Petrogenesis of Mesozoic High-Mg Diorites in Western Shandong: Evidence from Chronology and Petro-geochemistry

The high-Mg diorites, widely occurring in western Shandong, have important implications in the study of the relationship between the Mesozoic magmatism and the nature of the lithosphere and its thinning period in the eastern North China craton （NCC）. The Tietonggou and Jinling intrusions are typically representatives. LA-ICP-MS zircon U-Pb dating, major and trace element and Sr-Nd isotopic compositions of the Mesozoic intrusive rocks from western Shandong, eastern China, were analyzed. The weighted mean 106^pb/ 238^U ages from LA-ICP-MS zircon U-Pb dating results for early norite-diorite, late pyroxene-diorite from the Tietonggou intrusion and biotite-diorite from the Jinling intrusion are （131.4±4.9） Ma（n=15）, （134. 5±2.3） Ma（n=13）, and （132.8±4. 2） Ma（n=12）, respectively, implying that they were formed in the Early Cretaceous. The weighted mean 207^pb/ 204^Pb ages for round zircons from late pyroxene-diorite in the Tietonggou intrusion is （ 2 513 ± 54） Ma（ n= 8）, suggesting that the basement of the North China craton should exist in the research area. The high-Mg diorites are characterized by enrichment in MgO, Na20, and light rare earth elements （LREE）, and they are poor in heavy rare earth elements （HREE） and high field strength elements （HFSE）, being similar to adakite. The existence of the mantle peridotite xenoliths with a high-Mg feature for these intrusive rocks implies that their primary magma should be derived from the upper mantle. However, Sr-Nd isotopic composi- tions （Is： 0.704 75--0.707 15;ENd （130 Ma） values： --3.95 to -- 13.30）, depletion in HFSE, and the occurrence of Archean inherited zircons suggest that crustal materials could be involved in the derivation of the primary magma. The compositional difference between the diorites from the Tietonggou and Jinling intrusions could be attributed to those of magma sources and degrees of partial melting. The Early Cretaceous high-Mg diorites are considered to have been formed by the mixed melting of the delaminated lithosphere （lithospheric mantle ＋ crust） and asthenosphere, based on their geochemistry, the mantlederived xenoliths, and the Early Mesozoic lithospheric evolutionary history of the eastern North China craton.

U-Pb geochronology,geochemistry and tectonic implications ofdiorite from Nangnimsan of Mehe in northern Da Hinggan Mountains

LA-ICP-MS zircon U-Pb dating indicates that the weighted average age of diorite from Nangnimsan,Mohe in the northern Da Hinggan Mountains in Heilongjiang Province is 516.2±1.7 Ma,as a result of magmatic intrusion of Early Cambrian. Geochemistry analysis indicates that the rocks belong to high-K calc-alkaline series,with low content of SiO_2( 52.24%-53.64%) and high Mg( MgO = 5.67%-6.56%,Mg~#= 61. 05-65. 46).The rocks are characterized by the enrichment of LREE and LILE( e.g. Rb,Ba,Pb),and relative depletion in HREE and HFSE( e.g. Ta,Nb,P,Ti),and with a high content of Sr( 442. 3-622. 3) × 10^(-6),Yb( 2.49-3.42) ×10^(-6) and Y( 25.64-35.49) ×10^(-6),and slightly negative Eu anormaly( δEu= 0.60-0.81). Based on Rb/Sr( 0.15-0.25) and Rb/Nb( 8.27-15.12),it is concluded that the primary magma of diorite was derived from the mixture of the crust and mantle. Combined with background of regional tectonic evolution,it is suggested that diorite was formed in the extensional environment after the collage of the EGM with the Siberian.

Zircon U-Pb geochronology and geochemistry of diorite dikes from Nancha ore deposit in Tonghua area of Jilin and its geological significance

The authors presented geochronology and geochemical data of diorites from Nancha gold deposit in Tonghua region, with the aim to constraining its formation age, magma source and tectonic setting. LA-ICP-MS U-Pb dating results of zircons from the diorites indicate that the rocks were formed in the Middle Jurassic （171 ±2 Ma, MSWD = 1. 19）. Geochemically, these rocks have Si02 concentrations of 52. 52%-54. 90%,K20 of 2. 14%-3.84% , Na20 of 3. 17%-3. 35% , MgO of 7. 43%-9. 34% and high Mg# of 68. 57-72. 57. These rocks are characterized by enrichment in large ion lithophile elements（ LILE,such as K, Ba, Rb and Sr） and light rare earth elements （ LREE） , relatively depletion in high field strength elements （ HFSE, such as Ta, Nb, Ti and Zr） , and heavy rare earth elements （HREE）. These characteristics suggest that primary magma of the rocks were derived from the partial melting of mantle with miner crustal contamination, which may related to partial melting of mantle wedge by addition of sediment melt from subducting oceanic crust. Based on former and present studies, the authors consider that the Nancha ore deposit high-Mg diorites were formed in compres- sional structural setting which is similar to volcanic arc. It could be related to the subduction of the Paleo-Paci- fic plate beneath the Eurasian continent.

Petrogenesis of Paleoproterozoic diorite porphyries inLuojiazhuang, western Shandong： constraints fromLA-ICP-MS zircon U-Pb geochronology and geochemistry

Based on the study of LA-ICP-MS zircon U-Pb geochronology and whole-rock geochemistry for theLuojiazhuang diorite porphyries in Menying , western Shandong , the analyzed zircons exhibit oscillatory zoning in the cathodoluminescence images and have high Th/U ratios （0. 15-1.53） , indicating a magmatic origin.In addition, most of the zircons have narrow metamorphic edges, suggesting that late metamorphic eventsmay exist. The youngest group of magmatic zircon 207Pb/206Pb ages rangng from 2 384 Ma to 2 234 Ma, yieldinga weighted mean age of 2 353 ± 14 Ma, which represents the forming age of the diorite porphyries, as theEarly Paleoproterozoic. Geochemically , the samples are characterized by low Si〇2（54. 54% and 55. 47% ）,high MgO （5.22% and 5.49% ） and Mg# values （58 and 59） . Moreover , they show enrichment of light rareearth elements and large ion lithophile elements （ Rb , Ba and K） , depletion of heavy rare earth elements andhigh field strength elements （Nb, Ta , Zr and Hf） , positive anomaly of Pb , and negative anomaly of Ti. Thefact implies that the Luojiazhuang diorite porphyries might derive from partial melting of mantle and mixed with an amount of continental crust material. In summary , they may tectonic setting that stretching along the east-＂west direction at the North China Craton in the Early Paleoproterozoic.

Geochronology and geochemistry of Dongxigao diorite porphyries: implications for Late Neoarchean tectonic evolution of eastern North China Craton

Zircon LA-ICP-MS U-Pb age and whole-rock geochemistry data are presented for the Dongxigao diorite porphyries in Pingyi,western Shandong,to restrict its petrogenesis. The zircons from the Dongxigao diorite porphyries exhibit striped absorption and oscillatory growth zoning in the cathodoluminescence images,which have upward-type characteristics of rare earth elements( REEs) with positive anomaly of Ce and negative anomaly of Eu,and have high Th / U ratios( 0. 06--0. 91),indicating its magma origin. Zircon LA-ICP-MS UPb dating indicates that^(207) Pb /^(206) Pb ages of 16 spots of zircons are between 2476 Ma and 2701 Ma,yielding a weighted mean age of 2 481 ± 8 Ma,which represents the formation age of Dongxigao diorite porphyries,i. e.Late Neoarchaean. Geochemically,the samples have low contents of SiO_2( 54. 94% and 54. 86%) and high amounts of MgO( 7. 19% and 7. 58%) and Mg~#values( 66. 47 and 67. 59). Additionally,the Dongxigao diorite porphyries show enrichment of LREEs and prominent negative Eu anomaly( δEu = 0. 89 and 0. 91),and they are characterized by enrichment of large ion lithophile elements( LILEs)( e. g. Cs,Rb and Ba),depletion of high field strength elements( HFSEs)( e. g. Nb,Ta,Zr,Hf and Ti),and positive anomaly of K and Pb. The results imply that the Dongxigao diorite porphyries dominantly derived from partial melting of enriched lithospheric mantle with attributes of arc magma,and the magma source area was mixed with amounts of continental crust material,it suggests that they formed in transformation tectonic setting changing from compression to intraplate extension.

Discovery and Geological Significance of Early Carboniferous High-Mg Diorite in the Balikun Area, Eastern Tianshan

The granodiorites,monzogranites and diorites are widely developed in the Balikun area of Eastern Tianshan Orogen.Of which,LA–ICP–MS zircon U-Pb isotopic dating from the diorites revealed that they were emplaced at 327~333 Ma,representing an important period of magmatism in the Early Carboniferous.Geochemically,they are characterized by moderate SiO2(51.33–62.48 wt%),high but variable MgO(2.04–11.16 wt%,average 5.35),higher Mg#(40–73)and TiO2(0.67–1.29 wt%),Na2O/K2O(1.39–2.95)as well as variable Cr(2.49–675 ppm)and Ni(1.31–174 ppm),showing a geochemistry similar to those of high-Mg diorites or sanukitoids.In addition,they are enriched in the LILE,poor HFSE with an evident negative Nb anomalies and a REE pattern of moderate fractionator between LREE and HREE without or weak negative Eu anomalies.TheirεHf(t)are positive(+3.63–+15.65),suggesting a source from the depleted mantle.In addition,they have high TiO2 and Pb,and large quantity of amphibolite and biotite,indicating that they were most likely derived from the partial melting of depleted mantle metasomatized by the slabderived melt under a hydrous condition.Consequently,combined with the contemporary volcanics and granitoids formed in the island arc settings,we proposed that the subduction was continued till Early Carboniferous in the Bogda-Harlik tectonic belt.After that,wide occurrence of the post-collisional A-type granites and mafic-ultramafic intrusions indicate this tectonic belt entered the post-collisional environment from Late Carboniferous to Permian.

Rare-earth and trace element imprints on the origin and tectonic setting of gabbro-diorite complex in the Pan-African belt of Southeast Obudu Plateau,Nigeria

A gabbro-diorite plutonic complex from the Southeast Obudu Plateau, representing limited volumes of magma, was studied for its trace and rare-earth element characteristics, in an attempt to document its genetic and geodynamic history. Geochemical studies indicate that the gabbro samples are characterized by variable concentrations and low averages of such index elements as Cr (40×10-6–200×10-6; av. 80×10-6), Ni (40×10-6–170×10-6; 53.33×10-6) and Zr (110×10-6–240×10-6; 116.67×10-6); variable and high averages of Rb (3×10-6–270×10-6; 80.67×10-6), Sr (181×10-6–1610×10-6; 628.17×10-6) and U (0.14×10-6–3.46×10-6; 1.51×10-6), and fairly uniform Co (34×10-6–49×10-6; 36.33×10-6) and Sc (23×10-6–39×10-6; 34.5×10-6), while the diorite samples exhibit higher trace element compositions. The range of REE contents and distinctive chondrite-normalized patterns indicate moderate fractionation with slight positive Eu anomaly in the diorites to very low fractionation with flat patterns and slight positive Eu anomaly in the gabbros. However, the general element systematics of the samples, especially LILE (Ba, Rb, Sr, Cs and Pb), HFSE (Zr, Th, U, Hf, Mo, W, Nb and Sn), relatively immobile elements (Zr, Ni, Cr) and REE, suggests a differentiation model, involving fractional crystallization of olivine and clinopyroxene from a partial melt generated beneath an island arc complex. A possible model for the complex is therefore an island arc setting, the development of which was dominated by calc-alkaline magmatism across the Obudu Plateau.

Mylonitization of Diorites in Jiangshao Fracture Belt, Zhejiang Province,China

Characteristcs of progressive ductile deformation and remnant igneous fabrics indicate that thefoliatal diorites in the middle sector of the Jiangshao fracture belt in Zhuji County, Zhejiang, aremyonites deformed from diorites. The mylonithation occurred about 353 - 370 Ma ago under a condi-tion of 425-475℃ and 3.8-4.6 kb.Therelation between the deformation and metherphism was discussed based on petrographic evidence and mineral chemistry and assemblage. It is suggested that thedeformation was responsible for the deveopment of lowgrad greenschisthaes metamorphism ofmylonitic diorites by introducing fluid phase to aerelerate metamorphic reaction and diffosion.

An Unique Glomerophyric Diorite Porphyry from the Southern Margin of North China Craton:Geochronology,Geochemical and Quantitative Textural Analysis Constraints

1 Introduction The Wulong glomerophyric diorite porphyry has an extremely peculiar texture with plagioclase phenocrysts clustered as flower-like glomerocrysts(Figs.1a&b),which is never discovered elsewhere of the world.The

电感耦合等离子体质谱(ICP-MS)法测定闪长岩中的高场强元素

闪长岩中高场强元素主要赋存在难溶的矿物(角闪石、锆石等)中。采用常规的密闭酸溶法导致高场强元素特别是锆、铪元素溶出率偏低。针对这一问题,根据高场强元素的赋存状态,首先增加预消解过程,其次对溶解样品所需试剂添加量(氢氟酸、硝酸)以及消解时间设计了3因素3水平的正交实验,从而得到最佳试剂添加量为2 mL氢氟酸和1 mL的硝酸,消解时间为36 h,影响高场强元素溶出率的最主要因素是氢氟酸。以在最佳前处理实验方案下溶样,在所溶解完全的溶液介质中添加浓度为0.1%的盐酸(体积比),以保证高场强元素在溶液里的稳定性。建立的方法用于北山地区闪长岩样品分析,并与碱熔、X射线荧光光谱法测定值对比,分析结果具有良好的一致性,方法检出限0.004~2.5μg/g,相对标准偏差1.5%~8.4%,加标回收率93.0%~108%。实现了闪长岩中高场强元素的准确分析。

大兴安岭中段内蒙古扎赉特旗地区石炭纪高镁闪长岩、埃达克岩的发现及其对嫩江洋俯冲作用的指示

扎赉特旗地区的晚古生代岩浆作用,对于揭示嫩江洋的俯冲过程与机制具有重要的约束意义。通过野外地质调查、岩石学、岩石地球化学和锆石U−Pb定年研究,在扎赉特旗元宝山和贾家屯地区新发现了晚石炭世早期的高镁闪长岩(年龄加权平均值为320.5±1.2 Ma)和O型埃达克岩(年龄加权平均值为317.9±3.3 Ma)。元宝山高镁闪长岩具有低SiO_(2)、高MgO、高Mg^(#)和富Na_(2)O的特点,且Ni、Cr含量高,富集轻稀土元素和大离子亲石元素,亏损高场强元素,认为其形成于消减带之上的地幔楔环境,是由消减板片部分熔融衍生的富Si质流体交代地幔岩部分熔融形成的。贾家屯石英闪长岩具有高SiO2、富Na2O、高Sr和低Yb、Y的特点,K2O/Na2O值低,稀土元素强烈分异,富集轻稀土元素和大离子亲石元素,亏损高场强元素,无负Eu异常,且贫Mg、Cr、Ni,为消减板片部分熔融后经结晶分异形成的O型埃达克岩。新发现的晚石炭世早期的埃达克岩−赞岐岩组合,与研究区石炭纪花岗岩的形成时间(333~304 Ma)同步,且高镁闪长岩与辉长岩(325.2~317.3 Ma)伴生,反映扎赉特旗地区处于松嫩地块西缘的活动大陆边缘弧环境,推测嫩江洋至少从晚石炭世早期开始就存在向东南侧松嫩地块之下的俯冲作用。

安徽铜陵地区晚中生代中基性侵入岩成因与成矿:来自磷灰石矿物学和地球化学证据

辉石闪长岩是安徽铜陵地区晚中生代侵入岩的重要类型,与铜金多金属成矿密切相关。本文以白芒山岩体和舒家店岩体辉石闪长岩为研究对象,着重开展磷灰石矿物学和地球化学研究,探索中基性侵入岩成因及与成矿关系。结果显示:磷灰石强烈富集稀土元素,轻重稀土元素分异明显,弱—中等Eu负异常,富集Th、U等高场强元素,亏损Ta、Nb、Ti、Zr、Hf等高场强元素和Rb、Ba、Sr等大离子亲石元素,稀土—微量元素组成特征指示其寄主岩石成岩物质具有壳幔混源特征。岩相学特征显示磷灰石具有两种不同的晶体形态、产出状态和显微结构,即长柱状、包裹体相、均质结构和短柱状、晶间相、核—边/环带结构,其元素地球化学特征有显著差异,指示其寄主岩石成岩作用经历过壳源长英质岩浆冷凝结晶→高温幔源镁铁质岩浆注入和长英质岩浆早期结晶矿物熔蚀→混合岩浆侵位和结晶的复杂过程。核—边/环带结构磷灰石从核部到边部SO_(3)和Cl含量波动式变化特征,指示镁铁质岩浆幕式注入,并触发混合岩浆上升侵位,有利于流体出溶和热液成矿。磷灰石卤族元素(F、Cl)和SO_(3)高含量则提供板块俯冲环境证据,指示基性端元的镁铁质弧岩浆来自俯冲板片析出流体交代富集岩石圈地幔,镁铁质岩浆幕式注入有利于流体出溶和热液成矿。

智利月亮山地区中生代侵入岩成因及其构造意义:来自锆石U-Pb年代学、岩石地球化学的制约

月亮山铁铜矿区处于智利中北部海岸山带铁氧化物铜金矿(IOCG)成矿带上,位于一级控矿构造阿塔卡玛(ATACAMA)断裂带的南缘。全岩地球化学研究表明,本区二长闪长岩性质具有钙碱性、准铝质特征,其La/Nb比值大于1.5,La/Ta比值大于22,微量元素图显示均显著亏损Nb、Ta和Ti,表明二长闪长岩岩浆的源区起源于与俯冲相关的岩石圈地幔。二长闪长岩的LA-ICP-MS锆石U-Pb年龄为(108.2±1.9)Ma,表明其为早白垩世晚期的岩浆活动的产物。构造环境分析表明,太平洋纳斯卡板块向南美板块俯冲过程中,形成本区南北向的ATACAMA断裂带(AFZ)与母岩浆,深层岩浆侵位经过部分熔融、结晶分异过程形成了闪长岩岩体,与本区IOCG矿床的形成关系密切。

不同环境下酸性闪长岩沥青混合料长期水稳性能评价研究

通过浸水马歇尔试验、冻融劈裂试验以及车辙试验评价了采用酸碱复合集料、单掺水泥(2%水泥替代矿粉)、消石灰(30%消石灰水浸泡石料)以及抗剥落剂(0.3%抗剥落剂改性沥青)的酸性闪长岩沥青混合料的短期水稳性能,再通过反复冻融劈裂试验、反复冻融烘劈裂试验以及反复酸蚀冻融劈裂试验测试处置酸性闪长岩沥青混合料在不同环境下的长期水稳性能。结果表明:酸性闪长岩的物理力学性能均满足规范要求;处置后酸性闪长岩沥青混合料的短期水稳性能显著提升,满足规范使用要求;但经0.2%抗剥落剂处置的酸性闪长岩沥青混合料在高温下的长期水稳性能较差;经30%消石灰水处置的酸性闪长岩沥青混合料具有良好的长期水稳性能,可推荐应用于工程中。

辽吉古元古代造山带小女寨变辉长闪长岩的成因及其对钴镍富集成矿作用的制约

辽吉造山带是华北克拉通一条重要的古元古代造山带,该造山带在古元古代盆地拉张时期接受了大量陆壳沉积物,这些沉积物质组成和多期的岩浆-变质事件为辽吉造山带富集成矿提供了有利的条件。辽吉造山带内除了发育与千枚岩-片岩相伴生的沉积岩-变沉积岩容矿型铜钴矿床,还发育与基性岩相伴生的岩浆型铜镍钴矿床。然而,对于岩浆型Co-Ni矿的富集成矿模式及钴镍富集规律的研究较为薄弱。本文选取辽河群小女寨变辉长闪长岩开展了岩相学、矿物化学、锆石U-Pb年代学、全岩地球化学及硫化物硫同位素的研究,以进一步理清辽河群Co-Ni成矿机制及物质来源。变辉长闪长岩具有变化的SiO_(2)(26.1%~57.3%)、MgO(2.90%~25.0%)、CaO(3.17%~10.7%)和FeO^(T)(6.43%~38.94%)含量,属于钙碱性系列。具有轻稀土富集和重稀土平坦的稀土配分模式,相对亏损高场强元素(如Ta、Nb、Ti)。锆石U-Pb同位素分析获得的变辉长闪长岩变质原岩的形成时代为~2.17Ga。锆石εHf(t)值的变化范围为-1.3~+5.0,指示基性岩的岩浆源区来自富集地幔的部分熔融,可能与岩石圈伸展作用相关。变辉长闪长岩中钴镍主要赋存于辉砷钴矿(Co:14.8%~31.3%;Ni:2.92%~14.2%)和镍黄铁矿(Co:5.70%~8.53%;Ni:27.3%~34.0%)中,富Co-Ni的矿物与石英、绿帘石等矿物共生,指示其成矿作用可能与晚期热液有关。小女寨变辉长闪长岩硫化物的S同位素分馏程度较弱(+4.5‰~+5.5‰),表明成矿物质来源均一。且具有比地幔更重的δ^(34) S值,表明硫化物的S可能来源于大陆地壳。小女寨地区2个钻孔岩心样品均具有较高的Ni(0.09%~0.94%)、Co(0.01%~0.13%)和Cu(0.02%~0.79%)品位,表明辽吉造山带古元古代变基性岩具有Cu-Co-Ni的成矿潜力。

扬子西缘东炉房Cu-Mo矿床侵入岩年代学、地球化学特征及其成矿意义

东炉房Cu-Mo矿床位于扬子陆块西缘,矿床发育与石英二长斑岩相关的斑岩型Mo(-Cu)矿和接触带矽卡岩型Cu矿。前人开展的研究工作主要集中在斑岩Mo矿化的成因,但是对矽卡岩型Cu矿化的研究较为薄弱。本文基于系统整理项目组对该矿床的勘查成果,对矽卡岩型Cu矿化有关的石英闪长玢岩开展锆石U-Pb年代学和岩石地球化学分析。结果表明,石英闪长玢岩锆石U-Pb加权平均年龄为82 Ma,表明其形成于晚白垩世,与格咱弧晚白垩世W-Mo(Cu)成矿作用时代一致。石英闪长玢岩具有高硅(SiO_(2)=60.74%~63.36%)、富碱(Na_(2)O+K_(2)O=7.03%~9.29%)特征,属准铝质(A/CNK=0.63~0.86)、钾玄岩系列I型花岗岩。岩石具有轻、重稀土分异明显(右倾型)和典型的埃达克质岩亲和性特征,可能为幔源岩浆注入中-基性下地壳部分熔融的产物。岩浆岩源区性质、围岩类型等条件决定了东炉房矿床的矿化分带性,深部石英二长斑岩的钾化带内发育斑岩型Mo(-Cu)矿化,浅部石英闪长玢岩和碳酸盐岩接触带发育矽卡岩型Cu(-Mo)矿化,外围大理岩局部发育脉状Pb-Zn-Au-Ag矿化。矿床由深到浅、由内到外构成了Mo(-Cu)→Cu(-Mo)→Pb、Zn、Au、Ag的斑岩成矿系统。通过区域综合对比认为格咱弧晚白垩世岩浆岩及相关成矿作用向南延伸至扬子陆块西缘,形成于碰撞后伸展环境,且由北往南岩浆分异程度逐渐降低,幔源岩浆贡献逐渐增多,导致成矿作用差异明显(休瓦促W-Mo→热林Mo-W→红山、铜厂沟Mo(-Cu)→东炉房Cu(-Mo))。

东昆仑古特提斯造山带巴隆地区中性岩墙群的岩石成因与构造意义

岩墙群是研究造山带构造演化过程与大陆地壳生长机制的重要探针。本文以东昆仑古特提斯造山带巴隆地区中性岩墙群为研究对象,开展了岩石学、年代学和地球化学研究,分析其岩石成因及其对古特提斯造山作用过程的启示。巴隆中性岩墙群以闪长玢岩为主,其锆石U-Pb年龄为250.2±1.3 Ma,属于早三叠世岩浆作用的产物。岩墙群的SiO_(2)含量为52.8%~59.6%,全碱(K_(2)O+Na_(2)O)含量为3.98%~6.25%,Mg#值为24~46,铝饱和指数为0.91~0.98,属于高钾钙碱性、准铝质岩石。样品的轻重稀土元素分异显著,(La/Yb)N值为5.44~7.76,Eu异常不明显(δEu=0.91~1.11)。样品均富集大离子亲石元素,亏损高场强元素,且具有显著的Nb、Ta负异常。岩石成因分析表明巴隆早三叠世中性岩墙群主要起源于古老镁铁质地壳物质的部分熔融,且岩浆受到一定程度的壳–幔混合影响。综合分析区域地质资料,本文认为巴隆地区中性岩墙群形成于东昆仑古特提斯洋俯冲消减的陆缘弧环境,且大陆弧古老地壳物质重熔和壳–幔混合作用是东昆仑古特提斯造山旋回大陆地壳生长演化的重要方式。

鲁西地区中生代高镁闪长岩角闪石成分变化特征及其对矽卡岩型铁矿成矿作用的启示

矽卡岩型铁矿床是我国最重要的铁矿床类型之一,在华北克拉通东部广泛发育,时空上与中生代高镁闪长岩体紧密伴生,研究其物质来源和成岩成矿过程具有重要的意义。本文对鲁西地区与金岭铁矿床具有成因联系的中生代高镁闪长岩中的角闪石进行了详细的成分研究,限定高镁闪长岩的岩浆演化过程及其物理化学条件变化,探讨高镁闪长岩的岩石成因机制及其与矽卡岩型铁矿床成矿作用之间的联系。金岭高镁闪长岩的角闪石斑晶边部与基质角闪石具有一致的主量元素成分,记录了相似的T-P-fO_(2)-H_(2)O条件,显著不同于角闪石斑晶核部。角闪石斑晶核部的平衡岩浆来源于地幔部分熔融,而角闪石斑晶边部与基质角闪石的平衡岩浆中则存在地壳组分的贡献。高镁闪长岩-矽卡岩型铁矿床体系为极其复杂的成岩成矿系统,起源于高氧逸度和高水含量的地幔源区,并经历了包括结晶分异、同化混染、岩浆混合以及流体出溶、迁移和淋滤在内的诸多复杂岩浆热液演化过程。这些源区特征和岩浆-热液过程记录了不同深度岩石圈对华北克拉通破坏的构造响应。

东昆仑东段各玛龙闪长岩年代学、地球化学特征及成因分析

各玛龙地区位于东昆仑造山带东段南部,该地区构造活动与岩浆活动强烈。本文以两件花岗闪长岩和两件英云闪长岩为研究对象,开展LA-ICP-MS锆石U-Pb年代学和岩石全岩元素组成研究,探讨岩石成因类型和岩浆源区特征,分析闪长岩的构造演化环境。研究结果表明:两件具有代表性的闪长岩样品成岩年龄分别为405.3±1.1 Ma和405.8±1.2 Ma,说明成岩时代为早泥盆世;4件闪长岩样品具有高硅、高铝、高碱、贫钙、贫镁、弱过铝质特征,属于弱过铝质高钾钙碱性系列岩石;4件样品中未发育S型花岗岩的代表性矿物,并且Rb/Sr值为0.32~0.43,均小于0.9,A/CNK值为0.98~1.09,均小于1.1,符合I型花岗岩的地球化学特征;通过分析La-La/Sm图解与(Zr+Nb+Ce+Y)-(Na_(2)O+K_(2)O)/CaO图解,同时结合Nb/Ta、Zr/Hf、Nb/U、Rb/Sr、Ti/Y、Ti/Zr值,可以得知各玛龙地区闪长岩是由地壳岩石部分熔融形成的,并且可能伴有幔源物质的参与。结合前人研究及(Y+Nb)-Rb图解与Rb/30-Hf-Ta*3图解可知,各玛龙地区闪长岩形成于早泥盆世东昆仑造山带的后碰撞伸展环境。

Geochronology,Geochemistry,and Sr-Nd-Hf Isotopes of the Diorite Porphyrites from the Weining Beishan Area,Ningxia Hui Autonomous Region:Constraints on Their Source and Tectonic Implications

The Weining Beishan area of Ningxia Hui Autonomous Region is located at on the western edge of the Helanshan tectonic belt,which is a tectonic joint among Alxa Block,Ordos Block,and North Qilian orogenic belt.However,the tectonic evolution of this area remains unclear due to the lack of magmatic information.This paper conducted researches on geochronology,geochemistry,and Sr-Nd-Hf isotopes of the diorite porphyrites exposed in the Weining Beishan area.The zircon U-Pb dating yields two ages of 145.0±1.1 and 146.2±1.5 Ma,and the whole-rock geochemical data indicate that the diorite porphyrites are metaluminous to weakly peraluminous and high-K calc-alkaline series.The characteristics of highly initial^(87)Sr/^(86)Sr ratios(0.70816 to 0.71047),negativeε_(Nd)(t)(−8.9 to−8.4),and negativeε_(Hf)(t)(−13.8 to−21.2)indicate that the diorite porphyrites originated from partial melting of the middle-lower ancient crust related to the North China Craton.Combined with the regional geology,we suggested that partial melting was triggered by a tectonic activity of deep faults cutting through the crust under the regional stress transformation from compressing to extension during the Late Jurassic–Early Cretaceous,which is probably related to the westward subduction of the Paleo-Pacific Plate.