东疆白石头泉含黄玉天河石花岗岩体的地球化学：分带和岩浆演化

东疆白石头泉含黄玉天河石花岗岩体的地球化学：分带和岩浆演化

顾连兴，吴昌志，张遵忠，苟晓琴，刘四海，郑远川，张光辉

内生金属矿床成矿机制研究国家重点实验室（南京大学），南京大学地球科学系，南京 210093

收稿日期:2007-06-20 修回日期:2007-06-20 出版日期:2007-06-20 发布日期:2007-06-20

Geochemistry of the Baishitouquan Topaz-bearing Amazonite Granite: Zoning and Magma Evolution

GU Lian-xing，WU Chang-zhi, ZHANG Zun-zhong, GOU Xiao-qin,LIU Si-hai, ZHENG Yuan-chuan and ZHANG Guang-hui

State Key Laboratory for Mineral Deposit Research（Nanjing University）, Department of Earth Sciences；Nanjing University, Nanjing 210093, China

Received:2007-06-20 Revised:2007-06-20 Online:2007-06-20 Published:2007-06-20

摘要/Abstract

摘要： 白石头泉含黄玉的天河石花岗岩体Rb-Sr等时线年龄209.6±9.6 Ma，从下至上可分为5个连续过渡的岩相带，即淡色花岗岩（a带），含天河石花岗岩（b带），天河石花岗岩（c带），含黄玉天河石花岗岩（d带）以及黄玉钠长花岗岩（e带）。岩体的岩石地球化学特征是高F（> 2 %）、高 Rb (500×10-6～1 087×10-6)，低 P2O5 (≤0.06%)，Na2O>K2O，弱过铝 (A/NKC=1.00~1.11)、翼型稀土元素配分曲线 (ΣREE=28.6×10-6~231.9×10-6)、低(La/Lu)N值 (0.11~0.68)、强烈Eu负异常(Eu/Eu* = 0.0005~0.0110)、Nd同位素富集（εNd (t )= -4.4~-4.9）。该岩体的岩浆是中地壳云母片麻岩部分熔融的产物。从a带到e带的地球化学变化是：（1）F，A2O3和Na2O含量逐渐增加，而SiO2，（Fe2O3+FeO+MgO+MnO）、FeO和K2O含量逐渐减少，在标准矿物的Qz-Ab-Or图上总体向Ab角顶移动；（2）总体而言，Cr，Ni，Co，V，W，Nb，Zr，U，Th和Y含量逐渐减少，而F，Li，Rb，Hf，Ta，Sn，Sc，Ga和Zn含量逐渐增加，但d带到e带间存在Li，Rb，Sn，Sc和Zn含量的突降；（3）K/Rb，Al/Ga，Nb/Ta和Zr/Hf值下降，但K/Cs，Th/U，(La/Lu)N值上升；（4）全岩的δ18O 值从a带的9.25 ‰~9.75 ‰降低到e带的7.32 ‰，d带与e带间存在2.1‰的δ18O值突降。岩浆从a带到e带的垂向分带是分离结晶和流体输运的共同结果。岩体的d带与e带存在明显的成分间断。在矿物成分上表现为黄玉、钠长石和白云母的剧增，钾长石和天河石的剧减。在主量元素上表现为 Na2O和CaO含量的剧增，SiO2和K2O含量的剧减。在微量元素上表现为F，Ga，Sr和Ba含量的剧增，Li，Rb，Sc，Zn和Sn含量的剧减。在稀土元素上，Eu/Eu*和(La/Lu)N值增加，而ΣREE值降低。在氧同位素特征上，δ18O值显著降低。这种间断不仅受分离结晶和流体输运的制约，也与天水加入、围岩混染和亚固相线淋滤有关。

Abstract: The Mesozoic Baishitouquan (BST) topaz-bearing amazonite granite pluton has been dated at 209.6±9.6 Ma by the Rb-Sr isochron method. This pluton exhibits five lithological zones, which, gradational from the lowest level upwards, are leucogranite (zone a), amazonite-bearing granite (zone b), amazonite granite (zone c), topaz-bearing amazonite granite (zone d) and topaz albite granite (zone e). Geochemically, The rocks are characterised by higher F (>2%) and Rb (500~1087×10-6), lower P2O5 (≤0.06 %), Na2O>K2O, A/NKC=1.00~1.11, Σ14 REE=28.6~231.9×10-6 with gull wing-shaped distribution patterns (LaN/LuN=0.11~0.68) and strong Eu depletion (Eu/Eu* =0.0005~0.0110). δ18O=9.75~7.32 ‰, εNd (t )= -4.4~-4.9. The magma for this pluton was derived by partial melting of a mica gneiss in the middle crust. The pluton exhibits the following geochemical transition from zone a to zone e: 1) Increasing F, Al2O3 and Na2O, and decreasing SiO2, (Fe2O3+FeO+MgO+MnO) and K2O. Plots of normative compositions on the Qz-Ab-Or diagram move gradually towards the Ab apex. 2) Overall, contents of Cr, Ni, Co, V, W,Nb, Zr, U, Th and Y decrease, while contents of F, Li, Rb, Hf, Ta, Sn, Sc, Ga and Zn increase. 3）K/Rb, Al/Ga, Nb/Ta and Zr/Hf decrease, and K/Cs, Th/U, and (La/Lu)N increase; 4) Whole-rock δ18O decreases from 9.25~9.75‰ in zone a to 7.32‰ in zone e. It is interpreted that crystallisation of the magma started from zone a and proceeded upwards to zone e, and the vertical zoning was produced by fractional crystallisation accompanied by fluid fractionation. There is a compositional gap on the transition trend between zone d and e. This gap is manifested in mineralogy by sharp increase in topaz, albite and muscovite and decrease in K-feldspar and amazonite; in major elements by sharp increase in Na2O and CaO and decrease in SiO2 and K2O; in trace elements by sharp increase in F, Ga, Sr and Ba, and sudden decrease in Li, Rb, Sc, Zn and Sn; in REE behaviour by sudden increase in Eu/Eu* and （La/Lu）N, and decrease in ΣREE; and in isotope composition by sharp decrease inδ18O. Such a gap might have been constrained not only by fractional crystallization and fluid fractionation, but also by involvement of meteoric water, contamination of wallrock-derived components, and leaching and dispersion due to subsolidus metasomatism.

顾连兴，吴昌志，张遵忠，苟晓琴，刘四海，郑远川，张光辉. 东疆白石头泉含黄玉天河石花岗岩体的地球化学：分带和岩浆演化[J]. J4.

GU Lian-xing，WU Chang-zhi, ZHANG Zun-zhong, GOU Xiao-qin,LIU Si-hai, ZHENG Yuan-chuan and ZHANG Guang-hui. Geochemistry of the Baishitouquan Topaz-bearing Amazonite Granite: Zoning and Magma Evolution[J]. J4.