东昆仑祁漫塔格地区晚三叠世正长花岗岩岩石成因及构造意义     

张明玉  丰成友  王辉  李大新  瞿泓滢  刘建楠  周建厚 《岩石矿物学杂志》2018,37(2):197-210

青海省东昆仑祁漫塔格地区肯德可克矿区外围东部发育一正长花岗岩体,主要矿物组合为正长石(50%~60%)+石英(20%~30%)+斜长石(10%~20%)+黑云母(1%~5%)。其LA-ICP-MS锆石U-Pb加权平均年龄为217.9±1.7 Ma(MSWD=0.74,n=20),形成时代为晚三叠世,与祁漫塔格地区铁多金属矿床基本同时形成。岩石地球化学组成具有高硅(Si O2=74.53%~75.28%)、富碱(K2O+Na2O=8.81%~8.95%)、富铁贫镁(Fe OT/Mg O=18.02~31.48)的特征,并具强烈的负Eu异常(δEu=0.04~0.05),富集Rb、Th、U、K、Ga,亏损Sr、Ba、Ta、P、Ti,显示其为准铝质A型花岗岩。正长花岗岩锆石εHf(t)为2.0~12.4,平均6.4,显示其源区具有壳幔混合作用的特征,壳幔物质交换为区内铁多金属矿化提供了大量成矿物质。该正长花岗岩属A2型花岗岩,暗示其形成于造山后的伸展构造体制,反映了祁漫塔格地区晚华力西-印支期造山旋回于晚三叠世由造山后期转为伸展阶段。  相似文献   

The Late Triassic I–Type Granites from the Longmu Co–Shuanghu Suture Zone in the interior of Tibetan Plateau, China: Petrogenesis and Implication for Slab Break–Off     

ZHAO Zhen  WU Zhenhan  LU Lu  YU Junqiu  WU Yanjun 《《地质学报》英文版》2018,92(3):935-951

The Jiangaidarina granitic mass(JM) is an important part of the magmatic belt in Longmu CoShuanghu Suture Zone(LSSZ) in the central Tibetan Plateau. An integrated research involving wholerock geochemistry, zircon LA-ICP-MS U-Pb ages and Hf isotopic compositions was carried out to define the timing, genesis and tectonic setting of the JM. Zircon LA-ICP-MS U-Pb ages have been obtained ranging from 210 to 215 Ma, rather than the Early Jurassic as previously thought. Fifteen granite samples contain hornblendes and show a negative correlation between P_2 O_5 and SiO_2, indicating that the JM is an I-type granite. All the granites are enriched in LREE relative to HREE, with negative Eu anomalies(Eu/Eu*=0.56-0.81), and have similar trace elements patterns, with depletion of Ba, Nb, Sr and P. These suggest that the JM was fractionated, and this is also proved by the characteristic of negative correlations between oxide elements(TiO_2, MgO, FeOt, MnO, CaO) and SiO_2. Almost all ε_(Hf)(t) values of the granites are between-10.3 and-5.8, implying that the JM has a crustal source intimately related with the South Qiangtang Block(SQB), except for one(+10.2), showing a minor contribution from mantle source.Moreover, relatively low Na_2 O/K_2 O ratios(0.42-0.93) and high A/CNK values(0.91-1.50) reflect that the JM was predominately derived from the medium-high potassium basaltic crust, interacted with greywacke. Our new geochemical data and geochronological results imply that the Late Triassic magmas were generated in a post-collisional tectonic setting, probably caused by slab break-off of the Longmu Co-Shuanghu Tethyan Ocean(LSTO). This mechanism caused the asthenosphere upwelling, formed extension setting, offered an enormous amount of heat, and provided favorable conditions for emplacement of voluminous felsic magmas. Furthermore, the LSTO could be completely closed during the Middle Triassic, succeed by continental collision and later the slab broke off in the Late Triassic.  相似文献   

北淮阳东段西汤池岩体地球化学特征、锆石U-Pb定年及成因     

杨义忠  王徽  蔡杨 《江苏地质》2018,42(2):187-196

西汤池岩体位于安徽北淮阳地区舒城县西汤池一带。西汤池似斑状二长花岗岩具高硅、富碱质特征,为铝饱和碱性系列岩石。稀土元素含量中等,(La/Yb)_N与HREE/LREE值较高,重稀土相对轻稀土亏损明显,Eu呈弱负异常,属轻稀土富集型。大离子亲石元素(Rb、K、La、Nd等)明显富集,而高场强元素(Nb、Ta、P、Ti等)亏损。通过LA-ICP-MS锆石U-Pb定年,获得西汤池二长花岗岩~(206)Pb/~(238)U年龄为(125.5±1.6)Ma,为早白垩世岩浆活动的产物。基于前人关于北淮阳地区区域地质背景方面的研究成果和本次地球化学构造环境判别方面的研究,认为西汤池二长花岗岩属A_1型花岗岩,形成于后碰撞的伸展构造环境。  相似文献   

广东良口黄田埔高分异Ⅰ型花岗岩地球化学特征及大地构造意义     

苏扣林 《江苏地质》2018,42(2):197-205

广州从化区良口亚髻山霞石正长岩为典型岩石遗迹,在碱性岩体野外填图研究过程中,新发现东侧分布有黄田埔高分异花岗岩,形成时间约(146±13)Ma,为晚侏罗世岩浆活动产物。元素地球化学特征显示硅高、钾富、分异指数高、Rb/Sr比值高以及Rb/Ba、Nb/Ta、Zr/Hf、TFeO/MgO比值低;稀土元素ΣREE平均值为248 g/t,ΣCe/ΣYb平均值为2.34,δEu(0.16)负异常明显;Ga(×10~4)/Al比值较低(平均值为3.47),Zr+Nb+Ce+Y含量(平均值为264g/t)低于A型花岗岩(350 g/t);I(Sr)值为0.691 8~0.712 8,平均值为0.708 1;ε_(Nd)(t)值为-3.5~-10.0,平均值为-6.7。元素地球化学、同位素地球化学和同位素年代学综合研究结果表明,岩株的形成可能与上地幔岩浆分异有关,为高分异Ⅰ型花岗岩。  相似文献   

内蒙古阿拉善右旗大山口地区黑云母花岗岩地球化学特征及成因          下载免费PDF全文

李伟  赵飞  熊文勃  李延涛  黄瀚清 《甘肃地质》2018,(2):29-35

内蒙古自治区阿拉善右旗大山口地区发育有大面积侵入岩,主要为华力西中晚期和印支期酸性侵入岩体及各类脉岩。本次运用LA-ICP-MS锆石U-Pb测年方法获得黑云母花岗岩的成岩年龄为229.5±5.6 Ma,属晚三叠世,大山口黑云母花岗岩SiO_2含量68.89%～71.04%,相对富钾贫钠;A/NKC介于0.89～1.05,强烈富集强不相容元素,亏损高场强元素Na、Ta、Ti、P,Eu异常不明显,HREE呈近平坦型分布。通过黑云母花岗岩的成因研究和构造环境判别分析,认为大山口黑云母花岗岩为加厚的中下地壳物质拆沉进入地幔加热并发生部分熔融,且熔体可能与地幔基性熔体发生一定程度的混合作用后上升形成的花岗岩,形成于晚三叠世后碰撞伸展垮塌的构造环境。  相似文献   

花岗岩定量分类方法及与成矿空间相关关系分析 ——甘肃省西秦岭地区为例          下载免费PDF全文

王晓伟  罗建民  王玉玺  张琪  宋秉田  杨忠明  赵彦庆 《甘肃地质》2018,(1):26-31

以Q型系统聚类分析(以组内连接为聚类方法,相关性为计算模型)和判别分析交替使用的方法,对甘肃省西秦岭地区花岗岩样本中的11个氧化物测试数据进行定量处理,构建起"甘肃省西秦岭地区花岗岩(氧化物)定量分类系列模型",将西秦岭地区花岗岩分为3大类共8小类。分类结果偏重于找矿分类,依据其与西秦岭地区铜矿、铅锌矿、金矿等依据空间关系(距离岩体3 km以内),寻找"成矿相关岩体",确定找矿靶区。  相似文献   

张广才岭南段两个侏罗纪花岗岩体的地球化学特征及其地质意义     

句高  梁一鸿  孙晓  周静 《世界地质》2018,37(2):374-384

通过LA-ICP-MS锆石U-Pb定年和岩石化学分析,研究了张广才岭南段上营北岩体和帽儿山岩体的形成年代,地球化学特征和形成环境。上营北岩体为中粗粒钾长花岗岩,帽儿山岩体为中细粒黑云母钾长花岗岩。上营北岩体的加权平均年龄为178.9±2.7 Ma,帽儿山岩体为183.7±2.4 Ma,均为早侏罗世侵入岩。上营北岩体和帽儿山岩体主量元素都具有Si O_2和K_2O含量较高,Ti O_2、Mg O、Ca O含量较低,TFe O/Mg O值较高的特点;上营北岩体A/CNK=0.98~1.08,里特曼指数σ=1.51~2.66;帽儿山岩体含铝指数A/CNK=1.00~1.01,里特曼指数σ=2.12~2.36。上营北岩体稀土元素配分模式为海鸥型,轻重稀土分馏不明显;帽儿山岩体稀土元素配分模式为右倾型,轻稀土较重稀土富集;两个岩体均富集Rb、K,Ba、Nb、Ta、Sr、Ti、P、Ho、Er、U、Eu等元素出现不同程度的亏损。地球化学特征分析显示上营北岩体和帽儿山岩体均为A_2型花岗岩,为后造山型花岗岩,形成于兴蒙造山带后造山的伸展环境。  相似文献   

西藏双湖地区南措铜金矿区花岗闪长岩锆石U-Pb年代学、岩石地球化学及成因     

王启  孙丰月  王琳琳  王力  张志颖 《世界地质》2018,37(2):399-408

对南措铜金矿区与成矿相关的黑云母花岗闪长岩体进行了岩相学、锆石U-Pb年代学、岩石地球化学等方面的研究。结果表明:该岩体年龄为153.40±0.67 Ma,属晚侏罗世。岩石为准铝质-过铝质岩石,属钙碱性系列。LaN/YbN=9.31~12.65,轻重稀土元素分馏明显,δEu=1.21~1.66,Eu表现为正异常;样品微量元素表现为相对富集大离子亲石元素(LILE)K、与高场强元素(HFSE)Sr、Zr,而亏损高场强元素(HFSE)U、Nb、Ce、Nd、P的特征。岩体具有I型花岗岩特征。样品Zr/Hf值为42.23~45.82,平均值为44.2;Rb/Sr比值为0.07~0.19,平均值为0.13;Nd/Th值为1.65~2.18,平均为1.99,具壳源岩浆的特征,并有地幔物质混入。样品的Mg#值为49.80~57.22,Sr值为443.3~874.9,Yb值为0.80~1.39,Y值为8.96~16.60,Na2O/K2O2(2.18~2.97),为洋壳型埃达克岩,并在上升过程中可能有少量地幔楔物质混入。结合前人研究成果认为,该花岗闪长岩形成于晚侏罗世班公湖—怒江洋盆向北俯冲的火山弧环境。  相似文献   

Origin of abundant moonmilk deposits in a subsurface granitic environment     

《Sedimentology》2018,65(5):1482-1503

Subsurface granitic environments are scarce and poorly investigated. A multi‐disciplinary approach was used to characterize the abundant moonmilk deposits and associated microbial communities coating the granite walls of the 16th Century Paranhos spring water tunnel in Porto city (north‐west Portugal). It is possible that this study is the first record of moonmilk in an urban subsurface granitic environment. The morphology and texture, mineralogical composition, stable isotope composition and microbial diversity of moonmilk deposits have been studied to infer the processes of moonmilk formation. These whitish secondary mineral deposits are composed of very fine needle‐fibre calcite crystals with different morphologies and density. Calcified filaments of fungal hyphae or bacteria were distinguished by field emission scanning electron microscopy. Stable isotope analysis revealed a meteoric origin of the needle‐fibre calcite, with an important contribution of atmospheric CO ₂, soil respiration and from weathering of Ca‐bearing minerals. The DNA ‐based analyses revealed the presence of micro‐organisms related to urban contamination, including Actinobacteria, mainly represented by Pseudonocardia hispaniensis , Thaumarchaeota and Ascomycota, dominated by Cladosporium . This microbial composition is consistent with groundwater pollution and contamination sources of the overlying urban area, including garages, petrol stations and wastewater pipeline leakage, showing that the Paranhos tunnel is greatly perturbed by anthropogenic activities. Whether the identified micro‐organisms are involved in the formation of the needle‐fibre calcite or not is difficult to demonstrate, but this study evidenced both abiotic and biogenic genesis for the calcite moonmilk in this subsurface granitic environment.  相似文献   

Study of late-Mesozoic magmatic rocks and their related copper-gold-polymetallic deposits in the Guichi ore-cluster district,Lower Yangtze River Metallogenic Belt,East China     

Huangling Gu  Zhangxing Nie  Jianghong Deng  Liuan Duan  Qing Hu 《International Geology Review》2018,60(11-14):1404-1434

ABSTRACT

The Guichi ore-cluster district in the Lower Yangtze River Metallogenic Belt hosts extensive Cu–Au–Mo polymetallic deposits including the Tongshan Cu–Mo, Paodaoling Au, Matou Cu–Mo, Anzishan Cu–Mo, Guilinzheng Mo and Zhaceqiao Au deposits, mostly associated with the late Mesozoic magmatic rocks, which has been drawn to attention of study and exploration. However, the metallogenic relationship between magmatic rocks and the Cu–Au-polymetallic deposits is not well constrained. In this study, we report new zircon U–Pb ages, Hf isotopic, and geochemical data for the ore-bearing intrusions of Guichi region. LA-ICP-MS U–Pb ages for the Anzishan quartz diorite porphyrite is 143.9 ± 1.0 Ma. Integrated with previous geochronological data, these late Mesozoic magmatic rocks can be subdivided into two stages of magmatic activities. The first stage (150–132 Ma) is characterized by high-K calc-alkaline intrusions closely associated with Cu–Au polymetallic ore deposits. Whereas, the second stage (130–125 Ma) produced granites and syenites and is mainly characterized by shoshonite series that are related to Mo–Cu mineralization. The first stage of magmatic rocks is considered to be formed by partial melting of subducted Palaeo-Pacific Plate, assimilated with Yangtze lower crust and remelting Meso-Neoproterozoic crust/sediments. The second stage of magmatism is originated from partial melting of Mesoproterozoic-Neoproterozoic crust, mixed with juvenile crustal materials. The depression cross to the uplift zone of the Jiangnan Ancient Continent forms a gradual transition relation, and the hydrothermal mineralization composite with two stages have certain characteristics along the regional fault (Gaotan Fault). Guichi region results from two episodes of magmatism probably related to tectonic transition from subduction of Palaeo-Pacific Plate to back-arc extensional setting between 150 and 125 Ma, which lead to the Mesozoic large-scale polymetallic mineralization events in southeast China.  相似文献