矽卡岩中石榴子石在示踪热液流体演化和矿化分带中的研究现状及其展望

热液型矿床形成过程中流体的组成、运移、演化及其矿质沉淀机制是矿床学研究的重点内容和难点。矽卡岩矿床中具有震荡环带结构的石榴子石完整记录了热液流体的性质、组成及演化过程,这种震荡环带的出现暗示了不同成分系列的石榴子石对不同阶段热液流体成矿物化环境的特定选择性。石榴子石晶体元素化学分带现象是流体运移和矿物再沉淀过程周期性循环再现的结果,对指示早期矽卡岩阶段热液流体中主、微量元素化学分带机制具有重要意义。不同成分系列、不同期次石榴子石的Fe_2O_3和Al_2O_3含量差异显著,其对热液流体演化过程中氧化还原环境的变化具有较好的示踪作用;相对主量元素而言,微量元素在流体演化过程中具有更好的探针作用,钙铝榴石常富集Al、Ti、Zr、HREE元素,而钙铁榴石常富集As、W、Mo、Fe、LREE元素。借助EMPA和LA_ICP_MS技术对具震荡环带结构的石榴子石进行主、微量元素(包括稀土元素)的微区和原位分析是探讨成矿过程中流体组成和性质演化的重要手段,其有可能揭示矿物生长机制、成矿环境以及成矿流体组成与性质的演化,而这一地质信息对于全面理解矽卡岩型矿床的矿化分带及成矿作用非常重要。     

石榴子石U- Pb精确测年对斑岩- 矽卡岩型铜矿床成岩时限的制约——以西藏桑日铜矿为例

矽卡岩型矿床是全球最具经济价值且研究最为深入的矿床类型之一。其矿物分带、金属矿化机制、流体演化特征均已获得共识性的结论,但其矽卡岩的成岩作用时限一致是困扰成矿作用机理研究的难题。桑日铜矿是青藏高原班公湖- 怒江成矿带中段新发现的重要斑岩- 矽卡岩型矿床。金属矿物主要为黄铜矿、黄铁矿和少量辉钼矿,呈细脉状、块状、浸染状产于斑岩和矽卡岩中。文章以西藏班戈县桑日铜矿为实例,利用飞秒激光剥蚀系统高分辨率电感耦合等离子体质谱仪,对矿区内矽卡岩中的石榴子石进行U- Pb精确定年,获得其结晶时代为83. 2±2. 3Ma(MSWD=1. 2, n =26),有效限定矽卡岩成岩作用时代为晚白垩世。同时,将其与含矿斑岩锆石U- Pb年龄和辉钼矿Re- Os年龄对比,发现三者在误差范围内基本一致,说明三者属于同一成岩成矿作用事件的产物。因此,石榴子石U- Pb精确测年能够有效厘定矽卡岩矿床或斑岩- 矽卡岩成矿系统中矽卡岩成岩作用时限,也为诸多矽卡岩矿床成矿机理研究提供了新的测试手段和数据支撑,具有良好的应用前景。     

赣东北朱溪矿床云英脉型钨矿体及矽卡岩型钨铜矿体成因关系——来自石榴子石、白钨矿原位U-Pb年代学及微量元素特征的证据

朱溪矿床是江南钨矿带中产于燕山期中酸性侵入岩与晚古生代碳酸盐岩接触带附近以矽卡岩矿体为主的钨铜矿床,发育“上铜下钨”的空间分带。浅部发育矽卡岩型和脉型铜矿体,深部发育矽卡岩型钨铜矿体、云英细脉-网脉型钨矿体及蚀变花岗岩型钨矿体。浅部矽卡岩型铜矿体中石榴子石U-Pb年龄为152.6±2.6 Ma、深部云英脉型钨矿体中白钨矿U-Pb年龄为153.4±2.2 Ma、深部矽卡岩型钨铜矿体中白钨矿U-Pb年龄为153.9±2.7 Ma,三者时代在误差范围内一致,表明钨、铜矿化均形成于同一热液体系,结合云英脉型钨矿体和矽卡岩型钨铜矿体中两类白钨矿的微量元素特征分析,流体起源于富WO₄^2-、低Sr的高分异岩浆热液,白钨矿是以Ca²⁺空位的方式置换REE³⁺,稀土元素的分配行为记录了不同类型矿化流体性质。云英脉型钨矿化形成于还原环境,且氧逸度的显著降低以及围岩提供大量Ca²⁺促进了白钨矿的沉淀,而矽卡岩型钨铜矿化为相对开放的热液体系,后期经历了氧逸度升高,增强了流体富集金属Cu的能力,从而萃取...     

LA-ICP-MS石榴子石U-Pb定年方法在异剥钙榴岩和矽卡岩年代学研究中的应用

本文利用Coherent GeoLasHD型193 nm ArF准分子激光剥蚀系统和Agilent 7900型四极杆电感耦合等离子体质谱仪, 建立了LA-ICP-MS石榴子石U-Pb定年方法。利用该方法, 对采自冀北地区晚古生代镁铁质-超镁铁质混杂岩体中的异剥钙榴岩和闽西南马坑式铁矿含矿石榴子石矽卡岩这两种岩石中的石榴子石开展U-Pb定年研究。在冀北地区晚古生代镁铁质-超镁铁质混杂岩体中的异剥钙榴岩中, 获得石榴子石下交点年龄为(387.6±5.4) Ma (D496-1, MSWD=1.1, N=30)和(409.3±7.8) Ma (D493-1, MSWD=2.0, N=60), 在马坑铁矿石榴子石矽卡岩中, 获得石榴子石下交点年龄为(128.6±2.1) Ma (ZK7921-b24, MSWD=2.0, N=60)和(128.7±3.2) Ma (ZK7922-b1, 用锆石91500校正, MSWD=1.8, N=42); 在潘田铁矿的石榴子石矽卡岩中, 获得石榴子石的下交点年龄为(128.7±1.7) Ma (PT-b1, MSWD=1.7, N=30)和(132.1±1.3) Ma (PT-b1样品, 用锆石91500校正, MSWD=1.6, N=30)(除了指明使用锆石标样91500校正石榴子石未知样品外, 其他皆用石榴子石标样Willsboro校正石榴子石未知样品的U/Pb分馏)。以上结果与Sm-Nd等时线年龄及前人报道的锆石U-Pb年龄在误差范围内一致。对马坑式铁矿石榴子石矽卡岩U-Pb定年结果表明, 利用石榴子石标样Willsboro和锆石标样91500作为外标样校正同一样品中石榴子石U/Pb同位素分馏, 获得的下交点年龄一致, 206Pb/238U年龄的加权平均值也一致, 说明石榴子石与锆石之间的基体效应较小, 在缺乏石榴子石标样时, 可用锆石标样91500代替。在上述研究基础上分析了石榴子石U-Pb定年方法在矽卡岩型矿床成矿时代研究及异剥钙榴岩年代学研究中的应用潜力, 认为石榴子石U-Pb定年方法在矽卡岩型矿床及异剥钙榴岩年代学研究中具有巨大的应用推广前景, 具有重要的理论指导和实际应用意义。     

西藏洛巴堆矽卡岩型铁多金属矿床石榴子石和锆石U-Pb测年及地质意义

石榴子石是矽卡岩型矿床中最常见的蚀变矿物之一,因此,对石榴子石进行年代学研究能够准确限定矽卡岩型矿床的成矿时代.青藏高原冈底斯成矿带中部发育众多矽卡岩型多金属矿床,由于缺乏精确的成矿年代学数据,制约着对这些矿床成因和动力学背景的深入认识.因此,文章以该成矿带具有代表性的洛巴堆矽卡岩型铁多金属矿床为研究对象,通过对赋矿矽...     

Garnet and Zircon U-Pb Geochronology and Geochemistry Reveal Genesis of the Dafang Au-Pb-Zn-Ag Deposit, Southern Hunan

Garnet is a primary mineral in skarn deposits and plays a significant role in recording copious mineralization and metallogenic information. This study systematically investigates the geochemistry and geochronology of garnet and zircon in the Dafang Au-Pb-Zn-Ag deposit, which represents prominent gold mineralization in southern Hunan, China. Garnet samples with distinct zoning patterns and compositional variations were identified using various analytical techniques, including Backscattered Electron (BSE) imaging, Cathodoluminescence (CL) response, textural characterization, and analysis of rare-earth elements (REE), major contents, and trace element compositions. The garnet was dated U-Pb dating, which yielded a lower intercept age of 161.06 ± 1.93 Ma. This age is older than the underlying granodiorite porphyry, which has a concordia age of 155.13 ± 0.95 Ma determined by zircon U-Pb dating. These results suggest that the gold mineralization may be related to the concealed granite. Two groups of garnet changed from depleted Al garnet to enriched Al garnet, and the rare earth element (REE) patterns of these groups were converted from light REE (LREE)-enriched and heavy REE (HREE)-depleted with positive europium (Eu) anomalies to medium REE (MREE)-enriched from core to rim zoning. The different REE patterns of garnet in various zones may be attributed to changes in the fluid environment and late superposition alteration. The development of distal skarn in the southern Hunan could be a significant indicator for identifying gold mineralization.     

U-Pb Geochronology and Geochemistry of Stratiform Garnet from the Aqishan Pb-Zn Deposit, Eastern Tianshan, Xinjiang, NW China: Constraints on Genesis of the Deposit

The Aqishan lead-zinc deposit,located in the Jueluotag metallogenic belt of eastern Tianshan,Xinjiang,Northwest China,has a stratiform occurrence in the marine volcanic tuff of the Yamansu Formation.The ore body has a typical double-layer structure,having a stratified,stratoid,lenticular upper part and a veined,stockwork-like lower part.The occurrence of the upper orebody is consistent with that of the volcanic tuff wall rock.The ore minerals are mainly chalcopyrite,pyrite,sphalerite,galena and magnetite,the altered minerals mainly being silicified,such as sericite,chlorite,epidote,garnet.The garnetized skarn,being stratiform and stratoid,is closely related to the upper part of the orebody.Geological observations show that the limestone in the ore-bearing Yamansu Formation is not marbleized and skarnized.Spatially,it is associated with the ferromanganese deposits in the marine volcanic rocks of the Yamansu Formation.These geological features reflect the likelihood that the Aqishan lead-zinc deposit is a hydrothermal exhalation sedimentary deposit.The results from the EPMA show that the garnet is mainly composed of grossular-andradite series,contents being in a range of 34.791-37.8%SiO₂,32.493-34.274%CaO,8.454-27.275%FeO,0.012-15.293%Al₂O₃,0.351-1.413%MnO,and lower values of 0.013-1.057%TiO₂.The content of SiO₂ vs.CaO and FeO vs.Al₂O₃ has a significant positive correlation.The results of ICP-MS analysis for the garnet show that the REE pattern is oblique to right in general.The total amount of rare earth elements is relatively low,ΣREE=71.045-826.52 ppm,which is relatively enriched for LREE and depleted for HREE.LREE/HREE=8.66-4157.75,La_N/Yb_N=23.51-984.34,with obvious positive Eu and Ce anomalies(δEu=2.27-76.15,δCe=0.94-1.85).This result is similar to the REE characteristics of ore-bearing rhyolite volcanic rocks,showing that the garnet was formed in an oxidizing environment and affected by clear hydrothermal activity.The U-Pb isotopic dating of garnet by fs-LA-HR-ICP-MS gives an age of 316.3±4.4 Ma(MSWD=1.4),which is consistent with the formation time of the Yamansu Formation.According to the study of deposit characteristics and geochemical characteristics,this study concludes that the Aqishan lead-zinc deposit is a hydrothermal exhalation sedimentary deposit,the garnet being caused by hydrothermal exhalative sedimentation.     

南秦岭花红树坪花岗闪长岩年代学及地球化学特征

对出露于南秦岭陕西省凤县境内的花红树坪花岗闪长岩体进行LA-ICP-MS锆石U-Pb年代学和岩石地球化学研究,获得岩体表面年龄为214.3±2.7Ma(MSWD=2.6),表明其形成时代为晚三叠世。岩体的SiO_2=61.45%~65.10%,TiO_2=0.52%~0.63%;Al_2O_3=14.97%~15.74%,Mg O=2.33%~3.02%,Mg#=51.31~53.61,高Sr(485×10-6~563×10-6)和Sr/Y(28.2~30.4),低Y(17.0×10-6~19.1×10-6)和Yb(1.46×10-6~1.83×10-6),微弱负Eu异常(δEu=0.83~0.99),具有明显高镁埃达克岩地球化学特征。结合区域地质背景,认为花红树坪岩体是后碰撞构造环境下加厚下地壳拆沉熔融与先存地幔岩浆交代混染作用下的产物,其可能与凤太矿集区多金属矿成矿关系密切。     

桂北罗城地区云煌岩成因——地球化学及U-Pb年龄约束

对桂北罗城地区云煌岩开展系统的地球化学研究及LA-ICP-MS锆石U-Pb测年,获得锆石U-Pb年龄为248 ±1 Ma。其富钾（K2O/Na2O=4.23~136.2）,富碱（K2O+Na2O=6.86%~8.03%）,钾的含量显著高于大陆地壳平均值,富集轻稀土元素及大离子亲石元素,亏损高场强元素,具有较低的La/Nb值,Nb/U值低于洋中脊玄武岩、岛弧玄武岩及上地壳值,与全球平均俯冲沉积物接近,表明源区可能为早期俯冲交代作用形成的富集地幔。结合区域构造背景分析,推测桂北罗城地区云煌岩形成在中生代三叠纪（248±1 Ma）华南陆内岩石圈伸展减薄的背景下,软流圈上涌促使交代富集地幔发生部分熔融形成云煌岩岩浆,区域上NNE向的深大断裂为岩浆喷发提供通道。     

P–T–t evolution of garnet amphibolites in the Wutai–Hengshan area,North China Craton: insights from phase equilibria and geochronology

Garnet amphibolites can provide valuable insights into geological processes of orogenic belts, but their metamorphic evolution is still poorly constrained. Garnet amphibolites from the Wutai–Hengshan area of the North China Craton mainly consist of garnet, hornblende, plagioclase, quartz, rutile and ilmenite, with or without titanite and epidote. Four samples selected in a south–north profile were studied by the pseudosection approach in order to elucidate the characteristics of their metamorphic evolution, and to better reveal the northwards prograde change in P–T conditions as established previously. For the sample from the lower Wutai Subgroup, garnet exhibits obvious two‐substage growth zoning characteristic of pyrope (X_py) increasing but grossular (X_gr) decreasing outwards in the core, and both X_py and X_gr increasing outwards in the rim. Phase modelling using thermocalc suggests that the garnet cores were formed by chlorite breakdown over 7–9 kbar at 530–600 °C, and rims grew from hornblende and epidote breakdown over 9.5–11.5 kbar at 600–670 °C. The isopleths of the minimum An in plagioclase and maximum X_py in garnet were used to constrain the peak P–T conditions of ~11.5 kbar/670 °C. The modelled peak assemblage garnet + hornblende + epidote+ plagioclase + rutile + quartz matches well the observed one. Plagioclase–hornblende coronae around garnet indicate post‐peak decompression and fluid ingress. For the samples from the south Hengshan Complex, the garnet zoning weaken gradually, reflecting modifications during decompression of the rocks. Using the same approach, the rocks are inferred to have suprasolidus peak conditions, increasing northwards from 11.5 kbar/745 °C, 12.5 kbar/780 °C to 13 kbar/800 °C. Their modelled peak assemblages involve diopside, garnet, hornblende, plagioclase, rutile and quartz, yet diopside is not observed petrographically. The post‐peak decompression is characterized by diopside + garnet + quartz + melt = hornblende + plagioclase, causing the diopside consumption and garnet compositions to be largely modified. Thus, the pesudosection approach is expected to provide better pressure results than conventional thermobarometry, because the later approach cannot be applied with confidence to rocks with multi‐generation assemblages. U–Pb dating of zircon in the Wutai sample records a protolith age of c. 2.50 Ga, and a metamorphic age of c. 1.95 Ga, while zircon in the Hengshan samples records metamorphic ages of c. 1.92 Ga. The c. 1.95 Ga is interpreted to represent the pre‐peak or peak metamorphic stages, and the ages of c. 1.92 Ga are assigned to represent the cooling stages. All rocks in the Wutai–Hengshan area share similar clockwise P–T morphologies. They may represent metamorphic products at different crustal depths in one orogenic event, which included a main thickening stage at c. 1.95 Ga followed by a prolonged uplift and cooling after 1.92 Ga.     

新疆中天山南缘比开（地区）花岗岩地球化学特征及年代学研究

伊犁-中天山板块南缘比开地区出露的花岗岩和花岗闪长岩具钙碱性大陆弧花岗岩特征,其形成与南天山洋向北的俯冲事件相关.LA-ICP-MS锆石U-Pb年代学研究表明,岩浆活动在479～401 Ma间一直发生,其中419～401 Ma间岩浆活动强烈,形成大量钙碱性花岗岩组成的中天山南缘陆缘弧.（87Sr/86Sr）i=0.711578～0.704729,εNd（t）=-5.01～-2.19,表明花岗岩的形成过程中有地幔物质的加入,而Nd模式年龄tDM介于946～1661 Ma间,则反映花岗岩形成过程中有古老地壳物质混染.     

新疆天格尔地区碱长花岗岩的地球化学、年代学及其地质意义

新疆天格尔地区的碱长花岗岩出露于中天山与北天山构造带的结合部位,主要由石英和条纹长石组成,含少量斜长石和黑云母。对该岩体进行了全岩主量、微量元素分析和锆石LA-ICP-MS U-Pb定年。主量和微量元素分析结果表明,岩石具有高的SiO₂、K₂O＋Na₂O（K₂O＞Na₂O）、Rb、Th、U和∑REE（除Eu外）含量,低的CaO、TiO₂、Ba、Sr、P和Eu含量,属于富钾钙碱性花岗岩,具有向A型花岗岩过渡的后碰撞富钾钙碱性花岗岩的特征,形成于天山后碰撞由挤压向拉张构造体制转变的过渡时期。锆石LA-ICP-MS U-Pb定年研究获得269.7±0.7Ma的岩体侵位年龄,表明北天山古洋盆于晚石炭世闭合,天山与准噶尔、塔里木联结成统一的大陆后,石炭纪末期-中二叠世天山造山带处于挤压向拉张构造体制转变的过渡时期,在中天山北缘以发生大规模右行走滑剪切为标志,形成冰达坂韧性剪切带,同时发生强烈的韧性剪切成岩成矿作用,形成天格尔金矿带及其中的诸多金矿床和矿点,并引起壳、幔物质部分重熔产生岩浆、沿中天山与北天山间的地壳薄弱地带侵位。     

西藏班戈县拉青铜多金属矿床地球化学特征和年龄

拉青矿床位于班公湖-怒江缝合带南侧,属于矽卡岩型铜多金属矿床。矿区岩浆岩发育,矿化二长花岗岩为其成矿岩体。对二长花岗岩进行了LA-ICP-MS 锆石U-Pb测年,获得年龄加权平均值为114.24Ma±0.87Ma,表明拉青矿床形成于早白垩世晚期。岩石地球化学数据分析表明,A/CNK值为1.15~1.17、A/NK值为1. 53~1. 59,为过铝质花岗岩,属于高钾钙碱性系列。轻稀土元素较重稀土元素富集,负Eu异常较弱。在微量元素蛛网图上,富集大离子不相容元素Rb、K、Th、U,亏损高场强元素Nb、Ti。R1-R2图解及Rb-（Yb+Nb）图解表明,拉青二长花岗岩形成于同碰撞构造环境。结合区域地质矿产资料初步认为,二长花岗岩体形成于班公湖-怒江洋消减闭合后羌塘板块与冈底斯板片碰撞拼合阶段,拉青矿床即是该同碰撞背景下形成的与二长花岗岩岩浆活动密切相关的矽卡岩铜多金属矿床。     

南阿尔金迪木那里克花岗岩地球化学、锆石U-Pb年代学与Hf同位素特征及其构造地质意义

迪木那里克花岗岩侵入到南阿尔金迪木那里克浅海相沉积地层中,岩性为钾长花岗岩。地球化学数据显示该花岗岩具有高SiO₂、高钾、高铝的特征,富集Rb、Th、K、La、Zr,亏损Ba、Ta、Nb、Sr、P、Ti,属于弱过铝质高钾钙碱性系列,具有S型花岗岩的特征;其源岩为杂砂岩,熔融温度和压力约为>800℃与~10kbar。锆石ε_Hf(t)介于-3.52~0.95,LA-ICP-MS 锆石 U-Pb 定年确定其形成时代为452.8±3.1Ma。迪木那里克花岗岩的形成时代明显晚于南阿尔金高压-超高压变质岩的峰期变质时代(486~504Ma),而与超高压岩石的退变质时代(455Ma)基本一致,又与形成时代为467Ma的长沙沟-清水泉一带裂谷型层状镁铁质-超镁铁质杂岩体伴生,其成因可能是阿尔金深俯冲陆壳板片发生断离后,深部地幔物质上涌导致地壳杂砂岩熔融的产物,具有同折返岩浆作用的特点。结合以往研究,南阿尔金俯冲碰撞杂岩带中早古生代花岗岩的演化期次可初步划分为:1)约500Ma,与高压-超高压变质岩的峰期变质时代一致,形成于陆-陆碰撞造山作用过程中的陆壳相互叠置加厚阶段;2)为466~451Ma,与超高压岩石的退变质时代大致相当,形成于深俯冲陆壳断离后的伸展构造背景;3)为426~385Ma,形成于碰撞造山作用结束后的伸展减薄阶段。     

冈底斯成矿带东段努日矿床成矿斑岩年代学、地球化学及其意义

努日矿床是近年来在西藏冈底斯成矿带南缘发现的一个大型铜钼钨矽卡岩型矿床,由于成矿斑岩一直未能确定,一定程度上制约了区域成矿规律的总结和找矿方向的确定。文章基于野外地质观察和岩体成岩时代研究,识别出与成矿有关的一期花岗闪长斑岩体,锆石LA-ICP-MS U-Pb年代学研究显示其成岩时代为(24.94±0.28)Ma,略早于矿体的成矿年龄(23.62 Ma),结合岩体蚀变、矿化及围岩特征,确认其为成矿斑岩体。岩石地球化学特征表明其具高Sr、低Y、无Eu异常的特征,Rb-Sr、Sm-Nd、Pb同位素组成与冈底斯带中新世成矿岩体基本一致,说明其岩浆源区具壳幔混合来源的特征,岩浆相对富集放射性成因Pb同位素,暗示其演化中混染了较多古地壳物质,有效解释了矿床铜-钼-钨矿物组合。矿区成矿斑岩体的发现证实了努日矿床属于斑岩成矿系统中的矽卡岩矿床,岩浆形成于加厚下地壳部分熔融,上升演化过程中与上覆古老拉萨地壳发生过同化混染作用,是岩浆热液与比马组灰岩持续演化的结果。本研究对在冈底斯南缘寻找努日式矿床具有较好的借鉴意义。     

西藏班戈县拉青铜多金属矿床地球化学特征和年龄

拉青矿床位于班公湖-怒江缝合带南侧,属于矽卡岩型铜多金属矿床.矿区岩浆岩发育,矿化二长花岗岩为其成矿岩体.对二长花岗岩进行了LA-ICP-MS锆石U-Pb测年,获得年龄加权平均值为114.24Ma±0.87Ma,表明拉青矿床形成于早白垩世晚期.岩石地球化学数据分析表明,A/CNK值为1.15～1.17、A/NK值为1.53～1.59,为过铝质花岗岩,属于高钾钙碱性系列.轻稀土元素较重稀土元素富集,负Eu异常较弱.在微量元素蛛网图上,富集大离子不相容元素Rb、K、Th、U,亏损高场强元素Nb、Ti.R1-R2图解及Rb-(Yb+Nb)图解表明,拉青二长花岗岩形成于同碰撞构造环境.结合区域地质矿产资料初步认为,二长花岗岩体形成于班公湖-怒江洋消减闭合后羌塘板块与冈底斯板片碰撞拼合阶段,拉青矿床即是该同碰撞背景下形成的与二长花岗岩岩浆活动密切相关的矽卡岩铜多金属矿床.     

鲁西莱芜三岔河矽卡岩型铁金矿床岩体成因：锆石U-Pb年代学和岩石地球化学证据

【研究目的】莱芜三岔河矿床是鲁西地区首次发现的矽卡岩型铁金矿床（不含铜）,以往研究相对薄弱,本文旨在对成矿岩体形成时代、源区性质、岩石成因和构造背景进行讨论。【研究方法】本文开展了LA-ICP-MS锆石U-Pb测年、岩体主微量测试工作。【研究结果】结果显示辉石闪长岩侵位年龄为（138.4±1.2）Ma,属早白垩世。辉石闪长岩里特曼指数σ=2.20～2.54,为钙碱性岩石;辉石闪长岩具高Mg^#、富Na特征,Sc、Cr、Co、Ni含量较高,表明其具有幔源岩浆的属性;富集轻稀土元素（LREE）,亏损重稀土元素（HREE）,Eu异常不明显,富集大离子亲石元素（Cs、Ba、Sr）,亏损高场强元素（Nb、Ta、Zr）,暗示有地壳物质的涉入。【研究结论】三岔河辉石闪长岩可能起源于受华北克拉通古老地壳物质改造的富集岩石圈地幔的部分熔融,形成于岩石圈减薄的强烈伸展构造背景,可能与太平洋板块俯冲后撤引起的伸展构造环境有关。     

班公湖-怒江成矿带西段材玛花岗岩体岩石地球化学及年代学

材玛花岗岩体为班公湖-怒江成矿带西段日土-多不杂岩浆弧带的成矿岩体之一。对材玛岩体的中粒黑云二长花岗岩进行锆石LA-ICP-MS U-Pb同位素测试,结果为165.1±1.5Ma(n=17,MSWD=0.86);全岩Rb-Sr同位素年龄为163.5±2Ma(n=5),材玛岩体的形成年龄为163~165Ma(中侏罗世)。材玛岩体属于高钾钙碱性系列,ΣREE=109.5~225.2(10^-6),LREE富集,LREE/HREE=2.37~7.77,并伴随Eu的亏损。微量元素特征表现为着强烈的Ba、Nb、P、Ti亏损和Th、U、Pb富集,以及Zr的弱亏损。材玛岩体为班-怒带向北俯冲作用的产物,为岛弧型岩浆岩,物质来源为俯冲带之上的地幔部分熔融,并有地壳物质混熔。     

柴达木山花岗岩的岩石学、地球化学及锆石U-Pb年代学研究

正柴北缘高压—超高压变质带内发育的榴辉岩、蛇绿岩、麻粒岩及片麻岩等前人进行了大量的研究。大柴旦地区是柴北缘古生代超高压带的重要组成部分,与超高压岩石相伴的花岗岩十分发育,查明该超高压带上花岗质岩浆活动期次及其与超高压变质作用、造山带构造演化之间的关系,对探讨中国西部大地构造演化具有十分重要的意义(吴才来等,2007)。     

Investigation of the Ablation Behaviour of Andradite-Grossular Garnets and Rutile with Implications for U-Pb Geochronology

U-Pb dating of andradite-grossular garnet (grandite) and rutile by LA-ICP-MS can be used to constrain various metamorphic, metasomatic and igneous geological processes. In this study, we examine and compare the impact of different analytical conditions (fluence, pulse width, laser beam size and ablation frequency) on the ablation crater morphology, ablation rates, down-hole fractionation and U-Pb ages of grandite and rutile samples of different compositions. The shapes of grandite ablation craters suggest the mineral ablates by classical evaporation with significant melting that cannot be eliminated even at fluences just above the ablation threshold. Grandite garnets with higher andradite proportions have faster ablation rates. The overall low U contents of grandite require using large laser beam sizes to obtain acceptable precision of U-Pb ages. At such conditions and crater depths < 10 μm, fluences of 2.1 and 3.5 J cm^-2, laser pulse width of 5 ns and 20 ns, and ablation frequencies between 3.5 and 6.5 Hz, obtain similar and reproducible ages when the proportion of grossular is < 35%. Rutile ablation crater morphology shows evidence of melt splashing and thermal stress cracking. They have significant crater bottom features, which increase in relief with lower fluences and a higher number of laser shots, indicating the features are probably energy-related and making higher fluences, such as 5 J cm^-2, necessary for uniform ablation when using 193 nm excimer lasers. The slow ablation rate at low fluences and then steep increase at around 2.0 J cm^-2 suggests a transition in the ablation mechanism from exfoliation to classical vaporisation. Crater bottom features and other ablation behaviour vary between samples, which could be related to their difference in colour. Although the down-hole fractionation patterns of the samples are similar at 5 J cm^-2, the U-Pb ages of some samples vary significantly with different analytical conditions and/or measurement sessions, particularly when using laser beam sizes of 30 μm, suggesting differences in mass bias and more variable ablation behaviour. A laser beam size of at least 60 μm is recommended for reproducible U-Pb dating of rutile.