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41.
青藏高原拉萨地体南部广泛发育的渐新世-中新世埃达克质岩浆岩,是研究冈底斯岩浆弧后碰撞岩浆活动和地壳演化的理想载体。本文对冈底斯弧中段曲水地区的早中新世黑云母花岗岩进行了岩石学、地球化学、锆石U-Pb年代学和Hf同位素研究。全岩地球化学分析结果显示黑云母花岗岩具有高的SiO2、Al2O3和K2O含量,属于中钾钙碱性、准铝质到弱过铝质岩石。微量元素富Sr,贫Y和Yb,富集轻稀土元素而强烈亏损重稀土元素,具有高的Sr/Y值(165~278)和(La/Yb)N值(26.6~39.7),具有典型埃达克质岩石的地球化学特征。锆石U-Pb年代学分析结果表明花岗岩的结晶年龄为21~19 Ma,Hf同位素分析结果显示,岩浆锆石εHf(t)值(-0.9~+12.7)大部分为正值且具有较大的变化范围。根据Sr/Y和(La/Yb)N值估算早中新世冈底斯弧的地壳厚度已达到70~80 km。综合本文和已有的数据表明,印度-亚洲大陆碰撞和碰撞后持续的汇聚作用以及大体积幔源岩浆的底侵共同导致冈底斯岩浆弧经历了显著的新生代地壳加厚;渐新世—早中新世,俯冲印度大陆板片的断离或加厚岩石圈地幔的拆沉作用引起软流圈地幔物质上涌,导致冈底斯弧加厚下地壳(新生地壳和古老地壳)发生强烈的部分熔融,形成了广泛分布的后碰撞埃达克质岩浆岩。 相似文献
42.
基于青海省刚察地区1：5万电泵站等4幅区调项目,在拉脊山蛇绿构造混杂岩带药水泉组中识别一套玄武岩、玄武安山岩、安山岩类岩石组合,其岩相学、岩石地球化学特征与高镁安山岩相类似.岩石斑晶以斜长石和辉石为主,不含橄榄石,基质也含有大量的斜长石.岩石地球化学特征表现为K2O+Na2O含量2.55%~5.15%,Na2O > K2O,K2O含量0.22%~0.82%,为低钾;CaO含量5.31%~11.41%,TiO2含量0.27%~0.55%,变化范围较小;MgO含量为5.78%~11.06%,变化范围不大.总体具有低硅、钛、钾,高钙、镁,富钠之特征.稀土配分曲线为右倾斜状,多呈铕正异常,为轻稀土富集型.微量元素Rb、Ba、Th、Cr、Ni等变化幅度大,反映岩浆生成和演化过程复杂,但演变仍以部分熔融为主.选取玄武岩样品,通过LA-ICP-MS U-Pb锆石微区定年,获得了451.7±1.8 Ma年龄值,其时代为晚奥陶世.总体特征表明,刚察地区火山岩为埃达克型高镁安山岩,其构造环境为活动大陆边缘的岛弧. 相似文献
43.
新疆东准噶尔野马泉地区索尔巴斯塔乌石英闪长岩锆石U-Pb年龄为442.5±5.6 Ma。该岩体SiO_2为63.75%~65.40%,Al_2O_3为17.07%~18.00%,Na_2O/K_2O比值为5.28~6.82,MgO为1.11%~1.35%;富集大离子亲石元素(LILE,如K、Rb、Ba和Sr),而亏损高场强元素(HFSE,如Ta、Nb、Zr和Ti)及P,Sr为783×10~(-6)~1 030×10~(-6),Y为8.10×10~(-6)~10.80×10~(-6),Yb为0.84×10~(-6)~1.04×10~(-6),Sr/Y比值为82.59~112.32,具埃达克岩的典型特征;具有相对低的(~(87)Sr/~(86)Sr)i值(0.703 77~0.704 04)和相对高的εNd(t)值(+6.9~+7.2),且锆石具有相对高的εHf(t)值(+10.7~+13.7),暗示岩浆很可能起源于亏损的年轻地幔源区,与俯冲洋壳熔融形成的埃达克岩相似。结合区域地质背景,认为索尔巴斯塔乌石英闪长岩是由俯冲的大洋板片边缘受到来自板片窗高温软流圈地幔物质的烘烤发生部分熔融形成的,为阿尔曼泰蛇绿岩代表的古亚洲洋于早志留世向南俯冲消减过程中形成的岩浆弧记录。 相似文献
44.
西准达尔布特—包古图地区出露两类中酸性侵入岩,一类为海西晚期(<270Ma)花岗岩基,另一类为海西中晚期(330～320Ma)中酸性小斑岩体,包古图斑岩铜矿赋存于后者。岩石主量和微量元素分析表明,包古图含矿小斑岩基本满足埃达克岩的条件,即SiO2>56%,Al2O3>15%,MgO<3%,贫Y和Yb(Y<18×10-6,Yb<1.9×10-6),高Sr(>400×10-6),HREE明显亏损,其Nd和Sr同位素组成与洋中脊玄武岩(MORB)组成接近。但部分样品MgO含量较高(>3%),轻稀土元素丰度较低,偏离埃达克岩的组成范围。根据斑岩的地球化学组成并结合区域地质特征,笔者认为包古图含矿斑岩形成于与洋内俯冲有关的岛弧环境,但洋壳板片的初始熔体在上升过程中受到了地幔橄榄岩的不均匀混染。 相似文献
45.
ZHANG HongFei XIAO Long ZHANG Li YUAN HongLin & JIN LanLan State Key Laboratory of Geological Processes Mineral Resources China University of Geosciences Wuhan China Faculty of Earth Sciences China University of Geosciences Wuhan China State Key Laboratory of Continental Dynamics Northwest University Xi’an China 《中国科学D辑(英文版)》2007,50(7):972-983
This paper reports geochemical and Pb-Sr-Nd isotopic compositions of the Indosinian Yangba (215 Ma),Nanyili (225 Ma) and Mopi granitoids from the Bikou block of the northwestern margin of the Yangtze plate. These granitoids are enriched in Al (Al2O3:14.56%―16.48%) and Sr (352 μg/g―1047 μg/g),and depleted in Y (<16 μg/g) and HREE (e.g. Yb<1.61 μg/g),resulting in high Sr/Y (36.3―150) and (La/Yb)N (7.8―36.3) ratios and strongly fractionationed REE patterns. The Indosinian granotoids show initial Sr isotopic ratios (ISr) from 0.70419 to 70752,εNd(t) values from-3.1 to -8.5,and initial Pb isotopic ratios 206Pb/204Pb=17.891-18.250,207Pb/204Pb=15.494-15.575,and 208Pb/204Pb=37.788-38.335. Their geochemi-cal signatures indicate that the granitoids are adakitic. However,they are distinct from some adakites,generated by partial melting of subducted oceanic slab and/or underplated basaltic lower crust,be-cause they have high K (K2O: 1.49%―3.84%) and evolved Nd isotopic compositions,with older Nd iso-topic model ages (TDM=1.06―1.83 Ga). Geochemical and Sr-Nd isotopic compositions suggest that the magmas of the Insoninian adakitic rocks in the Bikou block were derived from partial melting of thick-ened basaltic lower crust. Combined with regional analyses,a lithospheric delamination model after collision between the North China and South China plates can account for the Indosinian adakitic magma generation. On the other hand,based on the Pb-Sr-Nd isotopic probing to the magma sources of the adakitic rocks,it is suggested that there is an unexposed continent-type basement under the exposed Bikou Group volcanic rocks. This can constrain on the Bikou Group volcanic rocks not to be MORB-or OIB-type. 相似文献
46.
东秦岭商丹构造带北侧的商南花岗岩体和吊庄花岗岩体属于钙碱性系列,具有岛弧花岗岩特征。这些岩石富Na2O(3.54％～5.52％)、贫K2O(0.75％～3.46％)、Na2O/K2O比值为1.09～6.16,SiO2含量＞56％(61.84％～74.57％),Al2O3含量变化于13.41％～19.01％,多数≥15％,MgO含量均小于3％(0.65％～2.41％),Mg#为43.87～66.12,低Y(＜18×10-6,
为1.90×10-6～18.4×10-6)和Yb(＜1.9×10-6为0.27×10-6～2.27×10-6),Sr含量高(350×10-6～830×10-6),多数大于400×10-6,Sr/Y比值在25.29～216.71之间,大于20～40;LREE富集,HREE亏损,多数La/Yb比值＞20(47.60～110.93),(La/Yb)N＞20(32.09～99.13),不显Eu异常或有弱的Eu正异常,大离子亲石元素(Rb、Ba、Th、Sr)相对富集,高场强元素(如Nb、Ta、Zr、Hf、Ti)相对亏损。同位素组成表明,花岗岩体具有相对低的143Nd/144Nd比值(0.512127～0.512134),与商南松树沟蛇绿岩的143Nd/144Nd比值(0.512651～0.512917)比较接近,εNd(t)为正值(+1.23～+2.51),暗示源岩以N-MORB为主。这些地球化学特征与洋壳俯冲MORB的部分熔融形成的埃达克质岩相似,表明这些晋宁期的花岗岩类可能属于埃达克质岩。研究表明,商丹地区埃达克质花岗岩类与新元古代沿商丹带-线曾发育有一个以松树沟蛇绿岩和黑河玄武岩为代表的古洋盆(古秦岭洋)向北发生俯冲消减作用有关,造成古洋壳俯冲板片MORB岩石部分熔融而形成。 相似文献
47.
西藏冈底斯斑岩铜矿带埃达克质斑岩含矿性：源岩相变及深部过程约束 总被引：51，自引：12，他引：51
西藏冈底斯斑岩铜钼成矿系统(13.6～16 .9Ma)发育在印_亚大陆后碰撞地壳伸展环境。成矿前斑岩成岩年龄≥17Ma ,以花岗闪长斑岩为主,成矿期斑岩形成于14 .5～17.6Ma之间,以二长花岗斑岩和石英二长斑岩为主,成矿后斑岩为花岗斑岩,其成岩年龄为11.2Ma。3期斑岩均为高钾钙碱性或钾玄岩系列,地球化学上类似于玄武质下地壳部分熔融产生的埃达克质岩。成矿前斑岩具有最低的ΣREE(2 7×10 -6～4 5×10 -6)、wY(2 .9×10 -6～3.4×10 -6)和wSm/wYb(3.0～4 .9) ,最高的wZr/wSm值(5 0～118) ;成矿后斑岩具有最高的ΣREE (12 2×10 -6～197×10 -6)和wY(8.2×10 -6) ,中等的wSm/wYb(5 .9～6 .2 )和wZr/wSm值(34～4 4 ) ;成矿期斑岩总体处于两者之间,其Sr_Nd同位素组成与CordilleraBlanca埃达克质花岗岩类似。研究提出,来自深部的软流圈物质或亏损地幔物质与下地壳物质交换,不仅导致冈底斯加厚、下地壳熔融,而且提供了巨量金属供应。部分熔融首先从下地壳底部开始,逐渐向上部迁移。下地壳石榴石角闪岩部分熔融过程中,残留相由角闪石向石榴石大规模转变导致角闪石的大量分解,释放出大量流体,是冈底斯斑岩含矿性的主导因素。 相似文献
48.
This article reports systematic zircon U–Pb dating, whole-rock geochemistry, and Sr–Nd isotopic data for the Early Cretaceous Jialou granitoids along the southernmost margin of the North China Craton (NCC), adjacent to the Tongbai Orogen. These results will provide significant constrains on the crustal evolution of the southern margin of the NCC. Zircon U–Pb analyses, using laser ablation–multicollector–inductively coupled plasma–mass spectrometry, indicate that the Jialou granitoids were emplaced at ~130 Ma. The granitoids have high SiO2, K2O, Al2O3, Sr, and Ba contents, high Sr/Y and (La/Yb)N ratios, and low concentrations of MgO, Y, and heavy rare earth elements, indicating a low-Mg adakitic affinity. They have relatively high initial 87Sr/86Sr ratios (0.707464–0.708190) and negative εNd(t) values (–11.8 to –15.2), similar to those of the Palaeoproterozoic lower crust in the NCC. These geochemical and isotopic features indicate that the Jialou low-Mg adakitic rocks were derived by partial melting of mafic Palaeoproterozoic lower crust of the NCC at >50 km depth, leaving behind a garnet amphibolite residue. The petrogenesis of the Jialou low-Mg adakitic rocks, plus the petrogenesis of Mesozoic granitoids and lower crustal xenoliths entrained in the Late Jurassic Xinyang volcaniclastic diatreme, suggests that the continental crust along the southern margin of the NCC was thickened during the Middle Jurassic to Early Cretaceous, but thinned after 130 Ma. We propose that crustal thickening was caused by a late Middle Jurassic to Early Cretaceous intra-continental orogeny, rather than continent–continent collision between the NCC and the Yangtze Craton. We also suggest that crustal thinning and Early Cretaceous magmatism were related to subduction of the palaeo-Pacific plate, rather than post-orogenic collapse of the Qinling–Tongbai–Dabie Orogen. 相似文献
49.
南祁连地区化石沟花岗闪长岩位于化石沟铜矿附近,东距阿克塞县城约120 km。花岗闪长岩LA-ICP-MS锆石U-Pb年龄为261.1±3.8 Ma,形成于中二叠世晚期。岩石属钙碱性系列,具有埃达克岩的地球化学特征,SiO_2含量在68.35%~69.14%之间,高铝(Al_2O_3=15.83%~16.06%)、Sr(367×10~(–6)~381×10~(–6))、低Y(15.12×10~(–6)~19×10~(–6))和Yb(1.34×10~(–6)~1.85×10~(–6)),富Na贫K(Na_2O=4.3%~4.47%,K_2O=2.22%~2.46%,Na_2O/K2O=1.75~2.01),MgO介于0.79%~0.89%之间,Mg~#为0.35左右。岩石富集强不相容元素Ba、Rb、Sr、Th、U和LREE,强烈亏损高场强元素Nb、Ta、Ti以及HREE,(La/Yb)_N=8.3~11.77,具轻微的Eu负异常(δEu=0.76~0.86),高Rb/Sr(≈0.2)值。化石沟花岗闪长岩的(~(87)Sr/~(86)Sr)i、ε_(Nd)(t)、(~(176)Hf/~(177)Hf)_i、δ~(18)O_(V-SMOW)分别为0.7065~0.7068、–1.45~–0.78、0.282765、12.1‰~12.5‰。综合以上特征,认为化石沟花岗闪长岩源于新生地壳物质在玄武岩浆底侵作用下发生的部分熔融,在岩浆作用过程中可能发生过轻微的分离结晶作用,形成于板内背景,处于造山挤压向后造山伸展的构造体制转变阶段。花岗闪长岩的Nd和Hf模式年龄(分别为1.1 Ga和0.9 Ga)指示玄武质岩浆上侵的时间应为中元古代晚期。化石沟埃达克质岩显示了良好的斑岩型Cu、Au成矿潜力,寻找与埃达克岩有关的斑岩型Cu、Au矿应是下一步找矿的重点方向。 相似文献
50.
Petrogenesis of Ore‐Related Granodiorite Porphyry in the Jiande Copper Deposit,SE China: Implications for the Tectonic Setting and Mineralization 
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下载免费PDF全文 Hui Chen Pei Ni Guo‐Guang Wang Ren‐Yi Chen Zhi‐Cheng Lü Zhen‐Shan Pang Lin Geng Bai‐Sheng Zhang Hui‐Xiang Yuan 《Resource Geology》2017,67(2):117-138
Adakitic rocks and related Cu–Au mineralization are widespread along eastern Jiangnan Orogen in South China. Previous studies have mainly concentrated on those in the Dexing area in northeastern Jiangxi Province, but information is lacking on the genesis and setting of those in northwestern Zhejiang Province. The Jiande copper deposit is located in the suture zone between the Yangtze and Cathaysia blocks of South China. This paper presents systematic LA–ICP–MS zircon U–Pb dating and element and Sr–Nd–Hf isotopic data of the Jiande granodiorite porphyry. Zircon dating showed that the Jiande granodiorite porphyry was produced during the Middle Jurassic (ca. 161 Ma). The Jiande granodiorite porphyry is characterized by adakitic geochemical affinities with high Sr/Y and LaN/YbN ratios but low Y and Yb contents. The absence of a negative Eu anomaly, extreme depletion in Y and Yb, relatively low MgO contents, and relatively high 207Pb/204Pb ratios, indicated that the Jiande granodiorite porphyry was likely derived from partial melting of the thickened lower continental crust. In addition, the Jiande granodiorite porphyry shows arc magma geochemical features (e.g., Nb, Ta and Ti depletion), with bulk Earth‐like εNd (t) values (?2.89 to ?1.92), εHf (t) values (?0.6 to +2.8), and initial 87Sr/86Sr (0.7078 to 0.7105). However, a non‐arc setting in the Middle Jurassic is indicated by the absence of arc rocks and the presence of rifting‐related igneous rock associations in the interior of South China. Combined with the regional Neoproterozoic Jiangnan Orogeny, it indicates that these arc magma geochemical features are possibly inherited from the Neoproterozoic juvenile continental crust formed by the ancient oceanic crust subduction along the Jiangnan Orogen. The geodynamic environment that is responsible for the development of the Middle Jurassic Jiande granodiorite porphyry is likely a localized intra‐continental extensional environment along the NE‐trending Jiangshan‐Shaoxing Deep Fault as a tectonic response to far‐field stress at the margins of the rigid South China Plate during the early stage of the paleo‐Pacific plate subduction. In terms of Cu mineralization, we suggest that the metal Cu was released from the subducted oceanic slab and reserved in the juvenile crust during Neoproterozoic subduction along the eastern Jiangnan Orogen region. Partial melting of the Cu rich Neoproterozoic juvenile crust during the Middle Jurassic time in the Jiande area caused the formation of adakitic rocks and the Cu deposit. 相似文献