新疆东准噶尔早志留世埃达克岩——来自锆石U-Pb年龄、地球化学及Sr-Nd-Hf同位素的证据

Early Silurian adakitic rocks of East Junggar,Xinjiang: Evidence from zircon U-Pb age,geochemistry and Sr-Nd-Hf isotope of the quartz diorite

新疆东准噶尔野马泉地区索尔巴斯塔乌石英闪长岩锆石U-Pb年龄为442.5±5.6 Ma。该岩体SiO_2为63.75%~65.40%,Al_2O_3为17.07%~18.00%,Na_2O/K_2O比值为5.28~6.82,MgO为1.11%~1.35%;富集大离子亲石元素(LILE,如K、Rb、Ba和Sr),而亏损高场强元素(HFSE,如Ta、Nb、Zr和Ti)及P,Sr为783×10^(-6)~1 030×10^(-6),Y为8.10×10^(-6)~10.80×10^(-6),Yb为0.84×10^(-6)~1.04×10^(-6),Sr/Y比值为82.59~112.32,具埃达克岩的典型特征;具有相对低的(^(87)Sr/^(86)Sr)i值(0.703 77~0.704 04)和相对高的εNd(t)值(+6.9^+7.2),且锆石具有相对高的εHf(t)值(+10.7^+13.7),暗示岩浆很可能起源于亏损的年轻地幔源区,与俯冲洋壳熔融形成的埃达克岩相似。结合区域地质背景,认为索尔巴斯塔乌石英闪长岩是由俯冲的大洋板片边缘受到来自板片窗高温软流圈地幔物质的烘烤发生部分熔融形成的,为阿尔曼泰蛇绿岩代表的古亚洲洋于早志留世向南俯冲消减过程中形成的岩浆弧记录。

The Suoerbasitawu quartz diorite in the Yemaquan area of East Junggar, Xinjiang, has a zircon U-Pb age of 442.5 ± 5.6 Ma. The quartz diorite has the data SiO2 = 63.75 % - 65.40%, Al2O3 = 17.07% - 18.00%, Na2O/K2O= 5.28-6.82, and MgO= 1.11%- 1.35%. They are characterized by enrichment of large ion lithophile elements （LILEs, such as K, Rb, Ba, and Sr）, and depletion of high field strength elements （HFSEs, such as Ta, Nb, Zr, and Ti） and P. They also have the data Sr=783 × 10^-6--1030× 10^-6, Y= 8.10 × 10^-6-10.80 × 10^-6, Yb = 0.84 × 10^-6 - 1.04 × 10^-6, and Sr/Y = 82.59- 112.32, showing typical characteristics of adakitic rocks. The rocks have relatively low （87Sr/86Sr）i（0. 703 77-0. 704 04） and high εNd （t） （ ＋ 6.9- ＋ 7.2）, and relatively high zircon εHf（ t ） （ ＋ 10.7- ＋ 13.7）, indicating that the magma was probably derived from an depleted juvenile mantle, similar to the adakitic rocks formed by the partial melting of subducted oceanic crust. In combination with the regional geological background, the authors hold that the Suoerbasitawu quartz diorite was formed by the partial melting of subducted oceanic slab edge heated by the astheno- spheric mantle, which was the magmatie arc formed by the southward subduction of the Paleo-Asian oceanic crust in the early Silurian period.