Formation of Esseneite and Kushiroite in Tschermakite-Bearing Calc-Silicate Xenoliths Ejected in Alkali Basalt
Skarnoid calc-silicate xenoliths composed of anorthite, clinopyroxene and Mg-Al spinel occur in alkali basalts of the Pliocene-Pleistocene intra-plate magmatic province in the northern part of the Pannonian Basin. Randomly oriented and elongated pseudomorphs are tschermakite crystals replaced by oli...
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MDPI AG
2022-01-01
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| author | Luca Reato Monika Huraiová Patrik Konečný František Marko Vratislav Hurai |
| author_facet | Luca Reato Monika Huraiová Patrik Konečný František Marko Vratislav Hurai |
| author_sort | Luca Reato |
| collection | DOAJ |
| description | Skarnoid calc-silicate xenoliths composed of anorthite, clinopyroxene and Mg-Al spinel occur in alkali basalts of the Pliocene-Pleistocene intra-plate magmatic province in the northern part of the Pannonian Basin. Randomly oriented and elongated pseudomorphs are tschermakite crystals replaced by olivine, spinel and plagioclase. The relict amphibole within the pseudomorphs is characterized by high <sup>VI</sup>Al, between 1.95 and 2.1, and very low occupancy of the A-site (<0.1 apfu)—these features are rarely found in nature and are thought to be diagnostic of high-pressure metamorphic rocks. Pyroxene compositions plot along continuous mixing line extending from nearly pure diopside-augite towards a Ca(Fe<sup>3+</sup>Al)AlSiO<sub>6</sub> endmember with an equal proportion of <sup>VI</sup>Al<sup>3+</sup> and Fe<sup>3+</sup>. Concentrations of kushiroite CaAlAlSiO<sub>6</sub> endmember, up to 47.5 mol%, are the highest recorded in terrestrial samples. The AlFe<sup>3+</sup>-rich pyroxenes originated at the expense of diopside-augite during the interaction with carbonate-aluminosilicate melt. Forsterite (Fo<sub>72–83</sub>) and hemoilmenite with up to 32 mol% geikielite (9.3 wt% MgO) also crystallized from the melt, leaving behind the residual calcic carbonate with minor MgO (1–3 wt%). Columnar habit of neoformed olivine growing across diopside-augite layers indicates rapid crystallization from eutectic liquid. Euhedral aragonite and apatite embedded in fine-grained calcite or aragonite groundmass indicate slow crystallization of the residual carbonatite around the calcite-aragonite stability boundary. Corundum exsolutions in rock-forming anorthite are products of superimposed low-pressure pyrometamorphic reworking during transport in alkali basalt. Concomitant alkali metasomatism produced neoformed interstitial sodalite, nepheline, sanidine, albite, biotite, Mg-poor ilmenite (10–18 mol% MgTiO<sub>3</sub>), Ti-magnetite and fluorapatite. Olivine-ilmenite-aragonite-calcite thermobarometry returned temperatures of 770–860 °C and pressures of 1.8–2.1 GPa, whereas plagioclase-amphibole thermobarometer yielded 781 ± 13 °C and 2.05 ± 0.03 GPa. The calculated pressures correspond to depths of 60–70 km. The calc-silicate xenoliths are most likely metamorphosed marbles; however, a magmatic protolith (metagabbro, metaanorthosite) cannot be ruled out owing to high Cr contents in spinels (up to 30 mol% chromite) and abundant Cu-sulfides. |
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| spelling | doaj.art-999765c15b4a4aca8b719f5d91dded472023-11-23T21:17:44ZengMDPI AGMinerals2075-163X2022-01-0112215610.3390/min12020156Formation of Esseneite and Kushiroite in Tschermakite-Bearing Calc-Silicate Xenoliths Ejected in Alkali BasaltLuca Reato0Monika Huraiová1Patrik Konečný2František Marko3Vratislav Hurai4Department of Mineralogy, Petrology and Economic Geology, Faculty of Natural Sciences, Comenius University, Ilkovičova 6, 842 15 Bratislava, SlovakiaDepartment of Mineralogy, Petrology and Economic Geology, Faculty of Natural Sciences, Comenius University, Ilkovičova 6, 842 15 Bratislava, SlovakiaDepartment of Special Laboratories, State Geological Institute of Dionýz Štúr, Mlynská Dolina 1, 817 04 Bratislava, SlovakiaDepartment of Geology and Paleontology, Faculty of Natural Sciences, Comenius University, Ilkovičova 6, 842 15 Bratislava, SlovakiaInstitute of Earth Sciences, Slovak Academy of Sciences, Dúbravská Cesta 9, 840 05 Bratislava, SlovakiaSkarnoid calc-silicate xenoliths composed of anorthite, clinopyroxene and Mg-Al spinel occur in alkali basalts of the Pliocene-Pleistocene intra-plate magmatic province in the northern part of the Pannonian Basin. Randomly oriented and elongated pseudomorphs are tschermakite crystals replaced by olivine, spinel and plagioclase. The relict amphibole within the pseudomorphs is characterized by high <sup>VI</sup>Al, between 1.95 and 2.1, and very low occupancy of the A-site (<0.1 apfu)—these features are rarely found in nature and are thought to be diagnostic of high-pressure metamorphic rocks. Pyroxene compositions plot along continuous mixing line extending from nearly pure diopside-augite towards a Ca(Fe<sup>3+</sup>Al)AlSiO<sub>6</sub> endmember with an equal proportion of <sup>VI</sup>Al<sup>3+</sup> and Fe<sup>3+</sup>. Concentrations of kushiroite CaAlAlSiO<sub>6</sub> endmember, up to 47.5 mol%, are the highest recorded in terrestrial samples. The AlFe<sup>3+</sup>-rich pyroxenes originated at the expense of diopside-augite during the interaction with carbonate-aluminosilicate melt. Forsterite (Fo<sub>72–83</sub>) and hemoilmenite with up to 32 mol% geikielite (9.3 wt% MgO) also crystallized from the melt, leaving behind the residual calcic carbonate with minor MgO (1–3 wt%). Columnar habit of neoformed olivine growing across diopside-augite layers indicates rapid crystallization from eutectic liquid. Euhedral aragonite and apatite embedded in fine-grained calcite or aragonite groundmass indicate slow crystallization of the residual carbonatite around the calcite-aragonite stability boundary. Corundum exsolutions in rock-forming anorthite are products of superimposed low-pressure pyrometamorphic reworking during transport in alkali basalt. Concomitant alkali metasomatism produced neoformed interstitial sodalite, nepheline, sanidine, albite, biotite, Mg-poor ilmenite (10–18 mol% MgTiO<sub>3</sub>), Ti-magnetite and fluorapatite. Olivine-ilmenite-aragonite-calcite thermobarometry returned temperatures of 770–860 °C and pressures of 1.8–2.1 GPa, whereas plagioclase-amphibole thermobarometer yielded 781 ± 13 °C and 2.05 ± 0.03 GPa. The calculated pressures correspond to depths of 60–70 km. The calc-silicate xenoliths are most likely metamorphosed marbles; however, a magmatic protolith (metagabbro, metaanorthosite) cannot be ruled out owing to high Cr contents in spinels (up to 30 mol% chromite) and abundant Cu-sulfides.https://www.mdpi.com/2075-163X/12/2/156xenolithkushiroiteesseneitemelilitealkali basaltCarpathians |
| spellingShingle | Luca Reato Monika Huraiová Patrik Konečný František Marko Vratislav Hurai Formation of Esseneite and Kushiroite in Tschermakite-Bearing Calc-Silicate Xenoliths Ejected in Alkali Basalt Minerals xenolith kushiroite esseneite melilite alkali basalt Carpathians |
| title | Formation of Esseneite and Kushiroite in Tschermakite-Bearing Calc-Silicate Xenoliths Ejected in Alkali Basalt |
| title_full | Formation of Esseneite and Kushiroite in Tschermakite-Bearing Calc-Silicate Xenoliths Ejected in Alkali Basalt |
| title_fullStr | Formation of Esseneite and Kushiroite in Tschermakite-Bearing Calc-Silicate Xenoliths Ejected in Alkali Basalt |
| title_full_unstemmed | Formation of Esseneite and Kushiroite in Tschermakite-Bearing Calc-Silicate Xenoliths Ejected in Alkali Basalt |
| title_short | Formation of Esseneite and Kushiroite in Tschermakite-Bearing Calc-Silicate Xenoliths Ejected in Alkali Basalt |
| title_sort | formation of esseneite and kushiroite in tschermakite bearing calc silicate xenoliths ejected in alkali basalt |
| topic | xenolith kushiroite esseneite melilite alkali basalt Carpathians |
| url | https://www.mdpi.com/2075-163X/12/2/156 |
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