Perogenesis of granites, Sharm El-Sheikh area, South Sinai, Egypt: petrological constrains and tectonic evolution

Precambrian granites of the Sharm El-Sheikh area in south Sinai, Egypt belong to collisional and post-collisional Magmatism (610–580 Ma). The granites are widely distributed in the northern part of the Neoproterozoic Arabian-Nubian Shield. South Sinai includes important components of successive multiple stages of upper crust granitic rocks. The earliest stages include monzogranite and syenogranites while the later stages produced alkali feldspar granites and riebeckite-bearing granites. Numerous felsic, mafic dikes and quartz veins traverse the study granites. Petrographically, the granitic rocks consist mainly of perthite, plagioclase, quartz, biotite and riebeckite. Analysis results portray monzogranites displaying calc-alkaline characteristics and emplaced in island-arc tectonic settings, whereas the syenogranites, alkali-feldspar granites and the riebeckite bearing-granites exhibit an alkaline nature and are enriched in HFSEs similar to granites within an extensional regime. Multi-element variation diagrams and geochemical characteristics reinforce a post-collision tectonic setting. REEs geochemical modeling reveals that the rocks were generated as a result of partial melting and fractionation of lower crust basaltic magma giving rise to A₁ and A₂ subtype granites. They were subsequently emplaced within an intraplate environment at the end of the Pan-African Orogeny.     

华南桂东南地区加里东期Ⅰ型花岗岩类的岩石成因及构造意义

龙新岩体和夏郢岩体位于扬子地块与华夏地块拼合带的西南端,岩体中的Ⅰ型花岗岩成因研究对揭示桂东南地区早古生代的地球动力学背景及其构造演化具有重要的地质意义.对龙新岩体的寄主岩和其暗色微粒包体,以及夏郢岩体岩石进行了LA-ICP-MS锆石U-Pb定年、Lu-Hf同位素和全岩地球化学研究.锆石U-Pb定年结果显示,龙新岩体的寄主岩(花岗闪长岩)的年龄为440±2 Ma;龙新岩体的暗色包体(闪长岩)的年龄为441±1 Ma,寄主岩与暗色包体为同期岩浆作用的产物.夏郢岩体花岗闪长岩和二长花岗岩年龄分别为447±3 Ma和436±3 Ma,说明夏郢岩体至少发生了2期岩浆侵入事件.Hf同位素研究表明,龙新岩体寄主岩和暗色微粒包体的锆石ε_Hf(t)值分别为-3.32～-5.83和-17.89～-1.82,二阶段模式年龄(T_DM2)分别为1.62～1.76 Ga和1.57～2.54 Ga;夏郢岩体早期花岗岩闪长岩和晚期二长花岗岩的锆石ε_Hf(t)值分别为-15.43～3.03和-4.79～6.82,T_DM2分别为1....     

辽东半岛丹东地区中生代花岗岩锆石U-Pb年龄、Hf同位素特征及其地质意义

为了确定辽东半岛丹东地区中生代花岗岩岩石类型、成岩时代及其形成构造背景.选取三股流岩体、五龙背岩体和丁岐山岩体开展岩相学、锆石LA-ICP-MS U-Pb年代学、岩石地球化学和锆石Hf同位素地球化学研究.结果表明:三股流岩体由花岗闪长岩、似斑状黑云母二长花岗岩和中粗粒黑云母二长花岗岩组成,后两者成岩年龄分别为137.2±1.2 Ma和123.2±1.3 Ma;丁岐山岩体由中细粒碱长花岗岩、石英正长岩和石英二长岩组成,获得中细粒碱长花岗岩成岩年龄为121.1±1.5 Ma;五龙背岩体由中粗粒二长花岗岩组成,成岩年龄为146.8±0.8 Ma.元素和同位素地球化学特征表明,三股流岩体的花岗闪长岩为钾玄岩系列,似斑状黑云母二长花岗岩和中粗粒黑云母二长花岗岩以及五龙背岩体和丁岐山岩体均为高钾钙碱性,3个岩体不同岩石类型的A/CNK均小于1.1,为I型花岗岩;岩体均富集轻稀土元素和大离子亲石元素,亏损重稀土元素和高场强元素,具Eu负异常;ε_Hf（t）值为-22.40~-9.77,两阶段Hf模式年龄T_DM2为2 999~1 915 Ma,揭示三股流岩体、五龙背岩体和丁岐山岩体可能是古元古代古老地壳部分熔融形成.结合区域构造演化认为三股流岩体、五龙背岩体和丁岐山岩体均形成于活动大陆边缘,五龙背岩体形成于古太平洋板块向欧亚板块的俯冲挤压的构造背景,三股流岩体和丁岐山岩体形成于古太平洋板块向欧亚板块的俯冲后的伸展环境.      

辽东五龙重融型花岗质岩体锆石U-Pb年代学、岩石地球化学、Sr-Nd-Pb-Hf同位素特征及地质意义

在华北克拉通东北缘的辽东半岛广泛发育一套形成于侏罗纪的花岗质岩体,出露于丹东地区的五龙花岗质岩体为五龙大型金矿床的围岩,岩体内分布有古元古界辽河岩群变质岩残留体和古元古代侵入岩残留体,多数发育碎裂岩化和糜棱岩化构造.对五龙岩体进行详细解体,认为其是由黑云母二长花岗岩、二云母二长花岗岩、黑云母花岗岩和花岗闪长岩组成的一套酸性侵入岩组合.根据锆石SHRIMP U-Pb测年结果,获得4种岩性的岩浆结晶年龄分别为162±3 Ma、169.3±3.1 Ma、157.5±1.7 Ma、158.0±2.7 Ma,形成于中-晚侏罗世.岩石地球化学特征显示,五龙岩体属于钙碱性-高钾钙碱性、过铝质、中温花岗质岩浆系列,富集Rb、Th、U、K等大离子亲石元素（LILE）,亏损Nb、Ta、P、Ti等高场强元素（HFSE）,δEu为0.56~1.97,异常变化范围较大,ε_Hf（t）值为-39.7~-22.9,二阶段模式年龄t_DM2为3 711~2 653 Ma,ε_Nd（t）值为-23.8~-20.2,t_DM2为2 782~2 487 Ma,显示岩浆源区来自太古代~古元古代壳源物质;结合Pb同位素特征以及石英、长石、云母的显微结构特征,认为五龙岩体是古元古代花岗岩和辽河岩群地层受侏罗纪~160 Ma陆壳重熔事件于上地壳原地重新结晶所形成的S型花岗质岩体,形成于中-晚侏罗世时期受古太平洋板块俯冲影响的挤压-造山构造背景.      

Neoproterozoic granites of Sharm El-Sheikh area,Egypt: mineralogical and thermobarometric variations

Calc-alkaline and alkaline intrusions of the late Neoproterozic form essential part of the Arabian–Nubian Shield. They were formed during the collision between East- and West-Gondwana. Sharm El-Sheikh area, Sinai, includes wide compositional array of these intrusions that can be considered as a case study. Variations in both tectonic and thermobarometric condition for granitic intrusions are studied. Four mappable granitic types are recognized namely monzogranite, syenogranite, alkali feldspar granites, and riebeckite-bearing granites. The monzogranite and the syenogranite of the study area are mostly I-type, whereas the alkali feldspar granite and the riebeckite-bearing granite belong to A-type granitoid. The calc-alkaline intrusions were formed in compressional setting due to decompressional melting of mafic lower crust. Partial melting and anatexing of crustal rocks are suggested to explain the protolith of the alkaline intrusions. The transition from the calc-alkaline magma to the alkaline one occurred as a result of the tectonic transition from compression regime to tectonic relaxation (extension setting) during the last stage of the Pan-African Orogeny. The amphiboles of the studied granites are classified as calcic- and alkali-amphiboles. The calcic-amphiboles are ferro-edenite while the alkali-amphiboles are typically riebeckite. Both amphibole types are of magmatic nature. Coexisting amphiboles and plagioclases are used to estimate the physicochemical parameters of magma crystallization. The syenogranite underwent temperature and pressure of formation range of 520–730 °C, <3 kbar. The alkali feldspar granite records 450–830 °C, <4 kbar, while the riebeckite-bearing granite records the lowest temperature condition among all varieties and estimate formation at 350–650 °C, <4 kbar.     

江西婺源东坑口酸性岩体年代学及成因研究

文章选取赣东北地区东坑口酸性岩体作为研究对象,对酸性岩体的岩相学、年代学及锆石原位Hf同位素、岩石地球化学进行研究。通过LA-ICP-MS锆石U-Pb定年得出东坑口酸性岩体中花岗斑岩的年龄为（134.25±0.99）Ma,花岗闪长斑岩加权平均年龄为（132.6±1.3）Ma,可以判断其形成时代属燕山晚期。东坑口酸性岩体主量元素地球化学特征基本一致,均为高钾钙碱性花岗岩,SiO₂含量较高,铝饱和指数A/CNK值均小于1.1,属于典型的I型花岗岩;微量元素地球化学表现为富集大离子亲石元素Rb、Th、U,明显亏损高场强元素Ti、P,轻微亏损Ba、Sr的特征;酸性岩体稀土元素特征具有一致性,Eu亏损不明显。结合Hf同位素表明酸性岩体的岩浆由下地壳变质砂岩部分熔融组合形成,且东坑口岩体具有典型的埃达克岩特征,为低Mg^#埃达克岩系。该酸性岩体是在陆陆碰撞过程中,碰撞挤压致使下地壳加厚以后,向伸展减薄转换的体制中形成的。产出环境为陆内造山环境,太平洋板块向华南大陆俯冲引起的弧后多阶段岩石圈伸展作用。     

Geochemistry and petrogenesis of post-collisional alkaline and peralkaline granites of the Arabian-Nubian Shield: a case study from the southern tip of Sinai Peninsula,Egypt

The southern Sinai Peninsula, underlain by the northernmost extension of the Arabian-Nubian Shield, exposes post-collisional calc-alkaline and alkaline granites that represent the youngest phase of late Neoproterozoic igneous activity. We report a petrographic, mineralogical and geochemical investigation of post-collisional plutons of alkaline and, in some cases, peralkaline granite. These granites intrude metamorphosed country rocks as well as syn- and post-collisional calc-alkaline granitoids. The alkaline and peralkaline granites of the southern tip of Sinai divide into three subgroups: syenogranite, alkali feldspar granite and riebeckite granite. The rocks of these subgroups essentially consist of alkali feldspar and quartz with variable amounts of plagioclase and mafic minerals. The syenogranite and alkali feldspar granite contain small amounts of calcic amphibole and biotite, often less than 3%, while the riebeckite granite is distinguished by sodic amphibole (5–10%). These plutons have geochemical signatures typical of post-collisional A-type granites and were most likely emplaced during a transition between orogenic and anorogenic settings. The parental mafic magma may be linked to lithospheric delamination and upwelling of asthenospheric mantle material. Differentiation of the underplated basaltic magma with contributions from the juvenile crust eventually yielded the post-collisional alkaline granites. Petrogenetic modelling of the studied granitic suite shows that pure fractional crystallization cannot quantitatively explain chemical variations with the observed suite, with both major oxides and several trace elements displaying trends opposite to those required by the equilibrium phase assemblage. Instead, we show that compositional variation from syenogranite through alkali feldspar granite to riebeckite granite is dominated by mixing between a low-SiO₂ liquid as primitive or more primitive than the lowest-SiO₂ syenogranite and an evolved, high-SiO₂ liquid that might be a high-degree partial melt of lower crust.     

甘肃西秦岭舟曲憨班花岗岩体的单颗粒锆石U-Pb年龄及地质意义

在 1:25万武都幅区域地质调查中对西秦岭憨班花岗岩体进行了调查研究,通过高 精度单颗粒锆石 U-Pb同位素测年,获得 ²⁰⁶ Pb/²³⁸ U表面年龄统计权重平均值分别为: 205±1 Ma 和212±1.4 Ma,属印支晚期。岩石化学和地球化学特征表明,憨班岩体属高钾钙碱性系列,在Rb-Yb+Nb和Nb-Y图解中,样品均投在火山弧花岗岩＋同碰撞花岗岩区。憨班岩体形成于陆陆碰撞造山阶段后期,可能形成于加厚地壳的部分熔融。     

Origin of Middle Cambrian and Late Silurian potassic granitoids from the western Kunlun orogen,northwest China: a magmatic response to the Proto-Tethys evolution

This paper presents new SHRIMP zircon U–Pb chronology, major and trace element, and Sr–Nd–Hf isotopic data of two Early Paleozoic granitic plutons (Yierba and North Kudi) from the western Kunlun orogen, in attempt to further constrain the Proto-Tethys evolution. SHRIMP zircon U–Pb dating shows that the Yierba pluton was emplaced in the Middle Cambrian (513?±?7 Ma) and the North Kudi pluton was emplaced in the Late Silurian (420.6?±?6.3 Ma). The Yierba pluton consists of quartz monzodiorite, quartz monzonite and granodiorite. These granitoids are metaluminous and potassic, with initial ⁸⁷Sr/⁸⁶Sr ratios of 0.7072–0.7096, ε_Nd (T) of ?0.2 to ?1.6 and ε_Hf (T) (in-situ zircon) of ?1.2. Elemental and isotopic data suggest that they were formed by partial melting of subducted sediments, with subsequent melts interacting with the overlying mantle wedge in an oceanic island arc setting in response to the intra-oceanic subduction of Proto-Tethys. The North Kudi pluton consists of syenogranite and alkali-feldspar granite. These granites are metaluminous to weakly peraluminous and potassic. They show an affinity of A₁ subtype granite, with initial ⁸⁷Sr/⁸⁶Sr ratios of 0.7077–0.7101, ε_Nd (T) of ?3.5 to ?4.0 and ε_Hf (T) (in-situ zircon) of ?3.9. Elemental and isotopic data suggest that they were formed by partial melting of the Precambrian metamorphic basement at a shallow depth (<30 km) during the post-orogenic regime caused by Proto-Tethyan oceanic slab break-off. Our new data suggest that the subduction of the Proto-Tethyan oceanic crust was as early as Middle Cambrian (～513 Ma) and the final closure of Proto-Tethys was not later than Late Silurian (～421 Ma), most probably in Middle Silurian.     

东昆仑东段都兰热水花岗岩锆石U-Pb年龄、地球化学及构造意义

都兰热水地区位于东昆仑造山带东段,发育着大量花岗岩岩石组合,主要岩石类型为二长花岗岩和花岗闪长岩,本文报道了对都兰热水地区二长花岗岩和花岗闪长岩的地球化学、LA-ICP-MS锆石U-Pb定年的研究结果,为建立完善的年代学格架和构造演化提供了新资料。锆石U-Pb同位素定年研究表明东昆仑东段都兰热水地区的二长花岗岩和花岗闪长岩的结晶侵位时代分别是232.4±1.3 Ma、230.8±1.1 Ma,属中三叠世花岗岩浆作用的产物。岩矿特征和岩石地球化学特征显示二长花岗岩和花岗闪长岩属高钾钙碱性I型花岗岩,具较高的K₂O含量(2.2%～4.74%);铝饱和指数A/CNK值都小于1.1,显示准铝质特征;P₂O₅与SiO₂之间存在明显的负相关性,还表现出富集轻稀土元素、大离子亲石元素(如K、Rb、La),亏损重稀土元素和高场强元素(如Nb、Ta、Ti、P)及Eu负异常特征。结合前人区域地质研究,我们认为东昆仑东段都兰热水地区花岗岩岩石组合是受幔源岩浆的底侵作用导致下地壳部分熔融而形成,幔源岩浆与壳源岩浆发生不同比...     

Origin of granites in an Archean high-grade terrane,southern India

Archean deep-level granites in southern India are similar geochemically to young granites from continentalmargin arc systems. They exhibit light REE enriched patterns with variable, but chiefly positive Eu anomalies. This is in striking contrast to the negative Eu anomalies typical in high-level Archean granites. In addition, the deep-level granites are relatively enriched in Ba and Sr and depleted in total REE and high field strength elements (HFSE). One pluton, the Sankari granite, has unusually low contents of REE and HFSE. Most of the deep-level granites appear to represent cumulates with variable amounts of trapped liquid and of minor phases, resulting from fractional crystallization of a granitic parent. Such parental granitic magmas can be produced by batch melting of Archean tonalite at middle to lower crustal depths. The Sankari granite requires a tonalitic source depleted in REE and HFSE. Archean tonalites and tonalitic charnockites exhibit original igneous geochemical signatures and their average composition does not show a significant Eu anomaly. Hence, they cannot represent the positive Eu-anomaly complement to the negative Eu-anomaly, high-level granites. Our results suggest that Archean deep-level granites may represent this complement. Such granite may form in waterrich zones in the middle or lower crust and be produced in response to dehydration of the lower crust by a rising CO₂-rich fluid phase.     

Timing,petrogenesis, and setting of granites from the southern Beishan late Palaeozoic granitic belt,Northwest China and implications for their tectonic evolution

Late Palaeozoic granites are widely distributed in the southeastern Beishan area, which is located in the central part of the southern Central Asian Orogenic Belt (CAOB). U–Pb zircon dates of five late Palaeozoic granitic plutons from the southeastern Beishan area yield Permian ages: 285 ± 2 Ma (Shuwojing and Western Shuwojing plutons), 269 ± 3 Ma (Jianquanzi and Jiuquandihongshan plutons), and 260 ± 1 Ma (Jiujing pluton). The early Permian Shuwojing pluton, an unfractionated calc-alkaline biotite monzogranite with slightly positive εNd(t) (+0.7 and +0.6) and low initial ⁸⁷Sr/⁸⁶Sr (0.70722 and 0.70712), and the early Permian Western Shuwojing pluton, a high-K calc-alkaline biotite granite with slightly negative εNd(t) (?0.2 and ?0.1) and low initial ⁸⁷Sr/⁸⁶Sr (0.70390 and 0.70919), are likely derived from a mixture of depleted (juvenile) mantle and upper continental crustal (or sedimentary) material. The mid-Permian Jianquanzi and Jiuquandihongshan monzogranites have highly fractionated potassium-rich calc-alkaline characteristics with negative εNd(t) (?4.3) and very high initial ⁸⁷Sr/⁸⁶Sr (0.71949), reflecting a continental crustal component. The compositionally diverse Jiujing pluton and the granodiorite and high-Sr monzogranite phases display adakite-like compositions with relatively low εNd(t) (?0.1 and ?2.2) and high initial ⁸⁷Sr/⁸⁶Sr (0.70822 and 0.70913). The Jiujing low-Sr monzogranite has higher initial ⁸⁷Sr/⁸⁶Sr (0.73464) and lower εNd(t) (?2.8), indicating a significant continental crustal component in its genesis. This work, combined with the regional geology and previous studies, suggest that the early to middle Permian southern Beishan plutons formed in a post-collisional environment, probably an intracontinental rift environment linked to asthenospheric upwelling in response to the break-off of a subducted slab. In the late Permian, the southern Beishan area was in a compressive tectonic regime and thickening of the continental crust resulted in the formation of the Jiujing adakite-like granite.     

胶东前垂柳金矿区花岗岩锆石U-Pb年代学和地球化学特征及其地质意义

前垂柳金矿为胶东胶莱盆地东北缘地区新发现的金矿床,推断其金资源量为13.5 t,金矿体主要赋存于厚大的构造-蚀变带内。主控矿构造-蚀变带上盘岩石为牧牛山岩体二长花岗岩和荆山群地层,下盘岩石为鹊山岩体糜棱岩化二长花岗岩。构造-蚀变带上下两种花岗岩在变质程度、矿物组合方面存在明显差异,为深入研究两类花岗岩的成因类型及其与金成矿的关系,选取岩心中的两类花岗岩作为研究对象,进行了详细的锆石U-Pb年代学和岩石地球化学、锆石Hf同位素研究。牧牛山岩体二长花岗岩的锆石U-Pb年龄为(1 844.1±4.4) Ma,说明其形成于古元古代造山纪;二长花岗岩具有高的SiO₂、Y、Yb含量,较低的MgO、Sr含量和Sr/Y比值,同时具有明显Eu负异常(δEu=0.30~0.48),表现为钙碱性、强过铝质板内花岗岩特征;锆石ε_Hf(t)大部分为负值(变化范围-9.5~3.0),但两颗锆石ε_Hf(t)为正值(0.2和3.0),对应的两阶段Hf模式年龄介于2 492~3 083 Ma之间,指示二长花岗岩是由古老的加厚下地壳熔融形成。鹊山岩体糜棱岩化二长花岗岩的锆石U-Pb年龄为(154.6±1.5) Ma,表明其侵位时代为晚侏罗世,与区域上著名的玲珑岩体、昆嵛山岩体属同期产物。糜棱岩化二长花岗岩全岩地球化学分析显示其具有较高的SiO₂含量,高Sr含量和Sr/Y比值,低MgO、Y和Yb值,以及显著的Eu正异常(δEu=1.61~2.20),属高钾钙碱性、过铝质花岗岩,其地球化学特征与典型的埃达克岩特征类似,具有活动大陆边缘火成岩特点;锆石ε_Hf(t)均为负值(变化范围为-26.6~-14.1),对应的两阶段Hf模式年龄介于2 681~3 860 Ma之间,表明花岗岩可能由古老的多期次加厚下地壳熔融形成,与太平洋板块俯冲导致地壳增厚和地壳重熔有关。上述研究表明两种花岗岩在成岩时代、岩石地球化学特征、构造背景等方面存在显著差异,牧牛山岩体不是鹊山岩体的组成部分。两种花岗岩与主控矿构造空间上关系密切,但时间上与金成矿时间相距较远,因此两种花岗岩与金成矿没有直接成因关系。控矿构造三层结构与鹊山变质核杂岩地质特征一致;前垂柳金矿的发现表明鹊山变质核杂岩周边广泛分布的韧性剪切带和低角度主拆离断层是该区金矿勘查的理想部位,该区找矿潜力十分巨大。     

Zircon and granite petrology

The typologic study of zircon populations from granitic rocks lead to the proposition of a genetic classification with three main divisions: (1) granites of crustal or mainly crustal origin [(sub) autochthonous and aluminous granites)]; (2) granites of crustal+mantle origin, hybrid granites (calc-alkaline and sub-alkaline series granites); (3) granites of mantle or mainly mantle origin (alkaline and tholeiitic series granites). In detail, there are many petrogenetic variants of each of the following granitic rocks: granodiorite, monzogranite and alkaline granite. The variations observed with zircon typology are accompanied petrographically by modifications of associations of other main and accessory minerals, and on the field by the presence or absence of basic microgranular xenoliths, associated microgranites, rhyolites or basic rocks. In the typologic diagram, some endogenous non granitic rocks (i.e. migmatites, tonalites, rhyolites ...) show a logical distribution with regard to different genetic stocks of granitic rocks.     

秦岭造山带中部两河口岩体花岗岩锆石U-Pb年代学、地球化学及地质意义

北秦岭两河口岩体位于太白地区,侵位于秦岭群杂岩中,主要岩性为眼球状花岗岩、片麻状花岗岩和二长花岗岩。 本文研究的眼球状花岗岩和片麻状花岗岩的结晶年龄分别为928±19 Ma 和940±12 Ma,岩石中还保留古元古代至中元古代的 继承锆石。眼球状花岗岩含有富铝矿物石榴子石和白云母。岩石的A/CNK 多大于1.1,具有高Si、富铝的特征,属于高钾钙 碱性系列。岩石轻、重稀土分馏明显,具有中等负Eu 异常。岩石富集大离子亲石元素（Rb, Ba, K 等）、亏损高场强元素 （Nb, Ta, Ti 等）,具有明显的Ba, P, Sr 负异常。矿物学和地球化学特征显示眼球状花岗岩和片麻状花岗岩为S 型花岗岩。两河 口岩体初始Sr 同位素组成变化大,87Sr/86Sr(t)=0.701067~0.739451,具有较低的εNd(t)=-5.7~-3.3, 两阶段Nd 模式年龄为TDM2= 1.9~2.1 Ga。样品具有高的放射成因Pb 同位素组成,指示两河口岩体是壳源成因岩石,其源岩可能为秦岭群斜长角闪岩和 片麻岩。结合区域地质背景,认为两河口岩体源于新元古代陆壳碰撞晚期的构造转换阶段古老中下地壳的熔融作用,是对 Rodinia 超大陆汇聚事件的响应。     

北天山四棵树花岗岩体锆石U-Pb年代学及地质意义

四棵树岩体位于北天山缝合带中,是侵入依连哈比尔尕岛弧带中最大的一个花岗岩体,具有"钉合岩体"的构造意义。组成该岩体的岩石类型较多,大体上可分为3个侵入期次,依次为石英闪长岩和花岗闪长岩、二长花岗岩和钾长花岗岩、花岗斑岩;其中第二侵入期次构成了该岩体的主体。岩石SiO2含量为57.85%~74.28%,K2O含量为1.95%~5.25%,Na2O含量为3.00%~4.50%,整体表现为高K、Ca碱性特征。∑REE=113.91×10-6~169.47×10-6,(La/Sm)N为1.77~3.16,(Gd/Yb)N为1.33~2.12,(La/Yb)N为3.41~5.64,δEu为0.37~0.82,表现为轻稀土元素富集的右倾型特征;岩石具有Nb、Ta、Eu的亏损以及Th、Zr、Hf相对富集。通过形成环境判别,第一期石英闪长岩和花岗闪长岩大部投在火山弧环境,板块碰撞前—后碰撞隆起阶段;第二期二长花岗岩和钾长花岗岩大部投在后碰撞阶段;第三期花岗斑岩主要投在晚造山阶段。通过LA-ICP-MS对该岩体中石英闪长岩、二长花岗岩和钾长花岗岩进行较为系统的锆石U-Pb测年,得出其加权平均年龄分别为(324.1±4.3)Ma、(314.9±4.1)Ma、(311.5±3.9)Ma。结合前人得出的巴音沟蛇绿岩中辉长岩的(344±3.4)Ma年龄,可初步得出北天山缝合带的形成时代应该为344~311.5Ma,碰撞造山作用主要发生在324~311Ma,随后进入后碰撞伸展阶段,而四棵树岩体3期侵入岩可能分别代表了北天山造山带俯冲汇聚-碰撞-陆内造山各阶段构造-岩浆作用的产物。     

福建龙岩永福岩体锆石U-Pb年龄、地球化学特征及Lu-Hf同位素组成

永福岩体位于永梅晚古生代拗陷带中部。利用LA-ICP-MS锆石U-Pb定年法测得永福岩体中YF-1样品的年龄为133±1 Ma(MSWD=0.50)、YF-2样品的年龄为143±1 Ma(MSWD=0.59),说明其形成于早白垩世,与燕山期岩浆活动有关。该岩体富硅、碱,里特曼指数σ=0.96~2.43,铝饱和指数(A/CNK)=0.98~1.66,属高钾钙碱性系列,准铝质到过铝质范围。稀土元素总量较高,LREE相对富集,HREE相对亏损;具中-弱Eu负异常,弱Ce负异常到无异常,轻重稀土的分馏较微弱;微量元素表现为亏损元素Ba、Sr、K、P和Ti,富集Th、U、Zr、Hf等元素。样品YF-2~YF-7具有S型花岗岩特征,为永福岩体主体,源岩可能来自古-中元古代下地壳沉积岩;而样品YF-1具有Ⅰ型花岗岩特征,源岩可能来自古-中元古代下地壳火成岩。锆石的εHf(t)值除一颗来自残留基底为正值外,其他锆石全部为负值(-4.30~-11.82),Hf同为素二阶段模式年龄tDM2为1.45~1.92 Ga,表明永福岩体可能形成于古老地壳物质的重融。岩体形成于燕山期地壳的伸展背景下,在岩石圈伸展作用下幔源岩浆底侵促使古-中元古代下地壳沉积岩先发生部分熔融,形成永福岩体早期的S型花岗岩,岩浆作用后期,古-中元古代下地壳火成岩部分熔融,形成永福岩体晚期的I型花岗岩。     

北秦岭五垛山花岗岩锆石U-Pb年代学和地球化学特征及成因

五垛山岩体是位于北秦岭地体东部的大型复式岩体,花岗岩类型复杂,并呈多期次侵位特征。对岩体中黑云母花岗岩和二长花岗岩的代表性样品进行锆石U-Pb 定年,显示其形成年龄为441~431Ma,部分样品保留古元古代至新元古代的继承锆石。五垛山岩体花岗岩具有高硅、低镁、富碱、弱过铝至强过铝特征。微量元素蛛网图显示富集Rb、Ba、K和Pb,亏损Nb、Ta、P、Ti。稀土元素的球粒陨石分配模式显示轻、重稀土分馏明显,δEu为0.36~1.45。五垛山岩体花岗岩的87Sr/86Sr(i)为0.70304~0.71290,εNd(t)值为-4.6~-1.9,两阶段Nd 模式年龄(TDM2)为1.34~1.58 Ga。稀土元素判别图显示这些花岗岩主要由部分熔融作用形成,同位素特征指示源区为北秦岭变沉积岩与幔源物质的混合,其中一部分花岗岩形成于下地壳的深度,另一部分花岗岩形成于中上地壳,而源区的幔源物质可能为早期侵位于地壳中的中基性岩体。结合北秦岭早古生代地壳演化背景,认为五垛山岩体花岗岩反映了早志留世北秦岭地体在后碰撞环境下加厚地壳的垮塌过程。     

北秦岭五垛山花岗岩锆石U-Pb年代学和地球化学特征及成因

五垛山岩体是位于北秦岭地体东部的大型复式岩体，花岗岩类型复杂，并呈多期次侵位特征。对岩体中黑云母花岗岩和二长花岗岩的代表性样品进行锆石U-Pb 定年，显示其形成年龄为441~431Ma，部分样品保留古元古代至新元古代的继承锆石。五垛山岩体花岗岩具有高硅、低镁、富碱、弱过铝至强过铝特征。微量元素蛛网图显示富集Rb、Ba、K和Pb，亏损Nb、Ta、P、Ti。稀土元素的球粒陨石分配模式显示轻、重稀土分馏明显，δEu为0.36~1.45。五垛山岩体花岗岩的87Sr/86Sr(i)为0.70304~0.71290，εNd(t)值为-4.6~-1.9，两阶段Nd 模式年龄(TDM2)为1.34~1.58 Ga。稀土元素判别图显示这些花岗岩主要由部分熔融作用形成，同位素特征指示源区为北秦岭变沉积岩与幔源物质的混合，其中一部分花岗岩形成于下地壳的深度，另一部分花岗岩形成于中上地壳，而源区的幔源物质可能为早期侵位于地壳中的中基性岩体。结合北秦岭早古生代地壳演化背景，认为五垛山岩体花岗岩反映了早志留世北秦岭地体在后碰撞环境下加厚地壳的垮塌过程。     

孙吴-嘉荫地区早中生代花岗岩的年代学、地球化学与成因

对小兴安岭北部孙吴-嘉荫地区早中生代花岗岩进行了年代学和地球化学研究,据此探讨其成因及形成的构造背景。锆石U-Pb同位素定年结果表明,研究区早中生代花岗岩分为晚三叠世和早侏罗世两期,形成时代分别为210 Ma和187~181 Ma。晚三叠世碱长花岗岩属铝质A型花岗岩,岩浆源区为新元古代从亏损地幔中增生的基性火成岩地壳。早侏罗世英云闪长岩-花岗闪长岩和二长花岗岩属埃达克岩,是由加厚下地壳物质部分熔融形成的;正长花岗岩-碱长花岗岩与同期埃达克岩具明显不同的地球化学特征,岩浆源区为中元古代从亏损地幔中增生的基性地壳物质。结合区域地质构造演化特征,认为晚三叠世花岗岩是华北板块和西伯利亚板块碰撞造山后伸展构造环境下的产物,早侏罗世花岗岩的形成与古太平洋板块俯冲产生的挤压构造环境有关。