Abstract
A shallow-level monzodioritic to quartz-monzodioritic pluton of the Upper Cretaceous age caused contact metamorphism of Tithonic–Kimmeridgian reef limestones at Măgureaua Vaţei (Metaliferi Massif, Apuseni Mountains, Romania). The preserved peak metamorphic assemblage includes gehlenite (Ak 33.64–38.13), monticellite, wollastonite-2M, Ti-poor calcic garnet, and Ca-Tschermak diopside (with up to 11.15 mol.% Ca-Tschermak molecule). From the monzodioritic body to the calcitic marble, the periplutonic zoning can be described as: monzodiorite/agpaitic syenite-like inner endoskarn/wollastonite + perovskite + Ti-poor grossular + Al-rich diopside/wollastonite + Ti-poor grossular + diopside + vesuvianite/gehlenite + wollastonite + Ti poor grossular + Ti-rich grossular (outer endoskarn)/wollastonite + vesuvianite + garnet (inner exoskarn)/wollastonite + Ti-rich garnet + vesuvianite + diopside (outer exoskarn)/calcitic marble. Three generations of Ca garnets could be identified, as follows: (1) Ti-poor grossular (Grs 53.51–81.03 mol.%) in equilibrium with gehlenite; (2) Ti-rich grossular (Grs 51.13–53.47 mol.%, with up to 19.97 mol.% morimotoite in solid solution); and (3) titanian andradite (Grs 32.70–45.85 mol.%), with up to 29.15 mol.% morimotoite in solid solution. An early hydrothermal stage produced retrogression of the peak paragenesis toward vesuvianite, hydroxylellestadite (or Si-substituted apatite), clinochlore, “hibschite” (H4O4-substituted grossular). A late hydrothermal event induced the formation of lizardite, chrysotile, dickite, thaumasite, okenite and tobermorite. A weathering paragenesis includes allophane, C-S-H gels and probably portlandite, unpreserved because of its transformation in aragonite then calcite. Overprints of these late events on the primary zoning are quite limited.
Highlights
The high-temperature skarn occurrence from Măgureaua Vaţei (Metaliferi Massif, ApuseniMountains, Romania) represents one of the very rare occurrences of high-temperature calc-skarns in the world
Analyses of material from Măgureaua Vaţei were done using a combination of electron microprobe analysis (EMPA), scanning electron microscopy (SEM), X-ray powder diffraction (XRD), single crystal X-ray diffraction (SCXRD), optical microscopy and cathodoluminescence (CL)
The maximum temperature conditions estimated for this M1 event of prograde evolution of the system are in the range of
Summary
The high-temperature skarn occurrence from Măgureaua Vaţei (Metaliferi Massif, ApuseniMountains, Romania) represents one of the very rare occurrences of high-temperature calc-skarns in the world. After the initial description of the occurrence [5], additional mineralogical investigations of the Măgureaua Vaţei skarn were done, but are quite brief, generally referring only to specific mineral species, e.g., gehlenite [6], monticellite [7], clinopyroxene [8]. While the petrographic descriptions were more thorough (i.e., [4]), there remains a paucity of data about the composition, optics and crystallographic parameters of the associated phases, and no structure determinations were carried out, in spite of the well-known tendency for polytypism and lowering symmetry of minerals such as garnets [9,10,11], wollastonite [12] or vesuvianite [13,14] in high-temperature skarns. The relative paucity of mineral associations and the large dimensions of the skarn minerals from Măgureaua Vaţei, as compared with the minerals from the two other occurrences of high temperature skarns in Romania (i.e., Cornet Hill and Oraviţa, described by [15,16,17], respectively), were an advantage for this study
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