DOI: 10.1016/j.epsl.2018.07.009
Scopus记录号: 2-s2.0-85050164506
论文题名: Not all moissanites are created equal: New constraints on moissanite from metamorphic rocks of Bulgaria
作者: Machev P. ; O'Bannon E.F. ; Bozhilov K.N. ; Wang Q. ; Dobrzhinetskaya L.
刊名: Earth and Planetary Science Letters
ISSN: 0012821X
出版年: 2018
卷: 498 起始页码: 387
结束页码: 396
语种: 英语
英文关键词: 15R-SiC
; 3C-SiC polytypes
; 6H-SiC
; metamorphic rocks
; moissanite (SiC)
; polytypical zonation of SiC
Scopus关键词: Amorphous carbon
; Garnets
; Lime
; Metamorphic rocks
; Mica
; Nanocrystals
; Silica
; Silicate minerals
; Volcanic rocks
; Zoning
; 15R-SiC
; 6H-SiC
; Moissanite
; polytypical zonation of SiC
; SiC polytypes
; Silicon carbide
; amphibolite facies
; continental crust
; crystal
; greenschist facies
; metamorphism
; metasedimentary rock
; moissanite
; Bulgaria
英文摘要: Terrestrial moissanite (SiC) is widely reported as an ultra-high pressure mineral occurring in kimberlites, diamonds and ultramafic/mafic rocks of mantle origin. However, the conditions of crystallization remain largely unknown. Moreover, dozens of SiC occurrences have been reported from continental crust sources such as granitoids, andesite–dacite volcanic rocks and their breccia, metasomatic and metamorphic rocks, and even limestones. The validity of many of these reports is still debated primarily due to possible contaminations from the widespread use of synthetic SiC abrasives in samples preparation. Indeed, reports of well-documented in-situ occurrences of moissanite in association with co-existing minerals are still scarce. The only condition of moissanite formation that is agreed upon is that extremely reducing media are required (e.g. 4.5–6 log units below the iron-wustite buffer). Here, we report the new occurrence of moissanite that was found in-situ within the garnet–staurolite–mica schists of Topolovgrad metamorphic group of Triassic age in Southern Bulgaria. The 10–300 μm moissanite crystals are situated within 0.1–1.2 mm isolated clusters, filled with amorphous carbon and nanocrystalline graphite. Most of moissanite crystals are 15R (rhombohedral) and 6H (hexagonal) polytypes, and one prismatic crystal, found within them, exhibits unusual concentric polytypical zoning with core (15R), intermediate zone (6H) and rim (3C-cubic). Experimental data show that this type of polytypical zonation is likely due to a decrease in temperature (or/and pressure?) and changes in Si/C ratio. Indeed, amphibolite facies metamorphism (500–580 °C – garnet–staurolite zone) followed by a subsequent cooling during the retrograde stage of green schist facies metamorphism (∼400–500 °C) could have provided a change in temperature. The SiC containing clusters exhibit evidence that they are pre-metamorphic, and we hypothesize that their protolith was a “black shale” material likely rich in carbon, hydrocarbon and terrigenous silica. The latter served as a source of isolated chemically-reduced media, which is required for SiC formation. Other concepts to explain moissanite occurrences in metasedimentary rocks are also discussed. Importantly, our findings show that the formation conditions of moissanite are likely more variable than previously recognized. © 2018 Elsevier B.V. Citation statistics:
资源类型: 期刊论文
标识符: http://119.78.100.158/handle/2HF3EXSE/109748
Appears in Collections: 影响、适应和脆弱性 气候变化事实与影响
There are no files associated with this item.
作者单位: Faculty of Geology and Geography, Sofia University “St. Kliment Ohridski”, Sofia, Bulgaria; Physical and Life Sciences, Physics Division, Lawrence Livermore National Laboratory, Livermore, CA 94550, United States; Central Facility for Advanced Microscopy and Microanalysis, University of California at Riverside, Riverside, CA 92521, United States; State Key Laboratory for Mineral Deposits Research, Department of Earth Sciences, Nanjing University, Nanjing, 210023, China; Department of Earth Sciences, University of California at Riverside, Riverside, CA 92521, United States
Recommended Citation:
Machev P.,O'Bannon E.F.,Bozhilov K.N.,et al. Not all moissanites are created equal: New constraints on moissanite from metamorphic rocks of Bulgaria[J]. Earth and Planetary Science Letters,2018-01-01,498