equigranular veinlets, penetrating the perthite grain often perpendicular to (010). A great compositional variation of the type A grains (from nearly 100% microcline to almost pure albite) excludes exsolution to be the main process responsible for the structure. On the other hand, a replacement process controlled by a simultaneous dissolution-precipitation can explain the structure of type A, which means that widespread Na-metasomatism (albitization) had to have taken place in the kakortokite. Due to the different twinning structure of K-feldspar (microcline) in type B, the albitization in these grains occurred by albite veining of the grains.

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“…The presence of neoformed fine‐grained albite crystals (as a rim around plagioclase porphyroclasts), the partial sericitization of plagioclase, chloritization of biotite and myrmekite shapes of quartz‐plagioclase, and sporadic islands of quartz within large new alkali feldspar in the granitic rocks (Figure 4h), reveal textural evidence of greenschist facies overprint, as well as Na‐metasomatism, during retrogression (e.g., Rong & Wang, 2016) (Figure S1).…”

Section: Petrographymentioning

confidence: 99%

Geochronology and geochemistry of the Ediacaran orthogneisses from the north Shahrekord (Sadegh‐Abad), Sanandaj‐Sirjan Zone: Insights into magmatic evolution of the Iranian basement

et al. 2022

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The metamorphosed Sadegh‐Abad granite from the north Shahrekord Metamorphic Complex (NSMC) of Sanandaj‐Sirjan Zone in west Iran shows evidence of ductile deformation. The augen to banded mylonitic granite (orthogneiss) involves sharp contacts with other rock units, including high‐grade metamorphic rocks, such as eclogite, amphibolite, and garnet amphibolite as well as schists. U–Pb zircon dating reveals that the crystallization of the granitic magma occurred at 568 ± 14 Ma (Late Neoproterozoic, Ediacaran). The Sadegh‐Abad mylonitic granite comprises high SiO2 (67–78 wt.%) and Na2O (3.23–7.79 wt.%) contents and low CaO (0.73–1.61 wt.%) and variable K2O concentrations (0.08–4.6 wt.%). The chondrite‐normalized REE diagram shows enrichment in LREE relative to HREE (Ce/Yb)N = 1.90 to 6.12), a negative Eu anomaly (Eu/Eu* = 0.10–0.66), and nearly flat HREE patterns (Tb/Yb)N = 0.94–1.44). These are interpreted to have originated from a continental crustal source. This is further supported by the high concentration of the alkali elements, U, Th, Rb, and the high 87Sr/86Sr(i) isotopic ratios (0.7086 to 0.7163). The lower HREEs abundances, negative Eu anomalies, and the low contents of mafic minerals may infer that partial melting of continental crust has taken place in low‐pressure conditions within the plagioclase stability field, possibly of pre‐existing calc‐alkaline bodies in the lower continental crust. The charge of heating probably occurred via the injection of mafic magmas into the tonalitic and granodioritic continental crust.

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Metasomatic Textures in Granites

Cited by 9 publications

References 0 publications

Fractal-Based Pattern Quantification of Mineral Grains: A Case Study of Yichun Rare-Metal Granite

Fractal-Based Pattern Quantification of Mineral Grains: A Case Study of Yichun Rare-Metal Granite

Perthite in nepheline syenite from the kakortokite unit in the Ilímaussaq Complex, south Greenland

Geochronology and geochemistry of the Ediacaran orthogneisses from the north Shahrekord (Sadegh‐Abad), Sanandaj‐Sirjan Zone: Insights into magmatic evolution of the Iranian basement

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