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1.
东昆仑五龙沟地区猴头沟二长花岗岩年龄、成因、源区及其构造意义 总被引：5，自引：0，他引：5
对东昆仑造山带五龙沟地区的猴头沟二长花岗岩开展了详细的岩相学、地球化学、锆石U-Pb年龄及Hf同位素的分析测试和研究工作。LA-ICP-MS锆石U-Pb测年表明,猴头沟二长花岗岩的206Pb/238U加权平均年龄值为(419.0±1.9)Ma,属于晚志留世。岩石地球化学数据表明:猴头沟二长花岗岩属于高钾钙碱性系列的A2型花岗岩,富SiO2、K2O、Y(>33×10-6)和Yb,贫Al2O3和Sr(<100×10-6),具有强烈的负铕异常;Rb、Th、U、La、Ce、Nd相对富集,Nb、Ta、Ba、Sr、P、Ti亏损。锆石的Hf同位素研究表明,其εHf(t)值为0.2~5.1,对应二阶段模式年龄(TDM2)为1066~1371 Ma,由此推测花岗岩源区来自中元古代镁铁质下地壳部分熔融。微量元素及其特征比值的构造判别图解表明,猴头沟二长花岗岩形成于早古生代晚志留世东昆仑造山旋回的造山后伸展阶段。据此认为,原特提斯洋在东昆仑地区的最晚闭合时限应该不晚于晚志留世末期(~419 Ma),而不是前人认为的早泥盆世。 相似文献
2.
淡色花岗岩是研究浅部地壳物质成分和碰撞造山带地球动力学过程的理想对象,也是稀有金属成矿的重要载体。本文研究的帕戈勒二云母花岗岩发育在西藏冈底斯念青唐古拉复式花岗岩岩基的西南侧,以岩株和岩枝形式产出,局部偶见绿柱石。精细的锆石U-Pb定年显示,岩体结晶成岩年龄为18.4 Ma和17.6 Ma,形成于中新世。岩体具有高的SiO2(72.78%～75.53%)和K2O(4.83%～5.52%)含量,低的Al2O3(13.42%～14.60%)、MgO(0.10%～0.24%)、TFe2O3(0.86%～1.65%)含量,A/CNK为1.04～1.12,属于过铝质高钾钙碱性-钾玄质花岗岩。(87Sr/86Sr)i=0.712139～0.713545,εNd(t)=-9.0～-8.3,Nd二阶段模式年龄tDM2=1211～1468 Ma,206 相似文献
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新疆阿尔泰额尔齐斯构造带片麻岩的锆石U-Pb SHRIMP定年及其地质意义 总被引：3，自引：1，他引：2
对包括额尔齐斯构造带中片麻岩在内的新疆阿尔泰地区中深变质岩石的时代一直存在争议,李天德等将阿尔泰山造山带中大部分中深变质岩划分为古-中元古界克木齐群和新元古代富蕴群,引起了广泛的关注和争议,特别是对位于额尔齐斯构造带中片麻岩的时代问题争议颇多。笔者对该片麻岩采样进行主量元素、微量元素分析及锆石U-Pb SHRIMP年龄测定,表明该处片麻岩以正变质岩为主,成分与闪长质、石英闪长质岩石相当,为后碰撞阶段岩浆活动的产物。锆石U-Pb SHRIMP定年结果表明其锆石主要为岩浆锆石,206Pb/238U年龄主要为350~295 Ma,其中10个点构成的谐和年龄为（326±6）Ma,为石炭纪构造-岩浆活动的产物。该片麻岩中没有前寒武纪古老锆石的年龄信息,基本上可以否定该片麻岩形成于前寒武纪的观点,应为晚古生代的产物。结合前人研究成果,认为阿尔泰造山带中深变质岩可能为不同时代的产物。 相似文献
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《四川地质学报》2022,(1)
运用磷灰石裂变径迹法对鹰咀山花岗岩进行了分析,所取样品的裂变径迹年龄位于50.669.6Ma之间,小于其地层时代或侵入年龄,表明摩天岭推覆构造带的隆升开始于晚白垩世,用磷灰石裂变径迹年龄来计算可知:研究区内花岗岩50.6Ma以来的冷却速率和剥蚀速率分别为2.08℃/Ma和0.063mm/a,50.669.6Ma之间,小于其地层时代或侵入年龄,表明摩天岭推覆构造带的隆升开始于晚白垩世,用磷灰石裂变径迹年龄来计算可知:研究区内花岗岩50.6Ma以来的冷却速率和剥蚀速率分别为2.08℃/Ma和0.063mm/a,50.669.6Ma之间的相对抬升与剥蚀速率为0.013mm/a,因此说明摩天岭推覆构造带从晚白垩世以来一直处于持续隆升冷却的过程。 相似文献
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赣西北蒙山岩体的锆石U-Pb-Hf、地球化学特征及成因 总被引：3，自引：0，他引：3
华南印支期花岗岩形成的构造背景和成因机制存在较大的争议,赣西北印支期岩浆活动的规模及该次岩浆活动是否与基性岩浆的底侵有关,仍缺乏可靠的资料.过去认为赣西北蒙山花岗岩形成于燕山期,而本次锆石LA-ICP-MS U-Pb年代学研究表明,蒙山3次花岗质岩浆活动的时间分别为236±3 Ma,220±3 Ma和217±1 Ma.蒙山花岗岩属准铝－过铝质,高硅、富钾,K2O+Na2O为7.53%~8.86%;稀土总量为213.09~380.75 μg/g,轻稀土元素富集,δEu=0.07~0.40,富集大离子亲石元素,Nb-Ta弱亏损,P、Ti亏损.大部分花岗岩的εNd(t)值为-9.9~-6.1,Nd二阶段模式年龄tDM2为1.5~1.8 Ga.第1次形成的灰白色粗粒花岗岩锆石的εHf(t)值大部分集中在1.10~2.65,Hf同位素单阶段模式年龄tDM1集中分布于782~866 Ma,二阶段模式年龄tDM2集中分布在1 096~1 186 Ma,说明其物源主要为新元古代早期形成的地壳;第3次形成的细粒花岗岩锆石的εHf(t)值集中分布于1.71~4.98,tDM1为671~832 Ma,tDM2集中在932~1 139 Ma.蒙山细粒花岗岩锆石的Hf同位素组成暗示成岩过程中有基性岩浆加入,为华南部分印支期花岗岩的成因与基性岩浆底侵有关的关系提供了证据.蒙山花岗岩的Nd同位素和锆石Hf同位素出现了解耦现象,解耦原因可能与花岗岩的物源主要为新元古代早期形成的具有Nd-Hf解耦特征的弧源地壳有关.根据目前获得的有关华南印支期火成岩的资料,总结了华南印支期花岗岩类岩石的成因类型及其时空分布规律,据此讨论了华南印支期的动力学背景和华南印支期花岗岩的成因机制,认为华南印支期的构造－岩浆活动与古太平洋西北向俯冲于华南板块之下有关. 相似文献
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阿尔泰造山带位于西伯利亚板块与哈萨克斯坦-准噶尔板块之间,是中亚造山带重要组成部分。长期以来,阿尔泰何时结束造山一直存在争议,阻碍了对中亚造山带晚古生代构造演化的认识。中国阿尔泰造山带南缘发育早二叠世花岗岩,具有碱性或A型花岗岩特征,能够反映碰撞后伸展的构造环境。青河岩体位于阿尔泰造山带东南部,主要由二长花岗岩和少量闪长岩组成,具有研究阿尔泰造山带晚期构造演化的条件。本文以此为切入点,对青河岩体开展年代学和地球化学工作。新的测年数据表明似斑状二长花岗岩(283±3Ma)、中细粒二长花岗岩(280±2Ma)、糜棱岩化二长花岗岩(286±2Ma)和辉长闪长玢岩(269±1)均形成于早二叠世。岩体高硅(SiO_2=61. 98%～73. 35%),富碱(K_2O+Na_2O=5. 84%～8. 72%,碱度率AR=2. 12～3. 65),低钙(CaO=1. 29～3. 76%),里特曼指数σ=2. 38～2. 54,K_2O/Na_2O=0. 78～1. 06,属于高钾钙碱性岩石系列。微量元素显示Ba、Sr、P、Ti、Nb、Ta亏损,Eu明显负异常(δ_(Eu)=0. 46～0. 78),10000×Ga/Al=2. 85～2. 47,反映具有A型花岗岩特征,可作为阿尔泰碰撞造山作用结束的标志。另外,这些岩体ε_(Hf)(t)值介于+4. 04～+11. 78之间,二阶段模式年龄(t_(DM2))分别变化于880～694Ma、923～633Ma、875～555Ma、1030～635Ma,揭示其源区主要由新元古代幔源物质或新生地壳组成。结合区域上同时代、同构造位置富碱性(A型)花岗岩研究结果,认为青河中酸性岩体成因与地幔岩浆底侵早期下地壳有关,是新元古代玄武质物质再熔,并发生结晶分异的结果。因此,阿尔泰造山带于早二叠世(286～280Ma)已经结束了碰撞造山作用,处于伸展的构造背景。 相似文献
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云岭锡矿位于保山地块东缘的云岭花岗岩体内,含矿岩石主要为黑云母二长花岗岩,局部显示片麻状构造。本文锆石U-Pb定年结果表明云岭花岗岩侵位于222.8±1.3Ma,其Si O2为64.83%～66.05%,K2O为3.30%～3.72%,Na2O为1.91%～2.19%,铝饱和指数(A/CNK)为1.26～1.30,显示过铝质高钾钙碱性花岗岩特征。花岗岩中岩浆锆石和继承锆石εHf(t)值分别在-10.6～-13.9和-1.16～-23.8之间,对应tDM2(Ma)分别在1926～2138Ma和1951～3387Ma之间,表明岩浆主要来源于古老的地壳物质重熔。云岭花岗岩中Sn含量在4.3×10-6～14.2×10-6之间,花岗岩中岩浆黑云母Sn含量在5.8×10-6～9.6×10-6之间,蚀变花岗岩中的热液黑云母Sn含量为75.8×10-6～244.0×10-6<... 相似文献
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为揭示鄂西南齐岳山地区晚三叠世须家河组物源与构造背景,以周家湾与颜家沟剖面为代表,对须家河组碎屑岩的颗粒组分、元素组成以及锆石年龄进行测试与统计.结果显示:砂岩碎屑颗粒石英含量高、岩屑与长石含量低,平均值分别为76.15%、8.90%与3.45%,具有锆石-板钛矿-磁铁矿-榍石-电气石重矿物组合,反映源岩以酸性岩或低级变质岩为主,Dickinson判别图解表明物源主要来自再旋回造山带;砂岩(TFe2O3+MgO)*与TiO2*含量低,Al2O3/SiO2比值低,K2O/Na2O比值高,最接近被动大陆边缘特征值;泥岩成分变异指数ICV分布于0.32~0.79之间,平均值为0.56,反映物源主要为再旋回沉积物;样品稀土元素配分模式、特征微量元素含量及比值指示晚三叠世沉积构造背景为被动与活动大陆边缘;碎屑锆石分为磨圆与自形两类,磨圆者具有2 480 Ma、1 880 Ma、832 Ma年龄峰值(n=133),年龄频数分特征与扬子陆块最接近;自形锆石具有435 Ma、217 Ma年龄峰值(n=42),年龄频数分布特征与秦岭造山带和雪峰造山带花岗岩年龄具有很好的对应关系.结合物源与构造背景判别图解,上述特征综合表明须家河组形成于被动大陆边缘(为主)与活动大陆边缘环境,其物源来自东南的雪峰造山带(为主)与北侧的秦岭造山带. 相似文献
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澜沧江西侧的临沧花岗岩带和怒江以西的腾冲花岗岩带是滇西最主要的两个花岗岩带,它们形成于不同构造环境。Pb、Sr 同位素研究表明,腾冲花岗岩主要来源于1200-2000Ma 的上地壳(或未分异的地壳)物质,同位素组成变化范围较小,说明源区物质组分较均一。临沧带 Pb 同位素组成变化较大,其物源是上地壳、造山带和上地幔不均匀的混合物,基底时代为800-1600Ma。因此,临沧地区和腾冲地区的基底时代和性质不同,应视为两个不同的基底地体。 相似文献
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《International Geology Review》2012,54(4):463-471
Several Pb-Zn deposits and occurrences within Iran are hosted by Mesozoic–Tertiary-aged sedimentary and igneous rocks. This study reports new Pb isotope analyses for galena from 14 Pb-Zn deposits in the Alborz and Central Iran structural zones. In general, Pb isotope ratios are extremely variable with data plotting between the upper crustal and orogenic curves in a plumbotectonic diagram. The latter may be attributed to Pb inputs from crustal and mantle end-members. Most of the galena samples are characterized by high 207Pb/204Pb ratios, suggesting significant input of Pb from old continental crust or pelagic sediment. Pb isotope data also indicate that some of the deposits, which are hosted by sedimentary rocks in Central Iran and Alborz, have similar Pb isotopic compositions and hence suggest similar source regions. Most of the galenas yield Pb model ‘ages’ that vary between ~140 and ~250 Ma, indicating that mineralization resulted from the extraction of ore-bearing fluids from Upper Triassic–Lower Jurassic sequences. The similarity in Pb isotope ratios for the Pb-Zn deposits located within these zones suggests analogous crustal evolution histories. Our preferred interpretation is that Pb-Zn mineralization within the sedimentary and igneous rocks of the Central Iran and Alborz tectonic regions occurred following a Late Cretaceous–Tertiary accretionary stage of crustal thickening in Iran. 相似文献
13.
Exposed cross‐sections of the continental crust are a unique geological situation for crustal evolution studies, providing the possibility of deciphering the time relationships between magmatic and metamorphic events at all levels of the crust. In the cross‐section of southern and northern Calabria, U–Pb, Rb–Sr and K–Ar mineral ages of granulite facies metapelitic migmatites, peraluminous granites and amphibolite facies upper crustal gneisses provide constraints on the late‐Hercynian peak metamorphism and granitoid magmatism as well as on the post‐metamorphic cooling. Monazite from upper crustal amphibolite facies paragneisses from southern Calabria yields similar U–Pb ages (295–293±4 Ma) to those of granulite facies metamorphism in the lower crust and of intrusions of calcalkaline and metaluminous granitoids in the middle crust (300±10 Ma). Monazite and xenotime from peraluminous granites in the middle to upper crust of the same crustal section provide slightly older intrusion ages of 303–302±0.6 Ma. Zircon from a mafic to intermediate sill in the lower crust yields a lower concordia intercept age of 290±2 Ma, which may be interpreted as the minimum age for metamorphism or intrusion. U–Pb monazite ages from granulite facies migmatites and peraluminous granites of the lower and middle crust from northern Calabria (Sila) also point to a near‐synchronism of peak metamorphism and intrusion at 304–300±0.4 Ma. At the end of the granulite facies metamorphism, the lower crustal rocks were uplifted into mid‐crustal levels (10–15 km) followed by nearly isobaric slow cooling (c. 3 °C Ma?1) as indicated by muscovite and biotite K–Ar and Rb–Sr data between 210±4 and 123±1 Ma. The thermal history is therefore similar to that of the lower crust of southern Calabria. In combination with previous petrological studies addressing metamorphic textures and P–T conditions of rocks from all crustal levels, the new geochronological results are used to suggest that the thermal evolution and heat distribution in the Calabrian crust were mainly controlled by advective heat input through magmatic intrusions into all crustal levels during the late‐Hercynian orogeny. 相似文献
14.
In the Serre mountains of Calabria, Italy, an exposed section of the continental crust, as left by the Hercynian orogeny, consists of intermediate-lower to upper crustal units. Huge masses of granitoids separate the lower from the upper crustal units. Many mica ages have been obtained from metamorphic and plutonic rocks, which have been interpreted as reflecting continuous cooling or discrete Mesozoic events. A reappraisal of previously determined isotopic data integrated with new Rb–Sr biotite ages is presented and assessed at regional scale to better constrain the post-Hercynian geological evolution of the continental crust of the Serre. The ages cover a wide span of time and form clusters which fit a model involving magmatic, hydrothermal and tectonic events preceding and accompanying the opening and closure of the Tethyan ocean. 相似文献
15.
《地学前缘(英文版)》2023,14(3):101525
So far, the nature and evolution of the lower crust under central Spain have been constrained mainly on the basis of a heterogeneous suite of granulite xenoliths from the Spanish Central System (SCS). In recent years, ultramafic volcanics from the Calatrava Volcanic Field (CVF) have also provided deep-seated crustal xenoliths which have not been studied in detail. Our data, combining mineral, whole-rock and isotopic geochemistry with U–Pb–Hf isotope ratios in zircons from the CVF and SCS xenoliths, highlight the felsic composition of the lower crust under central Iberia. A number of the Calatrava xenoliths represents Variscan igneous protoliths, which are a minor population in the SCS, and were likely formed by crystallisation of intermediate and felsic melts in the lower crust during the Variscan orogeny (leucodiorite protolith age of 314 ± 3 Ma and leucogranite protolith age of 308 ± 2.5 Ma). U–Pb data of metamorphic zircons show that granulite-facies metamorphism mainly occurred from 299 to 285 Ma in both areas. These ages are slightly younger than those of granitic intrusions that could be genetically related to the granulitic residue, which points to a main role of U–Pb isotope resetting in lower crustal zircons during HT or UHT conditions. The zircon U–Pb–Hf isotopic ratios support the idea that the lower crust in central Iberia consists mainly of Ordovician–Neoproterozoic metaigneous and metasedimentary rocks associated with the Cadomian continental arc of northern Gondwana. These rocks provide evidence of mixing between juvenile magmas and an enriched crustal component, ultimately extracted from an Eburnean crust. Other more evolved components present in detrital zircons are likely related to recycling of Archean crust derived from North Africa cratonic terranes. 相似文献
16.
E. J. Krogstad G. N. Hanson V. Rajamani 《Contributions to Mineralogy and Petrology》1995,122(1-2):159-173
Conspicuous Nd, Sr and Pb isotopic differences exist between the Archean gneiss terranes adjoining the suture at the Kolar
Schist Belt, south India. These gneisses, which are the deformed equivalents of plutonic and volcanic rocks, have known or
inferred igneous ages of 2630 to 2530 Ma. Initial isotopic ratios of Nd, Sr and Pb suggest that metaplutonic gneisses west
of the Kolar Schist Belt were emplaced into, and variably contaminated by, an evolved continental crust that formed prior
to 3200 Ma. Felsic metaigneous gneisses that occur as slivers on the western margin of the schist belt have an isotopic character
similar to that of the metaplutonic rocks on the same side of the Kolar Schist Belt. On the east side of the Kolar Schist
Belt the isotopic evidence suggests that the 2530 Ma granitic gneisses were not derived from or contaminated by an older continental
crust. Their source probably evolved with a Nd isotopic composition similar to that of typical Archean mantle, but became
light rare earth element enriched after 2900 to 2700 Ma. The inferred tectonic setting for the west side of the Kolar Schist
Belt is an Andean continental magmatic arc. For the east side of the Kolar Schist Belt, a possible Phanerozoic analog is an
evolved island arc, such as Japan.
Received: 24 June 1994/Accepted: 9 January 1995 相似文献
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鲁西地区绿岩带金矿床铅同位素研究 总被引：2，自引：0，他引：2
在鲁西太古宙绿岩带中,分布有较多的绿岩带变生热液－构造蚀变岩型金矿,具有良好的找矿前景。从铅同位素组成来看,区内铅同位素变化较大,多为放射性成因铅质量分数较高的异常铅。所测同位素样品中,以黄铁矿铅同位素组成变化最大,是铅同位素在演化过程中受到放射性铀铅和钍铅不同程度混染的结果,多数样品单阶段模式年龄不具计时意义。计算表明,区内铅来源于ｕ＝９．２０,ｗ＝３７．４５,ｋ＝３．９５的源区,在５９５Ｍａ前 相似文献
19.
V. M. Savatenkov V. V. Yarmolyuk A. M. Kozlovsky Z. B. Smirnova O. E. Sviridova 《Petrology》2018,26(4):351-367
The Khangai batholith is one of the largest groups of granitoid plutons produced in Central Asia in the Late Permian–Early Triassic, at 270–240 Ma. The batholith occurs in the Khangai collage of Precambrian terranes, which include Early Precambrian crustal blocks (Dzabkhan and Tarbagatai) and Early to Late Neoproterozoic structures of the Songino block in their surroundings. The axial zone of this collage is overprinted by a basin filled with Devonian volcanic–siliceous rocks and Early to Middle Carboniferous terrigenous rocks. The isotopic parameters (Nd and Pb) of granitoids in the Khangai batholith indicate that the melts were derived from compositionally contrasting crustal sources and a single mantle one. The massifs hosted in the Precambrian blocks were produced with the involvement of lower crustal material, with various ages of the origin of the crust and its differentiation into upper and lower ones. The crust of the Tarbagatai and Dzabkhan blocks was produced in the Early Archean and was differentiated at the Archean–Proterozoic boundary. The crust of the Songino block was formed in the Paleoproterozoic and differentiated in the Early Neoproterozoic. According to the Pb and Nd isotopic parameters of granitoids in the Khangai Basin, the regional continental crust was close to the juvenile one, i.e., the continental crust of the Khangai Basin had still not been differentiated by the time when the Khangai batholith was produced. A single mantle source was involved in the origin of the melts of granitoids of the Khangai batholith in various tectonic blocks. The evolution of the Pb isotopic composition of this sources is consistent with the Stacey–Kramers model at µ = 9.5. This source can be identified with the enriched mantle, which has a higher U/Pb ratio than the depleted mantle and lower εNd(T) of 0 to +2. 相似文献
20.
Geochronology of the Karadere basement (NW Turkey) and implications for the geological evolution of the Istanbul zone 总被引：48，自引：0，他引：48
F. Chen W. Siebel M. Satir M. Terzioğlu K. Saka 《International Journal of Earth Sciences》2002,91(3):469-481
Earlier geological work in the Istanbul zone, western Pontide tectonic belt, has revealed the presence of extensive basement outcrops exposed underneath Palaeozoic and Mesozoic to Tertiary cover sequences. The basement of suspected Neoproterozoic age plays an important role in understanding the crustal accretion process in NW Turkey. We report the first results of a detailed Pb-Pb and U-Pb zircon study complemented by Nd-Sr whole rock and mineral data from basement rocks exposed in the Karadere valley, Safranbolu area. Five samples were selected for this study, comprising three metagranitoids and two metasediments. Zircon geochronology indicates that the metagranitoids were formed during Late Proterozoic pan-African magmatic events between 590 and 560 Ma. The rocks are of tonalitic and granitic composition and have low Nb/Y ratios and Ti contents, consistent with those of arc rocks. A continental arc setting is supported by their Sr and Nd isotope data that indicate a contribution of a mantle source as well as crustal assimilation during magma genesis. The metasediments can clearly be distinguished from the metagranitoids by their higher 87Sr/86Sr ratios and lower )Nd-values at 580 Ma, which supports the suggestion that the arc was underlain by mature continental crust. Zircons from the metasediments yield a range of Pb-Pb ages between 1,860 and 710 Ma. Thirty per cent of them fall between 890 and 710 Ma, possibly suggesting a derivation from Gondwana (Afro-Arabian) regions. A Sm-Nd garnet-whole rock analysis obtained on a metagranite gives an age of 559NJ Ma, which either reflects pre-metamorphic magmatic growth of garnet in a felsic melt or a syntectonic high-temperature metamorphic event. Uplift and cooling of the basement is further constrained by Rb-Sr biotite ages of 548-545 Ma. These lower Cambrian mineral ages demonstrate that the Istanbul zone was not thermally reactivated during the Hercynian, Cimmerian or Alpine orogeny, in contrast to its neighbouring tectonic zones, confirming its role as a suspect terrane in the modern western Pontide tectonic belt. 相似文献