华北东南缘荆山花岗岩成因及其构造意义

对华北东南缘荆山花岗岩进行了锆石U-Pb定年、微量元素和Hf同位素分析,全岩主微量元素和Sr-Nd同位素分析.LA-ICP-MS锆石U-Pb定年结果表明,荆山花岗岩形成于晚侏罗世(160.9±0.8~161.6±1.5 Ma).残留锆石的U-Pb年龄主要为三叠纪和新元古代,分别与大别-苏鲁造山带超高压变火成岩的变质年龄和原岩年龄一致.这些花岗岩为钙碱性-高钾钙碱性,具有弧型的微量元素分布特征和富集的Sr-Nd-Hf同位素组成,即高的全岩(87Sr/86Sr)_i比值(0.708 0~0.709 1),低的ε_Nd(t)值(-15.6~-13.5)和锆石ε_Hf(t)值(-23.1~-9.5),对应的两阶段Nd-Hf模式年龄主要为古元古代.这些锆石U-Pb同位素年代学和地球化学特征与大别-苏鲁造山带超高压变火成岩一致,表明它们之间存在成因联系.特别地,残留锆石新元古代和三叠纪U-Pb年龄是俯冲华南陆壳的标志性特征.因此,荆山花岗岩是俯冲华南陆壳部分熔融的产物,华南陆壳是三叠纪大陆碰撞过程中进入华北地壳之中的.这些花岗岩具有低的Rb含量、高的Sr和Ba含量,低的Rb/Sr比值以及低的全岩锆饱和温度和锆石Ti温度(~700℃),表明它们源于俯冲华南陆壳低温加水部分熔融,可能与侏罗纪古太平洋板块俯冲于中国东部之下有关.      

扬子西缘祥云响水花岗岩体的成因:锆石U-Pb年代学、岩石地球化学和Sr-Nd同位素制约

滇西至滇中一带新元古代镁铁质岩类、花岗岩类等岩浆岩有广泛分布,前人利用不同岩石组合指示这些岩浆岩形成于不同的地质构造背景.通过对祥云一带调查研究,新确定了南华纪花岗岩体,花岗岩体中含有大量的超镁铁质岩（橄榄辉长岩）、闪长岩类包体,包体与花岗岩不规则边界呈成分渐变,混合形成为花岗闪长岩、石英闪长岩、英云闪长岩类岩石.对花岗岩和铁镁质包体进行锆石U-Pb LA-ICP-MS同位素测年,获得了相近的206Pb/238U平均年龄:761.9±4.1 Ma、761.7±4.2 Ma、761.3±3.7 Ma和757.5±5.9 Ma.花岗岩主量元素显示具有高碱（alk）、中等Mg#（38~57,平均值为50）、低TiO₂、P和亏损Ta、Nb、Sr特点,展现了富集轻稀土元素（LREEs）、亏损重稀土元素（HREEs）和选择性富集大离子亲石元素（LILEs）等特点,并且其ε_Nd（t）为负值（-2.73~-4.90）,表明花岗岩浆的物质应为早期古老地壳部分熔融的产物;橄榄辉长岩包体地球化学特征为:低K₂O,低稀土总量,LREEs和LILEs略富集或不富集,具明显P负异常,Nb-Ta和Zr-Hf无亏损,具有非常高的Mg#（71~83）等特点,这些特征都指示这些橄榄辉长岩来源于幔源,应为地幔边缘岩浆熔融的产物.花岗闪长岩、闪长岩具有略富集LREE和LILE、亏损HREE,其Mg#（45~71）较高,P亏损、负ε_Nd（t）值等特征,Ta、Nb、Ti、Sr、P略亏损或不亏损,组分介于花岗岩和橄榄辉长岩之间,显示了幔源和古老地壳部分熔融混合特点.这些岩石都展示陆源弧岩浆岩的构造背景,大洋板块向扬子板块俯冲导致幔源物质重熔的结果.      

东昆仑布尔汗布达早古生代岩浆弧的形成与演化初探

东昆仑布尔汗布达弧位于东昆中断裂南侧,不同于北昆仑晚古生代-中生代岩浆弧,是东昆仑早古生代岩浆岩广泛分布的地区,对研究原特提斯洋俯冲-增生过程具有重要意义.报道了布尔汗布达地区早古生代岩浆岩岩石学、地球化学、锆石U-Pb定年、Lu-Hf和Sr-Nd同位素资料,结合以往研究成果,推断布尔汗布达弧与增生造山作用相关的岩浆活...     

俯冲陆壳部分熔融形成埃达克质岩浆

在岛弧背景,埃达克质岩浆形成于俯冲洋壳板片的部分熔融已得到共识,但在大陆碰撞背景,埃达克质岩浆是否形成于俯冲陆壳的部分熔融尚未有研究报导。对祁连山东南部关山花岗岩（229 Ma）的地球化学和岩石成因研究提供了俯冲陆壳部分熔融形成埃达克质岩浆的一个实例。关山花岗岩以高K（K2O=4.12%~5.16%,K2O/Na2O=0.97~1.64）、高Sr/Y比值（13.6~84.1）、低Y （6.8×10-6 ~15.7×10-6 ）和低HREE（eg. Yb=0.62×10-6~1.31×10-6）为特征,并具有强分异的稀土元素组成模式[（La/Yb）N=17.5~41.6]和演化的Sr-Nd同位素组成[初始87Sr/86Sr=0.70587~0.70714, εNd（t）=-10.9~-5.16, tDM=1.10~1.49 Ga]。这些地球化学特征表明关山花岗岩属于大陆型（C型）埃达克质岩石,而明显不同于俯冲洋壳板片或底侵玄武质下地壳部分熔融形成的埃达克岩。关山花岗岩Pb-Sr-Nd同位素组成与商丹断裂北侧的祁连山前寒武纪基底岩石、早古生代火山岩和花岗岩类存在显著差异,但类似于商丹断裂南侧秦岭早中生代花岗岩类的Pb-Sr-Nd同位素组成,由此认为具有埃达克质的关山花岗岩的岩浆来自于南部俯冲陆壳物质的部分熔融,并提出了大陆碰撞背景中埃达克质岩浆产生的一个新的地质模型。     

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。     

大别造山带岳西地区中生代岩浆岩年代学研究

北大别岳西地区广泛分布燕山期侵入岩和火山岩。14个岩浆岩样品中锆石LA-ICP-MS U-Pb定年结果显示,这些岩浆岩形成于134~125 Ma之间。以130 Ma为界,岩浆岩可以分为两个期次:早期以石英闪长岩—石英二长闪长岩—似斑状二长花岗岩组合为主;晚期以二长花岗岩—钾长花岗岩组合及脉岩为主。早期岩浆岩含有古元古代(1900~2120 Ma)、新元古代(670~800 Ma)和三叠纪继承锆石;晚期岩浆岩中缺少古元古代继承锆石,以新元古代、三叠纪及140~160 Ma时期的继承锆石为主。高Sr低Y地球化学特征仅出现在早期岩浆岩中,结合继承锆石的年龄特征,表明早期岩浆岩物质来源于加厚的基性下地壳,下地壳的拆沉和岩石圈的减薄发生在约130 Ma;而晚期岩浆岩为以新元古代年龄的中—下地壳在减薄后的环境下发生深熔作用形成。     

Early Neoproterozoic evolution of Southeast Pakistan: evidence from geochemistry,geochronology, and isotopic composition of the Nagarparkar Igneous Complex

ABSTRACT

Rocks of the early Neoproterozoic age of the world have remained in discussion for their unique identity and evolutionary history. The rocks are also present in Sindh province of Pakistan and have been in debate for a couple of years. Yet, these igneous rocks have been studied very poorly regarding U-Pb and Lu-Hf age dating. The early Neoproterozoic rocks located in Nagarparkar town of Sindh have been considered as shoulder of Malani Igneous Suite (MIS) discovered in Southwest of India. The Nagarparkar Igneous Complex (NPIC) rocks are low-grade metamorphosed, mafic and silicic rocks. These rocks are accompanied by felsic and mafic dikes. Two types of granite from NPIC have been identified as peraluminous I-type biotite granites (Bt-granites), of medium-K calc-alkaline rocks series and A-type potash granites (Kfs-granites) of high-K calc-alkaline rocks series. Geochemical study shows that these Kfs-granites are relatively high in K and Na contents and low MgO and CaO. The Bt-granites have positive Rb, Ba, and Sr with negative Eu anomalies rich with HFSEs Zr, Hf, and slightly depleted HREEs, whereas Kfs-granites have positive Rb with negative Ba, Sr, and Eu anomalies and have positive anomalies of Zr and Hf with HREEs. In addition, these rocks possess crustal material, which leads to the enrichment of some incompatible trace elements and depletion of Sr and Ba in Kfs-granites and relatively high Sr and Ba in Bt-granites, indicating a juvenile lower continental crust affinity. Zircon LA-ICP-MS U-Pb dating of these granites yielded weighted mean ²⁰⁶Pb/²³⁸U ages ranging from 812.3 ± 14.1 Ma (N = 18; MSWD = 3.7); and 810 ± 7.4 Ma (N = 16; MSDW = 0.36) for the Bt-granites, and 755.3 ± 7.1 Ma (N = 21; MSDW = 2.0); NP-GG-01 and 736.3 ± 4.3 Ma (N = 24; MSWD = 1.05) for Kfs-granites, respectively. The Bt-granites and Kfs-granites have positive zircon ε_Hf^(t) values, which specify that they are derived from a juvenile upper and lower continental crust. Based on the geochemical and geochronological data, we suggest that the Bt-granites were formed through lower continental crust earlier to the rifting time, whereas the Kfs-granites were formed via upper continental crust, during crustal thinning caused by Rodinia rifting. These zircon U-Pb ages 812 to 736 Ma, petrographic, and geochemical characteristics match with those of the adjacent Siwana, Jalore, Mount Abu, and Sirohi granites of MIS. Thus, we can suggest that NPIC granites and adjacent MIS can possibly be assumed as a missing link of the supercontinent Rodinia remnants.     

西藏山南列麦始新世花岗岩独居石U-Th-Pb年龄及地质意义

西藏山南隆子县列麦地区始新世花岗岩的成岩时代和背景对喜马拉雅地区同碰撞阶段的构造演化具有重要意义。本文对隆子县列麦乡界归党村的白云母花岗岩开展独居石LA-ICP-MS U-Th-Pb测年,独居石40个测点的~(208)Pb/~(232)Th加权平均年龄为41±0.1Ma(MSWD=1.4),形成于始新世中期。结合区域上的始新世岩浆岩活动和区域变质作用,本文认为在50～45Ma印度下地壳发生中-高压变质和部分熔融;45Ma新特提斯洋洋壳板片断离,软流圈地幔上涌;45～41Ma喜马拉雅发生短暂的拉张环境导致大量的埃达克质岩浆岩侵位和麻粒岩的折返。     

滇西花岗岩类 Pb、Sr 同位素组成特征及其基底时代和性质

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。     

Petrochemical and Sr-Nd isotope investigations of A-type granites in the east of Misho, NW Iran

The Misho plutonic complex consists of a series of granitic bodies which range from syenogranite, alkali granite to monzogranites. They include metaluminous to peraluminous compositions. The garnitoid bodies are intruded into the unmetamorphosed late Paleozoic rocks and are located between two dextral, oblique-slip fault systems along which they have been uplifted as a major positive flower structure. The Misho granitoid belongs to the alkaline granitoid series that have been attributed to a Late Permian post-collisional setting. The studied granitoid displays high SiO₂ contents between 67.71 and 76.4 wt%. On both FeO/(FeO + MgO) and [(Na₂O + K₂O) ? CaO] vs. SiO₂ diagrams, the samples, plot in the ferroan and alkaline fields, therefore, show an A-type granitoid signature. Trace and rare earth elements distribution patterns for the Misho rocks indicate a distinctive depletion in Nb, Sr, Ba, P, and Ti relative to other trace elements and a greater enrichment in large-ion lithophile elements compared to high field strength elements that are also typical features of A-type granites. The granitoid samples are geochemically similar to typical A₂-type granites, e.g., high K₂O + Na₂O, FeO/MgO, Ga/Al, and Y/Nb values and low CaO, Ba, Sr, and Eu contents. They have initial Sr isotopic ratios in the range >0.712 and negative ε _Ndt values of ?1 to ?3.2 for a time of generation of 232 Ma. We suggest that shear zones play an important role in providing suitable conduits for ascending asthenospheric material and heat influx in the lower crust continental. It is proposed that the Misho parental granitoid magmas were produced by the partial melting of the lower crust continental at extensional setting in active continental margin setting that was formed after the collision of the Eurasia plate and Iranian plate following closure of paleo-Tethyan oceanic crust during Middle Jurassic times.     

Late Ediacaran crustal thickening in Iran: Geochemical and isotopic constraints from the ~550 Ma Mishu granitoids (northwest Iran)

The aim of this article is to examine the geochemistry and geochronology of the Cadomian Mishu granites from northwest Iran, in order to elucidate petrogenesis and their role in the evolution of the Cadomian crust of Iran. The Mishu granites mainly consist of two-mica granites associated with scarce outcrops of tonalite, amphibole granodiorite, and diorite. Leucogranitic dikes locally crosscut the Mishu granites. Two-mica granites show S-type characteristics whereas amphibole granodiorite, tonalities, and diorites have I-type signatures. The I-type granites show enrichment in large-ion lithophile elements (e.g. Rb, Ba and K) and depletion in high field strength elements (e.g. Nb, Ti and Ta). These characteristics show that these granites have been formed along an ancient, fossilized subduction zone. The S-type granites have high K, Rb, Cs (and other large ion lithophile elements) contents, resembling collision-related granites. U–Pb zircon dating of the Mishu rocks yielded ²³⁸U/²⁰⁶Pb crystallization ages of ca. 550 Ma. Moreover, Rb–Sr errorchron shows an early Ediacaran age (547 ± 84 Ma) for the Mishu igneous rocks. The two-mica granites (S-type granites) show high ⁸⁷Sr/⁸⁶Sr_(i) ratios, ranging from 0.7068 to 0.7095. Their ?Nd values change between ?4.2 and ?4.6. Amphibole granitoids and diorites (I-type granites) are characterized by relatively low ⁸⁷Sr/⁸⁶Sr_(i) ratios (0.7048–0.7079) and higher values of ?Nd (?0.8 to ?4.2). Leucogranitic dikes have quite juvenile signature, with ?Nd values ranging from +1.1 to +1.4 and Nd model ages (T_DM) from 1.1 to 1.2 Ga. The isotopic data suggests interaction of juvenile, mantle-derived melts with old continental crust to be the main factor for the generation of the Mishu granites. Interaction with older continental crust is also confirmed by the presence of abundant inherited zircon cores. The liquid-line of descend in the Harker diagrams suggests fractional crystallization was also a predominant mechanism during evolution of the Mishu I-type granites. The zircon U–Pb ages, whole rock trace elements, and Sr–Nd isotope data strongly indicate the similarities between the Mishu Cadomian granites with other late Neoproterozoic–early Cambrian (600–520 Ma) granites across Iran and the surrounding areas such as Turkey and Iberia. The generation of the Mishu I-type granites could be related to the subduction of the Proto-Tethyan Ocean during Cadomian orogeny, through interaction between juvenile melts and old (Mesoproterozoic or Archaean) continental crust. The S-type granites are related to the pooling of the basaltic melts within the middle–upper parts of the thick continental crust and then partial melting of that crust.     

黑河新生地区中侏罗世花岗质岩石锆石U-Pb年龄、地球化学特征及岩石成因

黑河新生地区西古兰河以北二长花岗岩的LA-ICP-MS锆石U-Pb同位素测试结果表明,其形成时代为中侏罗世((163.8±1)Ma)。这些中侏罗世二长花岗岩属于弱过铝质高钾钙碱性系列的Ⅰ型花岗岩,明显富集大离子亲石元素(Rb、Ba、Th)和亏损高场强元素(Zr、Hf、Nb、Ta),元素Sr具有明显的负异常,表明其原始岩浆起源于地壳火成岩的部分熔融。结合区域资料同时代火成岩的组合特征和古太平洋板块的构造演化,认为该二长花岗岩形成于活动大陆边缘,而其形成的地球动力学背景可能为古太平洋板块向欧亚板块俯冲造山后的伸展环境。     

The Yermakovsky deposit,Western Transbaikal Region,Russia: Isotopic and geochemical parameters and sources of beryllium-bearing granitoids and other rocks

An isotopic study of igneous and metamorphic rocks has been carried out at the Yermakovsky bertrandite-phenakite-fluorite deposit. It has been established that the model age of the schists pertaining to the Zun-Morino Formation is 1360–1260 Ma. In Nd and Sr isotopic composition, these schists deviate from the isotopic composition of the continental crust and are close in this respect to the enriched mantle reservoir (EM-II). The model age of carbonate rocks of the Zun-Morino Formation is 1330–1020 Ma. The Middle Riphean model age of the Zun-Morino Formation is interpreted as the age of its protolith. According to the Sr and Nd isotopic data, all preore igneous rocks (granitic dikes, gabbroic rocks, and gneissose granite of the Tsagan Complex) were formed with the participation of continental crustal material. Synore basic dikes, alkali leucogranite stock, and syenite intrusion are considered to be mixtures of mantle components (DM+HIMU) and various continental crustal components (Tsagan gneissose granite, crystalline schists, the mean composition of granitoids of the Angara-Vitim batholith as an estimate of average composition of the regional continental crust). Synore igneous rocks are genetically cognate and related to the magmatic activity in the Western Transbaikal Rift Zone presumably formed in the Triassic under effect of a mantle plume.     

大兴安岭中部乌兰浩特地区花岗岩锆石U-Pb年龄、地球化学特征及构造意义

对内蒙古乌兰浩特地区出露的花岗岩侵入体进行LA-ICP-MS锆石U-Pb定年和岩石地球化学研究,以探讨该区花岗岩形成时代、成因类型和区域构造演化。结果显示,其锆石²⁰⁶Pb/²³⁸U年龄的加权平均值为(214.4±2.6) Ma,反映岩体的结晶年龄为晚三叠世。岩石主量元素具高硅、高碱、富钾,贫钙、贫镁及低钛的特征;稀土元素配分曲线呈“海鸥式”较弱的右倾分布特征,具有强烈的Eu负异常;微量元素Rb、Th、Zr、Y和Yb含量较高,Ba、Sr含量较低,岩石具有高的Rb/Sr 、Rb/Nb 值,显示为低 Sr、高 Yb 型花岗岩的特征。综合分析显示花岗岩形成的压力较低,应为减薄地壳物质熔融的产物。综合区域构造演化和K₂O-Na₂O、(Zr+Nb+Ce+Y)-(Na₂O+K₂O)/CaO、SiO₂-TFeO/MgO、(Y+Nb)-Rb、(Yb+Ta)-Rb、Nb-Y-Ce图解分析,认为该岩体形成于造山后伸展构造背景,研究区由中三叠世的碰撞造山构造体制向晚三叠世造山后伸展构造体制转变,同时西伯利亚板块和华北板块的碰撞时限持续到中三叠世。     

扬子板块北缘光雾山地区钾长花岗岩年代学、地球化学特征及构造意义

为了限定扬子板块北缘地区新元古代岩浆活动事件的准确时间及和探讨岩石成因,本文对出露于四川省南江县光雾山钾长花岗岩进行了LA-ICP-MS锆石U-Pb定年和岩石地球化学研究。结果表明光雾山地区钾长花岗岩锆石U-Pb年龄为836.3Ma±8.3Ma,属于新元古代花岗岩。岩石具有高w(SiO2)(72.68%~78.10%),w(K2O)(4.26%~5.32%),w(Na2O)(1.68%~3.38%),相对富钾(K2O/Na2O=1.12~2.54),高碱(w(Na2O+K2O)=7.64%~8.99%),低P2O5含量等特征,铝饱和指数A/CNK=0.99~1.49,光雾山花岗岩属于过铝质高钾钙碱性花岗岩。岩石具有轻稀土元素相对富集,重稀土元素亏损的特征,具有明显Eu负异常,δEu为0.48~0.73。光雾山花岗岩微量元素表现出Rb,Th,K,Nd,Sm元素富集,Ba,Nb,Ta,Sr,P,Ti元素亏损的特点。地球化学研究表明,光雾山钾长花岗岩主要以粘土岩部分熔融为主及少部分含粘土的变质杂砂岩部分熔融形成的。岩浆可能来源于本区结晶基底新太古界-古元古界后河岩群和褶皱基底中-新元古界火地亚群中深变质岩为代表的地壳物质的部分熔融产物,为壳源成因类型,具有岛弧型花岗岩特征,形成于岛弧构造环境。光雾山钾长花岗岩的形成是新元古界时期扬子板块与华北板块之间的俯冲碰撞、岛弧形成构造演化过程中使区域地壳不断加厚和地壳深融作用的响应。扬子陆块北缘南江地区约836Ma同碰撞岛弧型钾长花岗岩的发现,表明该地区在约836Ma时为Rodinia超大陆汇聚形成阶段,此时期该区Rodinia超大陆尚未进入大陆裂解阶段。     

北山野马井地区泥盆纪富钾酸性岩浆岩地球化学特征及其地质意义

为了理清北山南部晚古生代构造演化过程,对野马井地区的二长花岗岩与流纹岩进行了岩石学、全岩主微量元素地球化学、锆石U-Pb年代学及Hf同位素等研究.LA-ICP-MS锆石U-Pb定年结果表明二长花岗岩与流纹岩的就位年龄分别为402.7±2.4 Ma与392.9±2.5 Ma.二者均为富钾钾质岩浆岩,呈现过铝质-强过铝质,轻重稀土弱到中等分馏且相对富集轻稀土,二长花岗岩呈现无或弱的负Eu异常,流纹岩呈现较明显的负Eu异常,二者均富集Rb、Th、U、Pb等,亏损Nb、Ta、Ba、Sr、Ti等,为I型酸性岩浆岩.二长花岗岩与流纹岩的锆石ε_Hf（t）值介于-2.2~+6.8,对应Hf模式年龄（t_DM2）为962~1 533 Ma;指示二者主要由中元古代陆壳物质熔融所形成.依据野马井地区泥盆纪富钾酸性岩浆岩的地球化学特征,结合该区域其他地质资料,可推测其为后碰撞构造环境的产物.      

中国东南部花岗岩成因与地壳演化

中国东南部不同时代花岗岩类的分布十分广泛 ,各类花岗岩的出露面积达 2 0 0 0 0 0km2 以上。其中 ,前侏罗纪花岗岩大部分具有较低的ε(Nd ,t)、较高的Ni(87Sr) /Ni(86Sr)和较古老的Nd模式年龄 ,相似于周围的前寒武纪基底变质岩。因此 ,它们的主体属壳源型 ,其成因可能主要同华夏地块与扬子地块之间的多次碰撞拼贴有关 ,由当时被加厚的地壳在降压条件下部分熔融形成。燕山期花岗岩在中国东南部分布最广。其中 ,呈东西向展布的燕山早期花岗岩 (南岭花岗岩 )被认为是与印支运动有联系的后造山花岗岩组合 ,多数具壳源型特征。而主要分布于东南沿海的燕山晚期花岗岩则不同 ,它们具有较高的ε(Nd ,t)、较低的Ni(87Sr) /Ni(86Sr)和相对年轻的Nd模式年龄 ,反映其源区中含有较多的地幔组分。它们的形成可能同太平洋板块俯冲、玄武岩浆底侵以及由此引起的地壳深熔和壳幔混合有关。根据花岗岩的Nd模式年龄以及地壳岩石中继承锆石U Pb年龄 ,认为中国东南部地壳具幕式生长特征 ,古—中元古代为主要的生长期。     

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。     

冀东-辽西中-晚三叠世柏杖子花岗质侵入岩地球化学、Sr-Nd-Hf同位素特征及岩石成因

关于冀东-辽西中-晚三叠世具有埃达克质岩石特征的花岗质岩石的源区性质,存在较大争议,且以往对位于其北东向隆起区内的柏杖子岩体的成因研究程度低.对柏杖子花岗质侵入岩进行了系统的年代学、地球化学、Sr-Nd-Hf同位素研究,结果显示:柏杖子岩体结晶年龄为233±3 Ma,岩石具有低MgO、Mg#和Co、Ni、Cr含量;富集大离子亲石元素,亏损高场强元素,显示明显的Pb、Th正异常和Nb、Ta、Ti、P负异常;轻、重稀土元素分馏明显;87Sr/86Sr (t) 为0.704 45~0.705 24,ε_Nd(t) 值为-7.3~-1.7;锆石ε_Hf(t) 为-13.4~-5.9.综合分析认为,高Sr/Y比值和低Y含量的柏杖子岩体属于华北克拉通正常厚度镁铁质下地壳熔融的产物,岩石高Sr/Y比值、低Y含量和Nb-Ta负异常特征为继承的华北克拉通下地壳内在性质,并具有与太古宙-古元古代TTG岩石系列相一致的Nb-Ta解耦特征,表明柏杖子岩体源区物质有TTG岩石的贡献;岩石Sr-Nd-Hf同位素组成和低相容元素含量特征同样表明岩浆来源于受改造的下地壳熔融.早中生代玄武岩底侵过程中幔源组分的加入对华北克拉通下地壳形成改造,同时提供热源诱发下地壳物质熔融,形成的熔体向浅表侵位,经历一定程度的斜长石分离结晶,并最终形成柏杖子岩体.      

华北陆块南缘燕山期花岗岩带岩浆演化:以小秦岭—外方山地区为例

根据华北陆块南缘小秦岭—外方山地区中生代花岗岩的时空分布特征,将其形成过程划分为160～155 Ma(Ⅰ)、150～125 Ma(Ⅱ)、120～110 Ma(Ⅲ)3个期次,与中国北方大规模岩浆活动期次并不完全一致。这3期花岗岩的地球化学元素演化较为特殊,Ⅰ期花岗岩(南泥湖、上房沟等岩体)与Ⅲ期花岗岩的地球化学特征较为相似,均以异常高的K含量、明显的负Eu异常及重稀土元素分馏较弱或不分馏为主要特征,为A型花岗岩。Ⅱ期花岗岩为偏铝质—弱过铝质高钾钙碱性系列花岗岩,富集Rb、Th、U和K等大离子亲石元素,亏损Nb和Ta等高场强元素,P2O5含量随SiO2含量增加呈递减趋势,为I型花岗岩,大部分样品Sr>300.00×10-6,Y<19.00×10-6,Yb<1.90×10-6,具有埃达克岩的属性。时代由老至新,Ⅰ、Ⅱ、Ⅲ花岗岩呈现出A型—I型—A型的演化规律。Ⅰ期花岗岩形成于挤压构造背景下的局部伸展环境;Ⅱ期花岗岩则形成于华北陆块南缘构造体制转换阶段,是地壳加厚导致的下地壳部分熔融的产物;Ⅲ期花岗岩则是扬子与华北陆块拼合后,板块逐渐稳定,岩石圈发生伸展,下地壳岩石减压熔融形成的。