【摘要】 拉萨地块南缘记录了新特提斯洋俯冲到印度-欧亚大陆碰撞及碰撞后的岩浆作用,其中晚白垩世的岩浆作用对研究印度-欧亚大陆碰撞前成岩成矿作用具有重要的意义。本文以拉萨地块南缘100Ma的角闪辉长岩和68Ma花岗斑岩的锆石、磷灰石、榍石为研究对象,利用背散射、阴极发光（CL）、电子探针（EPMA）和LA-ICP-MS原位微区分析等方法,查明锆石、磷灰石、榍石的主、微量元素特征,进一步反演岩石源区性质、结晶历史及结晶条件,并对岩体含矿性进行评价,有助于探讨冈底斯成矿带晚白垩世岩浆成因机制和成矿潜力。研究结果表明,角闪辉长岩锆石初始饱和温度为598～626℃,锆石Ti结晶温度为645～758℃,磷灰石饱和温度为690～819℃,榍石Zr温度为602～778℃;磷灰石具有中等-弱的负铕异常（δEu=0. 67）、富集LREE,早期高温阶段锆石的结晶主要受到磷灰石结晶影响,随着温度降低,受到少量榍石结晶的影响;角闪辉长岩中的锆石在低的Hf、温度较高时却具有较高的Th、U含量显示岩浆源区受到更多俯冲板片出溶流体的影响,磷灰石具有较高的（La/Sm）N值以及Sr含量低于主岩,显示岩浆源区均一、熔体富Cl特征。花岗斑岩的锆石初始饱和温度为704～736℃,锆石Ti温度为630～799℃,磷灰石饱和温度为846～891℃,结合锆石的Ce/Sm、Yb/Gd以及磷灰石较大的负铕异常（δEu=0. 29）,显示花岗斑岩中的锆石从高温到低温阶段都受到磷灰石和榍石的共同结晶影响,磷灰石的结晶受到斜长石影响;花岗斑岩中大部分锆石Ti结晶温度高于其初始饱和温度,磷灰石Sr-Ap/Sr-WR为0. 78～1. 45,具有较高的F/Cl（32. 87～67. 60）、低的（La/Sm）N,指示花岗斑岩岩浆源区不均一,受到多期岩浆熔体的脉冲式灌入并加入了更多镁铁质的岩浆熔体,其熔体具有低的Cl。此外,花岗斑岩锆石具有较高的Ce⁴⁺/Ce³⁺、磷灰石具有较高的SO₃、熔体中更富S,指示花岗斑岩具有高的氧逸度和成矿潜力。本文研究结果表明结合锆石、磷灰石和榍石微量元素特征可有效指示岩浆岩的源区组成、结晶历史、结晶条件以及成矿潜力,为岩石学的研究提供了一个新的思路。更多还原

【Abstract】 The southern Lhasa subterrane recorded magmatism related to Neo-Tethyan subduction,collision and post-collision between the two continents of Indian and Eurasian. The Late Cretaceous magmatism is of great significance to the study of precollisional petrogenesis and mineralization of the Indo-Eurasian continent. In this paper,zircon,apatite,and titanite from the 100 Ma hornblende gabbro and the 68 Ma granite porphyry in the southern Lhasa subterrane are studied. The main and trace elements of zircon,apatite,and titanite are identified by means of Back Scattering,Cathodoluminescence（ CL）,Electron Probe Analysis（ EPMA） and LA-ICP-MS in situ microanalysis. The purpose of this paper is to further identify the magma sources,the crystallization histories and conditions of the magmatic rocks,and also to evaluate their ore-bearing properties,which is helpful to explore the genetic mechanisms and metallogenic potential of the Late Cretaceous magmatism in the Gangdese magmatic belt. For the studied hornblende gabbro,the results show that its zircon saturation and crystallization temperatures vary from 598 ～ 626℃ and 645 ～ 758℃,respectively,the apatite saturation temperatures vary from 690 ～ 819℃,and the titanite crystallization temperatures vary from 602 ～ 778℃. The chondritenormalized REE patterns of apatite grains from the hornblende gabbro show enriched LREE values with moderate to negative negative Eu anomalies（ δEu = 0. 67）. The zircon compositions from the hornblende gabbro were initially a result of high-temperature apatite and further cooling by minor titanite crystallization. The low Hf but high crystallization temperature zircon grains from the hornblende gabbro have high Th and U contents,showing the magma source of hornblende gabbro was modified by more slab-derived fluids. The magma source of hornblende gabbro is homogeneous,and the melt is rich in Cl as evidenced by the higher Sr contents and（ La/Sm）Nvalues in apatite relative to the host rocks. For granite porphyry,the zircon saturation and crystallization temperatures vary from 704 ～ 736℃ and630 ～ 799℃,respectively,while the apatite saturation temperatures vary from 846 ～ 891℃. Combined with zircon Ce/Sm and Yb/Gd ratios and larger negative Eu anomalies of apatite（ δEu = 0. 29）,the results show the zircon compositions from granite porphyry were affected by the co-crystallization of apatite and titanite from high temperature to low temperature,and the crystallization of apatite grains were affected by plagioclase crystallization. Most zircons of the granite porphyry have higher crystallization temperatures than their zircon saturation temperatures combined with the apatite grains,since the later have low Sr-Ap/Sr-WR（ 0. 78 ～ 1. 45）,high F/Cl（ 32. 87～ 67. 60） and low（ La/Sm）N. The granite porphyry have heterogeneous magma source,which were affected by impulse magma melts and involved more mafic magma melts. Compared with hornblende gabbro,the melt of the granite porphyry has low Cl contents. In addition,the zircon grains have high Ce⁴⁺/Ce³⁺,high apatite SO₃ and more S contents in the melt of granite porphyry,indicating that granite porphyry have high oxygen fugacity and ore-forming potential. The results of this study show that the trace element geochemistry of zircon,apatite and titanite can effectively identify the magma source composition,crystallization history,crystallization conditions and metallogenic potential of magmatic rocks,which provide a new idea for petrological research.更多还原