Crystallization Conditions and Mineral Chemistry in the East of Tafresh,Central Iran,with Insights into Magmatic Processes     

Davood RAEISI  Hassan MRNEJAD 《《地质学报》英文版》2019,93(6):1755-1772

The Tafresh granitoids are located at the central part of the Urumieh-Dokhtar Magmatic Arc(UDMA) in Iran. These rocks, mainly consisting of diorite and granodiorite, were emplaced during the Early Miocene. They are composed of varying proportions of plagioclase + K-feldspar + hornblende ± quartz ± biotite. Discrimination diagrams and chemical indices of amphibole phases reveal a calc-alkaline affinity and fall clearly in the crust-mantle mixed source field. The estimated pressure, derived from Al in amphibole barometry, is approximately 3 Kb. The granitoids are I-type, metaluminous and belong to the calc-alkaline series. They are all enriched in light rare earth elements and large ion lithophile elements, depleted in high field strength elements and display geochemical features typical of subduction-related calc-alkaline arc magmas. Most crystal size distribution(CSD) line patterns from the granitoids show a non-straight trend which points to the effect of physical processes during petrogenesis.The presence of numerous mafic enclaves, sieve texture and oscillatory zoning along with the CSD results show that magma mixing in the magma chamber had an important role in the petrogenesis of Tafresh granitoids. Moreover, the CSD analysis suggests that the plagioclase crystals were crystallized in a time span of less than 1000 years, which is indicative of shallow depth magma crystallization.  相似文献   

甘肃柳园地区早二叠世正长花岗斑岩脉锆石U-Pb年代学、岩石地球化学特征——对北山造山带晚古生代构造背景的指示     

孙海瑞  吕志成  于晓飞  李永胜  杜泽忠  吕鑫  公凡影 《吉林大学学报(地球科学版)》2020,50(5):1433-1449

甘肃北山地区位于中亚造山带中段,是诠释中亚造山带构造演化的关键区域之一,长期以来受到地质学界的广泛关注。柳园地区位于甘肃北山南带,区内脉岩发育,这些岩脉的研究可以为阐释北山造山带晚古生代构造背景提供更多证据。基于此,本文选取位于甘肃柳园地区的正长花岗斑岩脉开展了系统的锆石U-Pb-Hf同位素和全岩主量、微量元素分析。LA-ICP-MS锆石U-Pb分析显示,岩脉侵位于早二叠世（（288.5±1.4）Ma）。全岩地球化学分析显示,正长花岗斑岩脉的SiO₂和全碱质量分数较高,Fe、Mg、Ca、Al和P质量分数较低,Rb、Th、U和Pb相对富集,Ba、Nb、La、Ce、Sr和Ti等元素相对亏损,Eu负异常显著,具有较高的Rb/Sr值和较低的K/Rb值及锆石饱和温度（730~844℃,集中于740℃左右）,显示该岩脉为高钾钙碱性高分异I型花岗岩,并具有俯冲带岩浆活动的地球化学特征。正长花岗斑岩脉具有较低的Zr/Hf值（18.42~28.01,平均值为22.37）和Th/U值（3.82~7.99,平均值为5.34）,与平均地壳组分接近,锆石ε_Hf（t）值为2.94~9.66,平均值为5.72,T_DM2值为955~611 Ma,指示源区主体为新元古代地壳的部分熔融,并存在幔源物质加入。根据构造判别图解并结合前人关于二叠纪区域构造变形、盆地沉积物源、岩浆演化等方面的研究结果,笔者认为该正长花岗斑岩脉形成于俯冲作用过程中的局部伸展环境,并认为北山地区增生造山事件至少持续到早二叠世。  相似文献   

川西甲基卡矿床外围中酸性侵入岩LA-ICP-MS锆石U-Pb年龄及地球化学特征     

李名则  秦宇龙  赵春  詹涵钰  周雄  孙光银 《中国地质调查》2020,7(5):1-9

在川西甲基卡矿床外围新发现了建巴村中酸性侵入岩体,为了探讨其形成时代、成岩构造背景及其成矿条件,开展了LA-ICP-MC锆石U-Pb年代学和地球化学特征研究。结果表明: 该岩体的结晶年龄为(211.8±1.0) Ma; 岩石属于钙碱性-高钾钙碱性准铝质中酸性侵入岩系列,具有I型花岗岩类的特征,其物质来源可能为壳源物质与幔源物质部分熔融。地球化学特征表明其形成于后碰撞环境,与此时期内川西地区的区域性岩浆活动相对应。建巴村岩体的构造位置及岩浆活动特征指示其可能不具备形成伟晶岩矿床的条件。  相似文献   

东昆仑夏日哈木地区二长花岗岩年代学、地球化学特征及地质意义     

郭峰  王盘喜  卞孝东  冯乃琦 《中国地质调查》2020,7(6):51-60

东昆仑夏日哈木地区首次发现了早泥盆世二长花岗岩,对其开展年代学和地球化学特征研究,进一步探讨其岩石成因和构造地质背景。二长花岗岩锆石U-Pb年龄为(412.1±5.7) Ma(MSWD=0.95),形成于早泥盆世早期; 岩石为过弱铝质亚碱性花岗岩,富SiO₂(含量为71.41%~72.46%)、K₂O(含量为5.27%~6.16%),贫Fe₂O₃(含量为1.86%~2.05%)、P₂O₅(含量为0.08%~0.12%),富集轻稀土元素,具明显的负Eu异常; 在原始地幔标准化微量元素蛛网图上可以看出,岩石明显富集Rb、Th、Zr、Hf,强烈亏损Nb、Sr、P、Ti、Ba。夏日哈木地区二长花岗岩属于I型花岗岩,其源岩可能由幔源岩浆底侵加热下地壳岩石致其部分熔融而形成,处于由同碰撞向后碰撞转换的构造环境,说明东昆仑夏日哈木地区在早泥盆世早期已进入伸展阶段。  相似文献   

内蒙古锡林浩特I型花岗岩的时代及构造意义   总被引：1，自引：0，他引：1  

范中林  柯于富  陈文  杨伟卫  孙孝峰 《火山地质与矿产》2012,(3):191-197

在内蒙古锡林浩特水库地区出露的花岗岩确定为I型花岗岩,具有较高的Cr、Co、Ni丰度。Ca、Al含量和N2O／K2O比值较高,Fe、Mg含量较低。微量元素蛛网图中显示出明显的Nb、Ta、P、Ti负异常。在SiO2-K2O及AFM图中,花岗质岩石投在钙碱性系列区;在构造环境判别图中,花岗质岩石样品都投在火山弧＋同碰撞花岗岩区。锆石测年结果显示平均年龄为317．0±4．0Ma,属晚石炭世。这套晚石炭世岛弧花岗岩的存在,表明加里东期古亚洲洋并未完全关闭,晚石炭世时仍然存在洋壳的俯冲消减事件。从区域上看,是北侧的贺根山洋盆向南俯冲的结果。  相似文献   

新疆东天山多头山铁-铜矿区花岗岩类的年代学、地球化学、岩石成因及意义   总被引：2，自引：0，他引：2  

张维峰  陈华勇  江宏君  陆万俭  梁培  许超  严学录  杨俊弢 《大地构造与成矿学》2017,41(6)

多头山矿床是东天山阿奇山?雅满苏成矿带铁铜矿床的典型代表,矿床成因与区内岩浆岩有紧密联系。矿区出露的侵入岩主要有花岗斑岩、二长花岗岩、钾长花岗岩及英安玢岩。LA-ICP-MS锆石U-Pb年代学研究获得花岗斑岩、二长花岗岩及英安玢岩的年龄分别为316.3±8.1 Ma、318.3±3.0 Ma和197.2±3.5 Ma。花岗斑岩A/CNK介于0.82~1.01之间,显示偏铝质特征,为Ⅰ型花岗岩;同时样品富集大离子亲石元素Th、U、Pb,亏损高场强元素Nb、Ta、Ti,显示弧岩浆特征。钠质蚀变导致了花岗斑岩显示出富Na、贫K、Rb、Ca、Sr的特征。钠化花岗斑岩Nb/Ta为12.4~16.0,具有较高的ε_(Nd)(t)(5.76~6.24)值和较低的I_(Sr)值(0.70353~0.70532),与安第斯中生代岩基地球化学特征相似,结合样品中出现古老锆石的捕掳晶,表明其源区为新生的下地壳,混合有少量幔源物质,并伴随有地壳混染。二长花岗岩与钠化花岗斑岩具有相近的形成年龄和相似的地球化学特征,如Nb/Ta比值(14.2),亏损高场强元素、富集大离子亲石元素,同为准铝质(A/CNK=0.97)弧岩浆,暗示它们可能具有相似的源区。而早侏罗世的英安玢岩具有高Sr(552×10~(-6))含量和较高的Sr/Y(73.6)比值,显示出钙碱性埃达克岩的特征,同时样品具有较高的K_2O(3.27%)含量、Mg~#指数(55),表明其来源于拆沉下地壳的熔融并混有少量幔源岩浆。综合区域研究资料、年代学、地球化学及同位素特征,我们认为多头山所在的阿奇山?雅满苏成矿带可能是晚古生代洋壳向南俯冲至中天山地块之下形成的大陆边缘弧。  相似文献   

小兴安岭伊春地区环斑花岗岩组合特征及其地质意义   总被引：6，自引：1，他引：5       下载免费PDF全文

赵寒冬  刘勇 邓晋福肖庆辉马丽玲杨元江 《中国地质》2009,36(3):658-668

通过1∶25万鹤岗市幅区域地质调查,首次在小兴安岭中南段摩天岭一带发现了具环斑结构的晚石炭世二长花岗岩.环斑长石多呈自形晶宽板状或宽板柱状,少数为圆球状.大小不一.2～3.5 cm,内核为肉红色碱性长石,外壳为宽1～2 mm的灰白色斜长石,有时也见无环的卵圆形斑晶.其岩相学、岩石地球化学特征研究表明,摩天岭环斑花岗岩及其岩石组合为不同于前寒武纪典型非造山环斑花岗岩的造山带型环斑花岗岩,为形成于造山带与板块俯冲体制有关的岛弧或活动大陆边缘环境下的Ⅰ型花岗岩.  相似文献   

Geochemistry and zircon U–Pb–Hf isotopes of the 780 Ma I-type granites in the western Yangtze Block: petrogenesis and crustal evolution     

《International Geology Review》2012,54(10):1222-1243

ABSTRACT

Neoproterozoic I-type granites could provide vital insights into the crust–mantle interaction and the crustal evolution along the western Yangtze Block, South China. This paper presents new zircon U–Pb ages, bulk-rock geochemistry, and in situ zircon Lu–Hf isotope on the Dalu I-type granites from the southwestern Yangtze Block. Zircon U–Pb dating show the crystallization ages of 781.1 ± 2.8 Ma for granodiorites and 779.8 ± 2.0 Ma for granites, respectively. The Dalu granodiorites are Na-rich, calc-alkaline, metaluminous to slightly peraluminous (A/CNK = 0.94–1.08). Zircons from granodiorite have positive εHf(t) values (+2.16 to +7.39) with crustal model ages of 1.21–1.54 Ga, indicating juvenile mafic lower crust source. The Dalu granites are high-K calc-alkaline, peraluminous rocks. They have variable zircon εHf(t) values (?4.65 to +5.80) with crustal model ages of 1.31–1.97 Ga, suggesting that they were derived from the mature metasediment-derived melts by the mixing of newly formed mafic lower crust-derived melts. The geochemical variations in Dalu pluton is dominated not only by the different source rocks but also by the different melting temperatures. Combining with the geochemistry and isotopic compositions of I-type granitoids and tectonic setting in the western Yangtze Block, we propose that the Dalu I-type granodiorites–granites associations are the magmatic response from different crustal levels, which were induced by the heat anomaly due to the asthenosphere upwelling in the subduction-related setting.  相似文献   

Petrogenesis of Dashenshan I-type granodiorite: implications for Triassic crust–mantle interaction,South China     

《International Geology Review》2012,54(3):332-350

Triassic granodiorites in South China (SC) provide an opportunity to examine crust–mantle interactions that may have been caused by a mantle plume. Here we present a combined study of chronological, geochemical, and Sr–Nd–Hf isotopic compositions for Dashenshan granodiorites. These are high-K, calc-alkaline, I-type granodiorites that yield a U–Pb zircon age of 211 ± 3 Ma. They are metaluminous to weakly peraluminous (A/CNK < 1.1), with 3.04–3.89 wt.% Na₂O and 3.24–3.86 wt.% K₂O, and Na₂O/K₂O ratio ranging from 0.79 to 1.11. These granodiorites contain 67.7–72.6 wt.% SiO₂ but show moderate Mg^# values (44.2–57.8) and variable contents of Ni (3.6–29.9 ppm) and Cr (7.6–53.5 ppm). They exhibit light rare earth element (REE) enrichment and flat, heavy REE patterns with negative Eu anomalies (Eu/Eu* = 0.52–0.87). They also display strongly negative Ba, Sr, Nb, Ta, P, and Ti anomalies and positive Rb, Th, K, and Pb anomalies. Dashenshan granodiorites have high whole-rock initial ⁸⁷Sr/⁸⁶Sr ratios (0.7121–0.7172), negative ε_Nd (t) values (–8.8 to –6.8), and negative zircon ε_Hf (t) values (–6.6 to –3.3). These results suggest that the Dashenshan granodiorites were generated by a mixing between crustal melt and mantle-derived magma in an extensional setting. We conclude that generation of the Dashenshan pluton may reflect an interaction between a mantle plume and the overlying SC crust.  相似文献   

蒙古国东南部巴音苏赫图晚古生代—早中生代二长花岗岩地球化学特征及其对构造环境的约束     

沈晓丽  张宝林  贾文臣  郭志华  黄雪飞  崔敏利 《吉林大学学报(地球科学版)》2012,(Z1):281-295

巴音苏赫图二长花岗岩位于西伯利亚板块东南缘陆缘增生带与二连—贺根山板块对接带北缘之间。该岩体由石炭纪及三叠—侏罗纪两期花岗岩组成,均以高硅、富Al2O3、K2O、Na2O,贫MgO、CaO为特征。微量元素表现为富集LILE、亏损HFSE。弱富集LREE,Eu负异常明显。岩石学和地球化学综合研究表明:两期花岗岩早期为高钾钙碱性、准铝质-过铝质花岗岩碰撞期I型花岗岩,晚期花岗岩具有A型花岗岩特点。Sr-Nd同位素研究表明:石炭纪二长花岗岩(87Sr/86Sr)i比值较低(0.700 62～0.704 82),εNd(t)为正值(0.9～1.5),岩浆来自于增生的岛弧或年轻的幔源物质,在岩浆上升过程中遭受了少量地壳物质的混染;晚三叠世—早侏罗世花岗岩(87Sr/86Sr)i比值较高(0.709 96～0.710 19),εNd(t)较低,为-0.3～0.3,该期次花岗岩与晚石炭世花岗岩同源,受地壳混染程度相对较高。应用LA-ICP-MS法测得石炭纪花岗岩U-Pb年龄为(296±3.5)Ma,结合区域构造演化特点及所测三叠纪花岗岩的地球化学特征认为,在晚石炭世,南蒙古额尔德尼查干地区已进入碰撞期构造环境,在三叠—侏罗纪仍有同碰撞花岗岩侵入,晚石炭世以后的碰撞期持续时间较长。  相似文献