Analysis of consolidation processes of granitic magma based on partition of rare earth elements between accessory minerals

利用x射线rf、EPMA分析和CHIME年代学研究了花岗岩岩浆的固结过程。主要结果如下：(1)副矿物中稀土元素的粒内分布与其结晶顺序密切相关。副矿物的相继出现和消失，可以解释为由于过饱和岩浆的动力学结晶而偏离共熔饱和水平。(2)利用CHIME法测定了北上南地体的Hikami、Okuhinotsuchi和Hirasawa花岗岩的年代。CHIME年龄（350-250 Ma）不支持目前认为这些花岗岩是前志留纪基底的观点。更确切地说，CHIME时代需要对南北上地体进行详细的地层重新检查。(3)良轭带三桥花岗岩为分带岩体。构造、石化和年代学分析表明，该分带岩体形成于约80 Ma以前，是由闪长岩母质熔体原位分馏形成的。(4)花岗岩中热液钛矿的组成受（Al, Fe^<3+>）FTi_<-1>0_<-1>和（Al, Fe^<3+>）（OH）TI_<-1>0_<-1>取代控制。花岗岩风化黑云母含钾蛭石微畴和钾蛭石与黑云母间层，铁含量远低于母母黑云母。八面体薄片中的Fe^<2+>氧化为Fe^<3+>导致铁损失以维持局部静电平衡。(5)形成花岗岩体壁的古生代和中生代沉积物中含有前寒武纪中期（2000-1400 Ma）和古生代（430-250 Ma）的碎屑独居石和锆石颗粒。

The consolidation processes of granitic magmas were investigated on the basis of the XRF and EPMA analyzes and CHIME geochronology. The main results are as follows :(1) The intra-grain distribution of rare earth elements in accessory minerals is closely related to the sequence of their crystallization. The successive appearance and disappearance of accessory minerals are explained in terms of deviation from cotectic saturation levels owing to kinetic crystallization from a supersaturated magma.(2) The Hikami, Okuhinotsuchi and Hirasawa granites in the South Kitakami terrane were dated through the CHIME method. The CHIME ages, 350-250 Ma, do not support a current view that these granites are pre-Silurian basement. Rather, the CHIME ages require the detailed stratigraphical re-examination of the South Kitakami terrane.(3) The Mitsuhashi granite in the Ryoke belt is a zoned pluton. Structural, petrochemical and geochronological analyzes revealed that the zoned pluton formed ca.80 Ma ago by in situ fractionation of a dioritic parent melt.(4) The composition of hydrothermal titanite in granite is controlled by both substitutions (Al, Fe^<3+>)FTi_<-1>0_<-1> and (Al, Fe^<3+>)(OH)TI_<-1>0_<-1>. Weathered biotite in granite contains microdomains of K-vermiculite and interstratification of K-vermiculite and biotite, and contains much lower iron than the parent biotite. Oxidation of Fe^<2+> to Fe^<3+> in the octahedral sheet causes the iron loss to maintain local electrostatic balance.(5) Paleozoic and Mesozoic sediments which form walls of granite bodies contain detrital monazite and zircon grains of middle Precambrian (2000-1400 Ma) as well as Paleozoic (430-250 Ma) ages.