论文部分内容阅读
皖东的滁州、上腰铺岩体位于扬子地块东缘、毗邻郯庐断裂带东侧,与之伴生有一些铜(金或铁)矿化。它们的黑云母的~(40)Ar-~(39)Ar 定年结果分别为127.17±0.40Ma,129.90±0.23 Ma。滁州、上腰铺侵入岩在地球化学特征上与埃达克岩基本一致:如 SiO_2>56%,高 Al_2O_3(14.84%～16.38%)、Sr(369×10~(-6)～1335×10~(-6))、Sr/Y(43～185)与 La/Yb(22～44),但低 Y(5.51×10~(-6)～11.0×10~(-6)),Yb(0.51×10~(-6)～1.09×10~(-6)),无明显 Eu 异常-正的 Eu 异常(δEu=0.75～1.28)。另外,岩体中部分样品具有较高的 MgO(2.23%～5.25%)、Mg~#(53～68)和 Cr(89.6×10~(-6)～206×10~(-6))、Ni(43.0×10~(-6)～72.0×10~(-6)),类似于高镁安山岩。这两个岩体的 Nd-Sr 同位素特征为:(~(87)Sr/~(86)Sr)_i=0.7060～0.7067,ε_(Nd)(t)=-11.53～-14.07,说明其由俯冲洋壳熔融形成的可能性较小。我们认为,滁州、上腰铺埃达克质侵入岩可能由拆沉下地壳熔融形成,熔融产生的岩浆在穿过上覆地幔的过程中,与地幔橄榄岩发生强烈相互作用,一方面,由于地幔橄榄岩的混染而使得埃达克质岩浆的MgO、Cr 和 Ni 含量显著增高;另一方面,岩浆中的 Fe_2O_3可能加入到地幔中,导致地幔的氧逸度(f_(o_2))增高,地幔中金属硫化物被氧化,地幔中亲铜元素则以硫酸盐的形式进入熔体中。富含 Cu、Au 等成矿物质的熔体在快速上升到地壳浅处时,可能由于温度、压力或氧逸度(f(o_2))的降低,释放出 Cu、Au 等成矿物质,导致矿化。
The Chuzhou and Shangjianpu rocks in eastern Anhui are located on the eastern margin of the Yangtze block adjacent to the east side of the Tan-Lu fault zone and are associated with some copper (gold or iron) mineralization. The ~ (40) Ar- ~ (39) Ar dating results of their biotite are 127.17 ± 0.40Ma and 129.90 ± 0.23 Ma, respectively. Chuzhou and Shangpupu intrusive rocks are basically the same in geochemical characteristics as adakites, such as SiO 2> 56%, high Al 2 O 3 (14.84% ~ 16.38%) and Sr (369 × 10 -6 ~ 1335 × 10) ~ (-6)), Sr / Y (43 ~ 185) and La / Yb (22 ~ 44), but low Y (5.51 × 10 -6 ~ 11.0 × 10 -6) 0.51 × 10 -6 ~ 1.09 × 10 -6). There is no obvious Eu anomaly-positive Eu anomaly (δEu = 0.75-1.28). In addition, some samples in the rock mass have higher contents of MgO (2.23% -5.25%), Mg ~ (53 ~ 68) and Cr (89.6 × 10 -6 ~ 206 × 10 -6) Ni (43.0 × 10 -6 ~ 72.0 × 10 -6), similar to the high-Mg andesite. The Nd-Sr isotopic characteristics of these two rock masses are: (87 Sr / 86 Sr) _i = 0.7060 ~ 0.7067 and ε Nd (t) = - 11.53 ~ -14.07, It is less likely that oceanic shells will melt. We think that Chu Chuang and Shangjianpu adakitic intrusive rocks may be formed by the melting of the crust and subsidence crust, and the melt-generated magma strongly interacts with the mantle peridotite as it passes through the overlying mantle. On the one hand, Mantle peridotite makes the contents of MgO, Cr and Ni in adakitic magma increase significantly. On the other hand, Fe_2O_3 in magma may be added to the mantle, resulting in an increase in oxygen fugacity (f_ (o_2)) in the mantle The metal sulfide in the mantle is oxidized and the copper-rich element in the mantle enters the melt as sulfate. When the melt of ore-forming materials rich in Cu and Au rapidly rises to the shallow crust, the ore-forming materials such as Cu and Au may be released due to the decrease of temperature, pressure or oxygen fugacity (f (o 2)), resulting in Mineralization.