Oversea Research on the Bou-Azzer Ophiolite (Morocco) of Proterozoic Age

Morroco的Bou-Azzer蛇绿岩具有保存完好的蛇绿岩地层。它是由橄榄岩、各向同性辉长岩、粗玄岩脉和火山岩组成的。岩石高度蚀变或变质。蛇绿岩的地幔部分为完全蛇纹化的方辉橄榄岩，面理强烈。少量纯橄榄岩和辉石岩分别为整合和不整合。小型整合铬铁矿豆荚并不罕见。纯橄榄岩在与辉长岩接触面附近占优势，有频繁的辉长岩带。该岩性相当于莫霍面过渡带。残余结构和尖晶石化学制约了橄榄岩的初始岩性和化学特征。方辉橄榄岩中尖晶石的Cr#>0.6，铬铁矿中尖晶石的Cr #>0.7，表明Bou-Azzer蛇绿岩地幔段的耐火性质。在辉长岩中发现了晚侵入的伟尔岩。除了地幔部分的耐火性质外，其组成岩石基本上与古生代蛇绿岩（如阿曼蛇绿岩）相似。地幔部分的高耐火性可能是元古宙蛇绿岩的特征之一。有趣的是，次生磁铁矿凝块或脉（有时含镍）在蛇纹化方辉橄榄岩中很常见。含锰、钴和镍的次生铬尖晶石偶尔在辉锑铅矿中发现。这些元素在蛇纹石化作用后从橄榄石中排出，因为相对于橄榄石而言，蛇纹石矿物含量较低。它们是移动的，并且可以沉淀形成磁铁矿凝块/脉，或并入铬尖晶石中。这些元素的流动性可能与沉淀有关的矿石（砷化物）（= Bou-Azzer钴矿石）周围的蛇绿岩蛇纹岩的边界。

The Bou-Azzer ophiolite, Morroco, of Proterozic age has been known to have a well-preserved ophiolite stratigraphy. It is significantly dismembered, being composed of peridotites, isotropic gabbro, dolerite dikes and volcanic rocks. The rocks are highly altered or metamorphosed. Completely serpentinized harzburgite with strong foliation comprises the mantle section of the ophiolite. Small amount of dunite and pyroxenite are concordant and discordant, respectively. Small concordant chromitite pods are not rare. Dunite is predominate near the contact with the gabbroic section, having frequent gabbroic bands. This lithology is equivalent to the Moho transition zone. Relic textures and spinel chemistry constrained initial lithology and chemical characteristics of the peridotites. The Cr# of spinet is >0.6 in harzburgite and >0.7 in chromitite, indicating a refractory character of the mantle section of the Bou-Azzer ophiolite. Late-intrusive wehrlite was found in the gabbroic rocks. Constituent rocks are basically similar to those in the Phanerozoic ophiolites, such as the Oman ophiolite, except for the refractory character of the mantle section. The highly refractory character of the mantle section may be one of characteristics of the Proterozoic ophiolite.To be interesting, secondary clots or veins of magnetite (sometimes Ni-bearing) are common to the serpentinized harzburgite. Secondary chromian spinels with appreciable amounts of Mn, Co and Ni are occasionally found in harzburgite. These elements were expelled from olivine upon serpentinization because serpentine minerals are low in them relative to olivine. They are mobile and could precipitate to form magnetite clots/veins of were incorporated in chromian spinels. The mobility of these elements are possibly related to precipitation as ores (arsenides) (= Bou-Azzer Co ores) around the boundary of the ophiolitic serpentinite.