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1.
东准噶尔和尔赛斑岩铜矿成岩成矿时代与形成的构造背景   总被引：4，自引：1，他引：3  
杜世俊  屈迅  邓刚  张永  程松林  卢鸿飞  吴琪  徐兴旺 《岩石学报》2010,26(10):2981-2996
东准噶尔和尔赛铜矿是近年来新发现的斑岩型铜矿,位于野马泉-琼河坝古生代岛弧带东段。成矿岩体为侵位于花岗闪长岩中的花岗闪长斑岩,花岗闪岩中包含有钾长花岗岩体。锆石CAMECA U-Pb测年结果显示,钾长花岗岩年龄为429Ma,并含有405Ma的锆石;花岗闪长岩年龄为411Ma,并含432Ma的碎屑锆石;花岗闪长斑岩主体年龄为410.5Ma。研究区经历了3期岩浆与热液活动,且至少在早志留世就已开始,琼河坝岛弧是开始于早古生代的岛弧。辉钼矿Re-Os等时线年龄为409Ma,与花岗闪长斑岩年龄一致。和尔赛斑岩铜矿的主成岩成矿时代为早泥盆世,年龄约为410Ma。和尔赛铜矿的花岗闪长岩和花岗闪长斑岩具有埃达克岩与岛弧岩浆岩的地球化学特征,包括63.79%～68.86%SiO2、14.91%～17.48%Al2O3、0.68%～2.35%MgO、高Sr(383×10-6～971×10-6)与Sr/Y比值(48.3～111)、低Y(7.92×10-6～9.69×10-6)与Yb(0.76×10-6～0.98×10-6),Ba、U、K、Sr等大离子元素富集,Th、Nb、Ta、Ti等高场强元素亏损,较低的(87Sr/86Sr)i值(0.703852～0.704565)、正的εNd(t)值(6.1～7.4)、与亏损地幔接近的较低的初始铅同位素比值((206Pb/204Pb)i=17.58～17.91,(207Pb/204Pb)i=15.40～15.48,(208Pb/204Pb)i=37.25～37.47)。这些地球化学特征说明其形成于岛弧环境,可能为古俯冲洋壳部分熔融的产物。琼河坝地区以花岗闪长岩和花岗闪长斑岩为代表的岩浆岩带是形成和寻找斑岩铜矿的有利地区。  相似文献   

2.
云南宾川小龙潭矿区斑岩体位于扬子板块西缘程海断裂带东侧,属金沙江-红河富碱侵入岩带组成部分.本文对矿区内与成矿密切相关的花岗斑岩进行了岩石学、年代学及地球化学研究.结果显示:花岗斑岩由二长花岗斑岩(MGP)和钾长花岗斑岩(KGP)组成,二者岩相学特征相似,空间上无明显分带关系,呈过渡渐变关系,具典型斑状结构.二长花岗斑岩和钾长花岗斑岩均具富碱、低钛和准铝质-弱过铝质特征,属准铝质-弱过铝质钾玄岩系列富碱斑岩;二者富集轻稀土元素(LREE)和大离子亲石元素(Rb、Ba、U),亏损重稀土元素(HREE)和高场强元素(Ta、Nb、Ti,Zr,Hf),具有较高Sr含量和Sr/Y值,中等负Eu异常(δEu=0.39～0.78),表现出C型埃达克质岩地球化学特征.二长花岗斑岩和钾长花岗斑岩具相似的地球化学特征,表明它们属同源岩浆演化产物.二长花岗斑岩锆石U-Pb年龄为34.7±0.3 Ma,反映其形成于古近纪始新世,与金沙江-红河富碱侵入岩活动高峰期(45～30 Ma)吻合.综合研究表明,小龙潭矿区花岗斑岩属具C型埃达克质岩地球化学特征的花岗岩,起源于底侵作用带来的幔源岩浆与石榴角闪岩相加厚下地壳部分熔融的混合岩浆,是印度-欧亚板块晚碰撞期力学性质由挤压向伸展转化动力学背景下的产物,具备成矿作用发生的物质基础,有较好的成矿潜力.  相似文献   

3.
孟祥舒  何艳红  陈亮  务磊 《地质学报》2017,91(12):2679-2696
阎家店闪长岩体位于北祁连造山带东段,是秦-祁构造结合部位最大的早古生代复合闪长岩体,主要岩性为石英闪长岩-闪长岩。早期研究显示阎家店闪长岩体北部样品的测年结果为~440Ma,是以红土堡基性火山岩为代表的弧间裂谷(或初始弧后盆地)在中晚奥陶世向北俯冲形成的岛弧侵入岩体。区域资料显示阎家店闪长岩自北向南岩体逐渐发育平行定向构造,具有糜棱结构,片麻状构造。南部糜棱岩化闪长岩LA-ICP-MS锆石U-Pb定年结果显示其形成于418±3.2Ma。主微量元素地球化学特征显示其与埃达克岩地球化学特征一致,具有高Si O2,Al2O3,Na2O和Sr,低Yb和Y以及高Sr/Y和(La/Yb)N比值,无或微弱的Eu异常。低Na/K,Nb/U和Ce/Pb比值以及负的εHf(t)值表明阎家店闪长岩体主要起源于壳源物质的部分熔融。较高的Y/Yb和Ho/Yb以及Nb/Ta暗示其源岩已经转变为榴辉岩相物质。高密度的榴辉岩相基性下地壳由于重力不稳定性拆沉进入地幔,受地幔橄榄岩交代导致了阎家店闪长岩体南部样品的高Mg O含量以及Mg#。因此,自~440Ma至~418Ma秦岭-祁连结合部位的地壳在不断地加厚,~418Ma的阎家店闪长岩形成于俯冲后碰撞造山阶段,其动力学背景和时限与北祁连构造带一致。  相似文献   

4.
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   

5.
海南岛屯昌地区侵入岩由花岗闪长岩、花岗岩及少量辉绿-闪长玢岩（脉）、镁铁质包体组成。本文报道了这些侵入岩的锆石LA-ICPMS U-Pb 定年结果和地球化学组成, 定年结果显示岩石形成于早白垩世晚期（~107 Ma）。地球化学特征显示, 花岗闪长岩和花岗岩具有高的SiO2、Al2O3 含量以及高的Sr 含量和Sr/Y 比值, 低的Y 和Yb 含量, Eu 异常不明显等, 属于埃达克质岩。屯昌埃达克质岩具有比较均一的Sr、Nd 同位素组成（ISr＝0.7082~ 0.7096, εNd（t）＝？6.55~ ？3.85）。镁铁质岩脉和包体则显示了稍低的ISr （0.7064~0.7086）和变化的εNd（t） （？5.10~ ＋0.13）。埃达克质岩的锆石原位Hf 同位素组成为： （176Hf/177Hf）i = 0.28257~0.28277, εHf（t）= ？4.86~ ＋2.09, 相应的两阶段模式年龄TDM2 变化于1.09 Ga 和1.54 Ga 之间。闪长玢岩脉的（176Hf/177Hf）i = 0.28257~0.28264, εHf（t） = ？4.94~ ？2.42, TDM2＝1.38~1.55 Ga, 类似于埃达克质岩。屯昌埃达克质岩很可能由新底侵的玄武质下地壳物质部分熔融所形成, 俯冲的古太平洋板块在早白垩世晚期（约107 Ma）的后撤作用所 导致的软流圈上涌为地壳熔融提供了热源。  相似文献   

6.
黑龙江洋灰洞子斑岩型铜矿床地处兴蒙造山带东段、吉黑褶皱带北部,矿体主要赋存在花岗闪长斑岩和构造角砾岩中。为厘定洋灰洞子铜矿床的成岩成矿时代和构造背景,笔者对洋灰洞子花岗闪长斑岩进行了元素地球化学和LA--ICP--MS锆石U--Pb年代学的相关研究。岩石地球化学特征显示,花岗闪长斑岩富硅贫镁,属于过铝质钙碱性系列,富集轻稀土元素(LREE),(La/Yb)N=10.49~19.79,Eu显示弱负异常或正异常,高Sr低Y和Yb,富集大离子亲石元素(LILE),相对亏损高场强元素(HFSE),具有埃达克岩或埃达克质岩的特征。LA--ICP--MS锆石U--Pb测年结果显示,花岗闪长斑岩锆石206Pb/238U加权平均年龄为204.4±2.8 Ma和201.2±1.7 Ma。综合研究认为,洋灰洞子斑岩型铜矿床的成岩成矿时代可能为晚三叠世—早侏罗世之交,该矿床形成于古亚洲洋闭合后的陆陆碰撞造山环境,是加厚下地壳部分熔融形成的岩浆流体作用的结果。  相似文献   

7.
滇西剑川富碱岩浆岩位于青藏高原东南缘的三江南段,是金沙江-红河富碱岩浆岩带的重要组成部分。剑川富碱岩浆岩包括花岗岩和正长岩两类岩石,前者主要有花岗斑岩和石英二长斑岩,后者主要是正长斑岩和粗面岩。本文对剑川富碱岩浆岩进行了主微量元素、锆石U-Pb年代学和Sr-Nd-Hf同位素特征研究。锆石U-Pb测年结果显示,剑川花岗岩结晶年龄为35. 1～36. 1Ma,正长岩结晶年龄为35. 7～35. 8Ma,均形成于始新世。花岗斑岩和石英二长斑岩的SiO_2含量为67. 92%～69. 93%,K_2O/Na_2O比值介于0. 86～1. 22,具有高钾钙碱性特征;正长斑岩和粗面岩的SiO_2含量为53. 94%～63. 51%,K_2O/Na_2O比值介于1. 30～2. 68,属于钾玄质岩石系列。两类岩石都富集轻稀土元素(LREE)和大离子亲石元素(LILE),相对亏损高场强元素(HFSE)。其中,花岗斑岩和石英二长斑岩有着较高的Sr、Sr/Y、La/Yb值和低的Y、Yb含量,具有埃达克质岩浆属性。结合Sr-Nd-Hf同位素研究认为,滇西剑川地区花岗岩起源于增厚的镁铁质新生下地壳部分熔融,正长岩是由交代富集的岩石圈地幔熔融产生的基性岩浆演化而来的产物。滇西剑川新生代富碱岩浆活动是对印度与欧亚板块晚碰撞阶段,岩石圈地幔发生对流减薄和软流圈物质上涌过程的响应。  相似文献   

8.
卢成忠 《中国地质》2007,34(6):1055-1061
江山—龙游南部地区晚中生代侵入岩分布广泛,以往被认为是钙碱性系列岩石,笔者通过野外地质、岩石学和元素地球化学研究表明,石英二长岩、二长岩、正长岩以及与之伴生的花岗岩与花岗斑岩属钾玄质系列岩石。这套岩石高碱(Na2O K2O=7.80%～10.47%)、富钾(K2O/Na2O=0.92～1.91)、贫钛(TiO2=0.2%～0.88%)、Al2O3含量较高且变化范围大(11.08%～17.77%),富集大离子亲石元素(LILE)和轻稀土元素(LREE),且Ce/Yb(27.29～85.64)、Ta/Yb(0.42～0.73)和Th/Yb(3.44～14.44)比值高,具有钾玄质系列的岩石地球化学特征。该区矿产资源较为丰富,矿床在时间与空间上多与钾玄质侵入岩密切共生,钾玄质侵入岩为成矿母岩,是重要的找矿岩石学标志。  相似文献   

9.
李继磊  钱青  高俊  苏文  张喜  刘新  江拓 《岩石学报》2010,26(10):2913-2924
西天山昭苏东南部阿登套地区大哈拉军山组火山岩主要由玄武质安山岩组成,具有富集大离子亲石元素、亏损高场强元素(如Nb、Ta、Ti)、稀土元素高度分馏的特征。这些玄武安山岩被一些钾长花岗岩和花岗斑岩脉体侵入。钾长花岗岩脉为准铝质,含有较高的Na2O+K2O、轻稀土元素、Zr、Nb、Y含量和较高的FeOT/MgO及Ga/Al比值。两类花岗岩均亏损Ba、Sr、P、Ti和Eu。钾长花岗岩和花岗斑岩给出的Laser-ICPMS锆石U-Pb年龄分别为354.2±2.3Ma和339.5±2.3Ma,表明其围岩即大哈拉军山组火山岩的形成时代不晚于早石炭世早期。综合野外地质观察、区域地质构造以及上述岩石的地球化学特征和时代,我们认为西天山昭苏南部大哈拉军山组火山岩及侵入其中的早石炭世A型花岗岩脉可能形成于活动陆缘弧后拉张环境。  相似文献   

10.
大黑山斑岩型钼矿花岗质岩体主要岩石类型为花岗闪长岩和花岗闪长斑岩,呈复式岩体状产出.含矿的花岗闪长斑岩体具有较高的Al2O3含量(A/CNK=1.04~1.25),较低的Mg指数(Mg#=21~44);轻重稀土分馏明显,没有或具有轻微的负铕异常(δEu=0.82~1),表明可能源区基本没有斜长石残留;富集大离子亲石元素Rb、Ba、Sr,相对亏损Nb、Ta、Y、Yb、Th、P和Ti,高Sr/Y、Sr/Yb比值,类似中国东部的"C型"埃达克岩.不含矿的花岗闪长岩A/CNK=1.01~1.03,轻稀土富集,重稀土亏损,中等的负铕异常(δEu=0.62~0.63),富集大离子亲石元素Rb、Th元素,亏损Nb、Ta、Zr等高场强元素,强烈亏损P和Ti元素相,比较低的Sr/Y、Sr/Yb比值.Hf同位素特征显示,大黑山花岗质岩体是由中—新元古代亏损地幔中增生的新生地壳,在中生代发生熔融而形成的.结合太平洋板块构造演化史以及近年获得的黑龙江杂岩碎屑锆石年龄和黑龙江群蛇绿混杂岩中蓝片岩相变质作用的年龄,表明太平洋板块晚三叠世—早侏罗世开始向西俯冲,说明大黑山花岗质岩体的形成与太平洋板块俯冲有关.  相似文献   

11.
The tectonic transition from the palaeo-Tethyan to palaeo-Pacific dynamic domains in the South China Block (SCB) is still a matter of debate. The A-type granites collected from the southeastern SCB offered an opportunity to illustrate this tectonic transition. This article records a set of petrographic, geochronological, and geochemical data for the Wengong granitic pluton from the eastern Nanling Range. LA-ICP-MS zircon U–Pb dating shows a crystallization age of 196.9 ± 4.4 Ma with εHf(t) values ranging from +2.1 to +7.7. The samples have high SiO2, Zr+Nb+Ce+Y, FeOt/MgO, Ga/Al, and Y/Nb and are depleted in Nb–Ta, Zr–Hf, Ba, Sr, Ti, and Eu, similar to those of the A2-type granite. Their initial 87Sr/86Sr ratios range from 0.70885 to 0.70983 and the εNd(t) values range from ?2.9 to ?1.1, close to those of the Early Palaeozoic mafic rocks in the southeastern SCB. The Wengong A2-type granite was derived from partial melting of the mafic rocks underplated into the lower crust during the Early Palaeozoic.

The Mesozoic A-type granites in the southeastern SCB can be subdivided into 229–215 Ma (Late Triassic), 197–152 Ma (Jurassic), and 135–92 Ma (Cretaceous). They differ in geochemical and spatial distribution characteristics. The Late Triassic A-type granites were formed in the post-collision extensional setting associated with the palaeo-Tethyan dynamic domain, whereas the Cretaceous A-type granites were under the control of the palaeo-Pacific dynamic domain. The A-type granites were hardly exposed during the Late Triassic–Early Jurassic and Late Jurassic–Early Cretaceous. The Jurassic A-type granites were formed in the intra-plate extensional setting, a response to the tectonic transition from the palaeo-Tethyan to palaeo-Pacific dynamic domains. Thus, the occurrence of the Wengong A2-type granite indicates that this tectonic transition possibly initiated at the earliest Early Jurassic.  相似文献   

12.
Early Ordovician A-type granites in the northeastern (NE) Songnen Block NE China were studied to better understand the geodynamic settings in this region. This research presents new zircon U–Pb ages and whole-rock geochemical data for the Early Ordovician granites in the NE Songnen Block. Zircon U–Pb dating indicates that the granite in the Cuibei, Hongxing, and Meixi areas in the NE Songnen Block formed in the Early Ordovician with ages of 471–479 Ma. The granites show geochemical characteristics of high SiO2 and K2O compositions and low FeOT, MgO, CaO, and P2O5 compositions. They belong to a high K calc-alkaline series and display a weak peraluminous feature with A/CNK values of 0.98–1.14. The rocks have a ∑REE composition of 249.98–423.94 ppm, and are enriched in LREE with (La/Yb)N values of 2.87–9.87, and display obvious Eu anomalies (δEu?=?0.01–0.29). Trace elements of the studied granites are characterized by enrichment in Rb, Th, U, Pb, Hf, and Sm, and depletion of Ba, Nb, Ta, and Sr. They display geochemical features of high Zr?+?Y?+?Nb?+?Ce values (324–795 ppm) and Ga/Al ratios consistent with A-type granites. Based on particular geochemical features, such as high Rb/Nb (7.98–24.19) and Y/Nb (1.07–3.43), the studied A-type granites can be further classified as an A2-type subgroup. This research indicates that the Early Ordovician A-type granites were formed by the partial melting of ancient crust in an extensional setting. Lower Sr/Y and (Ho/Yb)N ratios indicate that plagioclase and amphibole are residual in the source, and garnet is absent, implying that the magma was generated at low levels of pressure. By contrast, the contemporaneous granites in the SE Xing’an Block suggest a subduction-related tectonic setting, and its adakitic property indicates a thickened continental crust. We suggest that the Paleo-Asian Ocean plate between the Xing’an and Songnen blocks subducted northward during the Early Ordovician. Meanwhile, the NE Songnen Block was exposed to a passive continental margin tectonic setting.  相似文献   

13.
东南沿海分布大面积的白垩纪晚期侵入岩。这些岩石可分为两期:其中115~100Ma以钙碱性系列岩石为主,岩石组合为辉长岩-闪长岩-花岗闪长岩-二长花岗岩-碱性长石花岗岩;而100~86Ma的岩石为碱性系列,岩石组合为石英二长斑岩-正长斑岩-碱性长石花岗岩。115~100Ma的辉长岩以角闪辉长岩为主,具有极高的CaO、MgO和Al_(2)O_(3)含量,具有极低的SiO_(2)(42.9%~53.8%)、全碱(K_(2)O+Na_(2)O:0.86%~5.28%)、Ba、Nb、Th、Rb和Zr含量,也具有极低的FeO^(T)/MgO、La/Yb和Zr/Hf比值,较高的Eu/Eu^(*)、Sr/Y比值和Sr含量,为基性-超基性堆晶岩。与辉长岩同期的闪长岩和细粒暗色包体具有较高的SiO_(2)(50.34%~63.68%),较低的CaO、P_(2)O_(5)、MgO、Al_(2)O_(3)含量,相对低的Eu/Eu^(*)和Sr/Y比值,变化较大的La/Yb和Zr/Hf比值,代表了从基性岩浆储库中抽取的富硅熔体。115~100Ma的花岗闪长岩和二长花岗岩类岩石为准铝质岩石,SiO_(2)含量变化较大(61.7%~75.3%),具有较低的FeO^(T)/MgO、Ga/Al比值和Nb、Zr及Nb+Zr+Ce+Y元素含量,显示出典型I型花岗岩的特征。这些花岗岩具有相对高的La/Yb、Eu/Eu^(*)和Zr/Hf比值和高的Sr、Ba和Zr含量。结合岩相学特征,这些花岗岩为堆晶花岗岩。而115~100Ma的碱性长石花岗岩具有极高的SiO_(2)含量(大于75%),低的Eu/Eu^(*)、La/Yb、Zr/Hf和Sr/Y比值,具有低的Ba、Sr和Zr含量和高的Rb、Nb、Y和Th含量和Rb/Sr比值,表明这些花岗岩是由富硅岩浆储库中抽离的高硅熔体侵入地壳形成。100~86Ma期间形成的二长斑岩和正长斑岩具有极高的全碱含量,可以达到8%~12%,其SiO_(2)主要集中在60%~70%,具有极高的Zr、Sr和Ba含量和Eu/Eu^(*)、La/Yb和Sr/Y比值,显示出堆晶花岗岩的特征。而100~86Ma期间形成的大部分碱性长石花岗岩具有极高的SiO_(2)含量(大于75%),并显示出A型花岗岩的特征,具有高的Rb/Sr比值和高的Rb、Y和Th和低的Ba、Sr含量和低的Zr/Hf、La/Yb、Eu/Eu^(*)和Sr/Y比值,表明它们是由富硅岩浆储库抽离的高硅熔体侵入浅部地壳形成。东南沿海高硅花岗岩的形成和穿地壳岩浆系统密切相关,高硅花岗岩是由浅部地壳内晶体-熔体分异产生的熔体侵入地壳所形成,而高硅花岗岩的地球化学特征与岩浆储库的水及挥发份含量密切相关。115~100Ma期间,从富水的岩浆储库抽离的熔体形成具有低高场强元素含量和低Rb/Sr比值的高硅花岗岩,这一过程与古太平洋板块俯冲有关;100~86Ma期间,从富挥发份的岩浆储库抽离的熔体形成碱性特征、富含高场强元素和具有高的Rb/Sr比值的高硅花岗岩,这一过程和古太平洋板块回撤软流圈上涌有关。  相似文献   

14.
The Southeast Anatolian Orogenic Belt (SAOB), the most extensive segment of the Alpine-Himalayan Orogenic Belt, resulted from the northward subduction of the southern branch of the Neotethys oceanic crust beneath the Anatolian micro-plate. We present new whole-rock geochemistry, zircon U–Pb ages, and Lu–Hf isotope data from the stocks and dykes with a length of up to tens of meters belonging to the Keban magmatic rocks, eastern Turkey. These rocks are represented by syenite and quartz monzonite intruded into the Keban metamorphic complex. The geochemistry data indicates that the samples bear mostly metaluminous, variably high alkalines (K2O + Na2O), Ga/Al ratios and zircon saturation temperature, and typically the A-type granite characters. According to the Y/Nb vs Yb/Ta diagram, the Keban magmatic rocks show A1-type geochemical signatures modified by crustal melts. Syenite and quartz monzonite samples from Keban magmatic rocks give zircon U–Pb ages of 77.4 ± 0.34 Ma, 76.3 ± 0.3 Ma and 76.36 ± 0.34 Ma, respectively. On the primitive mantle-normalised trace element patterns, the Keban magmatic rocks show enrichment in large-ion lithophile elements (LILEs) relative to high field strength elements (HFSEs). They are coupled with slightly negative Nb–Ta anomalies. Chondrite-normalised rare earth-element patterns show strong enrichment in LREEs relative to HREEs, a typical A-type granites feature. The zircons have negative εHf(t) values that vary from ?2.68 to ?0.41, and Hf model ages (TDM2) range from 1171.54 to 1329.26 Ma, indicating the enriched lithospheric mantle sources and crustal contribution. The sources and evolution of the alkaline magmas might be related to the post-collisional tectonic setting.  相似文献   

15.
Early Palaeozoic granitoids in the South Qilian Belt, central China, record details of the tectonic evolution and crustal growth of the Qilian orogenic belt. Five representative granitoids from the western South Qilian Belt were sampled for zircon LA-ICPMS U–Pb dating, Lu–Hf isotopes, and whole-rock geochemical analyses. Zircon U–Pb dating of two porphyritic granodiorites and a porphyritic monzogranite yielded ages of 442.7 ± 3.5, 441.8 ± 4.3, and 435.4 ± 3.5 Ma, respectively. These granitoids exhibit a geochemical affinity to I-type granite, are metaluminous with a low aluminium saturation index (A/CNK = 0.75–1.15), have moderate Al2O3 and low MgO contents, high La/Yb and low Sr/Y ratios, and are depleted in Nb, Ta, P, and Ti, which suggests a subduction zone magmatic arc affinity, with mixing between a primary mantle-derived magma with lesser continental crustal material. The syenogranite and monzogranite from the South Qilian Belt, which yield U–Pb zircon ages of 440.4 ± 9.0 and 442.3 ± 1.2 Ma, respectively, have pronounced S-type geochemical affinities, are peraluminous with A/CNK values of 1.07–1.16, have relatively high SiO2, Al2O3, K2O, and Rb contents, low Y and Yb, low Sr/Y and La/Yb ratios, positive Th, U, and light Rare Earth Element (REE) anomalies, and depletions in Nb, Ta, Sr, and Ti. Their geochemical signature suggests derivation from partial melting of continental crust in a syn-collisional setting. The Hf isotopic data of zircons from the granitoids show a significant input of Paleoproterozoic crust in the crustal formation of the western South Qilian Belt in Palaeozoic. Compare the εHf(t) value of S-type granite with that of I-type granite, the former may have a comparatively homogeneous source. Together with regional evidence, it is proposed that a collisional event occurred between the South Qilian Belt and the Central Qilian Belt at ca. 442–435 Ma.  相似文献   

16.
Numerous granitic intrusions crop out in the eastern segment of the North Qaidam block (NQ), NW China. To evaluate their ages, petrogenesis and genetic relationships to other granitoids in the NQ, we present geochemical and geochronologic data for six intrusive bodies and review regional data. Zircon U-Pb (SHRIMP) dating yielded ages of 413 ± 3 Ma for the Hadesengou granite; 254 ± 3 Ma for the Xugeigou granite; 251 ± 1 Ma for the Qiluoshan granite; 249 ± 1 and 248 ± 2 Ma for the Chahannuo hornblende diorite and granite, respectively; 240 ± 2 Ma for the Chahanhe granite; and 250 ± 1 and 244 ± 3 Ma for the Shailekegoulei granodiorite and granite, respectively. Consequently, the Wulan plutons can be divided into two petrologic groups: Early Devonian (D1) quartz monzonite and syenogranite, and Late Permian to Early Triassic (P3-T1) hornblende diorite, granodiorite, and granite. The D1 granitic intrusions have geochemical affinities with A-type granites (A2-type) characterized by low Ca, Sr, Ba and Nb, and high Fe, Ga, Y and Rb, consistent with derivation by partial melting of metapelitic source rocks containing a small amount of metagraywacke. The P3-T1 I-type granitic intrusions are geochemically typical of active continental margin rocks, consistent with derivation by partial melting of metabasalt and clay-poor metagraywacke. Combined with previous studies, we recognize five periods of granitic magmatism in the NQ: (1) 465–473 Ma; (2) 423–446 Ma; (3) 391–413 Ma; (4) 372–383 Ma; and (5) 240–271 Ma. Based on the temporal-spatial distribution of granitic intrusions in the NQ and the regional tectonic evolution, we interpret the first and second periods of granitic magmatism as related to normal plate subduction, and the third period to slab break-off and exhumation of the subducted plate. The fourth stage of granitic magmatism is attributed to large-scale lithospheric mantle delamination, involving the differential movement of orogenic blocks. The fifth period of granitic plutonism probably reflects northward subduction of the East Kunlun Paleotethys oceanic crust and southward subduction of Zongwulong oceanic crust beneath the Oulongbuluke continental block.  相似文献   

17.
The late Paleozoic Bailingshan intrusions and volcanic rocks are located in the Aqishan–Yamansu arc belt in the southern part of the eastern Tianshan and are associated with an important group of iron skarn deposits. The exposed intrusive rocks are mainly granodiorite, monzonitic granite, and granite. Zircon U–Pb dating of the Tugutublak Formation tuffaceous dacitic lava yields an age of 324 Ma, whereas dates of the Bailingshan granodiorite, monzonitic granite, and granite yields ages of 317 Ma, 313 Ma, and 307 Ma, respectively. The results indicate that the Bailingshan granitoids were emplaced soon after the eruption of the Tugutublak dacite. All these rocks studied show calc-alkaline to high-K calc-alkaline and metaluminous affinities, with A/CNK values ranging 0.83–1.10. They are enriched in Rb, K, and Pb, depleted in Nb, Ta, Ti, and P, and contain low Sr/Y (4.16–23.7) and Sr (109.0–347.0 ppm) values, displaying typical arc geochemical affinities. The tuffaceous dacitic lava has low Nb/Ta (10.3–14.1) values, a wide range of Mg# (6–64), positive zircon εHf(t) (3.2–7.5) values, and elevated whole-rock εNd(t) (2.03–4.41), but low ISr values (0.70427–0.70530), indicating that the source magma may have been derived from the juvenile lower crust with minor mantle input. The Bailingshan I-type intrusions also exhibit a mixed source signal, as constrained by Nb/Ta ratios, Mg#, and isotopes characteristics. Because the granodiorite, monzonitic granite, and granite intrusions have higher zircon εHf(t) (3.3–7.5, 11.8–13.5, and 10.2–14.4, respectively) and εNd(t) (3.90, 5.78, and 5.94, respectively) values than those of the tuffaceous dacitic lava, it is suggested that mantle-derived materials may have played a more prominent role with their petrogenetic evolution. Integrating our new geological, age, geochemical and isotopic data we propose that the Aqishan–Yamansu iron skarn belt may have formed in a back-arc position or within an intra-arc basin generated by the southward subduction of the Kanggur oceanic plate beneath the Yili–Central Tianshan block during the late Paleozoic, with felsic-intermediate magmatism occurring during the basin inversion.  相似文献   

18.
ABSTRACT

We present zircon U-Pb crystallization ages combined with bulk rock major and trace element geochemistry and Sr-Nd-Pb and zircon in-situ Hf isotopic compositions of the Amand and Moro granitoid intrusions in northwest Iran. The Amand and Moro plutons include granite and syeno-diorite with LA-ICP-MS U-Pb zircon ages of 367 ± 6.8 Ma and 351 ± 1.3 Ma, respectively, representative of Late Devonian-Early Carboniferous magmatic activity in NW Iran. Geochemical characteristics such as typical enrichments in alkalis, Nb, Zr, Ga and Y, depletion in P and Sr and fractionated REE patterns with high Ga/Al ratios and Eu negative anomalies are consistent with A-type magmatic signatures. The granitoids are classified as A2-type and within-plate granitoids. The bulk rock geochemistry (enrichments in Th, Nb and, high Th/Yb, Zr/Y ratios) along with low variation of 143Nd/144Nd(i) and 87Sr/86Sr(i) ratios and positive zircon εHf(t) support the role of a mantle plume component for the evolution of the Amand and Moro A-type granitoids in an extensional tectonic environment. In fitting with wider regional knowledge, this magmatism occurred during Paleo-Tethys opening in northern Gondwana.  相似文献   

19.
班公湖蛇绿混杂岩带内分布着一系列小型斜长花岗斑岩和花岗闪长岩岩体,锆石U-Pb年龄分别为97.4±1.1Ma和91.94±0.78Ma,具埃达克质岩特征,高Si O2、Al2O3和Sr,低Y和Yb,Sr/Y35,轻重稀土分异明显,亏损Nb、Ta和Ti,Cr和Ni含量很低,推测为玄武质岩浆底侵加厚下地壳部分熔融形成。辉石闪长岩脉分布于南侧日土花岗岩内,推测年龄为80~76Ma,岩石地球化学显示亏损Zr、Hf、Ti、Y等高场强元素,富集大离子亲石元素,且具较高的Sc、Y、Cr、Co、HREE和Mg#值(40),源区为经过熔体交代的上地幔。结合前人资料,本文认为班公湖地区在97~92Ma仍处于持续碰撞造山、地壳加厚过程中;92Ma之后,构造体制从碰撞期的挤压转变为碰撞后的板内伸展;80~76Ma,板内的伸展进一步加剧。  相似文献   

20.
The Triassic (Indosinian) granites in the South China Block (SCB) have important tectonic significance for understanding the evolution of Eastern Asia. The Dengfuxian biotite granite in eastern Hunan Province, China, reported in this article, was recognized as Late Triassic (late Indosinian) weakly peraluminous A-type granite with a zircon laser ablation inductively coupled plasma mass spectrometry U–Pb age of 225.7 ± 1.6 Ma. It is enriched in F, Cs, Rb, Th, high field strength elements, and rare earth elements (REEs) and depleted in Ba, Sr, P, Ti, Nb, and Ta, with high Ga/Al ratios and zircon saturation temperatures. The Dengfuxian biotite granite shows high initial Sr isotope values (0.715932 to 0.716499) and negative ?Nd(t) (?10.46 to ?9.67) and ?Hf(t) (?9.92 to ?6.29) values, corresponding to the Nd model ages of 1.79 to 1.85 Ga and the Hf model ages of 1.65 to 1.88 Ga. It is proposed that the Dengfuxian biotite granite was derived from high-temperature partial melting of the Palaeoproterozoic lower crust undergoing granulitization. Some Late Triassic A-type granites were recently identified in the SCB with the ages between 202 and 232 Ma. These A-type granites have the same geochemical characteristics and petrogenesis as Dengfuxian A-type granite, and show A2-subtype granite affinity. The Late Triassic A-type granite formed a NE-trending granite belt, which is consistent with the main NE-trending faults in the SCB. The formation of these A-type granites was in response to the subduction of the palaeo-Pacific plate underneath the SCB, and indicates an extensional tectonic environment in the SCB. Combined with previous studies on tectonic evolution, we suggest that there may be a tectonic transition inside the SCB from compression to extension at least from 225 to 230 Ma.  相似文献   

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