摘要
在甘肃北山西三羊井东一带产有一种特殊类型的碳酸盐质岩体。该岩体呈不规则带状、小岩瘤状产出,岩体与围岩之间具明显的港湾状、枝状侵入接触、岩石不具层理、岩石表现出的细粒结晶等粒结构、岩体内见围岩捕掳体(碳酸岩内部发育的部分捕掳体与围岩成分一致)及与其伴生的超镁铁质岩(橄榄岩)等特征均表明其为火成碳酸岩岩体。岩石地球化学显示,岩石具富CaO(54.41%~54.52%)、CO_2(43.36%~43.39%),贫SiO_2、TiO_2、MgO、MnO、Fe_2O_3、FeO、Na_2O、K_2O的特点,CaO/(CaO+MgO+FeO+Fe_2O_3+MnO)比值为0.99,为方解石碳酸岩;岩石稀土总量低(ΣREE=11.20×10^(-6)~12.00×10^(-6))、铕负异常(δEu=0.30~0.33)明显,轻重稀土略有分馏(LREE/HREE为4.11~4.85,(La/Yb)N为9.30~9.70),明显不同于幔源成因的碳酸岩,也不同于沉积成因的碳酸盐岩,而与壳源成因的碳酸岩类似。根据上述特征并结合区域地质背景,认为该碳酸岩为沉积碳酸盐岩在内侵幔源岩浆作用下发生熔融而成的火成碳酸岩。
In east area of Beishan Xisanyangjing in Gansu province there is a special type of carbonate rock. The rock appears in irregular zoning, small rock nodular output. Between the rock and surrounding rock there is obvious embayment, dendritic intrusive contact and no rock stratification. It shows up fine crystal equigranular texture. In the rock body it can see surrounding rock xenoliths （carbonate rock internal development of part xenoliths composition is same as surrounding rock） and its associated super mafic rocks （peridotite）, and other characteristics indicate that it is igneous carbonate rock. Rock geochemistry shows that it rich of CAO（54.41% - 54.52% ）, CO2 （43.36%-43.39%）, and poor of SiO2, TiO2, MgO, MnO, Fe2O3, FeO, Na2O, K2O. CaO/（CaO＋ MgO＋Fe2O3＋FeO＋MnO） ratio of 0.99, is calcite carbonate rocks; the total rare earth rock is low （∑REE=11.20 ×10^-12.00×10-6）; europium negative anomaly （δEn=0.30-0.33） is obvious; light and heavy rare earth is slightly fractionation （LREE/HREE 4.11-4.85, （La/Yb）N, 9.30-9.70）; it significantly differs from carbonate rocks of mantle source genesis, and also differs from the carbonate which is sedimentary origin. According to the above characteristics and in combination with regional geological background, it thinks that the carbonate rocks are igneous carbonate rock which formed by sedimentary carbonate melting when invasion of mantle-derived magma.
出处
《甘肃地质》
2017年第2期31-37,共7页
Gansu Geology
