In:
Bulletin de Minéralogie, PERSEE Program, Vol. 104, No. 4 ( 1981), p. 441-444
Abstract:
Luobusha ophiolite suite is a part of the eastern member of the ophiolite zone in Yalu Tsangpo River Drainage area. It consists of three rock assemblages : (1) Assemblage of upper cretaceous sandstone-slate intercalated with altered intermediate — basic volcanic rocks and radiolarian siliceous rocks ; (2) Assemblage of dunite and hartzburgite ; (3) Assemblage of gabbro and diallage peridotite. Pumpellyite occurs in the contact metamorphic zone that occurred between the bottom wall of the ultramafic bodies of Luobusha ophiolite suite and two different country rocks. One of them is the strongly metamorphosed volcanic rock included in ultramafic bodies as xenoliths. And the other is the slate beneath the ultramafic bodies. The metamorphic zones are all several centimeters in thickness. Pumpellyite is the main constituent mineral of the metamorphic zones. Pumpellyite is white to yellowish white in color, and with vitreous luster. It is commonly massive with grain size less than 0.2 mm in diameter. Under polarizing microscope, pumpellyite is colorless and biaxial postive, 2 V = 7-18°, Ng = 1.6873, Nm = 1.6752, Np = 1.6722, c^Np = 35° ± Crystals long or short prismatic with no good cleavage. Sometimes, anomalous interference color is observed. The chemical composition includes : SiO₂ 39.60, Al₂O₃ 26.30, FeO 1.48, CaO 21.60, MgO 4.30, MnO 0.050, TiO₂ 0.00, SrO 0.00, BaO 0.0006, NiO 0.0025, Cr₂O₃ 00006, Na₂O 0.06, K₂O 0.04, P₂O₅ 0.05, H₂O⁺ 7.42, H₂O⁻ 0,00, Total 100.9037. The strongest lines of X-ray powder pattern are (in Å) : 2.09 (10), 1.599 (6), 4.6 (5), 3.76 (5), 2.45 (5). a = 8.65, b = 5.88, c = 18,80 Å, ß = 108.60°, probable space group : A2/m, A2, Am₀. Pumpellyite is associated with diopside. Under microscope, replacement of diopside by pumpellyite is frequently observed. Later grossularite veinlets penetrated the aggregates of pumpellyite and diopside.
Type of Medium:
Online Resource
ISSN:
0180-9210
DOI:
10.3406/bulmi.1981.7491
Language:
French
Publisher:
PERSEE Program
Publication Date:
1981
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