Garnet as a monitor for melt–rock interaction: Textural, mineralogical, and compositional evidence of partial melting and melt-driven metasomatism

Rodingite within an alpine ultramafic body in the Lower Palaeozoic metamorphics of the Major Bergen Are is at present the on! y known occurrence of this rock type in Norway. Amphibolite dykes in ultramafic bodies have developed metasomatic zones of chlorite and tremolite or epidote and chlorite along contacts with the host rock which itself has been serpentinized dose to the dykes. The rodingite dyke is zoned with chlorite and diopside selvages along contacts with serpentinite. Microprobe analyses of the rodingite mineral assemblage, of which hydrogarnet is the most characteristic, are presented. By means of chemical analyses of the dykes, individual metasomatic zones and the ultramafic host, the nature of the mass transport during metasomatism can be demonstrated.

Metasomatism

Ultramafic rock

Tremolite

Peridotite

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The Effects of Partial Melting and Metasomatism on Peridotite Water Contents: Insights from Shuangliao Volcano Group, Northeast China

Journal of Petrology (2024)

Chang-Yu Zhu Huan Chen Yan‐Tao Hao Qunke Xia

ABSTRACT Many minerals within the subcontinental lithospheric mantle (SCLM) contain structurally bonded hydrogen (commonly referred to as ‘water’), which significantly impacts their physical properties and associated geodynamic processes. Observations from different localities worldwide make understanding the behavior of hydrogen during partial melting and mantle metasomatism a contentious issue, as different localities reveal either melting or metasomatism as the controlling factor. To provide new insights, major elements, trace elements and water contents of peridotite xenoliths from three volcanoes of the Shuangliao Volcano Group in Northeast China were analyzed. Minerals display variations in major and trace elements, particularly in clinopyroxene. Most olivine contains no observable water, while orthopyroxene and clinopyroxene retained 14–157 and 46–351 μg/g of water, respectively. Samples were divided into three types according to clinopyroxene trace element patterns, namely, type 1: light rare earth elements (LREEs)-depleted samples; type 2: ‘spoon-shaped’ samples featuring slight enrichment of the most incompatible elements (La and Ce) and relative depletion of mid-rare earth element; and type 3: LREE-enriched samples. Combined with major element trends, the Shuangliao SCLM experienced varying degrees of partial melting and cryptic metasomatism. Different water contents in the Shuangliao SCLM are a combined result of melting and metasomatism: less metasomatized samples (LREE-depleted and ‘spoon-shaped’) preserved the control of water contents by partial melting, while strongly metasomatized samples (LREE-enriched), equilibrated at higher oxygen fugacity and temperature, display considerable post-melting modifications of water contents, possibly associated with Fe redox. These characteristics suggest that hydrous and oxidized melts/fluids likely released by the stagnant Pacific slab in the big mantle wedge have metasomatized the shallow SCLM beneath Shuangliao, which indicates the circulation of materials released by the stagnant slab throughout the upper mantle.

Peridotite

Metasomatism

10.1093/petrology/egae003

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Geology and fluid geochemistry of the Na-metasomatism U deposits in the Longshoushan uranium metallogenic belt, NW China: Constraints on the ore-forming process

Ore Geology Reviews (2019)

Jun Zhong Shengyun Wang Dazhao Gu Yuqi Cai Honghai Fan

Metasomatism

Uraninite

Uranium ore

Ore genesis

Fluorite

10.1016/j.oregeorev.2019.103214

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Citations (17)

Evolution of Montviel alkaline-carbonatite complex by coupled fractional crystallization, fluid mixing and metasomatism — Part II: Trace element and Sm–Nd isotope geochemistry of metasomatic rocks: implications for REE-Nb mineralization

Ore Geology Reviews (2015)

Olivier Nadeau Ross Stevenson Michel Jébrak

Magmatic volatiles are critically important in the petrogenesis of igneous rocks but their inherent transience hampers the identification of their role in magmatic and metasomatic processes. For example, while the role of magmatic volatiles in porphyry copper systems is relatively well understood, the behavior of volatiles and metasomatic fluids in mantle and crustal magmatic-hydrothermal systems remains a work in progress. Alkaline-carbonatite complexes usually originate from the mantle and typically host REE deposits which are thought to be almost always of a hydrothermal origin. The question thus arises as to the origin of the REE and fluids and if the alkaline and carbonatite magmas are accompanied by fluids from the mantle up and through the crust. This study presents the results of whole rock trace elements and Sm–Nd isotopes analyses of clinopyroxenites, melteigites, ijolites, melanosyenites, leucosyenites, granites, silicocarbonatites, magnesiocarbonatites, calciocarbonatites, ferrocarbonatites and polygenic breccias from the 1894 Ma Paleoproterozoic alkaline-carbonatite complex of Montviel, Abitibi, Canada. The metasomatic rocks range in REE concentrations from 100 ppm to 3.54 wt.% and show εNd values ranging from + 6.8 to − 7.2. Based on these results it is demonstrated that volatile-saturated magmas at Montviel were injected through 4 distinct mantle pulses which evolved by fractional crystallization, mixing of depleted mantle and crustal fluids and metasomatism.

Metasomatism

Carbonatite

Fractional crystallization (geology)

Trace element

Petrogenesis

Incompatible element

10.1016/j.oregeorev.2015.09.021

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Citations (9)

Evidence for multi-stage mantle metasomatism at the Dehsheikh peridotite massif and chromite deposits of the Orzuieh coloured mélange belt, southeastern Iran

Ore Geology Reviews (2011)

Sima Peighambari Hamid Ahmadipour Heinz-Günter Stosch Farahnaz Daliran