A hibonite-spinel-corundum-hematite assemblage in plagioclase-clinopyroxene pyrometamorphic rocks, Hatrurim Basin, Israel: mineral chemistry, genesis and formation temperatures

Abstract

The intergrowths of Fe-rich corundum + Al-rich hematite + spinel + hibonite have been found as an assemblage in a plagioclase-clinopyroxene rock (paralava, former hornfels) at the Hatrurim Basin, Hatrurim combustion metamorphic Formation. Most spinels show oriented exsolution structures and vary from (Mg0.75${\rm Fe}_{{\rm 0}{\rm. 25}}^{2 +} $)(Al1.80${\rm Fe}_{{\rm 0}{\rm. 20}}^{3 +} $)O4 (with exsolutions) to (Mg0.77${\rm Fe}_{{\rm 0}{\rm. 23}}^{2 +} $)(Al1.95${\rm Fe}_{{\rm 0}{\rm. 05}}^{3 +} $)O4 (homogeneous) indicating a tendency towards magnesioferrite and magnetite, and enrichment in NiO (up to 1.9 wt.%) and ZnO (up to 1.4 wt.%). Hibonite is Ti rich (TiO2 > 8 wt.%) and close to CaAl9Fe3+(Mg,Fe2+)TiO19. Corundum varies in Fe2O3 (4.2–11.8 wt.%). Hematite is also inhomogeneous and contains oriented exsolution structures of corundum. It shows variable concentrations of TiO2 (0.7–5.6 wt.%), Al2O3 (0.7–8.6 wt.%), Cr2O3 (0.2–1.5 wt.%), V2O3 (0.1–1.0 wt.%) and MgO (0.3–2.0 wt.%). Crystallization of this specific assemblage is assumed to be at 1000–1200°C using evaluations for the corundum hematite pair with reference to published experimental data. The active role of superheated oxidised volatiles is suggested during both crystallisation of this corundum-bearing association and host-rock transformation (melting event for hornfels → paralava).

Mineralogical Diversity of Ca2SiO4-Bearing Combustion Metamorphic Rocks in the Hatrurim Basin: Implications for Storage and Partitioning of Elements in Oil Shale Clinkering

“…The Masada-Zohar block stores small commercial gas fields and non-commercial heavy and light oil. The geological descriptions of different MZ complexes and the models explaining their origin have been largely published [1,4,25,40,[47][48][49][50][51]69,74]. The Hatrurim CM complex is remarkable among other MZ in the abundance of high-and ultrahigh-temperature rocks, including diverse paralavas, as well as in the presence of multiple outcrops of Ca2SiO4-bearing clinker-like CM rocks (Figures 2 and 3).…”

“…Among them, totally decarbonated Ca-rich and Al-poor larnite rocks are relatively widespread, while Al-enriched clinopyroxene-anorthite hornfelses as well as molten rocks-paralavas are sporadic and scarce. Clinopyroxene-anorthite paralavas contain K-feldspar and Fe-Ti-Al oxides (±fluorapatite, orthopyroxene, tridymite; fayalite; pyrrhotite; the whitlockite) [4,40,50,52,64]. Rock-forming minerals of Ca-rich paralavas are gehlenite, Ca 3 Si 3 O 9 and Ca 2 SiO 4 modifications, rankinite, Ti-rich andradite, kalsilite, fluorapatite-fluorellestadite solid solutions.…”

“…It is extremely rare in the Hatrurim Fm clinker-like CM rocks: we found it in a single sample of our collection as few ≤10 µm vuggy grains. This rarity cannot be due to the temperature of metamorphism as the Ca 3 SiO 5 phase is stable within the range from 2150 to 1250 • C [20], while the carbonate protolith was most often exposed to 1300-1250 • C during CM events [4,40,51,54]. Hatrurite may be lacking from the high-temperature Hatrurim CM rocks for two reasons: (1) decomposition of Ca 3 SiO 5 into CaO and Ca 2 SiO 4 during gradual cooling (without quenching above 1250 • C); (2) extremely high hydration reactivity of Ca 3 SiO 5 which thus cannot survive prolonged alteration processes.…”

Nataliakulikite, Ca4Ti2(Fe3+,Fe2+)(Si,Fe3+,Al)O11, a New Perovskite-Supergroup Mineral from Hatrurim Basin, Negev Desert, Israel

“…The highly porous rocks of the olive unit are mainly composed of calcite and zeolite, which cement quartz sand particles and clasts of the underlying sediments. Other rocks of the unit are high-temperature clinopyroxene-anorthite hornfels and paralavas which form specific swells and "ploughed land" structures [59,60].…”

Pyrometamorphic Rocks in the Molinicos Basin (Betic Cordillera, SE Spain): Insights into the Generation of Cordierite Paralavas

“…This might also explain why the observed stability of corundum, hematite, and hercynite (Table 2) could not be reproduced in our pseudosection calculation, in which the initial bulk rock composition was that corresponding to the deduced sedimentary protolith for the studied rocks (dark clay layer Y-43). Sharygin [62] suggests their possible formation due to hot oxidised gases, as indicated by the accumulation of Fe-Al oxides into, or near, gas vesicles. This could be also the case in the here studied rocks (Figure 13).…”