安徽大别山北部红刚玉岩石的成因

PETROGENESIS OF RED CORUNDUM ROCKS FROM THE NORTHERN DABIE MOUNTAIN, ANHUI

大别山北部红刚玉矿产在太古代大别山群黑云角门外长片麻岩以及超基性岩中。赋存红刚玉的刚玉黑云二长片麻岩的原始岩石为富铝泥质岩，在角门岩相变质条件下，通过两种脱硅方式，即变质分异作用和超基性岩侵位，形成刚玉黑云二长片麻岩。它们形成的温压条件：Ｔ＝５００℃～７００℃，Ｐ＝０．４～０．７ＧＰａ。刚玉形成的可能的化学机制是白云母在缺硅条件下的分解。

Red corundum rocks in the northern Dabie Mountain occur in biotite-amphiboleplagioclase gneisses as vein-like conformability and ultra-basic rock as enclosure. The stratum of this region belongs Archaeozoic Dabie group. The red corundum-bearing rocks are named as corundum-biotite-monzonic gneiss, whose mineral assemblage is corundum +biotite +oligoclase +K-feldspar+muscovite, and whose chemical composition is SiO2 47. 46 % -53. 84 %,Al2O3 23. 10 % - 27. 37 %, are a kind of Al2O3 enrichment and SiO2 deficiency. By comparing chemical composition and REE, it has been proved that their original rocks are a polite rich in Al2O3, which came from pre-Cambriam elastic deposits of continent inside and. margin. Red corundum, rose, specific gravity 3. 88-3. 99, hardness 8. 98, a content of Cr2O30. 05-0. 29%, part of them can get ruby grade.The polite rich in Al2O3, transforms a corundum-biotite-monzonic gneisses under amphibole factes conditions by means of two kinds of desilification way,i. e. metamorphic differentiation and ultra-basic rock intrusion, Their forming PT conditions are T=500℃ -700℃ and P = 4-7kb. A possible metamorphic neaction of corundum forming is that muscovite= K-feldspar + corundum +H2O.s