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1.
祁漫塔格地区岩浆岩的成岩时代和形成环境的确定能对东昆仑造山带加里东期构造演化时限加以约束.对祁漫塔格西北部阿确墩地区石英闪长岩和二长花岗岩进行了年代学和岩石地球化学研究,结果显示,石英闪长岩属准铝质-弱过铝质钙碱性系列岩石;轻重稀土分馏明显,具中等-轻微铕负异常（δEu=0.79~0.90）;相对富集Rb、K、Hf、Zr、Tb、Nd等元素,不同程度地亏损Ba、P、Ti、Nd、Ta、Y;具有I型花岗岩类特征.二长花岗岩属弱过铝质钙碱性系列岩石;轻重稀土分异程度极大,具明显铕负异常（δEu=0.42~0.45）;富集大离子亲石元素（如Rb、K、La、Ce、Nd、Tb等）,亏损高场强元素（P、Ti、Nd、Ta）和Ba、Sr、U等元素;为高分异I型花岗岩.Nd/Th、Nb/Ta、Mg#值等指标显示石英闪长岩为壳源特征且受到幔源岩浆的影响,推测是幔源岩浆底侵地壳物质发生部分熔融形成的;二长花岗岩则是壳源的,可能与幔源岩浆底侵诱发的上地壳物质部分熔融有关,且经历了强烈的结晶分离作用.石英闪长岩和二长花岗岩的LA-ICP-MS锆石U-Pb年龄分别为448.8±3.9 Ma和405.2±3.6 Ma,代表其形成时代.石英闪长岩总体显示出与俯冲消减作用有关的岛弧岩浆岩地球化学特征;二长花岗岩在构造环境图解中显示为碰撞背景,但微量元素与同碰撞花岗岩典型特征不符,综合分析认为形成于后碰撞构造背景下.结合区域构造演化,推测东昆仑祁漫塔格地区在晚奥陶世持续处于俯冲消减环境中,早泥盆世之前进入后碰撞造山阶段. 相似文献
2.
藏东怒江板块结合带郭庆复式花岗岩体特征及其成因 总被引：1，自引：0，他引：1
根据作者在“三江”地区进行１∶２０万洛隆幅区域地质调查工作中收集的资料,对产出于怒江板块结合带东侧的郭庆复式花岗岩体进行了解体,将岩体划分为燕山早期的黑云母二长花岗岩,燕山晚期的黑云母石英正长岩、黑云母花岗闪长岩三种岩石类型。通过对它们的地质学、岩石学、岩石地球化学特征的研究表明,这三种侵入岩分属陆壳改造Ｓ型花岗岩和壳幔同熔Ⅰ型中酸性岩。燕山早期花岗岩形成于同碰撞造山期,燕山晚期黑云母石英正长岩形成于板块碰撞后的抬升阶段,燕山晚期黑云母花岗闪长岩形成于造山晚期构造环境,是区内板块构造不同演化阶段的产物。郭庆复式岩体的形成与三江地区板块构造演化密切相关 相似文献
3.
以往将位于湘南、桂东北的都庞岭花岗岩基分为西体、中体和东体三部分。野外观察和岩相学研究表明,都庞岭中体和东体主要由黑云母正长花岗岩、黑云母二长花岗岩和二云母二长花岗岩组成,岩石具斑状结构,部分钾长石斑晶呈椭球状至球状,具斜长石环边,构成环斑结构。采用锆石SHRIMP U-Pb法获得都庞岭中体和东体中环斑花岗岩的侵位年龄分别为226.6±6.9 Ma和209.7±3.1 Ma,均属于晚三叠世,相当于印支晚期。都庞岭环斑花岗岩富硅、碱,贫钛、磷、镁和钙,其Rb、Cs、Th、U、REE、Pb、Y含量和Rb/Sr、Rb/Ba比值较高,而Sr、Ba含量和Zr/Hf比值(8.16~25.01)较低,具强烈的Eu负异常(δEu=0.02~0.13),10000×Ga/Al比值(2.64~4.38,平均3.15)高,显示A型花岗岩的地球化学特征。与华南印支早期S型花岗岩相比,都庞岭环斑花岗岩的εNd(t)值(-8.0~-8.3)明显偏高(前者低于-10),而tDM2值(1624~1645 Ma)则明显偏低(前者1800 Ma),表明它们可能直接源于地壳物质的部分熔融,但成岩过程中有地幔物质的参与。都庞岭环斑花岗岩的发现及其时代的确定,揭示了晚三叠世华南东部处于大陆裂解或造山后伸展的构造环境。结合华南东部沉积/岩石大地构造分析,认为华南早中生代构造体制的转换发生在中、晚三叠世,而非前人所认为的发生在中、晚侏罗世;同时,环斑花岗岩的出现,指示了华南中生代大规模成矿作用的来临,晚三叠世是华南中生代大规模成矿的第一个高峰期。 相似文献
4.
拉热拉新花岗岩体属于唐古拉-东达山花岗岩带西段羌塘花岗岩区的组成部分,岩石类型主要为黑云角闪闪长岩、黑云角闪石英闪长岩、黑云角闪石英二长岩、黑云花岗闪长岩、黑云二长花岗岩、黑云花岗岩。其地球化学特征表现为：富Si,K,贫Ti,Mg,Fe,Ca,铝饱和指数ACNK〈1．1,稀土元素球粒陨石标准化图式呈右倾斜的“V”字型,LREE富集,HREE相对亏损,铕亏损。其形成时代为早白垩世,为多期次同碰撞的同熔型花岗岩。 相似文献
5.
From Casper Mountain; at its northern end, to the northwestern margin of the Laramie anorthosite—syenite complex, in its central parts, the Laramie Range is underlain by granite and granitic gneiss that has a minimum age of 2.54 ± 0.04 Ga (Rb/Sr whole-rock isochron) and by metasedimentary rocks, including marble and quartzite, that appear to overlie the granitic gneiss nonconformably (minimum age: 1.7 Ga based on several horn-blende K/Ar dates). Southward from the anorthosite—syenite complex into Colorado, the Range is underlain chiefly by the Sherman Granite (1.41 Ga; Peterman and Hedge, 1968) and scattered patches of gneiss that are not dated, but are tentatively correlated wit similar gneiss in the southern Medicine Bow Mountains and in the Colorado Front Range, where they are dated as ? 1.7 Ga (Peterman and Hedge, 1968).The Laramie anorthosite—syenite complex (minimum age: ? 1.42 Ga or ? 1.51 Ga if a hornblende K/Ar date is accepted) apparently intruded the suture separating the old (? 2.5 Ga) continental edge from younger (? 1.7 Ga) geosynclinal rocks. The suture, which manifests itself as the Mullen Creek—Nash Fork shear zone in the Medicine Bow Mountains, also is the boundary between ensialic and ensimatic geosynclinal deposition that occurred during the interval 1.7–2.5 Ga ago.K/Ar dates on biotite and muscovite from rocks north of the anorthosite—syenite complex grade from 2.5 Ga on Casper Mountain down to 1.38 Ga near the complex. Near its northern tip, the Laramie Range is crossed by a geochronologic front, separating 2.5 Ga old gneiss whose K/Ar dates were not lowered by subsequent metamorphism from 2.5 Ga old gneiss whose mica dates were reset between 1.4 and 1.6 Ga ago. 相似文献
6.
通化地区古元古代晚期花岗质岩浆作用与地壳演化 总被引：20，自引：10，他引：10
广泛出露于华北板块东部辽吉地区的古元古代变质杂岩,多年来一直被认为是古老的陆内裂谷作用的产物,我们通过详细的野外地质调查工作发现,该变质杂岩中以往所划定的混合岩实际是不同变质程度和变形特征的岩浆成因花岗岩岩体,其岩石类型除典型的片麻状角闪正长花岗岩（俗称“条痕状花岗岩”或“辽吉花岗岩”）外,另有片麻状石英闪长岩、巨斑状黑云母二长花岗岩、巨斑状一环斑状舍石榴石花岗岩和角闪辉石正长岩等、,应用SHRIMP技术,本文对片麻状石英闪长岩和巨斑状一环斑状含石榴石花岗岩进行了结石U—Pb同位素年龄测定,结果显示它们的侵位时代为1872～1850Ma,与巨癍状黑云母二长花岗岩和角闪辉石正长杂岩侵位时代相近,岩石学一地球化学特征显示片麻状石英闪长岩是“Ⅰ”型花岗岩,具有岛弧型花岗岩地球化学特征;而巨斑状一环斑状含石榴石花岗岩（局部具有球斑状结构）属“S”型花岗岩结合区内与花岗岩形成同时发生的变质作用P—T特征,这种I-、S-和A-型花岗岩的同时产出,反映他们可能形成于造山后构造背景,结合朝鲜狼林一中国辽南和龙岗太古宙陆块的结晶基底差别,可以认定华北板块在太古宙末期并非仅由东、西部陆块组成,在东部陆块至少还存在朝鲜狼林-辽南-胶东联合陆块和龙岗-鲁西-五准陆块两个微陆块,这两个微陆块大约在1．90Ga左右发生拼合,然后它们再于1．85Ga左右与西部地块拼合 相似文献
7.
《Gondwana Research》2002,5(2):453-465
The Kunduru Betta Ring Complex (KRC), at the southern margin of Dharwar craton, South India, comprises metaluminous sub-solvus syenites and quartz monzonite with a concentric disposition younging towards the center. An outer mafic syenite (of lamprophyric affinity) is followed by porphyritic monzonite, quartz monzodiorite and finally a quartz monzonitic stock at the centre.SiO2, Al2O3 and Na2O increase from the primitive lamprophyric mafic syenite to the quartz monzonite through the intermediate members, while CaO, MgO, Fe2O3T, TiO2, P2O5 and MnO show an opposite trend suggesting fractionation of hornblende, clinopyroxene, biotite, apatite, sphene, and iron oxide minerals. Rb, Th and U increase with a complementary decrease in Sc, V, Cr, Co, Cu, Sr and Ba from the outer mafic syenite to the inner quartz monzonite. Y, Zr and Hf decrease from lamprophyric mafic syenite to quartz monzodiorite and the trend is reversed in the final quartz monzonite phase. However, the suite is characterised by a compositional gap between quartz monzodiorite and quartz monzonite. Total REE gradually decrease from the mafic syenite to quartz monzonite and the REE distribution patterns show LREE-enriched and HREE-depleted parallel distributions with negligible Eu anomalies.The geochemical data suggest that the rock types were formed as products of progressive differentiation by crystal fractionation of calc-alkaline lamprophyric parent magma which was derived by partial melting of metasomatically enriched mantle in the Kabini lineament. Although the quartz monzonites conform to the trend of differentiated Kunduru Betta suite, the compositional gap between them and the quartz monzodiorite precludes their origin by simple differentiation. It is suggested that convective liquid fractionation might have resulted in the discrete body of quartz monzonite. 相似文献
8.
大庙斜长岩的40Ar/39Ar年龄测定呈现出一条典型的马鞍型年龄谱,在中温阶段有二个明显的坪年龄1656±15 Ma和1029±7 Ma,结合其构造位置和全球斜长岩分布来看,它们分别代表了侵位年龄和后期热扰动的时代。密云奥长环斑花岗岩中角闪石的40Ar/39Ar坪年龄为1716±21 Ma。两者时空上密切相关,代表了裂谷作用初期非造山环境中双模式岩浆作用产物。斜长岩类和苏长岩之间稀土配分模式的相似性表明,它们明显为同一成因的岩浆分异系列的产物。 相似文献
9.
浙东南某些中生代侵入岩体的^40Ar—^39Ar年龄测定 总被引：13，自引：3，他引：13
采用~(40)Ar~(39)Ar定年技术测定了浙东南几个侵入于磨石山群中的燕山期中酸性岩侵入体的年龄。梁弄岩体的石英闪长岩和二长花岗岩的年龄为101Ma,龙王堂岩体的花岗岩和钾长花岗岩的年龄均为110Ma,山头郑石英闪长岩年龄为108Ma,洪公石英正长岩的年龄为124Ma。此年龄范围与早白垩世太平洋洋底快速扩张期相当。 相似文献
10.
This study of the Pikes Peak batholith includes the mineralogy and petrology of quartz syenite at West Creek and of fayalite-bearing and fayalite-free biotite granite near Mount Rosa; major element chemistry of the batholith; comparisons with similar postorogenic, intracratonic, sodic to potassic intrusives; and genesis of the batholith.The batholith is elongate in plan, 50 by 100 km, composite, and generally subalkalic. It was emplaced at shallow depth 1,040 m. y. ago, sharply transects its walls and may have breached its roof. Biotite granite and biotite—hornblende granite are predominant; quartz syenite, fayalite granite and riebeckite granite are present in minor amounts.Fayalite-bearing and fayalite-free quartz syenite, fayalite-biotite granite and riebeckite granite show a well-defined sodic differentiation trend; the less sodic fayalite-free granites exhibit a broader compositional range and no sharp trends.Crystallization was largely at PH2O < Ptotal; PH2O approached Ptotal only at late stages. Aplite residual to fayalite-free biotite granite in the north formed at about 1,500 bars, or 5 km depth. Feldspar assemblages indicate late stages of crystallization at about 720°C. In the south ilmenite and manganian fayalite indicate fO2 of 10?17 or 10?18 bars. Biotite and fayalite compositions and the ‘granite minimum’ imply completion of crystallization at about 700°C and 1,500 bars. Nearby fayalite-free biotite granite crystallized at higher water fugacity.All types of syenite and granite contain 5–6% K2O through a range of SiO2 of 63–76%. Average Na2O percentages in quartz syenite are 6.2, fayalite granite 4.2, and fayalite-free granite 3.3 MgO contents are low, 0.03–0.4%; FeO averages 1.9–2.5%. FeO/Fe2O3 ratios are high. Fluorine ranges from 0.3 to 0.6%.The Pikes Peak intrusives are similar in mode of emplacement, composition, and probably genesis to rapakivi intrusives of Finland, the Younger Granites of Nigeria, Cape Ann Granite and Beverly Syenite, Mass., and syenite of Kungnat, Greenland, among others — allowing for different levels of erosion. A suite that includes gabbro or basalt, anorthosite, quartz syenite, fayalite granite, riebeckite granite, and biotite and/or hornblende granites is of worldwide occurrence.A model is proposed in which mantle-derived, convecting alkali olivine basaltic magma first reacts with K2O-poor lower crust of granulite facies to produce magma of quartz syenitic composition. The syenitic liquid in turn reacts with granodioritic to granitic intermediate crust of amphibolite facies to produce the predominant fayalite-free biotite and biotite-hornblende granites of the batholith. This reaction of magma and roof involves both partial melting and the reconstitution and precipitation of refractory phases, as Bowen proposed. Intermediate liquids include MgO-depleted and Na2O-enriched gabbro, which precipitated anorthosite, and alkali diorite. The heat source is the basaltic magma; the heat required for partial melting of the roof is supplied largely by heats of crystallization of phases that settle out of the liquid — mostly olivine, clinopyroxene and plagioclase. 相似文献
11.
A suite of post-kinematic, 1.88–1.87 Ga, silicic plutons crosscut 1.89–1.88 Ga synkinematic granitoids in the Central Finland Granitoid Complex (CFGC) in south-central Finland. The plutons range from biotite±hornblende quartz monzonite to syenogranite and include pyroxene- and olivine-bearing varieties. Mineral chemical data on feldspars, biotite, amphibole, pyroxenes, olivine, and oxides of the post-kinematic plutons are presented. The data are interpreted to show that these plutons register (1) a considerable range in pressure from 2–4 kbar (amphibole barometry) to 5–7 kbar (olivine–pyroxene barometry), (2) temperatures mostly reflecting resetting during cooling (450–800°C; QUIlF thermometry), and (3) low fO2 (log fO2 ΔFMQ −0.3 to −1.5; QUIlF equilibria). In particular, plutons with olivine- and pyroxene-bearing margins and amphibole-dominated central parts record progressive oxidation and hydration upon cooling, shifting from the QUIlF equilibrium toward KUIlB. The post-kinematic granites can be considered post-collisional in regard to compressional events in the CFGC and display many of the characteristics of the anorogenic 1.6 Ga rapakivi granites further south. They were presumably derived from a deep and dry crustal source, like the rapakivi granites. 相似文献
12.
Mantle derivation of Archean amphibole-bearing granitoid and associated mafic rocks: evidence from the southern Superior Province,Canada 总被引：5，自引：0，他引：5
Richard H. Sutcliffe Alan R. Smith William Doherty Robert L. Barnett 《Contributions to Mineralogy and Petrology》1990,105(3):255-274
Amphibole-bearing, Late Archean (2.73–2.68 Ga) granitoids of the southern Superior Province are examined to constrain processes of crustal development. The investigated plutons, which range from tonalite and diorite to monzodiorite, monzonite, and syenite, share textural, mineralogical and geochemical attributes suggesting a common origin as juvenile magmas. Despite variation in modal mineralogy, the plutons are geochemically characterized by normative quartz, high Al2O3 (> 15 wt%), Na-rich fractionation trends (mol Na2O/K2O >2), low to moderate Rb (generally<100 ppm), moderate to high Sr (200–1500 ppm), enriched light rare earth elements (LREE) (CeN generally 10–150), fractionated REE (CeN/YbN 8–30), Eu anomaly (Eu/Eu*) 1, and decreasing REE with increasing SiO2. The plutons all contain amphibole-rich, mafic-ultramafic rocks which occur as enclaves and igneous layers and as intrusive units which exhibit textures indicative of contemporaneous mafic and felsic magmatism. Mafic mineral assemblages include: hornblende + biotite in tonalites; augite + biotite ± orthopyroxene ± pargasitic hornblende or hornblende+biotite in dioritic to monzodioritic rocks; and aegirine-augite ± silicic edenite ± biotite in syenite to alkali granite. Discrete plagioclase and microcline grains are present in most of the suites, however, some of the syenitic rocks are hypersolvus granitoids and contain only perthite. Mafic-ultramafic rocks have REE and Y contents indicative of their formation as amphibole-rich cumulates from the associated granitoids. Some cumulate rocks have skeletal amphibole with XMg(Mg/(Mg+ Fe2+)) indicative of crystallization from more primitive liquids than the host granitoids. Geochemical variation in the granitoid suites is compatible with fractionation of amphibole together with subordinate plagioclase and, in some cases, mixing of fractionated and primitive magmas. Mafic to ultramafic units with magnesium-rich cumulus phases and primitive granitoids (mol MgO/ (MgO+0.9 FeOTOTAL) from 0.60 to 0.70 and CT >150 ppm) are comagmatic with the evolved granitoids and indicate that the suites are mantle-derived. Isotopic studies of Archean monzodioritic rocks have shown LREE enrichment and initial 143Nd/144Nd ratios indicating derivation from mantle sources enriched in large ion lithophile elements (LILE) shortly before melting. Mineral assemblages record lower PH2O with increased alkali contents of the suites. This evidence, in conjunction with experimental studies, suggests that increased alkali contents may reflect decreased PH2O during mantle melting. These features indicate that 2.73 Ga tonalitic rocks are derived from more hydrous mantle sources than 2.68 Ga syenitic rocks, and that the spectrum of late Archean juvenile granitoid rocks is broader than previously recognized. Comparison with Phanerozoic and recent plutonic suites suggests that these Archean suites are subduction related. 相似文献
13.
Fatemeh Sarjoughian Ali Kananian Michael Haschke Jamshid Ahmadian 《Geological Journal》2016,51(3):387-404
The South Dehgolan pluton, in NW Iran was emplaced into the Sanandaj–Sirjan magmatic–metamorphic zone. This composite intrusion comprises three main groups: (1) monzogabbro–monzodiorite rocks, (2) quartz monzonite–syenite rocks, and (3) a granite suite which crops out in most of the area. The granites generally show high SiO2 content from 72.1%–77.6 wt.% with diagnostic mineralogy consisting of biotite and amphibole along the boundaries of feldspar–quartz crystals which implies anhydrous primary magma compositions. The granite suite is metaluminous and distinguished by high FeOt/MgO ratios (av. 9.6 wt.%), typical of ferroan compositions with a pronounced A‐type affinity with high Na2O + K2O contents, high Ga/Al ratios, enrichment in Zr, Nb, REE, and depletion in Eu. The quartz monzonite–syenites show intermediate SiO2 levels (59.8%–64.5 wt.%) with metaluminous, magnesian to ferroan characteristics, intermediate Na2O + K2O contents, enrichment in Zr, Nb, REE, Ga/Al, and depletion in Eu. The monzogabbro–monzodiorites show overall lower SiO2 content (48.5%–55.9 wt.%) with metaluminous and calc‐alkaline compositions, relatively lower Na2O + K2O contents, low Ga/Al ratios, and FeOt/MgO (av. 1.6 wt.%) ratios, low abundances of Zr, Nb, and lower REE element concentrations relative to the granites and quartz monzonite–syenites. These geochemical differences among the three different rocks suites are likely to indicate different melt origins. We suggest that the South Dehgolan pluton resulted from a change in the geodynamic regime, from compression to extension in the Sanandaj–Sirjan zone during Mesozoic subduction of the Neo‐Tethys oceanic crust beneath the Central Iranian microcontinent. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
14.
鞍山地区东鞍山花岗岩年代学、地球化学特征及成因研究 总被引：2，自引：1，他引：1
鞍山地区位于华北地台东北部辽宁省,区内保留有3.8~2.5Ga连续的地质记录。对位于鞍山市南侧的东鞍山花岗岩进行了SHRIMP锆石U-Pb同位素分析、白云母Ar-Ar同位素分析及岩石地球化学分析。SHRIMP测年结果为3004±7Ma,代表岩石的形成年龄,Ar-Ar测年结果为2545±16Ma,代表岩石受到构造热事件扰动的时间。岩体地化特征为富硅(Si O2=72.95%~75.37%,平均值为74.18%)、富碱(K2O+Na2O=7.05%~8.45%)、富铝(Al2O3=12.95%~15.44%),低钙(Ca O=0.13%~0.66%)。在稀土元素配分图上,曲线呈明显的右倾趋势,且有较明显的负Eu异常,重稀土分馏不明显。在微量元素洋中脊玄武岩标准化蛛网图上可以看出,东鞍山花岗岩强烈亏损Nb、P、Sr、Ti,富集大离子亲石元素Rb、K、Nd和高场强元素Th、U。岩石地球化学特征表明东鞍山花岗岩岩浆来源为壳源,残留相可能由石榴石+辉石+角闪石+斜长石组成。将鞍山-本溪地区3个3.0Ga花岗岩(东鞍山花岗岩岩体、铁架山二长花岗岩岩体以及弓长岭片麻状花岗岩)的地球化学数据进行对比,发现三者的地球化学存在较大差异,为三个独立的岩体。三个岩体最初可能发育在一个陆块之上,然后在25.5亿年左右分离开来,最后在25亿年左右再次拼贴到一起。 相似文献
15.
Jon Steen Petersen 《Lithos》1980,13(1):79-95
The intrusive Kleivan granite, Farsund area, SW Norway, shows a gradual unilateral zonation from charnockite through hornblende granite to biotite granite. Strong geochemical fractionation includes K/Rb variation from 478 to 121 and Rb/Sr from 0.13 to 26.4, and points towards a petrogenetic relationship with anorthosite suite rocks not apparent in the more homogeneous charnockites of the area. Close geochemical and petrographic similarity between the charnockitic part of the Kleivan granite and the Farsund charnockite suggest derivation of both plutons from a common source. Quantitative trace element modelling, based on crystal fractions derived from petrographic mixing calculations relating four main rock types, suggests that the Kleivan granite zonation may result from a fractional crystallization process, involving noritic and mangeritic cumulate-kindreds. The results therefore indicate strongly that simple relationships exist between charnockite and anorthosite rock-kindreds. A partial fusion model for the Farsund charnockite is favoured, since this explains the development of an anomalous Sr-87/Sr-86 ratio (0.7128 compared with 0.7053 for the Kleivan granite) and higher Rb/Sr ratios, other trace elements being similar for the two related charnockites. The recognition of substantial amounts of acid end members to the anorthosite suite of the Rogaland province supports an origin in common with andesine-type anorthosites for this igneous province. 相似文献
16.
《International Geology Review》2012,54(9):832-849
Pitinga Province is one of the main tin provinces of the Amazonian craton. The oldest unit in the studied area is the Iricoumé Group, which consists of rhyolites and rhyodacites with a 207Pb/206Pb zircon age of 1888 ± 3 Ma. This volcanic sequence is intruded by five A-type granite plutons. The studied portion of the Europa pluton is homogeneous, and composed of a peralkaline alkali-amphibole hypersolvus granite that yielded a 207Pb/206Pb zircon age of 1829 ± 1 Ma. The early facies of the Madeira pluton consists of a metaluminous amphibole-biotite syenogranite (rapakivi facies) with a 207Pb/206Pb zircon age of 1824 ± 2 Ma. It is intruded by a 1822 ± 1 Ma, mildly peraluminous biotite syenogranite. The later facies of this pluton consist of a porphyritic, hypersolvus, alkali-feldspar granite and an albite granite. Field relationships and an extensive drilling survey indicate that these two facies are sheet-shaped and were emplaced almost simultaneously. The hypersolvus alkali-feldspar granite has a 207Pb/206Pb zircon age of 1818 ± 2 Ma. Taking in account its field relationships with the albite granite, a similar age is assumed for the latter. The albite granite intrudes the biotite granite and rapakivi granite facies of the Madeira pluton, which was emplaced by shallow-level cauldron subsidence. The albite granite is sheet shaped and consists of a magmatic peralkaline cryolite-bearing core facies partially surrounded by an autometa-somatic peraluminous fluorile-bearing border facies. Both albite granite facies are strongly tin-mineralized and display anomalous contents of Nb, Rb, Zr, and REE. A massive body of cryolite and pegmatitic rocks is associated with the albite granite. The contrast in age between the Iricoume Group and the Europa + Madeira granites demonstrates that the plutons are not subvolcanic intrusions related to the extrusives. The ages of 1824 ± 2 Ma, 1822 ± 2 Ma, and 1818 ± 2 Ma obtained, respectively, for the amphibole + biotite syenogranite, biotite granite, and porphyritic hypersolvus granite of the Madeira pluton are consistent with the emplacement sequence inferred for these facies. These ages indicate that the Madeira pluton was emplaced in a relatively short time. Its facies are a little younger than the peralkaline granite of the Europa pluton, suggesting that the latter is not coeval with the Madeira peralkaline albite granite. 相似文献
17.
华北地块南缘老牛山杂岩体时代、成因及地质意义——锆石年龄、Hf同位素和地球化学新证据 总被引：13，自引：1，他引：12
老牛山杂岩体位于华北地块南缘。野外侵入关系和锆石LA-ICP-MS U-Pb定年显示,其由晚三叠世(印支期)和晚侏罗(燕山期)花岗质岩石组成。印支期岩石类型为石英二长岩、石英闪长岩和粗粒黑云母二长花岗岩,年龄分别为223±1Ma、222±1Ma和214±1Ma; 燕山期为中粒-中粗粒黑云母二长花岗岩和细粒-中细粒黑云母二长花岗岩,年龄分别为152±1Ma和146±1Ma。印支期石英闪长岩、石英二长岩的SiO2相对含量低、富碱、高铝,为钾玄系列,准铝质Ⅰ型花岗岩;印支期粗粒黑云母二长花岗岩具富硅、碱、高铝、低镁的特点,属于高钾钙碱性系列,为准铝质-过铝质Ⅰ型花岗岩;燕山期黑云母二长花岗岩具高硅和铝、富碱,低镁的特点,为高钾钙碱性系列,准铝质Ⅰ型花岗岩。组成老牛山杂岩体的花岗岩从早到晚SiO2含量由低变高,MgO、CaO和Na2O由高变低。各期次岩石均表现出稀土元素总量较高,轻稀土元素明显富集,轻、重稀土元素分馏明显,具有较弱的铕异常。两期花岗质岩石均富集大离子亲石元素(K、Rb、Ba、Sr),而相对亏损高场强元素(Nb、Ta、P)。印支期花岗质岩石的全岩εNd(t)为-11.3~-14.87,tDM为1.7~1.9Ga,锆石的εHf(t)为-9.57~-25.11,tDM2为1863~2841Ma;燕山期花岗岩的全岩εNd(t)为-13.32~-16.83,tDM为 1.7~1.9Ga,锆石的εHf(t)为-18.28~-24.79,tDM2 为2360~2767Ma,表明该杂岩体的源区物质以壳源物质为主,可能与太古宙太华群相似,印支期有年轻地幔物质贡献。 相似文献
18.
文章对位于南岭西段湘桂交界处的都庞岭东侧岩体开展了锆石SHRIMP U-Pb年代学、岩石学、矿物化学、岩石地球化学和Sm-Nd、Lu-Hf同位素分析研究。锆石SHRIMP U-Pb定年结果显示,粗中粒斑状黑云母二长花岗岩年龄为215.6±2.1 Ma,中粒斑状黑云母二长花岗岩年龄为220.5±1.8 Ma,中粒环斑黑云母二长花岗岩年龄为222.8±1.5 Ma,结合以往研究获得的细粒白云母二长花岗岩年龄209.7±3.1 Ma,认为岩体侵位时限介于222.8~209.7 Ma,为印支期岩浆活动产物,非以往认为的燕山期。环斑钾长石、黑云母聚晶的矿物化学特征表明环斑黑云母二长花岗岩形成过程中岩浆温度、压力、成分发生震荡变化,在玄武质岩浆的底侵作用下发生多次熔融作用形成黑云母聚晶。都庞岭黑云母二长花岗岩具有较高的SiO2和K2O+Na2O含量,A/CNK值为1.02~1.39,里特曼指数(δ)为0.93~2.18,属过铝质钙碱性系列;微量元素地球化学性质表现为富集REE、Rb、Th和U及较高的HFSE(Nb、Y和Ga),亏损Ba、Sr、Eu,具有高的TFeO/MgO、Ga/Al比值,地球化学特征显示为A型花岗岩;Nd同位素εNd(t)值为-8.74~-8.13,T2DM值为1.71~1.66 Ga;锆石Hf同位素εHf(t)值为-14.1~-1.4,T2DM值为2.14~1.34 Ga,显示都庞岭黑云母二长花岗岩主要源于古老地壳物质的部分熔融,并受到了一定程度的亏损地幔物质的混染。印支运动的变质峰期在258~243 Ma,233 Ma以后华南地区处于伸展的构造背景并受到幔源玄武质岩浆大范围底侵,诱发地壳物质重熔形成伸展背景下的都庞岭印支期铝质A型(环斑)花岗岩。 相似文献
19.
Petrological and geochemical evolution of the Kymi stock, a topaz granite cupola within the Wiborg rapakivi batholith, Finland 总被引：5，自引：0，他引：5
The 6×3 km Kymi monzogranite stock represents the apical part of an epizonal late-stage pluton that was emplaced within the 1.65 to 1.63 Ga Wiborg rapakivi batholith. The stock has a well-developed zonal structure, from the rim to the center: stockscheider pegmatite, equigranular topaz granite, porphyritic topaz granite. The contact between the two granites is usually gradational within a few centimeters, but local inclusions of the porphyritic granite in the equigranular granite indicate that the latter solidified later. Hydrothermal greisen and quartz veins, some of which contain genthelvite, beryl, wolframite, cassiterite, and sulfides, cut the granites of the stock and the surrounding country rocks. The equigranular granite contains 1 to 4 vol.% topaz, and its biotite is lithian siderophyllite; the porphyritic granite has 0 to 3 vol.% topaz, and the mica is siderophyllite. The equigranular granite is geochemically highly evolved with elevated Li, Rb, Ga, Ta, and F, and very low Ba, Sr, Ti, and Zr. The REE patterns show deep negative Eu anomalies and tetrad effects indicating extreme magmatic fractionation and aqueous fluid–rock interaction. The zonal structure of the stock is interpreted as a result of differentiation within the magma chamber. Internal convection in the crystallizing magma chamber and upward flow of residual melt as a boundary layer along sloping contacts resulted in accumulation of a layer of highly evolved, volatile-rich magma in the apical part of the chamber. Crystallization of this apical magma produced the stockscheider pegmatite and the equigranular granite; the underlying crystal mush solidified as the porphyritic granite. Much of the crystallization took place from volatile-saturated melt, and episodic voluminous degassing expelled fluids into opened fractures where they or their derivatives reacted with country rocks and caused alteration and mineralization. 相似文献
20.
通过对桂北平英花岗质岩体详细的锆石U-Pb年代学、Hf同位素组成及岩石地球化学特征的研究,论证了岩体的形成时代、成因类型、源区性质及其与宝坛锡矿的成矿关系。该岩体中心相-粗粒黑云母花岗岩的锆石LA-MC-ICP-MS U-Pb定年表明,其~(206)Pb/~(238)U加权平均年龄为834.2±5.1 Ma,属新元古代构造岩浆活动的产物。平英花岗岩具有高硅、富碱、强过铝质的特征,岩石富集Cs、Rb、U、Ta而亏损Ba、Sr、Ti等元素。球粒陨石标准化稀土配分曲线呈右倾形和强烈的Eu负异常(Eu/Eu*=0.05~0.31)。花岗岩中锆石的εHf(t)值介于-12.6~-1.6之间,峰值在-4.8~-3.0之间;二阶段模式年龄T_(DM)~C(Hf)在1.83~2.51 Ga之间,峰值在1.9~2.0 Ga之间。这些特征表明平英岩体形成于该区古元古代富硼基底的部分熔融作用,并经历了高度的分异演化过程。桂北九万大山—元宝山地区的新元古代黑云母花岗岩具有良好的锡成矿潜力,是华南多时代花岗岩演化及锡多金属成矿系列的重要组成部分。 相似文献