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1.
内蒙古赵井沟铌钽多金属矿是近年来取得较大找矿进展的大型稀有金属矿床,初步探明铌钽氧化物储量超过8200吨,前人对其矿床地质特征已有初步研究,但其成矿时代尚未精确厘定。本文以赵井沟铌钽多金属矿区内天河石花岗伟晶岩脉中的白云母为研究对象,利用~(40)Ar-~(39)Ar同位素年代学方法,以确定其成矿时代。研究发现矿区内铌钽矿化主要赋存在碱长花岗岩、碱长花岗细晶岩、云英岩和天河石花岗伟晶岩中,且铌钽矿物与白云母同时形成,有重要的共生关系,故本次研究获得的白云母坪年龄123.57±0.66 Ma和等时线年龄124.0±2.0 Ma具有地质意义,可代表成矿年龄。这一成果表明赵井沟铌钽多金属矿床形成于燕山晚期(至少延续至早白垩世),与前人获得的锆石年龄有较大差异,这对分析其矿床成因有重要意义。同时,结合区域地质资料,本文认为华北地台北缘内蒙古地轴中部在燕山运动的晚期存在一次重要的稀有金属成矿事件。  相似文献   

2.
内蒙古武川县赵井沟铌钽矿是新近取得勘查突破的一例大型铌钽矿床.矿体赋存岩石为含天河石钠长花岗岩,其次为花岗细晶岩、云英岩及天河石花岗伟晶岩.运用LA-MC-ICP-MS法对矿区钠长花岗(细晶)岩脉、正长花岗岩中的独居石、锆石进行了U-Pb同位素年龄测定,同时对石英-黑云母脉中的黑云母进行了40Ar-39Ar定年.4件独居石的LA-MC-ICP-MS U-Pb年龄分别为124±2 Ma(MSWD=2.9,n=27)、124±3 Ma(MSWD=2.0,n=46)、121±1 Ma(MSWD=3.3,n=43)和124±2 Ma(MSWD=3.2,n=12),1件锆石的LA-MC-ICP-MS U-Pb年龄为125±1 Ma(MSWD=1.6,n=18);黑云母40Ar-39Ar坪年龄为133.84±0.79 Ma(MSWD=3.31),40Ar/36Ar-39Ar/36Ar等时线年龄为134.55±0.79 Ma(MSWD=1.93),反等时线年龄为134.58±0.80 Ma(MSWD=1.99),这些年龄限定赵井沟铌钽矿形成于早白垩世.综合分析表明,燕山期是内蒙古地区重要的铌钽成矿期,赵井沟铌钽矿是燕山期伸展体制下构造岩浆活动的产物.   相似文献   

3.
内蒙古武川县赵井沟钽铌多金属矿床是近年来华北板块北缘新发现的大型稀有金属矿床,然而前人对该矿床的形成时代以及构造背景存在较大争议。本文以与成矿关系密切的天河石化花岗岩和钠长石化花岗岩为研究对象,开展了岩相学、岩石地球化学、岩浆和热液锆石LA-ICP-MS U-Pb年代学及Lu-Hf同位素的研究,探讨了岩浆源区性质和成岩成矿的构造环境。研究结果表明,钠长石化花岗岩中热液锆石加权平均年龄为118.9 ± 1.8Ma;天河石化花岗岩岩浆锆石年龄为116±2Ma,热液锆石加权平均年龄结果为112.8±2.2Ma;热液锆石年龄略晚于岩浆锆石,说明热液锆石是在岩浆演化最后的熔体-流体相互作用阶段形成的。天河石化花岗岩和钠长石化花岗岩在主量元素上富硅、碱和铝,贫镁、钙、铁、钛和磷;在微量元素上均富集Rb、Th、U、Nb、Ta、Hf,强烈亏损Ba、Sr;其轻重稀土元素分异不明显,具有强烈的Eu负异常。岩体中发育以钠长石化,天河石化为主的蚀变,稀土元素呈现似M型"四分组"效应,Nb/Ta小于5,表明天河石化、钠长石化花岗岩经历了熔体和流体的相互作用。Lu-Hf同位素分析结果显示较负的ε_(Hf)(t)值(天河石化花岗岩:-10.91~-8.17;钠长石化花岗岩:-10.98~-9.19),其对应的两阶段模式年龄t_(DM2)分别为1689~1867Ma和1762~1871Ma,暗示富含Nb、Ta的中元古代渣尔泰山群、白云鄂博群为其岩浆源岩或提供了成岩、成矿物质。燕山晚期伸展的构造背景下,玄武质岩浆高位底侵富铌钽地壳造成减压部分熔融而形成的岩浆,岩浆在F、Cl等挥发组分的作用下发生结晶分异作用,造成铌、钽等成矿物质初步富集,并在岩浆晚期先后发生了以钠长石化、天河石化为代表的两期自交代作用及Nb、Ta的矿化作用,形成赵井沟钽铌多金属稀有矿床,该矿床为岩浆结晶分异-热液自交代作用混合成因。  相似文献   

4.
粤北大宝山矿床矿区出露船肚和大宝山矿化岩体。本文分析了两个岩体矿物组成特征和锆石LA-ICP-MS U-Pb年龄。船肚岩体为似斑状结构,块状构造,主要由似斑状花岗岩、似斑状二长花岗岩及似斑状花岗闪长岩等组成,和云英岩型及矽卡岩型Mo-W矿化紧密共生。大宝山岩体为斑状结构,块状构造,主要由碱长花岗斑岩、普通花岗斑岩、二长花岗斑岩及花岗闪长斑岩组成,矿物组成和船肚岩体的基本相同,和细脉浸染状Mo-W矿化紧密共生。船肚似斑状二长花岗岩和大宝山二长花岗斑岩锆石LA-ICP-MS U-Pb年龄分别为162.1±1.6 Ma,MSWD=2.72和165.8±2.0 Ma,MSWD=1.38。据船肚和大宝山岩体矿物组成基本相同、岩石结构不同及两者锆石Th/U比值不同和U-Pb年龄存在约4 Ma左右时差,提出大宝山矿区在燕山期发生了两阶段岩浆成矿事件,第一阶段岩浆成矿事件发生在166 Ma左右,形成大宝山斑岩型矿床,第二阶段岩浆成矿的形成时间约为162 Ma左右,形成船肚似斑状二长花岗岩及与岩体紧密共生的矽卡岩型和云英岩型矿化;大宝山斑岩体和船肚似斑状岩体是同一岩浆房两次脉动侵入形成的。  相似文献   

5.
黑龙江鹿鸣钼矿床地质特征及成矿年龄   总被引:7,自引:0,他引:7  
邵军  杨宏智  贾斌  彭明生 《矿床地质》2012,31(6):1301-1310
黑龙江鹿鸣钼矿床位于小兴安岭-张广才岭多金属成矿带翠宏山-二股成矿亚带中南段。矿化发生在花岗岩体内,矿石为石英细脉浸染状的花岗斑岩、二长花岗岩,围岩蚀变具有岩浆热液蚀变的分带特征。成矿作用与花岗岩浆侵入活动密切相关,矿床成因类型为斑岩型。岩石地球化学研究表明,矿区花岗斑岩、二长花岗岩具有同一岩浆来源,属于"A"型花岗岩,是在伸展大地构造环境背景下岩浆侵入形成的岩体。通过锆石SHRIMP U-Pb年龄测定,获得二长花岗岩年龄为(201.1±3.90) Ma和(176.2±4.3) Ma,获得花岗斑岩年龄为(182.3±4.0) Ma,确定鹿鸣钼矿床的成矿年龄在182~176 Ma之间,成矿时代为燕山早期。  相似文献   

6.
福建大坪花岗斑岩体位于永定县城南部的大石凹—蓝地火山喷发盆地,具斑状结构,基质呈霏细结构、细-微粒结构。文章运用电子探针(EMPA)和激光剥蚀电感耦合等离子体质谱仪(LA-ICP-MS)等技术,对大坪岩体ZK10001钻孔中不同深度的岩石样品进行了矿物和岩石化学分析。分析结果表明,大坪岩体岩性为黑鳞云母碱长花岗斑岩,属于过铝质钙碱性花岗岩,具有较高的分异演化程度,Nb2O5和Ta2O5含量达到了花岗岩型稀有金属矿床的工业品位。铌钽矿物主要与黄玉、萤石的集合体呈稀疏浸染状、星点状产于基质间隙内,其次以星点状存在于石英和长石斑晶中。矿石矿物赋存特征与宜春钽铌矿床类似,可能具有一定的可选性和经济价值。大坪岩体的铌钽富集特征不同于斑岩型铜、钼矿床,与花岗岩型铌钽矿床也存在较大的差别,铌钽的富集过程经历了深部斑晶阶段和浅部基质阶段两阶段岩浆结晶分异作用,F等挥发分促进了铌钽在结晶残余岩浆中富集,在基质间隙间沉淀。大坪矿化岩体的发现暗示斑岩型铌钽矿床存在的可能性。  相似文献   

7.
铌钽矿研究进展和攀西地区铌钽矿成因初探   总被引:12,自引:3,他引:9  
王汾连  赵太平  陈伟 《矿床地质》2012,31(2):293-308
铌钽矿主要产出类型包括伟晶岩型、富Li-F花岗岩型、碱性侵入岩型、碳酸岩型及冲积砂矿型。前2种类型以钽为主,后3种则以铌占主导。铌和钽大多以铌钽独立矿物(铌铁矿、钽铁矿、细晶石、烧绿石等)呈浸染状分布于含矿岩石中,也有部分以类质同象的形式分布于云母、榍石、霓石、钛铁矿等矿物中。关于铌钽矿的富集机制,一些学者认为可由富F-Na和稀有金属(铌、钽等)的花岗质熔体经结晶分异作用形成;另一些学者则根据铌钽矿化与岩石的钠长石化、锂云母化等紧密共生的特点,认为铌钽的富集是岩浆期后流体交代早期形成的花岗岩所致。攀西(攀枝花-西昌)地区的铌钽矿床(化)基本上都是沿着断裂带分布,矿体赋存于印支期碱性岩脉(碱性正长伟晶岩)中,有少数存在于碱性花岗岩中,与区域上邻近的正长岩体及花岗岩体关系密切。其矿石矿物主要为烧绿石、褐钇铌矿等。初步推断,攀西地区的铌钽矿与二叠纪地幔柱活动有关。碱性的正长岩体及花岗岩体与广泛分布的峨眉山玄武岩、辉长岩均是地幔柱岩浆活动的产物,长英质岩体(包括正长岩体和花岗岩体)是富铌钽岩石的母岩体。碱性伟晶岩脉(如炉库和白草地区)是碱性岩浆逐步演化的产物,含矿的碱性花岗岩是花岗质岩浆分异演化的结果。此外,在该地区的铌钽矿床中,铌钽矿物几乎都富集在钠长石化发育的地段,说明后期的热液交代对铌钽的富集也起到了一定作用。因此,攀西地区铌钽的富集是岩浆结晶分异和岩浆期后热液交代共同作用的结果。  相似文献   

8.
通过对云南省腾冲市小龙河地区古永复式岩体原生构造、蚀变和矿化的类比、对比,结合构造地球化学、年代学研究和初步预查,新发现与之有关的热液弥散状蚀变、侵入角砾岩和大型稀土金属矿体,并伴生稀有金属铷(Rb)、铌(Nb)和稀散金属镓(Ga),存在晚期同岩浆断裂。花岗蚀变岩独居石、锆石和未蚀变黑云钾长花岗岩锡石、锆石U-Pb年龄分别为(75.61±0.47)Ma、(75.68±0.72)Ma、(76.3±3.2)Ma和(77.29±0.54)Ma,年龄相近,反映它们可能是岩浆晚期同构造活动的产物。  相似文献   

9.
戴盼  吴胜华  丁成武 《岩石学报》2018,34(9):2598-2614
王坞斑岩型Mo-Cu矿床位于北武夷地区,地处钦杭构造岩浆成矿带北段。目前钻孔信息显示,该矿床的矿体主要由网脉状石英-辉钼矿-黄铜矿矿石组成,也含少量的浸染状和细脉浸染状Cu-Mo矿化,主要的蚀变作用包括硅化、绢英岩化和绿泥石化。矿区内隐伏燕山期的花岗斑岩脉及石英闪长玢岩脉。本文对该矿床的花岗斑岩进行了LA-ICP-MS锆石U-Pb测年,对主要矿石类型(网脉状石英-辉钼矿矿石)中的辉钼矿进行了Re-Os同位素测年。结果显示,花岗斑岩的锆石U-Pb年龄为136. 7±2. 2Ma,辉钼矿的Re-Os同位素模式年龄为132. 6±1. 8Ma~134. 5±2. 0Ma,加权平均值为133. 7±0. 94Ma,对应的Re-Os等时线年龄为134. 8±2. 1Ma。花岗斑岩的锆石U-Pb年龄和辉钼矿的Re-Os年龄在误差范围内基本一致,且花岗斑岩和矿体之间具有密切的空间关系,指示王坞Mo-Cu矿床的Mo矿化可能与矿区内的花岗斑岩存在密切的成因联系。北武夷地区主要的斑岩-矽卡岩和岩浆热液脉型Cu-Mo多金属矿床的成岩成矿年龄数据的统计结果显示,北武夷地区的Cu-Mo-Pb-ZnAg成矿作用主要集中在燕山期,可被划分为150~165Ma和140~125Ma两个阶段。结合区域构造背景资料,王坞Mo-Cu矿床形成于早白垩纪伸展的构造背景下。  相似文献   

10.
内蒙锡林浩特石灰窑铌钽矿床是我国最近发现的一处大型稀有金属矿床.通过详细分析该矿床地质特征、控矿因素及其成因,主要获得如下认识:1)该矿床矿石属于碱性花岗岩系列;2)矿石中的铌钽矿物主要包括铌锰矿、铌钽铁矿、铌钽锰矿、锡锰钽矿和细晶石;3)该矿床可能是前期花岗岩岩浆结晶和后期热液交代综合作用的产物,热液交代是铌钽铷主要成矿阶段;4)从铌钽铷矿化成因和富集规律可知,金属矿化与钠长石化、云英岩化密切相关,且矿体赋存于蚀变花岗岩中,分布上严格受北东向构造的控制,因此,钠长石化、云英岩化的花岗岩是寻找上述稀有金属的直接找矿标志,同时石灰窑燕山早期花岗岩出露地段很可能是寻找稀有金属矿的有希望地区;5)围绕石灰窑花岗岩主岩体周围寻找晚期侵位的钠长石化花岗岩小岩体的隆起和浅部部位,是寻找钽铌铷矿的基本思路.  相似文献   

11.
Collisional granitoid magmatism caused by the Early Neoproterozoic orogeny in the west of the Siberian craton is considered. New data on the petrogeochemical composition, U-Pb (SHRIMP II), Ar-Ar, and Sm-Nd isotopic ages of the Middle Tyrada granitoid massif in the northwestern Yenisei Ridge are presented. Plagiogranites, granodiorites, and quartz diorites of the massif are of calcareous and calc-alkalic composition. The elevated alumina contents and presence of accessory garnet permit them to be assigned to S-type granitoids. Their spidergrams show Rb, Ba, and Th enrichment, minimum Nb, P, and Ti contents, and no Sr depletion. The granitoids formed through the melting of plagioclase-enriched graywacke source, obviously Paleoproterozoic metaterrigenous rocks of the Garevka Formation and Teya Group (TNd(DM) = 2.0-2.5 Ga), judging from the isotope composition of the granitoids (TNd(DM-2st) = 2200 Ma and 8Nd(T) = − 6.0) and the presence of ancient zircon cores (1.80-1.85 Ga). Formation of granitoids took place in the final epoch of the Grenville collision events in the late Early Neoproterozoic (U-Pb zircon age is 857.0 ± 9.5 Ma). In the Late Neoproterozoic, the granitoids underwent tectonothermal reworking caused by Vendian accretion and collision events on the southwestern margin of the Siberian craton, which explain the younger K-Ar biotite age, 615.5 ± 6.3 Ma.  相似文献   

12.
Most rare-metal granites in South China host major W deposits with few or without Ta–Nb mineralization. However, the Yashan granitic pluton, located in the Yichun area of western Jiangxi province, South China, hosts a major Nb–Ta deposit with minor W mineralization. It is thus important for understanding the diversity of W and Nb–Ta mineralization associated with rare-metal granites. The Yashan pluton consists of multi-stage intrusive units, including the protolithionite (-muscovite) granite, Li-mica granite and topaz–lepidolite granite from the early to late stages. Bulk-rock REE contents and La/Yb ratios decrease from protolithionite granite to Li-mica granite to topaz–lepidolite granite, suggesting the dominant plagioclase fractionation. This variation, together with increasing Li, Rb, Cs and Ta but decreasing Nb/Ta and Zr/Hf ratios, is consistent with the magmatic evolution. In the Yashan pluton, micas are protolithionite, muscovite, Li-mica and lepidolite, and zircons show wide concentration ranges of ZrO2, HfO2, UO2, ThO2, Y2O3 and P2O5. Compositional variations of minerals, such as increasing F, Rb and Li in mica and increasing Hf, U and P in zircon are also in concert with the magmatic evolution from protolithionite granite to Li-mica granite to topaz–lepidolite granite. The most evolved topaz–lepidolite granite has the highest bulk-rock Li, Rb, Cs, F and P contents, consistent with the highest contents of these elements and the lowest Nb/Ta ratio in mica and the lowest Zr/Hf ratio in zircon. Ta–Nb enrichment was closely related to the enrichment of volatile elements (i.e. Li, F and P) in the melt during magmatic evolution, which raised the proportion of non-bridging oxygens (NBOs) in the melt. The rims of zoned micas in the Li-mica and topaz–lepidolite granites contain lower Rb, Cs, Nb and Ta and much lower F and W than the cores and/or mantles, indicating an exotic aqueous fluid during hydrothermal evolution. Some columbite-group minerals may have formed from exotic aqueous fluids which were originally depleted in F, Rb, Cs, Nb, Ta and W, but such fluids were not responsible for Ta–Nb enrichment in the Yashan granite. The interaction of hydrothermal fluids with previously existing micas may have played an important role in leaching, concentrating and transporting W, Fe and Ti. Ta–Nb enrichment was associated with highly evolved magmas, but W mineralization is closely related to hydrothermal fluid. Thus these magmatic and hydrothermal processes explain the diversity of W and Ta–Nb mineralizations in the rare-metal granites.  相似文献   

13.
Extremely U-depleted (<1 ppm) zircons from H8 banded ores in the East Orebody of the Bayan Obo REE–Nb–Fe deposit are presented, with mineral compositions, textures, 232Th–208Pb SHRIMP ages and petrological context. Cores of East Orebody zircon contain up to 7 wt% HfO2 and are zoned, depicting bipyramidal crystal forms. A distinct generation of patchy, epitaxial rim zircon, similarly depleted in U, is intergrown with rare earth ore minerals (bastnäsite, parisite, monazite). Overprinting aegirine textures indicate paragenetically late, reactive Na-rich fluids. Chondrite-normalized REE patterns without Eu anomalies match closely with those from the Mud Tank and Kovdor carbonatitic zircons. Increased HREE in rims ((Lu/Gd)N 43–112) relative to cores ((Lu/Gd)N 6–7.5) and the localized presence of xenotime are attributable to reactive, mineralizing fluid compositions enriched in Y, REE and P. Cathodoluminescence further reveals HREE fractionation in rims, evidenced by a narrow-band Er3+ emission at 405 nm. The extreme depletion of U in core and rim zircon is characteristic for this mineral deposit and is indicative of a persistent common source. U depletion is also a characteristic for zircons from carbonatitic or kimberlitic systems. 232Th–208Pb (SHRIMP II) geochronological data reveal the age of zircon cores as 1,325 ± 60 Ma and a rim-alteration event as 455.6 ± 28.27 Ma. The combined findings are consistent with a protolithic igneous origin for zircon cores, from a period of intrusive, alkaline–carbonatitic magmatism. Fluid processes responsible for the REE–Nb mineralizations affected zircon rim growth and degradation during the widely reported Caledonian events, providing a new example in a localized context of HREE enrichment processes.  相似文献   

14.
内蒙古大苏计和曹四夭大型钼矿床的发现及意义   总被引:7,自引:5,他引:2  
大苏计矿床和曹四夭矿床是近几年在内蒙古中部地区找到的2处大型特大型钼矿床,产出规模分别达到20万吨和200万吨.钼矿化主要在太古宙变质岩及中生代石英斑岩、正长斑岩和花岗斑岩体内呈浸染状、网脉状和脉状产出,并且构成筒状、倒扣“碗状”和囊状矿体.两处矿床无论在产出环境和地质特征上,还是在矿物种属、元素组合和热液蚀变方面,均与美国克莱麦克斯钼矿床和黑龙江岔路口钼矿床较为相似,是中生代构造-岩浆活动的产物,属古大陆碰撞造山后伸展环境产出的斑岩型矿床.文章所提出的地壳4个演化阶段和3个成矿期次的成矿模式对于提高大苏计和曹四夭钼矿床理论研究水平,推动低山丘陵覆盖区大型隐伏钼矿床的找矿勘查工作深入进行,均具有重要意义.  相似文献   

15.
A mass of granitoid and dioritic intrusions are distributed in the southern Yidun Arc, among which the representative Indosinian intrusions include the Dongco and Maxionggou granitoid intrusions in Daocheng County and hypabyssal intrusions intruding into arc volcanic rocks near the Xiangcheng town. The Dongco and Maxionggou granitoid intrusions consist mainly of porphyraceous monzogranites, megacryst monzogranites and aplite granites. The Xiangcheng hypabyssal intrusions are composed dominantly of dioritic porphyries. SHRIMP zircon ages of 224±3 Ma and 222±3 Ma have been obtained for the Dongco granitoid intrusion and the Xiangcheng dioritic porphyries, respectively. The Xiongcheng dioritic porphyries show a cak-alkaline geochemical feature, and are characterized by higher Sr/Y ratios, depletive Nb, Ta, P and Ti, enriched LILEs, and lower εNd (t) (= -3.27), suggesting that they might be derived from mantle source magmas that were obviously contaminated by continent crustal materials. However, the Dongco and Maxionggou granitoids belong to high-potassium calc alkaline series with a per-metaluminous feature, and are characterized by higher CaO/(∑FeO+MgO) and Al2O3/(∑FeO+ MgO) ratios, lower (La/Yb)n and Sr/Y ratios, depletive Nb, Ta, Sr, P and Ti, enriched LILEs, and very low εNd (t) (= -8.10), indicating that the granitoids might be derived from partial melting of continental crust materials mainly of graywacke. Petrogenesis of Dongco and Maxionggou granitoids implies that there was an oceanic crust between the Zongza continental block (ZCB) and western margin of the Yangtze Craton (WMYZC). And the oceanic crust slab subducted westward during the Indosinian Epoch, producing an Andes-type continent marginal arc and a back arc basin at the WMSCC. Then the oceanic basin closed and a sinistrally lateral collision occurred at ca. 224 Ma-222 Ma between the ZCB and the WMYZC, causing partial melting of sediments in the back-arc basin to generate granitoid magmas of the Dongco and Maxionggou intrusions.  相似文献   

16.
Voluminous Neoproterozoic granitoid sheets of the Imorona–Itsindro Suite are important components of exposed basement in west-central Madagascar. Here, we report precise new zircon U–Pb ages and whole-rock geochemistry for granitoids within the Maevatanana area of Madagascar. The new laser ablation inductively coupled plasma mass spectrometry zircon U–Pb dating undertaken during this study indicates that Antanimbary granitoid and Antasakoamamy granitoid were emplaced at 747 ± 9 Ma and 729 ± 9–727 ± 8 Ma, respectively. Geochemically, the Antanimbary granitoids show poor Nb, Ta anomalies, pronounced positive Zr anomalies, and are K-rich (K2O/Na2O > 1), but the Antasakoamamy granitoids are relatively depleted in Nb, Ta, show slightly negative Zr anomalies, and are Na-rich (Na2O/K2O > 1). Both suites contain zircons with strongly negative εHf(t), indicating participation of much older (Palaeoproterozoic and Archaean) crust. Their geochemical characteristics, along with the use of various discrimination diagrams, reveals that crustal delamination and asthenospheric upwelling resulted in crustal extension of the region before ~747 Ma, with subsequent lithospheric subduction and arc magmatism after 729–727 Ma.  相似文献   

17.
《International Geology Review》2012,54(14):1843-1860
Permian granitoid emplacement represents one of the most important tectonothermal events in the northern margin of the North China Craton (NCC). In this study, we collected geochronological and geochemical data of the regional Permian granitoid in the northwestern margin of the NCC, and investigated the Dongshengmiao pluton, using it as an example to constrain the regional granitoid petrogenesis and its geodynamic settings. The Dongshengmiao pluton contains porphyritic granite and quartz diorite. LA-ICP-MS zircon U-Pb dating results have constrained the granitoid emplacement to be ca. 287?275 Ma. The Dongshengmiao granitoids have a SiO2 range of 58.4?76.5%, moderate to high alkali content (Na2O + K2O = 5.16–7.94%), and are rich in large-ion lithophile elements (LILEs; e.g. Rb, Ba) and depleted in high-field strength elements (HFSEs; e.g. Nb, Ta, Ti). The zircons in quartz diorite have εHf(t) values of ?15.6 to ?11.1 with two-stage Hf model ages (TDM2) of 1997–2281 Ma, suggesting that the magma was derived from partial melting of old continental materials. In contrast, porphyritic granite shows variable Hf isotopic composition with εHf(t) values of ?13.7 to ?2.6 and TDM2 of 1471–2167 Ma, indicating a heterogeneous magma source. Besides the Dongshengmiao pluton, all the Permian granitoids in the northwestern margin of the NCC exhibit similar geochemical characteristics, including enrichment in LILEs, depletion in Nb and Ta, and enriched Hf isotopic signatures. The comprehensive geochemical data indicate that these Permian granitoids are derived from magma mixing between dominant partial melting of ancient felsic crustal materials and minor juvenile basaltic magma. Tectonically, the Dongshengmiao and other granitoids in the northwestern margin of the NCC may have been formed in a post-collisional extensional setting.  相似文献   

18.
ABSTRACT

We present zircon U-Pb crystallization ages combined with bulk rock major and trace element geochemistry and Sr-Nd-Pb and zircon in-situ Hf isotopic compositions of the Amand and Moro granitoid intrusions in northwest Iran. The Amand and Moro plutons include granite and syeno-diorite with LA-ICP-MS U-Pb zircon ages of 367 ± 6.8 Ma and 351 ± 1.3 Ma, respectively, representative of Late Devonian-Early Carboniferous magmatic activity in NW Iran. Geochemical characteristics such as typical enrichments in alkalis, Nb, Zr, Ga and Y, depletion in P and Sr and fractionated REE patterns with high Ga/Al ratios and Eu negative anomalies are consistent with A-type magmatic signatures. The granitoids are classified as A2-type and within-plate granitoids. The bulk rock geochemistry (enrichments in Th, Nb and, high Th/Yb, Zr/Y ratios) along with low variation of 143Nd/144Nd(i) and 87Sr/86Sr(i) ratios and positive zircon εHf(t) support the role of a mantle plume component for the evolution of the Amand and Moro A-type granitoids in an extensional tectonic environment. In fitting with wider regional knowledge, this magmatism occurred during Paleo-Tethys opening in northern Gondwana.  相似文献   

19.
《International Geology Review》2012,54(15):1877-1888
The Hai Van granitoid complex constitutes an important part of the Indosinian batholith of the northern Kontum massif in central Vietnam. The Kontum massif is a key region for understanding the palaeo-Tethyan accretionary history and the crustal evolution of the Indochina terrane. In this study, zircon U–Pb ages and geochemical data on the Hai Van complex are reported to shed more light on these geological processes. Zircon U–Pb isotopic analyses of six representative samples by the LA-ICP-MS technique show that granitoids from this complex crystallized between 242 and 224 Ma, indicating a prolonged period of magmatism in a late orogenic stage. Rocks from the Hai Van complex have S-type geochemical characteristics with high SiO2, Na2O + K2O, and Zr contents as well as typical S-type minerals such as cordierite and muscovite. Trace elements of the samples are depleted in Ba, Nb, P, Sr, and Ti and enriched in Rb, K, Th, U, and Pb. Negative Eu-anomalies indicate feldspar fractionation during magma crystallization. The Hai Van granitoids exhibit Nd–Hf isotopic features similar to Proterozoic rocks exposed in South China, with low initial ?Hf and initial ?Nd values and two-stage Hf model ages of 1.9–1.7 Ga. It is suggested that during the palaeo-Tethyan orogeny, central Vietnam experienced strong early Mesozoic magmatism that originated from partial melting of crustal material similar in composition to the basement of the South China block.  相似文献   

20.
Petrochemical study and U–Pb SIMS (SHRIMP–II) zircon analyses of subalkaline leucogranite of the Khariusikha Massif have been carried out. They have revealed for the first time a rare-metal mineralization. The elevated concentrations of rare elements (wt %) are Nb (0.5–0.7), Ta (0.12–0.16), REEs (0.08–0.24), Y (0.06–0, 1), Zr (2.3–2.6), Hf (0.1–0.12), U (0.05–0.1), and Th (0.08–0.1) and are confined to albitized granites. The main mineral phases concentrating the rare elements, U and Th, are tantalo–niobates: fergusonite, euxenite, U–pyrochlore, tantalite, as well as thorite, monazite, zircon, and sphene. These minerals associate with cassiterite, sulfides, and gold. The simultaneity of the intraplate granitoid magmatism (753 ± 4 Ma) and bimodal rhyolite–basalt volcanism (753 ± 6 Ma) in the neighboring rift structure has been demonstrated. Presumably, the Neoproterozoic rifting and intraplate magmatism relate to the plume activity that caused the supercontinent Rodinia to break up.  相似文献   

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