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Crystal chemistry and origin of epidote-(Sr) in alkaline rocks of the teschenite association (Silesian Unit, Outer Western Carpathians, Czech Republic)
Mineralogy and Petrology ( IF 1.8 ) Pub Date : 2023-11-13 , DOI: 10.1007/s00710-023-00847-w
Kamil Kropáč , Zdeněk Dolníček , Pavel Uher , David Buriánek , Tomáš Urubek

A new occurrence of epidote-(Sr) CaSr(Al2Fe3+)[Si2O7][SiO4]O(OH), Sr-REE-rich epidote and Sr-rich allanite-(Ce) is located in Lower Cretaceous, Sr-rich hydrothermally altered leucocratic dykes penetrating alkaline igneous rocks (teschenites) near the Nový Jičín town (the Silesian Unit, Outer Western Carpathians). The dykes contain phenocrysts of pyroxene, amphibole, biotite, fluorapatite and dominant felsic groundmass consisting mostly of alkali feldspars and zeolites (analcime, natrolite and thomsonite-Ca). Accessory minerals include Ti-rich magnetite, prehnite, chamosite, pyrite, calcite, (OH, F)-rich grossular, epidote-group minerals, HFSE-, REE-rich minerals, Sr-rich baryte and slawsonite. The Sr-rich epidote forms columnar crystals or irregular aggregates, which are mostly spatially related to chamosite-titanite pseudomorphs; it contains 0.15–0.81 apfu Sr, ≤ 0.55 apfu REE; Fe3+/(Fe3+ + Al) = 0.16–0.48. The Sr2+ substitutes Ca2+ in the A2 site by a coupled substitution involving other A2 (REE3+, Th4+) or M (Al3+, Fe3+, Fe2+) cations. The Sr-rich epidote crystallized from hydrothermal solutions, probably at temperatures between ~ 250–430 °C, during cooling of the host rock. The dykes show higher Sr contents (5680–7830 ppm) and 87Sr/86Sri(120 Ma) ratios (~ 0.7046–0.7047) compared to host mesocratic teschenites (1310–1470 ppm Sr and ~ 0.7038–0.7045, respectively). The Sr isotopes indicate origin of most Sr from primary magmatic plagioclase in parent teschenite. Nevertheless, there also participated external fluids, derived from the Lower Cretaceous seawater or diagenetic waters related to associated siliciclastic sediments with 87Sr/86Sri(120 Ma) = ~ 0.7073–0.7083. These more radiogenic sources contributed at least 6–21% of the bulk Sr budget of the studied Sr-rich epidote-bearing leucocratic dykes.



中文翻译:

绿帘石-(Sr) 的晶体化学和起源于泰石英石协会的碱性岩石(西里西亚单元,外西喀尔巴阡山脉,捷克共和国)

新出现的绿帘石-(Sr) CaSr(Al 2 Fe 3+ )[Si 2 O 7 ][SiO 4 ]O(OH)、富Sr-REE绿帘石和富Sr铜铝石-(Ce)位于下白垩纪,富含锶的热液蚀变的白质岩脉穿透新伊钦镇(西里西亚单元,外喀尔巴阡山脉)附近的碱性火成岩(特切岩)。岩脉含有辉石、角闪石、黑云母、氟磷灰石斑晶和主要由碱长石和沸石(方沸石、钠沸石和菱钠石-Ca)组成的长英质基质。副矿物包括富钛磁铁矿、葡萄石、硅锰矿、黄铁矿、方解石、富(OH,F)钙铝榴石、绿帘石族矿物、富HFSE、REE矿物、富Sr重晶石和斜斜铝石。富Sr绿帘石形成柱状晶体或不规则聚集体,在空间上大多与绿铜矿-钛铁矿假象有关;含有 0.15–0.81 apfu Sr,≤ 0.55 apfu REE;Fe 3+ /(Fe 3+ + Al) = 0.16–0.48。Sr 2+通过涉及其他A2 (REE 3+、Th 4+ )或M (Al 3+、Fe 3+、Fe 2+ )阳离子的耦合取代来取代A2位点中的Ca 2+ 。富含 Sr 的绿帘石在母岩冷却过程中从热液中结晶,温度可能在 250-430 °C 之间。与主体中层细晶岩(分别为 1310–1470 ppm Sr 和约 0.7038–0.7045)相比,岩脉显示出更高的 Sr 含量(5680–7830 ppm)和87 Sr/ 86 Sr i(120 Ma)比率(约 0.7046–0.7047)。Sr 同位素表明大多数 Sr 源自母体白石英岩中的原生岩浆斜长石。然而,也有来自下白垩统海水或与87 Sr/ 86 Sr i(120 Ma)  = ~ 0.7073–0.7083相关硅质碎屑沉积物相关的成岩水的外部流体参与。这些放射源较多,占所研究的富含锶绿帘石淡色岩脉的大量锶预算的至少 6-21%。

更新日期:2023-11-14
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