Chemical Characteristics and Evolutionary Patterns of Groundwater in the Daqing River Plain Area of Haihe Basin
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摘要:
地下水超采引发大清河流域范围内一系列生态环境负效应，地下水与地表水关系密切，厘清大清河流域平原区地下水化学特征及演化规律，对大清河流域水资源合理开发利用具有重要意义，然而目前尚缺乏对大清河流域地下水化学特征特别是其历史以来的演变规律作系统的分析。本文以海河流域大清河平原区地下含水系统为例，采集浅层含水层组47个水样和深层含水层组32个水样，测试了主要阴离子(Cl-、SO42-、NO3-)和阳离子(K+、Na+、Ca2+、Mg2+)等指标，利用水化学类型、吉布斯模型、离子比值关系等方法，研究其水化学特征及演化规律。测试结果显示：浅层含水层组受到气象和人为因素影响较大，浅层和深层含水层组pH值(7.35~8.92)差异不大，偏碱性；浅层含水层组由于农业活动等影响，造成局部地区的硝酸盐和硫酸盐污染。水岩相互作用分析显示：硅酸盐矿物风化是研究区主要的矿物来源，硅酸盐矿物溶解、阳离子交换为主要的水化学作用。研究区浅层地下水水化学特征总体上受地形和水文地质条件的影响，由山前平原-中部平原呈规律性分布。现状地下水化学类型为沿地下水径流方向由山前的HCO3-Ca·Mg(Ca)型，经HCO3-Mg·Ca、HCO3-Mg·Ca·Na、HCO3-Na·Mg·Ca向HCO3·Cl-Na·Ca、HCO3·Cl·SO4-Na至平原中部冲湖积平原的Cl(SO4)-Na转变。水化学演变分析显示中部平原地下水由以Cl·HCO3-Ca·Na、HCO3·Cl-Ca·Na型为主，转变为当前条件下以Cl·HCO3-Ca·Na、SO4·Cl-Na·Mg型为主。总体上，研究区现状水化学类型复杂多样，且分布上虽然仍受地形与地质条件的控制，但越来越多地受到以开采为主的人类活动的影响，应重视人类活动对该区域地下水的影响，合理布置开采方案。本文利用水化学方法研究了大清河流域平原区地下水化学特征及演化规律，厘清了大清河流域平原的水化学特征以及水化学类型演变规律，初步分析了演变趋势造成的原因，特别是指明地下水化学演变越来越受到人类活动的影响，后续将在水化学未来的演变预测上进行相关的研究。
要点(1) 浅层含水层组TDS变化幅度大，深层含水层组TDS变化幅度小，浅层含水层组受到气象和人为因素影响较大。
(2) 硅酸盐矿物风化溶解、阳离子交换为主要的矿物来源和水化学作用。
(3) 浅层地下水化学特征总体上受地形和水文地质条件的影响，由山前平原-中部平原呈规律性分布。
(4) 研究区水化学类型复杂多样，且越来越多地受到以开采为主的人类活动的影响。
HIGHLIGHTS(1) The TDS of the shallow aquifer groups varies greatly, while the TDS of the deep aquifer groups has a small variation. The shallow aquifer groups are more influenced by meteorological and anthropogenic factors.
(2) Weathering dissolution of silicate minerals and cation exchange are the main mineral sources and water chemistry.
(3) The chemical characteristics of shallow groundwater are generally influenced by the topography and hydrogeological conditions and are regularly distributed from the piedmont plain to the central plain.
(4) The current water chemistry types are complex and diverse and are increasingly influenced by human activities such as mining.
Abstract:BACKGROUNDGroundwater is closely related to surface water. Groundwater over-extraction has triggered a series of negative ecological effects in the Daqing River basin. The evolution of groundwater chemical characteristics is influenced by both natural and anthropogenic factors. The analysis of groundwater chemical characteristics can indicate the meteorological-hydrological and water-rock interaction during groundwater runoff, thus reflecting the groundwater circulation path, groundwater system characteristics and evolution laws, etc. It also helps to monitor groundwater dynamics and prevent the occurrence of groundwater pollution.
OBJECTIVESTo clarify the chemical characteristics and evolution of groundwater in the plain area of the Daqing River basin, which will be important for the rational development and utilization of water resources in the basin.
METHODS47 water samples from the shallow aquifer groups and 32 water samples from the deep aquifer groups were collected to analyze the main anions (Cl-, SO42-, NO3-) and cations (K+, Na+, Ca2+, Mg2+). The water chemistry characteristics and evolution laws were studied by using the water chemistry type, Gibbs model and ion ratio relationship. On-site portable water quality analyzer (HACH-HQ40d) was used to test pH (accuracy 0.01), total dissolved solids (TDS, accuracy 0.01) and other parameters, and groundwater samples were collected after the indicators were stabilized. All samples were sent to the laboratory at low temperature and stored in a refrigerator at 4℃, and groundwater alkalinity was determined by titration on the same day. Seven days later, the samples were sent to the Institute of Hydrogeology and Environmental Geology, Chinese Academy of Geological Sciences for testing of major anions (Cl-, SO42-, NO3-) and major cations (K+, Na+, Ca2+, Mg2+) using inductively coupled plasma-optical emission spectrometry (iCAP6300). The anion and cation charge balance error was less than 5%, and the anion and cation test accuracy was 0.01mg/L.
RESULTSThe test results showed that the largest deviation was in the water sample from Hanbao Village, Liu Lizhuang Town, Anxin County, Baoding City, Hebei Province, which was from the shallow aquifer groups, and the maximum TDS reached 6015.00mg/L. The TDS of the shallow aquifer groups ranged from 254.10 to 6015.00mg/L, with an average of 664.14mg/L, a large coefficient of variation and a large variation in TDS, indicating that the shallow aquifer groups were affected by meteorological and human factors. The TDS of the deep aquifer groups ranged from 197.10 to 691.40mg/L, with an average of 278.58mg/L, and the coefficient of variation was small, indicating that the groundwater of the deep aquifer groups was less affected by meteorological and human activities than that of the shallow aquifer groups. A small portion of the sampling points of the shallow aquifer groups in the area were brackish water and salt water. The TDS of the deep aquifer groups was generally less than 1000mg/L, which was suitable for use as a mining layer. The pH values of the shallow and deep aquifer groupss in the study area were not very different (7.35-8.92) and were alkaline. The NO3- maximum value of 298.40mg/L and SO42-maximum value of 3091.00mg/L in the shallow aquifer groups, but the average value was not significant, indicating that the shallow aquifer groups have caused nitrate and sulfate pollution in local areas due to agricultural activities and other effects.
In the shallow layer of the study area, except for the difference in hydraulic conditions in the northern piedmont plain where flaky or spotty HCO3-Cl-SO4 and HCO3-Cl type water occurred, the anions in most of the piedmont plain were mainly HCO3 type, and the cations were mainly Ca and Ca-Mg and Mg-Ca. During the discharge of groundwater along the piedmont plain to the mouth of the alluvial fan, the cations changed from Ca-Mg type to Na type in order through Ca-Mg-Na, Na-Ca-Mg, Na-Mg-Ca, Na-Ca to Na type, and anions from HCO3 type to SO4 and Cl type via HCO3-SO4, HCO3-SO4-Cl, HCO3-Cl-SO4, SO4-Cl. The deep groundwater cations were relatively more complex, and the zonation was more obvious: from the piedmont plain to the bottom of the alluvial fan, the cations transition from Ca, Ca-Mg, Mg-Ca, Na-Mg-Ca (Mg-Ca-Na) type to Na-Ca and Na type water.
The shallow aquifer groups were basically located in the area of water-rock interaction, and individual points showed some influence of evaporation concentration. The deep aquifer groups were subjected to water-rock interaction and less affected by evaporation and atmospheric precipitation. The analysis results showed that the milligram equivalent concentration ratio of (Ca2++Mg2+)+(HCO3-+SO42-) to Na++K+-Cl- was close to -1, indicating a more significant cation exchange effect. The groundwater samples in this study area were mostly distributed near the end elements of silicate minerals, indicating that weathering of silicate minerals (such as feldspar) was the main hydrogeochemical control factor in the study area, which was consistent with the lithological characteristics of aquifers in the groundwater of the Daqing River basin plain, and the test results also showed that HCO3- was the dominant ion in both shallow and deep aquifer groups.
The SI values of calcite in the shallow aquifer groups in this study area ranged from -0.46 to 1.35, dolomite SI values from -0.88 to 3.02, gypsum SI values from -3.1 to -0.68, and rock salt SI values from -8.53 to -4.75, indicating that calcite and dolomite were partially saturated and partially unsaturated, and both gypsum and rock salt were unsaturated. Cl-/(Na++K+) could determine whether the groundwater was influenced by the dissolution of silicate rock. Most of the groundwater samples in this study area exhibited Cl-/(Na++K+) < 1, indicating that, in addition to rock salt in dissolved state, silicate mineral dissolution (e.g., potassium feldspar and sodium feldspar) was the main source of excess Na+ and K+. The Na+ content may also originate from cation exchange, and the high Cl-, the higher concentration may be the input of foreign contamination. The HCO3-/(Ca2++Mg2+) of the samples from the shallow aquifer groups was basically less than 1, showing excess Ca2+ and Mg2+, suggesting other sources of Ca2+ or Mg2+, while the (HCO3-+SO42-)/(Ca2++Mg2+) of the shallow aquifer groups was distributed above and below the 1∶1 line on both sides, suggesting that evaporite minerals (e.g. gypsum) may also be an important source of Ca2+ for the shallow aquifer groups, as evidenced by the unsaturated state of gypsum in groundwater, in addition to the increase in SO42- due to human activities. Both HCO3-/(Ca2++Mg2+) and (HCO3-+SO42-)/(Ca2++Mg2+) of the deep aquifer groups lay above the 1∶1 line, and the excess HCO3- implied silicate dissolution dominance, or the presence of cation exchange, leading to a lower Ca2+ content. (Cl-+SO42-)/(HCO3-) could indicate the dissolution status of evaporites and carbonates, and water samples from shallow and deep aquifer groups were mainly distributed in the (Cl-+SO42-)/(HCO3-)=1∶1 line below, which indicated that its chemical components were more dissolved by carbonate rocks.
In the influence zone of the Caohe River in the northern part of Mancheng District, the water chemistry changed from HCO3-Ca-Mg water to Cl-HCO3-Ca-Na water; at the alluvial fan margin of Jiehe River in Shunping County and at the alluvial fan margin of Rejected Horse River in Zhuozhou City, the proportion of Na content in groundwater gradually exceeded that of Mg as the cation content second only to Ca, and the water chemistry changed from HCO3-Ca-Mg water to HCO3-Ca-Na-Mg type water. The groundwater in the central plain changed from Cl-HCO3-Ca-Na and HCO3-Cl-Ca-Na type water with island and strip distribution of SO4-HCO3-Na-Mg, SO4-HCO3-Na, SO4-Na-Mg and HCO3-Na-Mg type water to Cl-HCO3-Ca-Na, SO4-Cl-Na-Mg type water dominated and mingled with HCO3-Cl-Ca-Mg, Cl-SO4-Na-Mg, HCO3-Cl-SO4-Na, HCO3-SO4-Na, HCO3-SO4-Na, HCO3-SO4-Na-Mg, and Cl-SO4-Na-Mg type water.
The average NO3- content of the shallow aquifer was 28.78mg/L, and the average NO3- content of the deep aquifer was 4.55mg/L, indicating that nitrate pollution was serious in the shallow groundwater local area of the study area. Referring to the groundwater quality standard (GB/T 14848—2017) for ClassⅢ water, there were 17 sampling points in the shallow aquifer groups with NO3- content over 20mg/L and 5 sampling points in the shallow aquifer groups with SO42- greater than 250g/L, indicating that these sampling sites were affected by anthropogenic activities, resulting in nitrate and sulfate pollution. A ratio of SO42-/Ca2+ to NO3-/Ca2+ greater than 1 indicated that industrial and mining activities had a greater impact on groundwater, and a ratio less than 1 was more disturbed by agricultural activities and residential sewage. The results showed that the ratio of the deep aquifer groups was greater than 1, and only the 240m well in the north of Erlangmiao Village, Dingzhou City, Baoding City, Hebei Province, was less than 1. This indicated that the deep aquifer groups were basically affected by industrial and mining activities, but not by agricultural activities and residential sewage. In the shallow aquifer groups, there were 27 water samples with SO42--Ca2+ to NO3-Ca2+ ratio greater than 1, and 20 water samples with SO42--Ca2+ to NO3--Ca2+ ratio less than 1, indicating that the shallow aquifer groups were partly influenced by industrial and mining activities, and partly influenced by agricultural activities and domestic sewage of residents.
CONCLUSIONSThe characteristics and evolution of groundwater chemistry in the plain area of the Daqing River basin was investigated by using the water chemistry method, clarifying the characteristics of the water chemistry and the evolution of water chemistry types in the plain area of the Daqing River Basin. Reasons for the evolution trend were also investigated, indicating that the evolution of groundwater chemistry is increasingly influenced by human activities. Relevant research will be conducted on the prediction of the future evolution of water chemistry.
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花岗质岩岩石是地球大陆地壳有别于其他行星的重要标志，且与大量的岩浆-热液矿床在时空和成因上密切相关[1-3]，有关花岗质岩石的形成与演化一直是地质学者研究的热点。花岗质岩石主要矿物组成比较简单，一般由长石、云母和石英组成，但有关其岩石起源与演化一系列问题一直存在激烈的争议。绝大多数情况下，人们大多借助元素和同位素地球化学来限定花岗质岩石成因，如以往常采用全岩的Sr、Nd、Pb等放射成因同位素来进行示踪，遗憾的是这些同位素在很多情况下难以对花岗质岩浆的形成与演化提供明确的制约[4-5]。这是因为全岩同位素示踪存在三个方面的局限性：①岩浆在侵位过程当中如果发生了多次岩浆改造(Modification)，如岩浆混合、围岩同化混染和结晶分异等，Sr-Nd同位素测定值代表的是均一化后某一个时间点(snapshot)的信息，无疑会隐藏许多岩浆来源的信息[6]；②全岩放射成因同位素能够较合理地监测到古老地壳和软流圈地幔物质，但很难监测到年轻物质的具体混入量，因为后者的放射成因子体同位素难以准确测量，而且年轻的幔源岩石或者岛弧火山岩在参与花岗岩形成之前如果遭受热液蚀变，Sr同位素只有少量变化，而Nd和Pb同位素没有变化[4]，故难以准确地判断其源岩性质；③使用全岩放射成因同位素分析问题时，我们通常假定岩石中各矿物相具有相同的来源并且保持同位素平衡，但近年来人们发现一些矿物与其寄主岩石在同位素组成上可以存在很大差别[7]。因此，仅借助全岩放射成因同位素来示踪岩浆来源，许多详细的岩浆来源信息及源岩性质变化细节不能被有效地揭露出来，况且与成矿有关的花岗质岩石常普遍遭受不同程度的热液蚀变，这就给用全岩化学成分限定岩浆起源与形成过程带来了更大难度。
为了攻克这个难题，越来越多的研究者试图利用花岗岩中矿物的元素和同位素来揭示岩石成因和演化过程，但由于侵入岩缓慢的冷却过程，亚固相线下大部分矿物的化学成分得到重新平衡，许多详细的岩石成因信息已经丢失[8]。而副矿物具有难熔、惰性和化学性质稳定等特征，一般不易受后期热事件的影响[8-9]，即使在特定的条件下发生改变，也能通过结构及成分有效地辨别出来[10-12]。同时，副矿物中含有岩石中大部分高场强元素和稀土元素，这些元素和相关同位素在副矿物中扩散速率缓慢，其结晶过程随着岩浆物理化学条件的改变而表现出不同的结构与地球化学特征，甚至能保存元素和同位素环带，被视为岩浆来源和演化过程的监测器，最大限度地保留了岩浆来源与演化过程的地球化学指纹[12-13]。近年来，随着激光剥蚀电感耦合等离子体质谱(LA-ICP-MS)和激光剥蚀多接收等离子体质谱(LA-MC-ICP-MS)等微区原位分析技术的快速发展和日趋成熟，使得对副矿物进行原位成分测定、获得高精度微量元素和同位素组成得以实现，极大地促进了副矿物在岩石成因中的应用[13-14]。如Bruand等[13]通过对副矿物锆石、磷灰石和榍石进行了原位氧同位素分析，识别出古老花岗岩受后期变质作用的影响，而全岩分析无法揭示出来。越来越多的研究表明，副矿物榍石[CaTi(SiO4)O]微区原位元素和Nd同位素组成，也能够详细揭示岩浆来源和岩浆变化的细节，可显著提高岩浆作用过程的空间分辨率，是探讨岩浆来源与岩石成因的新的有效手段，避免了利用全岩分析为我们探讨花岗岩类成因带来的困扰[15-17, 14]。
湘南构造岩浆带是华南地区花岗质岩浆活动的重要组成部分，发育有多个高钾钙碱性花岗闪长质小岩体，如水口山、宝山和铜山岭等，这些闪长质小岩体主要形成于155~160Ma[18-19]，在时空和成因上与铜铅锌多金属成矿密切相关，普遍遭受了不同程度的热液蚀变作用[19-21]。以往基于全岩元素和Sr-Nd-Pb同位素分析，先后提出壳-幔混合成因、残留体再造及中下地壳脱水熔融等多种不同成因模型[22-23]，有关这些花岗闪长质岩体的源区特征及岩浆性质一直存在非常大的争议。本文以铜山岭岩体为对象，在详细的野外和镜下观察基础上，采用电子探针(EPMA)、激光剥蚀等离子体质谱(LA-ICP-MS)技术对暗色包体和花岗闪长岩两种岩石类型中榍石的主量、微量元素进行原位分析，采用激光剥蚀多接收等离子体质谱(LA-MC-ICP-MS)技术分析两类样品中榍石的原位Nd同位素组成，准确限定花岗闪长质岩石形成的源区特征和岩浆物理化学性质，为深入理解该地区花岗闪长质岩石成因及其大规模铜铅锌多金属成矿机制提供重要支撑。
1. 地质背景
湘南位于华夏地块和扬子地块的结合部位，其东为华夏地块，西为扬子地块，是一个极富特色的铜铅锌多金属成矿密集区(图 1a)[24-25]。该地区主要出露的地层为古生界灰岩、碎屑岩[26]。岩浆作用强烈，花岗闪长质小岩体成带状密集分布，区域上自北向南分布的水口山、宝山、铜山岭是该地区铜铅锌多金属成矿有关的花岗闪长质小岩体的典型代表。
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图 1 (a)湘南地区地质简图和(b)铜山岭岩体分布图(据文献Wang等[24]和卢友月等[25]修改)。湘东南的花岗闪长质侵入体位于华夏和扬子地块的结合部位，铜山岭岩体位于湘东南的南部，由Ⅰ、Ⅱ、Ⅲ等3个小岩体组成，本次研究的样品采自Ⅰ号岩体Figure 1. (a)The simplified geological map of southern Hunan Province and (b) the distribution of the Tongshanling granitic pluton (modified from Wang, et al.[24] and Lu, et al.[25]). Granodioritic pluton in southeast Hunan Province (South China) emplaced at the junction between Cathaysia and Yangtze bocks. The Tongshanling pluton is located in the south of southeast Hunan Province, and is composed of three small plutons Ⅰ, Ⅱ and Ⅲ. The studied samples were collected from No.Ⅰ pluton.铜山岭岩体位于湘东南地区南部，由Ⅰ、Ⅱ、Ⅲ三个小岩体组成，近东西向分布，总面积12km2(图 1b)。该岩体侵入于寒武纪浅变质岩、泥盆纪海相碳酸盐岩夹碎屑岩地层中，形成年龄为159±1Ma[18]。岩体周边分布一系列铜铅锌多金属矿床(点)，自北向南有铜山岭矽卡岩型-热液脉型铜多金属矿床、江永矽卡岩型银铅锌矿床、桥头铺矽卡岩型铜钼多金属矿床(图 1b)。前人通过年代学、同位素(S、Pb、C)及流体包裹体研究，大多认为这些矿床与铜山岭岩体在时空和成因上密切相关[21, 25, 27-28]。
2. 实验部分
2.1 实验样品
本次研究的所有样品均采自铜山岭Ⅰ号岩体，岩性主要为角闪石黑云母花岗闪长岩(图 2a)，主要矿物组成为角闪石、黑云母、长石和石英，角闪石一般呈棕色和浅绿色(图 2)，局部可见有明显的蚀变特征。岩体中发育有大量的铁镁质暗色包体如图 2b所示。主要由角闪石和黑云母等暗色矿物组成。
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图 2 铜山岭岩体岩性特征和暗色包体照片及榍石透射光和背散射电子图像。铜山岭岩体中的花岗闪长岩主要由角闪石、长石、石英和黑云母组成。榍石在反射光和背散射电子图像中没有显示出明显的成分环带a—花岗闪长岩的主要矿物组合；b—花岗闪长岩中暗色包体；c—代表性花岗闪长岩镜下照片；d—角闪石镜下特征；e—透射光下榍石照片；f—榍石的背散射电子图像。Figure 2. Characteristics of mafic microgranular enclave and hosted granodiorite, and photomicrographs of accessory mineral titanite.a—The major mineral assemblages of granodiorite; b—The mafic microgranular enclave hosted by granodiorite; c—Photomicrograph of the representative granodiorite; d—Photomicrograph of amphibole; e—Photomicrograph of titanite under transmission light; f—Black scatter electric image of titanite. The granodiorites are mainly composed of amphibole, feldspar, quartz, and biotite. Accessory mineral titanite grains in the MME and host granodiorite of the Tongshanling granitic pluton show little or no intra-grain concentric zoning in transmission and BSE images.本文对花岗闪长岩和暗色包体样品进行粉碎后采用电磁法分选榍石，将分选的榍石颗粒制成环氧树脂靶，然后对榍石进行抛光处理，之后对榍石进行透反射光和背散射照相(图 2中e，f)，检查榍石的内部结构，选择无裂痕、无微小矿物包裹体和表面平整的区域进行激光原位分析。
2.2 分析方法
2.2.1 榍石主量元素分析
榍石主量元素利用EPMA进行分析，在中国科学院地球化学研究所矿床地球化学国家重点实验室完成，仪器型号为日本电子生产的JXA8530F-plus型场发射电子探针。仪器工作条件为：加速电压25kV，加速电流10nA，束斑5μm。采用自然界和人工合成国际标样对榍石中元素进行校正，用Kaersutite角闪石国际标样校正榍石的Na、K、Mg、Al、Si、Ca、Mn和Fe等元素的含量，磷灰石和金红石标样分别用来校正榍石中F和Ti的含量。元素特征峰测试时间为10s，背景测试时间为5s，所有测试数据均进行了ZAF校正处理。
2.2.2 榍石原位微量元素分析
榍石微量元素分析实验在中国科学院地球化学研究所矿床地球化学国家重点实验室利用LA-ICP-MS完成。激光剥蚀系统为GeoLasPro 193nm ArF准分子激光器，电感耦合等离子体质谱为Agilent 7900。激光剥蚀过程中采用氦气为载气，氩气为补偿气，并加入少量氮气提高灵敏度，三者在进入ICP之前通过一个T形接头混合。样品仓为标配的剥蚀池，其中加入树脂制作的模具来获得一个较小体积的取样空间，以降低记忆效应，提高冲洗效率。分析过程中，激光工作参数频率为5Hz，能量密度5J/cm2，束斑44μm，分析点靠近电子探针点的位置，每个样品的总测试时间为90s，采集背景信号15s，样品剥蚀时间60s，冲洗管路和样品池时间15s。在测试之前用美国地调局研制的硅酸盐玻璃NIST610对ICP-MS性能进行优化，使仪器达到最佳的灵敏度和电离效率(U/Th≈1)、尽可能小的氧化物产率(ThO/Th < 0.3%)和低的背景值。微量元素含量校正、仪器灵敏度漂移校正等都采用ICPMSDateCal软件处理，以对应点电子探针获得的Ca含量作为内标，标准物质NIST610和NIST612玻璃作为外标进行数据校正，微量元素分析的准确度优于10%。
2.2.3 榍石原位Sm-Nd同位素分析
榍石Sm-Nd同位素分析实验在中国科学院地球化学研究所矿床地球化学国家重点实验室利用LA-MC-ICP-MS完成。激光剥蚀系统是澳大利亚瑞索公司生产的RESOlution-155 ArF193-nm，多接收电感耦合等离子体质谱仪是英国Nu公司生产的Nu Plasma Ⅲ。分析过程中，激光的束斑72μm，剥蚀频率6Hz，能量密度6J/cm2。使用144Sm/147Sm=0.205484和146Nd/144Nd=0.7129分别校正Sm同位素和Nd同位素的质量歧视[29]。利用144Sm/149Sm=0.22332校正144Sm对144Nd的同质异位数干扰[30]。榍石标样BLR-1作为外标校正147Sm/144Nd的质量歧视和元素分馏。实验测得的4个监控标样MAD、Otter Lake、LAP和SAP的143Nd/144Nd比值分别为0.511352±0.000008、0.511956±0.000008、0.511355±0.000015、0.511011±0.000007，与相应样品的143Nd/144Nd参考值在误差范围内基本一致(MAD：0.511322±0.000053、Otter Lake：0.512940±0.000009、LAP：0.512352±0.000024、SAP：0.511007±0.000030)[17]。
3. 榍石微区原位元素和同位素分析结果
3.1 榍石主量和微量元素特征
表 1 铜山岭花岗闪长岩和暗色包体中榍石电子探针分析数据Table 1. Representative EPMA data of titanite in granodiorite and mafic microgranular enclave of the Tongshanling pluton元素/分析点 暗色包体(%) 花岗闪长岩(%) TSL4-1 TSL4-2 TSL4-3 TSL4-4 TSL4-5 TSL5-1 TSL5-2 TSL5-3 TSL5-4 TSL5-5 TSL5-6 Na2O 0.014 0.013 - 0.056 0.009 - - 0.003 - - - K2O 0.009 0.004 0.001 0.006 0.008 - - - - - - F 1.45 0.48 1.45 1.69 1.23 1.84 0.255 1.57 1.10 1.09 1.07 MgO - 0.003 0.001 - 0.005 0.031 0.001 0.017 - - 0.002 Al2O3 3.62 2.70 3.60 4.14 3.31 5.61 1.81 4.68 3.03 3.37 2.48 SiO2 31.7 31.4 31.2 31.3 30.7 31.3 31.1 31.4 31.6 31.0 31.6 Cl 0.017 - 0.008 0.012 0.002 0.005 - - 0.007 - 0.004 CaO 29.4 29.3 30.0 29.9 29.4 29.9 29.6 29.0 29.6 29.5 29.4 TiO2 33.9 35.7 35.1 33.7 34.0 30.6 38.2 32.9 35.0 34.2 36.8 MnO 0.059 0.043 0.024 0.045 0.061 0.028 0.044 0.053 0.066 0.024 0.027 FeO 0.220 0.356 0.366 0.190 0.184 0.465 0.378 0.191 0.606 0.456 0.432 总计 100 99.9 102 101 98.9 99.7 101 99.8 101 99.7 102 以O=5计算的阳离子个数(afpu) Na 0.001 0.001 - 0.003 0.001 - - - - - - Mg - - - - - 0.001 - 0.001 - - - Al 0.069 0.052 0.068 0.078 0.064 0.107 0.034 0.089 0.057 0.065 0.047 Si 1.021 1.020 0.996 1.004 1.008 1.013 1.001 1.015 1.016 1.010 1.007 Ca 1.013 1.020 1.026 1.025 1.032 1.038 1.020 1.002 1.020 1.030 1.006 Ti 0.822 0.872 0.841 0.812 0.840 0.745 0.925 0.800 0.847 0.839 0.883 Mn 0.002 0.001 0.001 0.001 0.002 0.001 0.001 0.001 0.002 0.001 0.001 Fe 0.006 0.010 0.010 0.005 0.005 0.013 0.010 0.005 0.016 0.012 0.012 F 0.008 0.003 0.008 0.009 0.007 0.010 0.001 0.008 0.006 0.006 0.006 F和Cl 0.001 - - 0.001 - - - - - - - Al+Fe 0.075 0.061 0.078 0.083 0.069 0.120 0.044 0.094 0.074 0.077 0.058 注：“-”代表低于检测限，下同。 表 2 铜山岭花岗闪长岩和暗色包体中榍石原位微量元素组成Table 2. Trace element compositions of titanite in granodiorite and mafic microgranular enclave of the Tongshanling pluton元素/分析点 暗色包体(μg/g) 花岗闪长岩(μg/g) TSL4-1 TSL4-2 TSL4-3 TSL4-4 TSL4-5 TSL5-1 TSL5-2 TSL5-3 TSL5-4 TSL5-5 TSL5-6 Li 0.431 0.565 0.141 0.264 0.050 1.17 - 0.082 0.260 0.942 - V 1461 571 610 1317 701 781 553 643 687 795 717 Ni 0.178 0.560 0.417 0.032 0.619 0.042 0.185 0.431 - 0.338 - Cu 0.532 0.510 0.589 0.329 0.761 0.648 0.596 0.265 0.357 0.347 0.651 Zn 2.22 2.36 3.49 1.91 2.59 1.76 1.02 2.94 1.15 2.21 1.31 Ga 8.27 6.41 6.58 7.61 6.31 3.56 3.88 7.71 7.68 2.23 6.38 As 0.776 2.36 0.632 0.365 2.66 7.54 1.51 2.63 3.80 3.25 0.796 Rb 0.063 0.742 0.088 - 0.003 0.242 0.051 0.033 0.137 0.087 0.099 Sr 4.66 6.61 6.16 4.74 6.29 7.23 7.51 6.22 7.62 11.3 6.42 Y 270 74.0 131 32.4 90.9 118 872 333 1706 74.9 906 Zr 16.5 143 26.8 59.4 486 11.1 154 190 536 474 67.0 Nb 384 584 354 306 1489 650 625 1069 1455 1217 963 Sn 861 4116 3960 1353 6594 90 1162 3503 1233 829 651 Cs 0.112 0.320 0.038 0.039 0.004 0.317 0.002 0.005 0.044 0.110 0.011 Ba 0.093 0.342 0.055 0.108 0.053 1.323 - 0.080 0.033 1.263 0.048 La 5.33 9.87 8.07 4.19 5.92 16.5 4.37 14.1 15.8 15.7 2.75 Ce 24.8 43.1 48.4 16.6 21.5 63.9 43.2 73.9 98.1 51.4 25.7 Pr 5.45 6.39 9.19 2.58 3.91 11.9 15.5 15.8 27.0 7.02 9.56 Nd 37.6 29.6 49.9 13.1 24.9 69.8 135.2 97.8 214 32.6 86.8 Sm 19.8 7.79 13.2 4.95 10.7 22.2 86.8 35.8 135 26.4 68.5 Eu 8.94 10.9 13.4 5.71 15.7 10.2 46.0 17.4 32.5 28.8 20.3 Gd 29.7 9.59 16.2 5.09 13.8 22.6 118 42.2 192 25.9 108 Tb 5.95 1.58 2.85 0.84 2.18 3.50 21.7 7.20 37.03 1.42 21.3 Dy 42.7 10.5 19.8 5.3 13.3 20.1 143 47.5 259 9.8 151 Ho 9.84 2.45 4.44 1.12 3.05 4.20 30.2 10.9 55.4 2.14 31.2 Er 29.0 7.2 13.5 3.3 9.0 11.0 85.5 33.9 166.4 6.5 89.3 Tm 4.63 1.18 2.21 0.51 1.40 1.58 13.73 5.69 26.6 1.12 13.6 Yb 32.1 10.3 17.2 3.5 9.8 10.1 103 47.5 206 10.8 100 Lu 4.52 1.97 3.38 0.52 1.29 1.49 17.3 9.48 33.0 1.91 14.1 Hf 0.639 5.09 0.849 2.10 19.0 0.387 7.36 6.77 21.0 16.4 2.13 Ta 28.4 52.1 34.0 24.7 109.5 56.0 56.2 85.7 104.8 91.0 80.3 W 10.2 167 50.5 13.3 173 11.1 3.24 609 366 144 6.15 Pb 0.495 1.386 0.502 0.280 1.14 5.52 0.540 1.43 1.39 1.68 0.427 Th 2.13 3.76 1.44 6.40 2.52 2.35 5.04 63.5 62.0 6.92 2.41 U 17.2 52.8 16.9 18.2 19.8 4.39 18.0 262 205 45.4 10.1 ΣREE 258 152 222 67 136 269 864 459 1498 187 742 LaN/YbN 0.12 0.69 0.34 0.85 0.43 1.17 0.03 0.21 0.06 1.04 0.02 T(℃) 762 878 786 828 956 743 883 895 963 954 834 Eu/Eu* 1.13 3.86 2.80 3.48 3.94 1.39 1.39 1.37 0.62 1.10 0.72 Ce/Ce* 1.13 1.33 1.38 1.24 1.09 1.12 1.29 1.22 1.17 1.20 1.23 Zr/Hf 25.9 28.1 31.5 28.3 25.6 28.7 21.0 28.0 25.5 29.0 31.4 Nb/Ta 13.5 11.2 10.4 12.4 13.6 11.6 11.1 12.5 13.9 13.4 12.0 Y/Ho 27.4 30.2 29.6 28.8 29.8 28.0 28.9 30.7 30.8 35.0 29.0 分析结果显示，铜山花岗闪长岩及暗色包体中榍石的主量元素变化范围基本一致，SiO2为31.0%~31.7%，Al2O3为1.81%~5.61%，CaO为29.0%~30.0%，TiO2为30.6%~38.2%，FeO为0.184%~0.606%，F为0.48%~1.84%。对榍石原位微量元素分析显示，单个样品的微量元素含量变化范围不大，没有明显的成分环带。两类样品中榍石的稀土元素总量变化范围较大，为67~1498μg/g，但二者稀土配分模式存在一定差别(图 3)[31]，暗色包体中榍石具有微弱的重稀土富集，LaN/YbN比值为0.12~0.85，具有明显的Eu正异常，Eu/Eu*值为1.13~3.94；而花岗闪长岩中榍石稀土配分模式变化较大，Eu正异常变小，部分分析点显示出负异常，Eu/Eu*值为0.62~1.39。两类样品中榍石的微量元素对Zr/Hf、Nb/Ta、Y/Ho比值变化范围较小(表 2)，Zr/Hf比值为21.0~31.5，Nb/Ta比值为10.4~13.9，Y/Ho比值为27.4~35.0。
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图 3 铜山岭榍石稀土元素配分模式图，暗色包体中榍石的稀土含量低于花岗闪长岩中榍石的稀土含量并具有明显的正Eu异常，而花岗闪长岩中的榍石显示出弱的正Eu或者负Eu异常。球粒陨石标准化数据据Sun和McDonough[31]Figure 3. Chondrite-normalized REE patterns for titanite from the Tongshanling granitic pluton. Titanite from MME is characterized by Eu positive anomaly. The titanite from granodiorite has REE content higher than those from MME and shows weak positive or negative Eu anomaly on REE pattern. It is indicate that the granitic melts of the Tongshanling are characterized by high oxygen fugacity (The chondrite values are from Sun and McDonough[31]).3.2 榍石Sm-Nd同位素特征
3个样品中榍石的微区原位Sm-Nd同位素分析结果见表 3。单颗粒榍石的Sm-Nd同位素组成非常均一，暗色包体中榍石的147Sm/144Nd比值为0.2399~0.4026，144Nd/143Nd变化范围为0.512321~0.512675，εNd(t)值为-3.5~-8.9，平均值为-7.2±2.4。花岗闪长岩中榍石147Sm/144Nd比值为0.2850~1.4020，144Nd/143Nd变化范围为0.512269~0.513399，εNd(t)值为-5.4~-9.9，平均值为-6.9±2.4。花岗闪长岩中榍石的Sm-Nd同位素比值变化范围略大于暗色包体中榍石的Sm-Nd同位素比值，但两者的初始Nd同位素组成非常相似(图 4)。
表 3 榍石原位Sm-Nd同位素组成Table 3. In-situ Sm-Nd isotope compositions in titanite from granodiorite and mafic microgranular enclave of the Tongshanling pluton暗色包体分析点 147Sm/144Nd 2σ 143Nd/144Nd 2σ εNd(t) 2σ fSm/Nd 2σ T4TNd07 0.3415 0.0099 0.512337 0.000442 -8.9 0.6 0.736 0.050 T4TNd09 0.3894 0.0010 0.512392 0.000095 -8.8 1.9 0.980 0.005 T4TNd10 0.4026 0.0026 0.512675 0.000057 -3.5 1.1 1.047 0.013 T4TNd11 0.2416 0.0048 0.512321 0.000283 -7.1 1.5 0.228 0.024 T4TNd12 0.2399 0.0072 0.512504 0.000744 -3.5 1.5 0.220 0.037 T4TNd13 0.2626 0.0018 0.512346 0.000509 -7.0 0.9 0.335 0.009 花岗闪长岩分析点 147Sm/144Nd 2σ 143Nd/144Nd 2σ εNd(t) 2σ fSm/Nd 2σ T3TNd01 1.4020 0.0098 0.513399 0.000267 -9.9 1.2 6.127 0.050 T5TNd01 0.4059 0.0026 0.512580 0.000166 -5.4 1.2 1.063 0.013 T5TNd02 0.5917 0.0046 0.512761 0.000140 -5.7 0.7 2.008 0.023 T5TNd05 0.3743 0.0047 0.512404 0.000270 -8.2 1.3 0.903 0.024 T3TNd03 0.2850 0.0048 0.512269 0.000693 -9.0 3.5 0.449 0.024 ![]()
图 4 铜山岭花岗闪长岩和暗色包体中榍石Sm-Nd同位素组成，暗色包体和花岗闪长岩中的榍石具有相似的初始Nd同位素组成a—榍石147Sm/144Nd与143Nd/144Nd相关图；b—榍石147Sm/144Nd与εNd(t)相关图；c—榍石εNd(t)加权平均值；d—榍石εNd(t)柱状图。Figure 4. The Sm-Nd isotope compositions of titanite from the Tongshanling granitic pluton. All titanite grains have coincident negative initial Nd isotopic compositions.(a) Plot of 147Sm/144Nd against 143Nd/144Nd for titanite; (b) Plot of 147Sm/144Nd against εNd(t) for titanite; (c) Weighted mean εNd value(t) for titanite; (d) Histogram of εNd(t) value for titanite. Titanite from MME has homogenous Nd isotope compositions. Their present 144Nd/143Nd ranges from 0.512321 to 0.512675, corresponding to εNd(t) value from -3.5 to -8.9 with an average of -7.2±2.4 (N=6). Titanite from granodiorite overall have 144Nd/143Nd ratio ranging from 0.512269 to 0.513399. Their time-corrected initial εNd(t) value vary between -5.4 and -9.9 with an average of -6.9±2.4 (N=5). All titanite grains have negative initial Nd isotopic compositions.4. 榍石地球化学特征对岩石成因的指示
4.1 榍石形成条件及其对岩浆性质的约束
副矿物榍石主量元素通常存在较大的差异，且含有较高的稀土元素和高场强元素，常被应用于判别榍石成因进而揭示寄主岩石的形成条件。因此，元素在榍石晶格位的替代方式得到了地质学者的广泛关注[32]。铜山岭花岗闪长岩及其中暗色包体中榍石普遍含有Al、Fe和F等元素，具有相似的元素变化趋势，Al+Fe与Ti具有明显的负相关关系(图 5a)，暗示Al和Fe主要通过替代八面体位置上的Ti进入榍石，具体的替代方式是(Al，Fe3+)+(F，OH)=Ti4++O2-。然而，在Al+Fe和F的关系图中，Al和Fe超过了(Al，Fe3+)+(F，OH)=Ti4++O2-理论替换线(图 5b)，说明还有额外的Al通过替换进入榍石晶格。铜山岭花岗闪长岩及暗色包体中榍石具有较高的REE含量，很可能还发生了Al+Fe+REE一起替换了Ti位和Ca位，替代方式是(Al，Fe3+)+REE=Ti4++O2-。因此，榍石中微量元素可能同时通过上述两种替代方式进入其晶格中。
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图 5 铜山岭榍石主量元素(a，b)和微量元素比值(c，d，e，f)相关图。榍石中主微量元素受离子半径和电荷控制，不受热液活动的影响，能反映初始岩浆的信息a—Ti和Al+Fe相关图；b—F和Al+Fe相关图；c—Zr/Hf比值和Nb/Ta比值相关图；d—Zr/Hf比值和Y/Ho比值相关图；e—Eu异常Eu/Eu*和Zr/Hf比值相关图；f—Eu异常Eu/Eu*和Ce异常Ce/Ce*相关图。Figure 5. Selected major element variational diagrams (a, b) and trace element ratios variational diagrams (c-f) for titanite. The variation of Zr/Hf, Nb/Ta and Y/Ho ratios of titanite grains range from 21.0 to 31.5, 10.4 to 13.9 and 27.4 to 35.0, respectively. These trace element ratios are consistent with those of normal crust and are not fractionated. Therefore, the trace elements of titanite were completely controlled by ion radius and charge, and not affected by late hydrothermal alteration.元素进入榍石晶格与其形成条件密切相关[33-35]。一般而言，岩浆成因榍石具有低CaO和TiO2含量，高FeO、Na2O和MgO含量，稀土和高场强元素含量较高，稀土元素配分模式呈现出平坦的中-重稀土型式，这些地球化学特征明显有别于热液和变质成因的榍石[36-37, 35]。当有流体参与作用时，矿物中的等价微量元素对Zr-Hf、Nb-Ta和Y-Ho会发生明显分异，偏离地壳岩石的正常范围[38-40]，由于流体作用中，这些元素在矿物和熔体之间的分配不再受电价和离子半径控制[41]。铜山岭花岗闪长岩与铜多金属成矿在时空和成因上密切相关，岩体普遍遭受了强烈的热液蚀变作用[25, 27-28]，热液活动是否对榍石的形成存在影响目前尚不明确。本次研究的榍石具有平坦的中-重稀土元素配分模式(图 3)，与苏鲁大别超高压变质岩中残留岩浆榍石的稀土配分模式完全一致[34]。所有榍石均具有低的CaO、Al2O3和TiO2含量及高的Fe2O3和MgO含量(表 1)，元素的含量也与苏鲁大别超高压变质岩中残留岩浆榍石及三江地区碱性岩中岩浆榍石的元素含量相当[36, 34-35]。这些元素地球化学特征均说明所研究的榍石都属于岩浆成因。而且，铜山岭花岗闪长岩和暗色包体中榍石中Nb/Ta、Zr/Hf和Y/Ho比值变化范围非常小(图 5)，Nb/Ta比值一般小于13.5，Zr/Hf比值一般大于21，Y/Ho比值大于27.4，完全处于离子半径和电价控制的范围。因此，榍石未受热液活动的影响，保持岩浆初始信息，可以用于限定寄主岩石的岩浆性质。
已有实验研究表明，微量元素Zr可以取代榍石中的Ti，其取代量的多少与体系的温度和压力相关，因此，榍石被广泛应用于地质温压条件的估算[42-44]。系统的实验研究证实，榍石中Zr含量与温压条件存在以下关系式[42]：
$$ \begin{aligned} \log \left(\mathrm{Zr}_{\text {榍石 }}\right) & =10.52( \pm 0.10)-7708( \pm 101) / T- \\ & 960( \pm 10) P / T-\log \left(\alpha_{\mathrm{TiO}_2}\right)-\log \left(\alpha_{\mathrm{SiO}_2}\right) \end{aligned} $$ 式中：Zr榍石为榍石中Zr含量(μg/g)；T为温度(K)；P为压力(GPa)，αTiO2和αSiO2分别为Ti和Si的活度。
前人通过角闪石的Al压力计获得了铜山岭花岗闪长岩形成的压力约为2.0GPa[22]。由于铜山岭花岗闪长岩中含有金红石和石英，假定αTiO2和αSiO2均为1，即Ti和Si的活度均为1，根据榍石中Zr含量，计算得到暗色包体中榍石的形成温度为762~956℃，略高于花岗闪长岩中榍石的形成温度743~963℃(表 2)，并明显高于前人通过角闪石、黑云母和斜长石等矿物计算的温度[22]。因此，榍石记录的是初始岩浆温度条件，暗色包体中的榍石形成时间略早于寄主花岗岩闪长中的榍石。根据Chappell等[45]提出的高温和低温花岗岩类分类标准，铜山岭花岗闪长岩属于高温花岗岩类。同时，榍石中Ce和Eu异常通常与岩浆氧化还原状态密切相关，由于不同的氧化还原条件下，Ce可以Ce3+和Ce4+，Eu可以Eu2+和Eu3+存在[46, 35]。还原条件下，Ce主要以低价态的Ce3+形式存在，Ce3+离子半径为1.02Å，与7次配位Ca2+离子半径1.06Å相似，容易置换榍石中的Ca2+进入晶格，从而导致较高的Ce/Ce*比值；而Eu主要以Eu2+形式存在，Eu2+离子半径为1.17 Å，与榍石中7次配位Ca2+离子半径相差较大，难以置换进入榍石晶格，从而具有较低的Eu/Eu*比值[46]。氧化条件下，榍石中Ce/Ce*比值和Eu/Eu*比值则反之。铜山岭花岗闪长岩暗色包体中榍石具有Eu的正异常，而花岗闪长岩中榍石分析点大部分显示出Eu的弱负异常，少量点具有Eu正异常(图 3)，Eu/Eu*比值降低(图 5)，二者的Ce/Ce*比值都大于1.0，且与Eu/Eu*比值变化存在相关性(图 5)。因此，榍石中Eu、Ce异常说明岩浆的初始氧逸度较高，随着岩浆演化，氧逸度有降低趋势。
4.2 榍石Nd同位素对岩浆源区示踪
铜山岭花岗闪长岩具有明显的富钾、高铝特征[47, 28]，全岩初始Sr-Nd同位素变化范围较大，初始87Sr/86Sr变化范围为0.707962~0.710396，εNd(t)值为-2.3~-7.0[47, 28]。基于全岩Sr-Nd同位素和元素特征，前人认为铜山岭花岗闪长岩主要由壳幔物质混合形成或者残留体再造[45-46]。由于花岗质岩石在风化和热液蚀变过程中Sm-Nd同位素体系容易重置，难以限定岩浆源区特征，而榍石抗风化抗热液蚀变能力强，其原位Sm-Nd同位素代表了榍石结晶时岩浆的Nd同位素组成，可以有效地示踪岩浆来源和演化过程物质的变化细节，榍石原位Nd同位素成为了示踪岩浆源区和演化过程一个新的有效手段[15, 14, 35]。铜山岭花岗闪长岩中暗色包体的榍石εNd(t)值为-3.5~-8.9，平均值为-7.2±2.4，花岗闪长岩中榍石εNd(t)值为-5.4~-9.9，平均值为-6.9±2.4，二者变化范围相似(图 4)，而且同一颗粒不同生长环带的Nd同位素组成比较均一，说明在榍石结晶过程中岩浆来源没有发生明显变化，没有明显的岩浆混合特征。
在Nd同位素演化曲线上，铜山岭花岗闪长岩和暗色包体中榍石都具有负的初始Nd同位素组成，靠近华南大陆中下地壳Nd同位素区域，与湘南地区下地壳麻粒岩包体的Nd同位素组成相似[εNd(t)值为-6.59~-7.34][48]，处于元古代麻源群中基性变质岩的范围(图 6)。因此，铜山岭地区的花岗闪长岩很可能由均一的镁铁质中下壳熔融形成。然而，中下地壳什么样的物质能产生富钾、富铝的岩浆？前人通过实验研究发现，角闪岩脱水熔融过程产生的水不饱和岩浆具有高铝、高钾特征，而产生的水饱和岩浆具有高铝、高钙，但亏损铁、镁和钾特征[52-53]，因此，铜山岭岩体很可能由镁铁质角闪岩相中下地壳发生脱水熔融形成的水不饱和岩浆形成。
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图 6 铜山岭榍石Nd同位素演化曲线。铜山岭榍石的初始Nd同位素靠近华南中下地壳Nd同位素演化线，暗示铜山岭花岗闪长质岩石的物质源区是华南中下地壳物质。所有初始同位素比值根据年龄159±1Ma进行校正，华南中下地壳Sr-Nd同位素数据据Yu等[49]和孔华等[48]，元古代中基性变质岩数据据袁忠信等[50]，Nd同位素演化曲线据Chen等[51]Figure 6. Nd isotopic evolution diagrams for titanite from the Tongshanling granodiorite. All titanite grains have negative initial Nd isotopic compositions, which is consistent with the evolution trend of Nd isotopes of the middle-lower continental crust of South China. It is indicated that granodiorites from the Tongshanling pluton were probably formed by the amphibole-dehydration melting of a mafic source in the middle-lower crust beneath South China. All the initial ratios were corrected to 159±1Ma. The Nd isotopic data of middle/lower crust are from Yu, et al[49] and Kong, et al[48]. The data of Proterozoic metamorphic rocks are from Yuan, et al[50]. Nd isotopic evolution diagram was modified after Chen, et al[51].5. 结论
利用LA-ICP-MS和LA-MC-ICP-MS等现代原位分析测试技术，精确测定了铜山岭岩体中镁铁质暗色包体(MME)和寄主花岗闪长岩中副矿物榍石的微量元素和Nd同位素组成，确定了REE与Al和Fe主要通过(Al，Fe3+)+REE=Ti4++O2-方式替换榍石的Ti位和Ca位而进入晶格。榍石中微量元素对Zr/Hf、Nb/Ta、Y/Ho比值变化范围完全受控于离子半径和电荷，不受热液蚀变的影响，保留岩浆初始信息。榍石原位化学组成对示踪岩浆性质和起源具有明显的优势。
榍石微量元素分析结果表明铜山岭花岗闪长质岩浆初始氧逸度高，随岩浆演化有降低趋势。暗色包体和寄主花岗闪长岩中榍石具有均一的、负的Nd同位素组成，变化范围较小，与华南大陆中下地壳Nd同位素演化趋势一致，暗示铜山岭花岗闪长岩很可能由镁铁质角闪岩相中下地壳脱水熔融形成的水不饱和岩浆形成。
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图 1 研究区水系分布及采样点分布
Figure 1. Distribution of water systems and sampling points in the study area.
The red dots in the figure are shallow groundwater sampling points, blue dots are deep sampling points, and the solid blue line is the boundary between shallow water and deep water. According to the spatial structure and distribution of the aquifer and the relative water barrier, the Quaternary water-bearing system is divided into Ⅰ, Ⅱ, Ⅲ and Ⅳ water-bearing groups. As the thickness of the Ⅰ aquifer group is small, most of them are not exploited separately, and the hydraulic connection between the Ⅰ and Ⅱ aquifer groups is close, so it can be regarded as a unified aquifer system, i.e. Ⅰ+Ⅱ aquifer groups, which are "shallow aquifer groups" and are the main exploited layer section for agricultural water. The Ⅲ and Ⅳ aquifer groups are "deep aquifer groups", where the Ⅲ aquifer group is the main mining section for urban life and industrial water in the working area. The direction of groundwater runoff and runoff characteristics of the Ⅰ+Ⅱ aquifer groups and the Ⅲ aquifer group in this area are basically the same, and the direction of groundwater runoff is roughly the same as the topographic tendency and the direction of surface water runoff, i.e. the northern part flows from north west to south east, while the southern part moves from south west to north east.
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图 2 研究区现状地下水化学类型分布图
a—浅层含水层; b—深层含水层。
Figure 2. Distribution of current groundwater chemical types (a. shallow aquifer, b. deep aquifer).
The study area is a single-structure diving area in front of the mountain, with coarse aquifer particles, abundant groundwater recharge, strong alternating circulation, and simple water chemistry type, mainly bicarbonate calcium-magnesium (HCO3-Ca-Mg) type water with low mineralization. Along the direction of groundwater runoff, the water chemistry type changes from HCO3-Ca-Mg(Ca) type in piedmont plain, through HCO3-Mg-Ca, HCO3-Mg-Ca-Na, HCO3-Na-Mg-Ca to HCO3-Cl-Na-Ca, HCO3-Cl-SO4-Na to Cl(SO4)-Na in the central alluvial plain. The distribution of chemical characteristics of deep groundwater is generally controlled by hydrogeological conditions, and is regularly distributed from the piedmont plain to the central plain; compared with shallow groundwater, the chemical type of deep groundwater is relatively simple, from the top of the piedmont plainalluvial floodplain fan to the bottom of the alluvial floodplain fan, and the main anion in most parts of the plain is HCO3 type; the cations of deep groundwater are relatively complex, and the zonation is more obvious: from the piedmont plain to the bottom of the alluvial floodplain fan, the cations change to HCO3-Cl-Na and HCO3-Cl-SO4-Na. The deep groundwater cations are relatively more complex and more obvious: from the piedmont plain to the bottom of the alluvial fan, the cations transition from Ca, Ca-Mg, Mg-Ca, Na-Mg-Ca (Mg-Ca-Na) type to Na-Ca, Na type water.
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图 3 地下水样品(a, b)吉布斯图; (c)Mg2+/Na+与Ca2+/Na+比值关系图; (d)HCO3-/Na+与Ca2+/Na+比值关系图
Figure 3. (a, b) Gibbs diagrams of groundwater samples; (c) Ratio relationship chart of Mg2+/Na+ and Ca2+/Na+; (d) Ratio relationship charts of HCO3-/Na+ and Ca2+/Na+.
Most of the water sample points in the TDS vs. Na+/(Na++Ca2+) diagram are located in the middle of the diagram, and a few are distributed outside the box, and the points in the TDS vs. Cl-/(Cl-+HCO3-) diagram are all distributed inside the box. The shallow aquifer groups are basically located within the water-rock interaction area, and individual points show some influence of evaporation concentration. The deep aquifer groups are all subject to water-rock interaction and is less affected by evaporation and atmospheric precipitation. The analysis results show that the milligram equivalent concentration ratio of (Ca2++Mg2+)+(HCO3-+SO42-) to Na++K+-Cl- is close to-1, indicating that the cation exchange is more significant. Groundwater samples in the study area are mostly distributed near the end elements of silicate minerals, indicating that weathering of silicate minerals is the main hydrogeochemical control factor in the study area.
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图 4 研究区地下水样品主要离子比值图
Figure 4. Major ion ratios of groundwater samples.
Most of the groundwater samples exhibit Cl-/(Na++K+) < 1, indicating that silicate mineral dissolution (such as potassium feldspar and sodium feldspar) is the main source of excess Na+ and K+, except for rock salt in dissolved state. The HCO3-/(Ca2++Mg2+) of the shallow aquifer groups samples is basically<1, showing excess Ca2+ and Mg2+, indicating other sources of Ca2+ or Mg2+, while the (HCO3-+SO42-)/(Ca2++Mg2+) of the shallow aquifer groups is distributed above and below the 1∶1 line on both sides, suggesting that evaporite minerals (e.g. gypsum) may also be an important source of Ca2+ for the shallow aquifer groups. Both HCO3-/(Ca2++Mg2+) and (HCO3-+SO42-)/(Ca2++Mg2+) of the deep aquifer groups are located above the 1∶1 line, with excess HCO3- implying silicate dissolution dominance, or the presence of cation exchange, leading to lower Ca2+ content. The water samples of the shallow and deep aquifer groups are mainly distributed below the (Cl-+SO42-)/(HCO3-)=1∶1 line, indicating that their chemical components are subject to great dissolution by carbonate rocks
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图 5 地下水样SO42-/Ca2+与NO3-/Ca2+的比值关系图
Figure 5. Relationship between SO42-/Ca2+ and NO3-/Ca2+ in groundwater samples.
The SO42-/Ca2+ to NO3-/Ca2+ ratios of the deep aquifer groups were all greater than 1, except for the 240m water well in the north of Erlangmiao Village, Dingzhou City, Hebei Province, which was less than 1. This indicates that the deep aquifer groups are basically affected by industrial and mining activities, but not by agricultural activities and residential sewage. In the shallow aquifer groups, the SO42-/Ca2+ to NO3-/Ca2+ ratio of 27 water samples is greater than 1, and the SO42-/Ca2+ to NO3-/Ca2+ ratio of 20 water samples is less than 1, which means that the shallow aquifer groups are partly influenced by industrial and mining activities, and partly influenced by agricultural activities and domestic sewage of residents
表 1 研究区地下水水化学参数统计
Table 1 Statistical results of groundwater hydrochemical parameters in the study area
地下水类型 特征值 pH TDS
(mg/L)K+
(mg/L)Na+
(mg/L)Ca2+
(mg/L)Mg2+
(mg/L)Cl-
(mg/L)SO42-
(mg/L)HCO3-
(mg/L)NO3-
(mg/L)浅层含水层组 最小值 7.35 254.10 0.26 7.61 12.88 14.44 5.26 6.48 177.30 0.20 最大值 8.92 6015.00 2.69 1393.00 194.00 341.40 693.30 3091.00 558.30 298.40 平均值 7.90 664.14 1.14 87.49 76.15 47.60 70.66 162.27 333.28 28.78 标准偏差 0.35 907.40 0.66 218.22 39.03 51.66 120.67 483.46 90.21 48.99 变异系数 0.04 1.37 0.58 2.49 0.51 1.09 1.71 2.98 0.27 1.70 深层含水层组 最小值 7.40 197.10 0.30 8.26 4.43 1.12 1.75 4.99 155.60 0.71 最大值 8.80 691.40 2.61 189.80 58.29 20.82 86.22 255.70 305.10 17.46 平均值 8.03 278.58 1.46 56.52 28.98 10.60 15.37 27.41 221.23 4.55 标准偏差 0.38 88.95 0.65 37.97 14.91 5.54 19.14 43.89 39.67 4.05 变异系数 0.05 0.32 0.45 0.67 0.51 0.52 1.25 1.60 0.18 0.89 Note: The test results showed that the largest deviation was in the water sample from Hanbao Village, Liu Lizhuang Town, Anxin County, Baoding City, Hebei Province, which was from the shallow aquifer groups, and the maximum TDS reached 6015.00mg/L. The TDS of the shallow aquifer groups ranged from 254.10 to 6015.00mg/L, with an average of 664.14mg/L, with a large coefficient of variation and a large variation in TDS, indicating that the shallow aquifer groups were affected by meteorological and human factors. The TDS of the deep aquifer group ranged from 197.10 to 691.40mg/L, with an average of 278.58mg/L, and the coefficient of variation was small, indicating that the groundwater of the deep aquifer groups was less affected by meteorological and human activities than that of the shallow aquifer groups. The pH values of the shallow and deep aquifer groups in the study area were not significantly different (7.35-8.92) and were alkaline. The NO3-maximum value of 298.40mg/L and the SO42-maximum value of 3091.00mg/L in the shallow aquifer groups, but the average value is not significant, indicating that the shallow aquifer groups have caused local nitrate and sulfate pollution due to agricultural activities and other influences. 
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