青藏高原东南部寒武纪花岗岩类:岩石学和锆石Hf同位素研究

青藏高原南部广泛分布的冈底斯岩基,记录了其强烈的中、新生代造山作用;而古生代以前岩浆作用的报道却屈指可数,限制了我们对青藏高原起源及构造演化的研究。本文研究报道了位于青藏高原东南部南拉萨地体和高喜马拉雅带的寒武纪花岗质岩石,岩石类型包括闪长岩、花岗闪长岩和花岗岩。锆石U-Pb年代学表明其结晶年龄为503~490Ma。南拉萨地体中的寒武纪花岗岩具有高的铝饱和指数和刚玉分子数,矿物化学成分区别出岩浆成因的过铝质矿物白云母和石榴石,结合岩石中锆石的内部结构和微量元素特征表明其为S型花岗岩。岩石中锆石的Hf同位素具有近一致的负εHf(t)值,地壳Hf模式年龄集中在1.8~1.6Ga,说明寒武纪花岗岩可能来源于元古代物质的部分熔融。因此,南拉萨地体存在古老的结晶基底,而并不是一个年轻的岛弧地体。高喜马拉雅带中近同期的花岗质片麻岩具有较负的εHf(t)值和老的地壳Hf模式年龄(2.3~1.5Ga),说明其可能为元古代的地壳物质部分熔融的产物。结合同期的火山和变质作用以及区域性的不整合,本文认为青藏高原南部经历了广泛的古生代早期原特提斯洋俯冲导致的安第斯型造山作用。     

满洲里南部中生代花岗岩的锆石U--Pb年龄及Hf同位素特征

满洲里南部地区花岗岩主要由碱长花岗岩、正长花岗岩、二长花岗岩及花岗斑岩组成。采用LA--ICP--MS技术,对满洲里南部花岗岩进行的锆石U--Pb年龄测定表明,该区中生代花岗岩浆活动分为3期:中—晚三叠世(208~239 Ma)、早侏罗世(179~185 Ma)和晚侏罗世—早白垩世(137~151 Ma),与整个大兴安岭中生代花岗岩的年代学格架基本一致,与东部的张广才岭—小兴安岭地区中生代岩浆活动时代也可以对比。锆石LA--MC--ICP--MS Hf同位素研究显示,本区中生代花岗岩的锆石εHf(t)多数为+0.7~+9.5,二阶段模式年龄为0.6~1.2 Ga,表明花岗岩浆主要源于中—新元古代增生的地壳物质。结合额尔古纳地块其他花岗岩的锆石Hf同位素资料,认为额尔古纳地块在中—新元古代时期曾发生一次重要的地壳增生事件,与兴安地块的地壳增生时间为新元古代—显生宙的特点不同。     

南澜沧江带曼兵岛弧花岗岩成因与构造启示:元素地球化学、锆石U-Pb年代学及Hf同位素约束

昌宁-孟连缝合带是中国西南三江特提斯重要的古特提斯洋残余,但其消减过程仍然存在争议。南澜沧江构造带曼兵岛弧花岗岩体为探究古特提斯洋俯冲过程提供了新的线索。本文对曼兵花岗岩体内的片麻状黑云花岗闪长岩和斜长角闪岩进行了锆石U-Pb年代学、Hf同位素和全岩元素地球化学研究。二者的LA-ICP-MS锆石U-Pb年龄分别为251.5±2.7Ma、253.8±1.1Ma和241.8±0.8Ma、259.5±1.9Ma,指示其为晚二叠世-早三叠世的岩浆活动产物。曼兵花岗闪长岩属于钙碱性到高钾钙碱性系列I型花岗岩,富集轻稀土元素和大离子亲石元素,亏损Nb、Ta、Ba、Sr和高场强元素,具有Eu的负异常（δEu=0.45~0.69）。花岗闪长岩和斜长角闪岩¹⁷⁶Hf/¹⁷⁷Hf平均值分别为0.2829035和0.2829762,锆石ε_Hf（t）平均值为11.0和12.5;地壳模式年龄t_DM^C加权平均值分别为578.4Ma和469.3Ma,类似俯冲相关的新生下地壳演化的岛弧花岗岩。曼兵花岗岩具有低的Ce/Pb（3.89~6.57）、Th/La（0.32~0.58）和Sm/La（0.11~0.15）指示了新生下地壳被上部围岩的混染。综合区域古特提斯洋演化历史,认为曼兵岛弧花岗岩体形成于洋陆俯冲向地块增生转换的构造环境,提出三江地区古特提斯主洋盆的闭合延续至早三叠世才完成。

     

Crustal formation in the Nanling Range,South China Block: Hf isotope evidence of zircons from Phanerozoic granitoids

Granitic rocks are the principle agent of crustal differentiation, therefore their origins yield important information on crustal formation and reworking. An extensive survey of zircon Hf isotopes from granitic rocks in a large region can provide a profile of crustal characteristics that may be further linked to previous crustal evolution. In this study, we measured U–Pb ages and Hf isotope compositions of zircon grains extracted from twenty-five Jurassic, five Triassic and two Ordovician granitic plutons from the Nanling Range, South China Block (SCB). Combined with the published Lu–Hf isotopic data for the granitic rocks in the studied and adjacent areas, three domains with different crustal formation histories have been identified in the southern part of the SCB: eastern side, middle part and western side. The eastern side extends to the coastal area of the SCB, with dominant Hf crustal model ages (T_DM2) in zircons falling within the range of 2.2–1.6 Ga. The middle part is partly coincided with the low-Nd model age belt proposed by Chen and Jahn (1998), with zircon Hf T_DM2 ranging from 1.6 to 1.0 Ga. The western side covers the westernmost Nanling Range and the western end of the Jiangnan orogen, in which the granitoids have zircon Hf T_DM2 model ages spanning 2.2–1.8 Ga. The Paleo- to Meso-Proterozoic model ages of the Phanerozoic granitoids in the Nanling Range imply a long-term crustal reworking. Zircons from the western and eastern sides have an average ε_Hf(155 Ma) at around −10, about 4 epsilon units lower than the middle part (ε_Hf(155 Ma) = −6). Hf T_DM2 histogram from the western Nanling Range is similar to that of the Neoproterozoic granitoids in northern Guangxi Province to the west but much lower to the granites in the middle part to the east. The eastern side has a broader range of Hf model ages in zircons, with the main peak low to ca 1.6 Ga, suggesting the reworking of Mesoproterozoic crust. However, granitoids in the middle part have zircon Hf T_DM2 ages at 1.6–1.0 Ga, which indicates the incorporation of younger crust materials into the magma sources. The Hf model ages of granitoids, as well as four zircon xenocrysts with ages around 920 Ma within the Mesozoic granitoids in the middle part, indicate that the middle part has similar crustal features with the eastern Jiangnan orogen. We propose that this low T_DM2 granite belt is probably part of the early Neoproterozoic arc-continent collision belt between different continents (possibly Yangtze and Cathaysia) during the early assembling processes, while the granitoids in the western and eastern sides have similar crustal compositions.     

Hf isotope compositions and HREE variations in off-craton garnet and spinel peridotite xenoliths from central Asia

Garnet-facies continental mantle is poorly understood because the vast majority of mantle xenoliths in continental basalts are spinel peridotite. Peridotite xenoliths from Vitim (southern Siberia) and Mongolia provide some of the best samples of garnet and garnet-spinel facies off-craton lithospheric mantle. Garnets in those fertile to moderately depleted lherzolites show a surprisingly broad range of HREE abundances, which poorly correlate with modal and major oxide compositions. Some garnets are zoned and have Lu-rich cores. We argue that these features indicate HREE redistribution after the partial melting, possibly related to spinel-garnet phase transition on isobaric cooling. Most peridotites from Vitim have depleted to ultra-depleted Hf isotope compositions (calculated from mineral analyses: ε_Hf(0) = +17 to +45). HREE-rich garnets have the most radiogenic ε_Hf values and plot above the mantle Hf-Nd isotope array while xenoliths with normal HREE abundances usually fall within or near the depleted end of the MORB field. Model Hf isotope ages for the normal peridotites indicate an origin by ancient partial melt extraction from primitive mantle, most likely in the Proterozoic. By contrast, an HREE-rich peridotite yields a Phanerozoic model age, possibly reflecting overprinting of the ancient partial melting record with that related to a recent enrichment in Lu. Clinopyroxene-garnet Lu-Hf isochron ages (31-84 Ma) are higher than the likely eruption age of the host volcanic rocks (∼16 Ma). Garnet-controlled HREE migration during spinel-garnet and garnet-spinel phase transitions may be one explanation for extremely radiogenic ¹⁷⁶Hf/¹⁷⁷Hf reported for some mantle peridotites; it may also contribute to Hf isotope variations in sub-lithospheric source regions of mantle-derived magmas.     

Igneous and metamorphic geochronologic evolution of granitoids in the central Eastern Segment,southern Sweden

The Eastern Segment abutting the Transscandinavian Igneous Belt (TIB) mostly consists of rocks with overlapping igneous ages. In the Eastern Segment west of Lake Vättern, granitoids of clear TIB affinity exhibit strong deformational fabrics. This article presents U–Pb zircon ages from 21 samples spanning the border zone between these deformed TIB rocks in the east, and more thoroughly reworked rocks in the west. Magmatic ages fall in the range 1710–1660 million years, irrespective of the degree of deformation, confirming the overlapping crystallization ages between deformed TIB rocks and orthogneisses of the Eastern Segment. A common history is further supported by leucocratic rocks of similar ages. Prolonged orogenic (magmatic) activity is suggested by continued growth of zircon at 1.66–1.60 Ga. Six of the weakly gneissic rocks show zircons with cathodoluminescence-dark patches and embayments, possibly partly replacing metamict parts of older magmatic crystals, with ²⁰⁷Pb/²⁰⁶Pb ages dominantly between 1460 and 1400 million years, whereas three of the gneisses have zircon rims with calculated ages of 1440–1430 million years. Leucosome formation took place at 1443 ± 9 and 1437 ± 6 Ma. The minimum age of SE–NW folds was determined by an undeformed 1383 ± 4 million years crosscutting aplitic dike. Sveconorwegian zircon growth was not found in any of the samples from the studied area. To our knowledge, 1.46–1.40 Ga metamorphism affecting the U–Pb zircon system has not previously been reported this far northeast in the Eastern Segment. We suggest that the E–W- to SE–NW-trending deformation fabrics in our field area were produced during the Hallandian–Danopolonian orogeny and escaped later, penetrative Sveconorwegian reworking.     

Character and origin of variably deformed granitoids in central southern Sweden: implications from geochemistry and Nd isotopes

We present major and trace element data for eighteen 1.71–1.66 Ga granitoid samples, and Sm–Nd whole‐rock isotope data for eleven of these samples, in a transect across the border between the Transscandinavian Igneous Belt (TIB) and the Eastern Segment in central southern Sweden. The geochemistry of the granitoids varies from alkalic to alkali‐calcic and peraluminous in the east to predominantly calc‐alkaline and metaluminous in the west. Rocks in the west also have lower SiO₂ contents. Trace element signatures favour formation in an active continental margin setting. Nd isotope data are completely overlapping along the transect and initial ε_Nd values are mildly depleted in the range +0.3 to +2.6. The combined data suggest that the magmas were derived mainly from juvenile, pre‐existing crust, increasingly mafic and less alkaline towards the west. Copyright © 2011 John Wiley & Sons, Ltd.     

Carbonic fluid inclusions in ultrahigh-temperature granitoids from southern India

The granite plutons of Vattamalai (VT), Gangaikondan (GK) and Pathanapuram (PT) intruding granulite facies rocks in southern India were emplaced during the Late Neoproterozoic tectonothermal event. Feldspar thermometry of mesoperthites from the granites yield temperatures of 800–1000?°C indicating high- to ultrahigh-temperature conditions, comparable to similar estimates derived from some of the host granulite facies rocks in the region. This study reports results from a detailed investigation of fluid inclusions in the three granite plutons. Carbonic inclusions characterize the major fluid species in all the cases and their unique abundance in some of these plutons indicates up to 1 wt.% CO₂. In most of the cases, the inclusions show a near-pure CO₂ composition as deduced from melting temperatures which cluster close to $?56.6°$C, and as confirmed by laser Raman spectroscopy. The VT granite preserves the highest density CO₂ fluids among all the three plutons with a density up to 0.912 g?cm^?3 (molar volume of 48.25 cm³?mol^?1). A combination of CO₂ isochores, feldspar thermometry data and dehydration melting curves, and liquidus for water-undersaturated granitic systems clearly bring out a genetic link between these granites and granulitic lower crust. The ultimate origin of the CO₂-rich fluids is linked to sub-lithospheric mantle sources through tectonic processes associated with the assembly of the Gondwana supercontinent. To cite this article: M. Santosh et al., C. R. Geoscience 337 (2005).     

西藏措勤麦嘎岩基的锆石U-Pb年代学、地球化学和锆石Hf同位素:对中部拉萨地块早白垩世花岗岩类岩石成因的约束

西藏中部拉萨地块大规模早白垩世花岗岩类的岩浆源区和岩石成因迄今尚未得到很好约束,对这些问题的深入理解将有助于揭示拉萨地块白垩纪时期的岩浆作用过程及成矿背景。本文报道了中部拉萨地块代表性花岗岩基——措勤麦嘎岩基的锆石U-Pb年代学、全岩元素地球化学、Sr-Nd同位素和锆石Hf同位素数据。本文锆石U-Pb定年结果表明,麦嘎岩基花岗质岩主要侵位于122±1Ma和113±2Ma,闪长质包体与后者同期(113±2Ma)。122±1Ma花岗质岩属I型弱过铝质高钾钙碱性系列,(87Sr/86Sr)i值高(0.7147),全岩εNd(t)(-12.0)和锆石εHf(t)(-15.7～-11.1)为较大的负值,表明其很可能来源于古老下地壳物质的重熔。113±2Ma寄主花岗质岩为I型偏铝质-弱过铝质高钾钙碱性系列,相对于122±1Ma花岗质岩石,其(87Sr/86Sr)i比值偏低(0.7094～0.7156)、全岩εNd(t)值(-12.1～-7.3)和锆石εHf(t)值(-11.1～0.1)较高,很可能来源于古老下地壳物质的部分熔融,并含有更多幔源物质。闪长质包体(113±2Ma)为偏铝质中-高钾钙碱性系列,以变化范围大的(87Sr/86Sr)i(0.7058～0.7105)、负的全岩εNd(t)值(-10.7～-9.8)及负的锆石εHf(t)值(-14.0～-5.6)为特征,可能是古老富集岩石圈地幔物质部分熔融的产物或亏损地幔物质经历强烈地壳混染作用的结果。在目前已有资料条件下(缺乏同期基性岩石的相关数据),本文暂将麦嘎岩基113±2Ma寄主花岗质岩及同期闪长质包体解释为镁铁质岩浆与长英质岩浆发生不同程度岩浆混合作用的产物,这一解释可能对中部拉萨地块同期花岗类的岩石成因具普遍意义。麦嘎岩基及中部拉萨地块同期岩浆岩约113Ma幔源物质增加现象,可能是南向俯冲的班公湖-怒江洋壳岩石圈板片断离的结果。     

Sm-Nd systematics and petrology of postorogenic granitoids in the northern Baltic Shield

In the northern part of the Baltic Shield, quartz diorites, diorites, and monzodiorites compose massifs of postorogenic granites, in which younger granite phases are restricted to their central parts, and dike rocks (aplites, pegmatites, and granite porphyries) occur in the apical parts. The rocks of the Litsa-Araguba Complex (which is located in the northwestern part of the Kola Peninsula and was examined most thoroughly) compose seven intrusions 850 km² in total area, which were formed in mesoabyssal and hypabyssal depth facies. The massifs consist of quartz diorites and monzodiorites dated at 1774 ± 9 Ma, diorites, diorite porphyries, and lamprophyres, which are distinguished as phase 1. The porphyritic and equigranular granites, granodiorites, quartz monzonites, granites, alaskites and related vein leucogranites, pegmatites, and granite porphyries of phases 2 (main), 3, and 4 have an age of 1772–1762 Ma. Data obtained on the Sm-Nd systematics of the rocks indicate that their ?_Nd(1765) values are close to those for rocks of phases 1, 2, and 3 (from ?6.8 to ?8.8) and vary from ?5.0 to ?11.9 for the leucocratic granites of phase 4. The model age values are, respectively, 2.37–2.62 and 2.58–3.23 Ga. These data suggest that the parental melts were of anatectic genesis and were produced by the melting of mostly metasomatically altered garnet granulites from the lower crust. The leucogranites and alaskites of phase 4, which occur as relatively thin bodies in the rocks of the Archean Complex penetrated by the Kola Superdeep Borehole, were derived from a Neoarchean sialic source or produced by the contamination of the parental melts with the material of the Late Archean upper crust. The SHRIMP-II zircon age of the lower crustal migmatized garnet granulites lies within the range of 1831 ± 23 to 1392 ± 21 Ma in the concordia plot. All dates of the rocks are characterized by a unimodal distribution with most values lying within the range of 1650–1800 Ma and approximated by a discordia with T₁ = 1750 ± 30 Ma, MSWD = 3.1. This age value can be interpreted as an averaged age of the lower crustal granitization and corresponds, within the errors, to the age of postorogenic granite intrusions in the upper crust.     

Carbon isotope stratigraphy of Lochkovian to Eifelian limestones from the Devonian of central and southern Europe

Lower to Middle Devonian carbonates of the Prague Syncline, the Carnic Alps, the Montagne Noire, and the Cantabrian Mountains were investigated for δ¹³C_carb and δ¹³C_org. These values were measured on bulk rocks, selected components and cements. Many carbonates exhibit primary marine values, but some are altered by diagenesis. A δ¹³C curve can be presented for the latest Pridolian to Emsian time interval. Several sharp or broad positive excursions are obvious in the woschmidti-postwoschmidti, sulcatus, kitabicus, Late serotinus, and kockelianus conodont zones. The excursion at the Silurian–Devonian boundary is known worldwide and therefore considered global in nature. Some of the others are described for the first time from central and southern Europe, and their global nature has to be verified by further investigations in other regions. Most excursions relate to and/or started during major regressions whereas sea-level highstands correspond to minimal δ¹³C values. Similar relationships between sea-level changes and δ¹³C have been observed from other early Palaeozoic intervals. The transgressive Chote? (?) and Ka?ák events are marked by positive isotope excursions, this type of combination is usually observed in late Palaeozoic to Cenozoic black shale events.     

U---Pb and Rb---Sr systematics in a polyorogenic segment of the Precambrian shield, central southern Norway

U---Pb analyses of zircon, monazite and sphene as well as Rb---Sr analyses of whole rocks and minerals have been carried out in an attempt to elucidate the evolution of the Precambrian shield underlying the Caledonian Jotun-nappe in central southern Norway. The earliest event recognized in the area is a high grade metamorphism at 1518 ± 17 m.y. which followed intense magma formation, igneous activity, erosion and sedimentation over a period of maximum 300 m.y. The Sveconorwegian cycle is characterized by the intrusion of two anatectic magma generations at 1014 ± 35 m.y. and 930±10 m.y. that disturbed and partly reset the isotopic systems of the country rocks. A post-magmatic fracturing stage at 875 m.y. concludes this cycle. Rb---Sr mineral systems were not completely equilibrated in the undeformed shield during the Caledonian event in contrast to new grown minerals in strongly deformed overlying Lower Paleozoic sediments which record the main deformation at 384±18 m.y. Zircon lower intercept ages ranging between 330–370 m.y. show that lead loss of zircon in rocks subjected to low grade metamorphic conditions may be the result of such processes as annealing, alteration, dilation or a combination of them.     

南秦岭华阳花岗岩LA-ICP-MS锆石U-Pb 年龄、地球化学和Hf同位素组成 ——对五龙岩体群成因的约束

华阳岩体位于南秦岭中部地区,岩体主体岩性为黑云母二长花岗岩。对中粒黑云母二长花岗岩和细粒黑云母二长花岗岩的LA-ICP-MS锆石U-Pb定年分别获得214Ma±2Ma和228Ma±2Ma的年龄,表明该岩体形成于晚三叠世。华阳花岗岩属于弱过铝质和高钾钙碱性系列,具有I-A型花岗岩过渡的特征,A/CNK值为1.01~1.14,Na2O为3.15%~3.83%,K2O为3.04%~5.70%,K2O/Na2O为0.84~1.80,Mg#为0.24~0.48;稀土元素配分曲线表现为右倾型,轻、重稀土元素分馏明显,具有显著的Eu负异常。该花岗岩富集Rb、K、Pb、Sr等大离子亲石元素,亏损Zr、Hf、Ta、Nb、P、Ti等高场强元素,表明华阳花岗岩的物源以壳源物质为主。锆石饱和温度和Ti温度计等的估算显示,华阳岩体岩浆源区的初始温度为750~800℃。花岗岩的锆石εHf(t)值变化范围较小,为-6.17~2.27,平均值为-3.19;二阶段模式年龄TDM2为1.65~1.12Ga,加权平均值为1.46Ga,结合区域地质背景和前人研究成果认为,华阳花岗岩是早—中元古代古老地壳物质部分熔融的结果,伴有少量幔源物质的加入;岩体的形成与华南板块和华北板块碰撞有关,是同碰撞向后碰撞构造体制转变或后碰撞伸展早期的产物。     

西藏南拉萨地块西部鸭洼地区侵入岩的锆石年代学和Hf同位素特征

拉萨地块南缘发育了广泛的中、新生代岩浆作用,然而与中、东部地区相比,南拉萨地块西部地区的研究程度还相对偏低,尤其是缺乏中生代以前岩浆活动的发现和研究。本文对南拉萨地块西部鸭洼地区新发现的中、新生代侵入岩开展了详细的锆石U-Pb定年和Hf同位素研究,发现鸭洼地区发育了晚三叠世(210～208Ma)辉长岩和闪长玢岩、晚侏罗世(约155Ma)似斑状二长花岗岩和始新世(约50Ma)花岗斑岩。晚三叠世辉长岩和闪长玢岩具有相对亏损的锆石Hf同位素组成,ε_(Hf)(t)值分别是+1.9～+6.2和-3.0～+7.4。晚侏罗世似斑状二长花岗岩和始新世花岗斑岩则具有明显富集的锆石Hf同位素组成,其ε_(Hf)(t)值分别是-10.0～-5.2和-7.9～-2.7,对应的地壳模式年龄分别是1534～1836Ma和1297～1624Ma,分别反映了古元古代和中元古代古老陆壳物质为主的再循环作用。结合区域文献数据,鸭洼-打加错地区中生代以来由于新特提斯洋的俯冲而发生了明显的地壳增生作用,新生地壳的生长从中生代到新生代早期逐渐进行,并且具有从陆内向海沟逐渐增加的趋势。     

Gold abundance in granitoids in southern China

Gold abundance in granitic rocks of different geological periods in southern China has been estimated. A review of the quantitative data available indicates that unaltered granitic rocks have a rather restricted range in gold content, rarely exceeding 4 ppb and generally ranging from 1.4 to 3.3 ppb. The mean gold content tends to decrease from basic to acidic granitoids. This tendency suggests that gold isnot concentrated in the residual silicate meltduring the formation of granitic rocks. It is necessary to establish the background values of gold for various rock types although it seems that gold abundance data for the granitic rocks of southern China can necessarily provide any geochemical clues or guides to areas favorable or unfavorable for gold mineralization.     

赣南地区寒武系牛角河组碎屑锆石U-Pb年龄 和Hf同位素特征及其地质意义

通过对赣南地区寒武纪牛角河组变余长石石英砂岩锆石U-Pb年代学和Hf同位素分析表明,牛角河组地层沉积年龄晚于556Ma。LA-ICP-MS U-Pb数据结果显示550～600Ma、700～900Ma、900～1100Ma、1500Ma和2500Ma为五个主要年龄峰值,其中900～1100Ma和700～900Ma两个峰值最显著,表明Rodinia超大陆的裂解聚合在华南地区的响应为赣南地区寒武纪地层提供了主要物源,该物源曾遭受泛非运动的影响,进一步说明华夏地块与冈瓦纳大陆具有一定亲缘性。此次工作中3568Ma锆石的捕获,说明华夏地块可能存在太古宙结晶基底。对具有不同年龄峰值的锆石进行稀土元素分析,其结果表明研究区锆石具有重稀土富集、强Ce正异常、弱或不明显的Eu负异常的地球化学特征,与岩浆锆石特征相似,指示其物源区以岩浆岩为主。此外,Lu-Hf同位素分析显示源区锆石除少数源于新生地壳物质组分熔融产生的岩浆,大多结晶于古老地壳部分熔融产生的岩浆;综合锆石年代学结果,暗示华南地区存在强烈的古元古代到新元古代岩浆活动,其中中元古代末期-新元古代的岩浆事件最甚;而新太古代为一个重要的新生地壳生长时期。     

赣南西华山成矿花岗岩锆石U-Pb年代学和Hf同位素特征及其地质意义北大核心CSCD

赣南西华山钨矿是与侏罗纪花岗岩有关的大型石英脉型矿床,也是我国南岭成矿带赣南地区典型的钨矿床。本文选取西华山钨矿成矿花岗岩进行了锆石LA-ICP-MS U-Pb定年、微量元素和Hf同位素分析,旨在揭示花岗岩的形成时间并推断岩石成因及其对成矿的指示。锆石U-Pb测年结果表明,西华山中粒黑云母花岗岩锆石206 Pb/238 U加权平均年龄为154.8±6.0 Ma。锆石形态、激光拉曼和地球化学特征表明,该花岗岩受到岩浆热液的影响。锆石的176 Yb/177 Hf和176 Lu/177 Hf比值较高,表明源岩浆有强烈的流体出溶作用。西华山黑云母花岗岩的εHf(t)变化范围较小,呈明显负值(-12.8~-10.8),且集中在华夏地块古老基底范畴内,指示其形成于古老地壳物质的部分熔融。