东秦岭商丹带黑山变质沉积岩系的沉积构造环境

Sedimentary-Tectonic Setting of Heishan Meta-sedimentary Rock Series in Shangzhou-Danfeng Belt, East Qinling

陕西商丹黑山的沉积岩系是一套浅变质沉积岩系，其原岩沉积建造可以分为三个不同的沉积环境的岩石组合，包括Ⅰ岩组的泥岩及碳酸盐岩、Ⅱ岩组的杂砂岩和火山碎屑岩和Ⅲ岩组的石英质砾岩、砂岩及粉砂岩。由下向上，其沉积相从深海相经浊积岩盆地相变化到斜坡滨岸相。特征碎屑矿物组成从火山碎屑经燧石岩屑变化到变质岩岩屑，地球化学特征表现为ＳｉＯ２、Ｅｕ／Ｅｕ＊和（Ｌａ／Ｙｂ）Ｎ依次增加，Ｆｅ２Ｏ３＋ＭｇＯ和ΣＲＥＥ依次减小．以上特征表明黑山沉积岩系并非单一的沉积组合，而是与秦岭区域造山作用过程的俯冲－初始接触碰撞阶段协调一致的同造山沉积。

Heishan meta-sedimentary rock series consists of a set of low grade metamorphic sedimentary rocks. Its protolith can be separated into three different sedimentary rock associations (Ⅰ,Ⅱ, andⅢ ) with Ⅰ composed of mudstone and carbonatite,Ⅱ composed of graywacke and volcaniclastic rock and Ⅲcomposed of conglomerate, sandstone and siltite. From Ⅰ to Ⅱ, the sedimentary facies changed from abyssal facies to turbidite facies, then to littoral facies ; characteristic detritus changed from volcanic debris to chert, then to metamorphic debris ; SiO2. Eu/Eu* and (La/Yb)N increased, Fe2O3 +MgO and ΣREE decreased. All of these characters indicate that Heishan sedimentary rock series is not a unitary sedimentary system, but a compliated system of a synorogenic basin that corresponds to the subduction--initial contact collission orogenic phase of Qinling orogenic zone.