冀北尚义变质沉积岩的岩石学、地球化学及岩石成因

发布时间：2018-04-30 06:10

本文选题：岩石学 + 地球化学　；参考：《成都理工大学》2017年硕士论文

【摘要】：冀北尚义变质沉积岩位于华北克拉通北缘中段西部,主要分布在朝力盖、郝报沟、黄土窑、五十家一带,其总体呈近东西向分布。黄土窑变质沉积岩的主要岩石类型包括(含石榴)黑云斜长片麻岩、蛇纹石化大理岩、变质长石石英砂岩。其中以(含石榴)黑云斜长片麻岩为主体,蛇纹石化大理岩和变质长石石英砂岩呈透镜状产出于尚义变质火山岩之中,长短大小不一,长度几米到几千米不等。(含石榴)黑云斜长片麻岩呈灰色,片麻状构造,斑状变晶结构,基质为细粒鳞片粒状变晶结构。主要矿物组合为斜长石(35%)、石英(35%)、黑云母(20%)及少量石榴石(约5%),角闪石(1%)和石墨(3%)。黑云母的化学成分变化不大,均为高铁黑云母。斜长石(An=22.79-34.66)大部分为更长石,少部分为中长石,不发育环带。石榴子石主要由铁铝榴石(Alm=55.43%-65.62%)、锰铝榴石(Spe=15.36%-29.8%)、和镁铝榴石(Pyr=8.36%-13.34%)及少量钙铝榴石(Gro=2.39%-7.58%)组成。部分石榴子石具有成分环带。蛇纹石化大理岩呈灰白色、白色,块状构造,中粒粒状变晶结构。主要矿物组合为方解石(65%)和蛇纹石(30%),次要矿物为橄榄石(2%)和金云母(3%)。变质长石石英砂岩呈灰色、褐灰色,块状构造,中粒粒状变晶结构。主要矿物组合为石英(70%)和钾长石(微斜长石,10%),次要矿物有黑云母(5%)、斜长石(5%)和白云母(3%)。(含石榴)黑云斜长片麻岩SiO_2含量变化较大,介于63.56%-77.34%之间,Al2O3的含量比较高(13.15%-15.82%)。Na2O含量为(2.35%-3.3%),MgO含量为(1.23%-3.12%)。CaO含量介于1.91%~3.35%之间。其微量元素Rb、Cs平均含量为78×10-6、5.2×10-6,均明显低于地壳中平均值(Rb、Cs在地壳中的平均值分别为150×10-6、30×10-6),Ba、Sr平均含量为409×10-6、614×10-6,都高于地壳中平均值(Ba、Sr在地壳中的平均值分别为0.05×10-6、40×10-6)。高场强元素Zr、Hf、Nb及Ta的含量,均低于地壳中相对应元素的平均值,Hf同位素基本与地壳中的平均值相等,Zr/Hf比值低于地壳中的平均值(Zr/Hf=66.7)。尚义变质沉积岩稀土元素总量(∑REE)变化范围不大,为84.03×10-6-171.21×10-6。球粒陨石标准化稀土元素配分模式图显示LREE富集、HREE平坦,并且大部分样品具有轻度的负Eu异常,少部分不见Eu异常。其δEuCN值的变化范围为0.81-0.95。岩石样品的(La/Yb)CN值变化范围比较大,介于4.98-24.72之间,LREE/HREE比值较低,变化于2.28-6.26之间。(含石榴)黑云斜长片麻岩的碎屑锆石的LA-ICPMS U-Pb年龄,具有多个年龄值,有新太古代、古元古代、中元古代、早-中奥陶世、晚奥陶世、早泥盆世、早石炭世和晚石炭世~早二叠世,表明碎屑锆石物源区的多样性。测得变质锆石的谐和年龄为为262.4±4.4Ma,表明该石榴黑云斜长片麻岩变质时代为晚古生代。蛇纹石化大理岩的碎屑锆石龄数据有新太古代、古元古代、中元古代以及早二叠世~中二叠世等,表明尚义蛇纹石化大理岩中碎屑锆石的物源区具有多样性特点。该蛇纹石化大理岩的原岩形成于280.9 Ma之后。在变质长石石英砂岩的碎屑锆石中获得了包括新太古代、古元古代、中元古代的年龄。变质长石石英砂岩的原岩应该形成于中元古代(1776Ma)之后。根据Bhatia和Crook的研究成果显示,其原岩形成环境介于大陆岛弧环境与大洋岛弧环境之间,可能更靠近前者。由西蒙南图解显示,(含石榴)黑云斜长片麻岩落于砂质沉积岩到泥质沉积岩区域,部分位于由砂质沉积岩岩区向泥质沉积岩过渡区域。研究区样品的Al/(Al+Fe+Mn)的摩尔比值介于0.76-0.86之间,平均值为0.81,W(Al)/W(Al+Fe+Mn)的比值介于0.61-0.75之间,平均值为0.67。所以(含石榴)黑云斜长片麻岩的原岩物质来源是陆源碎屑物。同时其沉积环境位于大陆边缘。(含石榴)黑云斜长片麻的(Ce/Ce*)CN值为0.697-1.001(平均为0.868),介于大洋盆地与大陆边缘之间,且更类似后者的稀土元素特征。因此可以推断尚义黄土窑变质沉积岩的原岩应该为泥质(或含泥质)砂岩,是一套形成于晚古生代的陆源碎屑岩,可能形成于大陆岛弧环境。
[Abstract]:The Shangyi metamorphic sedimentary rocks in northern Hebei Province, located in the western part of the north margin of the North China Craton, are mainly distributed in the north of the north of the north of the north margin of the North China Craton, which are mainly distributed in fifty areas. The main rock types of the metamorphic sedimentary rocks of the Loess kiln include (pomegranate) black cloud and inclined marbles, serpentine petrified marble, and metamorphic feldspar quartz sandstone. (pomegranate) black cloud inclined gneiss as the main body, serpentine petrified marble and metamorphic feldspar quartz sandstone are lensed in the form of Shangyi metamorphic volcanic rocks. The length and size vary from a few meters to thousands of meters in length. (pomegranate) black cloud inclined long slice gneiss is gray, flax like structure, porphyritic and crystalline structure, the matrix is fine granular granular granular metamorphism. Structure. The main mineral assemblage is plagioclase (35%), quartz (35%), black mica (20%) and a small amount of garnet (about 5%), hornblende (1%) and graphite (3%). The chemical composition of the black mica has little change, all of which are high iron black mica. Most of An=22.79-34.66 is more feldspar, a few is the feldspar, and the undeveloped ring is not developed. The garnet is mainly ferric and granite. (Alm=55.43%-65.62%), manganese and aluminite (Spe=15.36%-29.8%), and magnesia and aluminate (Pyr=8.36%-13.34%) and a small amount of calcite (Gro=2.39%-7.58%). Some of the garnet have a composition ring. Serpentinite marble is gray white, white, massive, and granular crystalline structure. The main mineral assemblage is calcite (65%) and serpentine (30%). Secondary minerals are olivine (2%) and gold mica (3%). Metamorphic feldspar quartz sandstone is gray, brown gray, massive and granular granular structure. The main mineral assemblages are quartz (70%) and potash feldspar (10%), secondary minerals are biotite (5%), cable-stayed feldspar (5%) and Muscovite (3%). (pomegranate) black cloud slanted gneiss content changes Between 63.56%-77.34%, the content of Al2O3 is higher (13.15%-15.82%).Na2O content (2.35%-3.3%), MgO content is (1.23%-3.12%).CaO content between 1.91%~3.35%. The trace element Rb, Cs average content is 78 x 10-6,5.2 * 10-6, all obviously lower than the average value in the crust. The average value in the crust is 150 * * 10, respectively. -6), the average content of Ba and Sr is 409 x 10-6614 x 10-6, which are higher than the average in the crust (Ba, Sr in the crust is 0.05 * 10-6,40 x 10-6 respectively). The content of high field elements Zr, Hf, Nb and Ta are lower than the average value of the corresponding elements in the crust, and the Hf isotopes are basically equal to the average in the crust, and the Zr/Hf ratio is lower than the average in the crust. Value (Zr/Hf=66.7). The total amount of rare earth elements (sigma REE) of the Shangyi metamorphic sedimentary rocks is small. The normalized REE distribution pattern map of 84.03 x 10-6-171.21 10-6. chondrites shows LREE enrichment and HREE flat, and most of the samples have mild negative Eu anomalies and few Eu anomalies. The variation range of the Delta EuCN value is 0.81-0.95.. The variation range of (La/Yb) CN values of rock samples is relatively large, between 4.98-24.72 and low LREE/HREE ratio, which varies between 2.28-6.26. The LA-ICPMS U-Pb age of the detrital zircon of the black cloud slanted gneiss (including pomegranate) has multiple age values, and there are new Archaean, Proterozoic, Mesoproterozoic, early Middle Ordovician, late Ordovician, early Devonian, early Devonian, and Early Devonian. The Carboniferous and Late Carboniferous ~ Early Permian shows the diversity of the source area of the detrital zircon. The dating age of the metamorphic zircon is 262.4 + 4.4Ma, indicating that the metamorphic age of the pomegranate black cloud is late Palaeozoic. The data of the clastic zircon age of the serpentine marble have the Neo Archaean, Proterozoic, Mesoproterozoic and Early Permian. In the Middle Permian, it is indicated that the source area of the detrital zircon in the serpentine marble of Shangyi is diverse. The protolith of the serpentine marble is formed after 280.9 Ma. In the detrital zircon of the metamorphic feldspar quartz sandstone, the age of the Neoarchean, Proterozoic, Mesoproterozoic and metamorphic feldspar quartz sandstone should be obtained. It is formed after the Middle Proterozoic (1776Ma). According to the research results of Bhatia and Crook, the original rock formation environment is between the continental island arc environment and the oceanic island arc environment, which may be closer to the former. The mole ratio of Al/ (Al+Fe+Mn) in the study area is between 0.76-0.86, the average value is 0.81, the ratio of W (Al) /W (Al+Fe+Mn) is between 0.61-0.75 and the average value is 0.67. so the source of the original rock material of the black cloud slanted gneiss (pomegranate) is the terrigenous clastic. The (Ce/Ce*) CN value of (pomegranate) black cloud is 0.697-1.001 (average 0.868), which is between the ocean basin and the continental margin, and is more similar to the latter's rare earth elements. Therefore, it can be concluded that the original rock of the metamorphic sedimentary rocks in Shangyi loess kiln should be a muddy (or argillaceous) sandstone, which is formed in the late Paleozoic. Terrigenous clastic rocks may be formed in the continental island arc environment.

【学位授予单位】：成都理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：P588.2

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