铜陵地区中酸性侵入岩的包体岩石学研究

Enclave Petrology of Intermediate-Acid Intrusive Rocks in Tongling District, Anhui

铜陵地区中生代中酸性侵入岩中含有捕虏体、残余体和岩浆包体三大类型，其中岩浆包体包括堆积岩包体、堆积晶包体、混杂岩包体和冷凝边包体。各类岩石包体的岩石学、矿物学、地球化学特征均不相同。

Enclaves in intermediate-acid intrusive rocks of Tongling district can be devided into three types as follows: xenolithes, relics and magmatogenic enclaves that consist of cumulates, micrograined dioritite mixtites and dioritic chilled border enclaves. Petrologically, the relics with eyed and meta poikilitic texture is characterized by high content of biotite (>80%) and low content of cordierite; the cumulates with accumulate texture consist of a great number of pyroxen, hornblande and minor spinel and phlogopite; the micrograined dioritic mixtites are composed of more hornblandes and feldspar, and less needle apatites and ellipsoid basic core included in plagioclase; the chilled border enclaves have the same mineral association as that of their host rock, but more dark minerals than those of the host rocks consisting of plagioclase, quartz, alkaline feldspar, hornblende and biotite. Geochemically, the relics exhibit high REE content and ratio of LREE/HREE, more obvious Eu negative anomaly and rich Cr and Ni, poor Ba, Nb and Sr. All kinds of magmatogenic enclaves have the same REE patterns, no Eu anomaly, and their total of REE values are 74.9×10 -6 for the spinel pyroxene cumulate, 179.7×10 -6 for hornblende cumulate, 289.9×10 -6 for micrograined dioritic mixtites and 131.2×10 -6 for chilled border enclaves, respectively. Thermometers and barometers of minerals show that the temperatures and pressure of formation are 1126℃ and 844MPa (715-904MPa) for the spinel pyroxene cumulate, 1065℃-1029 ℃ and 823MPa (713-950MPa) for hornblende cumulate, 959℃ and 340MPa (286-409MPa ) for micrograined dioritic enclaves, and 951℃ and 59 MPa for dioritic chilled border enclaves, respectively. From mentioned above it can be seen that relics enclaves derived from the crustal partial melting, all cumulate enclaves from the deep magma chamber near Moho in lower crust, which are cumulate fragments formed by fractional crystallization of basic magma, mixtites from the shallow magma chamber in middle-upper crust, which was formed by the mixing between magma derived from the upper mantle and acide magma derived from the crustal partial melting, and the chilled border enclaves from the border fragmental of early intrusive bodies.