摘要
大别山区高压变质岩类呈数以千计的板状、透镜状和团块状产出在太湖、潜山和岳西一带,】1000km^2范围内断续出露的片麻岩和大理岩中。岩石类型有:(1)榴辉岩;(2)石榴辉石岩;(3)石榴二辉麻粒岩和(4)石榴橄榄岩。(1)、(2)两类的围岩为含硬玉片麻岩和硬玉岩。金刚石、柯石英(及其假象)和硬玉产出在榴辉岩,石榴辉石岩和硬玉岩中。前两种岩石矿物成分为:石榴石(Gt)、绿辉石(Omph)、透辉石(Di)、金红石(Ru)、蓝晶石(Ky)、黝帘石(Zo)、绿帘石(Ep)、捐石(Ti)、黑云母(Bi)、绿泥石(Chl)、闪石(Amph)、金刚石(Diam)、柯石英(Cs)、斜长石(PI)、石英(Q)、多硅白云母(Ph)、蓝闪石(Glau)、冻蓝闪石(Barr)、硬玉(J)、硬柱石(Law)、方解石(Cc)、文石(Ar),有时有顽火辉石(En)和金云母(Phl)。根据矿物共生组合的关系,可将它们分为4个世代:(1)Glau+Ep+Barr+Q+Ph+Piem;(2)Omph+Gt+Cs+J+Diam十Ar+Ru+Ky+Zo+Phl;(3) Di+Gt+Pl+Amph+Q+Cc+Ti;(4)Amph+Pl+Chl+Bi。代表榴辉岩类的4个变质作用阶段。金刚石在石榴石中呈包体产出,已发现40余粒,大部分为10)μm左右,最大一粒直径达720/480μm。晶形大部分为八面体和六面体,其次为菱形+二面体和四面体。四个世代共生矿物组合表明此带的变质作用是经由浅部绿片岩一蓝闪片岩相到深度】100km的榴辉岩相,然后逐渐抬升到近地表而经历了角闪一蓝片岩相到绿片岩相。大别山变质成因金刚石是苏联北哈萨克斯坦之后的世界第2例,但这里的矿物组合和岩石组合则为世界鲜见。
Eclogite bands and lenses, impure marble bands and very rare ultra-mafic lenses occur intercalated within the leucocratic gneisses. There are thousands of eclogite bands, lenses and nodules in various stages of preservation and ranging in size from a few centimetres to thousand metres. By the diagnostic mineral assemblages, eclogitic rocks are subdivided into ; (1) eclogite ; (2) garnet-pyroxenite; (3) garnet-low pyroxene-granulite and (4) garnet-peridotite. There are jadeite-bearing gneiss and lenticular jadeitite in the immediate country rock of eclogite and garnet-pyroxenite. Diamonds, coesite with its quartz pseudomorphs and, sometimes, jadeite occur in eclogite, garnet-pyroxenite or jadeitite, in which the mineral components are garnet, omphacite, diopside, rutile, kyanite , zoisite, epidote, titanite, biotite, chlorite, amphibole, diamond, coesite, plagioclase, quartz, phengite, glaucophane, barroisite, jadeite, lawsonite, calcite aragonite, with rare orthopyroxene and phlogopite. By the formation condi- tions and the relation between them, four generations of mineral parageneses are discerned: (1) Glau +Barr+Ep+Q+Ph; (2) Omph+Gt+Cs+Diam+J+Ar+Ru+Ky+Zo+Phl; (3) Di+Gt+Pl +Amph+Ti+Cc+Q; (4) Amph+Pl+Chl+Bi. These Show that there are four stages in the meta- morphic process of the diamond-bearing rocks in Dabie Shan. Average size of 40 discovered diamond grains is about 100μm, and some larger ones up to 300μm. Most diamond crystals are euhedra oc- tahedron and hexahedron, a few dodecahedron and tetrahedron. Diamonds in thin sections are identified by using X-ray diffraction and Raman spectrum microscopically. Diamonds extracted from artificial heavy sand are identified by X-ray with triaxial Gandolfi camera (designed by Dr. Zhang Hanging) The presence of the assmblage, Diam+Cs+J, indicates that diamonds and diamondiferous rocks are meta- morphic products under the pressure more than 4. 0 GPa and temperature above 900℃. The presence of four generations of mineral parageneses indicates that the continental rock slice containing eclogites once subducted from shallow level (where blue schist facies formed) to depth more than 120km (where diamond or eclogite facies formed) and returned to surface (where amphibolite and greenschist facies formed) finally. Diamonds from Dabie Shan is the second occurrence of the diamond of metamorphic origin after that from north Kazakhstan, USSR, whereas the mineral assemblage and rock association in Dabie Shan are the first one in the world.
出处
《安徽地质》
1991年第1期3-18,82-83,共18页
Geology of Anhui
