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1.
The Yunmengshan Geopark in northern Beijing is located within the Yanshan range. It contains the Yunmengshan batholith, which is dominated by two plutons: the Yunmengshan gneissic granite and the Shicheng gneissic diorite. Four samples of the Yunmengshan gneissic granite give SHRIMP zircon U–Pb ages from 145 to 141 Ma, whereas four samples of the Shicheng gneissic diorite have ages from 159 Ma to 151 Ma. Dikes that cut the Yunmengshan diorite record SHRIMP zircon U–Pb age of 162±2 and 156±4 Ma. The cumulative plots of zircons from the diorites show a peak age of 155 Ma, without inherited zircon cores, and the peak age of 142 Ma for granite is interpreted as the emplacement age of the Yunmengshan granitic pluton, whose igneous zircons contain inherited zircon cores. The data presented here show that there were two pulses of magmatism: early diorites, followed c13 Ma later by true granites, which incorporated material from an older continental crust.  相似文献   

2.
The Central Hebei Basin （CHB） is one of the largest sedimentary basins in the North China Craton, extending in a northeast-southwest direction with an area of 〉350 km2. We carried out SHRIMP zircon dating, Hf-in-zircon isotopic analysis and a whole-rock geochemical study on igneous and metasedi- mentary rocks recovered from drill holes that penetrated into the basement of the CHB, Two samples of gneissic granodiorite （XG1-1） and gneissic quartz diorite 048-1） have magmatic ages of 2500 and 2496 Ma, respectively. Their zircons also record metamorphic ages of 2.41-2.51 and ～2.5 Ga, respec- tively. Compared with the gneissic granodiorite, the gneissic quartz diorite has higher REE contents and lower Eu/Eu＊ and （La/Yb）n values. Two metasedimentary samples （MG1, H5） mainly contain ～2,5 Ga detrital zircons as well as late Paleoproterozoic metamorphic grains. The zircons of different origins have eHf （2.5 Ga） values and Hf crustal model ages ranging from 0 to 5 and 2.7 to 2,9 Ga, respectively, Therefore, ～2.5 Ga magmatic and Paleoproterozoic metasedimentary rocks and late Neoarchean to early Paleoproterozoic and late Paleoproterozoic tectono-thermal events have been identified in the basement beneath the CHB. Based on regional comparisons, we conclude that the early Precambrian basement beneath the CHB is part of the North China Craton.  相似文献   

3.
The Tashan porphyry tin polymetallic deposit is located at the southwest part of the Lianhuashan Fault in the eastern Guangdong province. It is one of the three typical porphyry tin deposits in China. In this paper, we reported cassiterite and zircon U-Pb ages, geochemistry and Lu-Hf isotopes of the ore-bearing granite porphyry in the orefield. Zircon LA-ICP-MS U-Pb dating yielded a concordant ages of 136.8±1.1 Ma, whereas analyses of cassiterite yielded a 206Pb/238U-207Pb/238U concordia lower intercept age of 133.6±8.6 Ma and a Tera-Wasserburg lower intercept age of 136.5±8.1 Ma, which suggest a genetic link between the granite porphyry and the ore mineralization. The εHf(t) values of -4.87 to -2.07 and tDM2 ages 1322 Ma to 1507 Ma for zircon from the granite porphyry show that the Tashan granite porphyry was likely derived from partial melting of the Mesoproterozoic crustal rocks with minor input of mantle material. © 2018, Science Press. All right reserved.  相似文献   

4.
We have determined the ages of the ore-bearing Tinggong porphyries and the Eocene granites using the LA-ICPMS zircon U-Pb method. Zircons from one adamellite porphyry and two diorite porphyries yield ages of 15.54±0.28 Ma, 15.02±0.25 Ma and 14.74±0.22 Ma, respectively. The ages of two granites are 50.48±0.71 Ma and 50.16±0.48 Ma. Light Rare Earth Elements(LREE) are enriched in the ore-bearing adamellite porphyries, which are high-K calc-alkaline and metaluminous, while Heavy Rare Earth Elements(HREE) and Y are strongly depleted, indicating an adakitic affinity. The Large Ion Lithophile Elements(LILE) of the adamellite porphyries are highly enriched, whereas some High Field Strength Elements(HFSE) are depleted. The diorite porphyry in this study is chemically similar to the adamellite porphyries, except that the Mg# of the diorite porphyry is a little higher, demonstrating more mantle contamination. Four samples from different rocks are selected for in situ zircon Hf isotopic analyses. The samples show positive εHf(t) values and young Hf model ages, indicating their derivation from juvenile crust. However, the adamellite porphyry and diorite porphyry formed in the Miocene exhibit more heterogeneous Hf isotopic ratios, with lower εHf(t) values than the granites formed in the Eocene, suggesting the involvement of old Indian continent crust in their petrogenesis. The geochronology and geochemistry of the adamellite porphyries and the diorite porphyries indicate that they formed from the same source region in a post-collisional environment, but contaminated by crust and mantle materials in different ratios. The metallic minerals formed mainly during the older adamellite porphyry stage, but they were recycled and reactivated by the diorite porphyry intrusion.  相似文献   

5.
The newly discovered Laomiaogou porphyry-skarn Mo deposit is located south of the Machaoying fault in western Henan province. The ore-body is hosted in the contact between the Laomiaogou granite porphyry dyke and the Duguan Formation. LA-ICP-MS U-Pb analyses for zircons from the granite porphyry yield a weighted mean 206Pb/238U age of 152.1±0.6 Ma, and seven molybdenite separates yield a weighted mean age of 151.9±0.9 Ma and isochron age of 151.6±5.1 Ma. Thus, the granite porphyry dyke and Mo mineralization are contemporaneous. The ore-related granite porphyry dyke is a peraluminous I-type granite with high contents of SiO2 and K2O. The rocks are strongly depleted in P, Nb, Ta and Ti, indicative of intensive fractionation of apatite and Fe-Ti oxides, and characterized by low whole-rock εNd(t) (-20.6 to -17.6) and zircon εHf(t) values (-26.9 to -22.6). The old tDM2(Nd) ages (2.37 to 2.61 Ga) and zircon tDM2(Hf) ages (2.62 to 2.88 Ga) suggest that the granite porphyry was likely derived from an ancient crustal source. Considering the tectonic evolution and geochemical characteristics of the granite as well as other Mesozoic granites in the southern margin of the North China Craton, we suggest that the Laomiaogou granite porphyry dyke and Mo were most likely derived from partial melting of the Taihua Group metamorphic rocks under extensional tectonic regime related to the subduction of the paleo-pacific plate. © 2018, Science Press. All right reserved.  相似文献   

6.
The recently identified Huashan ophiolitic melange was considered as the eastern part of the Mianliie suture in the Qinling orogenic belt. SHRIMP zircon U-Pb geochronology on gabbro from the Huashan ophiolite and granite intruding basic volcanic rocks indicates crystallization ages of 947±14 Ma and 876±17 Ma respectively. These ages do not support a recently proposed Hercynian Huashan Ocean, but rather favor that a Neoproterozoic suture assemblage (ophiolite) is incorporated into the younger (Phanerozoic) Qinling orogenic belt.  相似文献   

7.
The Feidong district is located in the southern segment of the Tan–Lu fault zone that separates the South China Block (NCB) from the North China Craton (NCC). We report zircon U-Pb geochronology and Hf isotope data, as well as whole-rock geochemistry for Xishanyi granodiorite and Jianshan granite in the Feidong district. Zircon U-Pb dating results show that the emplacement ages of the Xishanyi and Jianshan intrusions are 124 ± 3 Ma and 130 ± 1 Ma respectively, coeval with magmatic events linked to large-scale lithospheric thinning in eastern China. The whole-rock geochemistry of the Xishanyi and Jianshan intrusions demonstrate that they are peraluminous, high potassium calc-alkaline I-type granites with adakitic characteristics. Both intrusions underwent weak crustal assimilation during emplacement. The in situ zircon εHf(t) values of the Xishanyi granodiorites range from ?26.4 to ?21.8, with TDM2 model ages of 2552 to 2841 Ma. The in situ zircon εHf(t) values of the Jianshan granite are from ?27.5 to ?23.0 with TDM2 model ages of 2632 to 2904 Ma. The peak age of inherited zircon grains from the Xishanyi granodiorite and the Jianshan granite were ~2.07 Ga and ~1.94 Ga, respectively. After compared with the regional magmatism, we suggest that both the Xishanyi and Jianshan granitoid intrusions were derived from partial melting of the NCC lower crust.  相似文献   

8.
The Marwar Supergroup(NW Peninsular India)is thought to be of Ediacaran-Cambrian age,based on previous paleontological and geochronological studies.However,direct constraints on the onset of sedimentation within the Marwar basin are still scarce.In this study,we report U–Pb zircon,LA-ICP-MS,and SIMS ages from the Chhoti Khatu felsic volcanic rocks,interlayered with the Jodhpur Group sandstones(Lower Marwar Supergroup).The cathodoluminescence images of the zircons indicate complex morphologies,and core-rim textures coupled with the wide range of ages indicate that they are likely inherited or in the case of thin poorly indurated ash-beds,detrital in origin.The age spectra of 68 zircon analyses from our sampling display a dominant 800–900 Ma age peak corresponding to the age of basement"Erinpura granite"rocks in the region.The youngest inherited zircon from a felsic ash layer yielded a U–Pb age of651 Ma±18 Ma that,together with previous studies and paleontological evidence,indicates a postCryogenian age for the initiation of Marwar sedimentation following a~125 Ma hiatus between the end of Malani magmatism and Marwar deposition.  相似文献   

9.
The Mesozoic porphyry assemblage in the Jinduicheng area is a special molybdenum area in China, the Mo deposits, including the Jinduicheng, Balipo, Shijiawan, Huanglongpu, are distributed. The emplacement age and geochemical features of the granites in the Jinduicheng area can provide essential information for the exploration and development of the porphyry molybdenum deposit. In this study, we report LA–ICP–MS zircon U–Pb age and zircon Hf isotopic compositions of granite porphyries from the Jinduicheng area, and provide insights on the petrogensis and source characteristics of the granites. The results show that the zircon U–Pb ages of the Jinduicheng granite porphyry (143±1 Ma) and the Balipo granite (154±1 Ma), agree well with the Re–Os ages of molybdenite in the Jinduicheng molybdenum polymetallic deposit (139±3 Ma) and the Balipo molybdenum polymetallic deposit (156±2 Ma), indicating that the emplacement of granite porphyries occurred between Late Jurassic and Early Cretaceous. Zircons granite from the Jinduicheng area give the εHf(t) values mainly ranging from ?10 to ?16, and ?20 to ?24, respectively, corresponding to two–stage model ages (tDM2: mainly focused on 1.86–2.0 Ga, and 2.2–2.6 Ga, respectively) of zircons of the granite from the Jinduicheng values. The ore–forming materials are mainly derived from crust, with minor mantle substances. Zircons of the granite from the Balipo area give εHf(t) values ranging from ?18 to ?20, ?28 to ?38, and ?42 to ?44, respectively, corresponding to two–stage model ages (tDM2: mainly focused on 1.88–3.0 Ga, and 3.2–3.90 Ga, respectively). the εHf(t) values of the Jinduicheng porphyry more than that of the Balipo porphyry, and two–stage model ages (tDM2) less than that of the Balipo porphyry, shows that he source of the porphyries originated from ancient lower crustal materials in the Jinduicheng area, and mixed younger components, more younger components contributed for the source of the Jinduicheng porphyry.  相似文献   

10.
A-type granites, as an important petrologic sign to build up environmental recognition, were mainly formed in extensional tectonic settings. A biotite syenogranite from the Fenghuangshan pluton in Dandong, Liaoning Province gave SHRIMP zircon U-Pb ages of 122.5 ± 1.6 Ma, 124.9 ± 1.7 Ma and 126.9 ± 1.1 Ma. The monzogranites have SHRIMP zircon U-Pb ages of 118.2 ± 1.6 Ma, 128.1 ± 1.7 Ma and 131.6 ± 1.9 Ma, giving an emplacement age for the pluton in the Early Cretaceous. SiO2 is 65.48–74.49 wt%, whereas that of K2O is 4.16–6.44 wt%, and that of Na2O is 2.99–4.70 wt%. They also contain 13.24–15.76 wt% of Al2O3, with an A/CNK ratio of 0.92–1.10, averaging 1.02. The alkalinity rate (AR) ranges from 2.68 to 5.12, and this range is within the AR of peraluminous type rocks. The granites of Fenghuangshan pluton are characterized by high contents of Na and K and low contents of Ca (thermophile element) and Mg, which are features of A-type granites. The (Na2O + K2O) ? Fe2O3* × 5 ? (CaO + MgO) × 5 discrimination diagram also shows that Fenghuangshan pluton is an A2-type granite. The above granite has zircon εHf(t) values ranging from ?17.06 to ?9.09, with single-stage Hf model ages (TDM) of 1141 Ma to 1498 Ma and two-stage Hf crustal model ages (TDMC) of 1762 Ma to 2263 Ma. A comprehensive analysis suggests that the Fenghuangshan pluton might have been formed from the lithospheric-plate sliding during the late stages of evolution of hot rift structures and might have been closely associated with the tectonic settings of Mesozoic Eurasia and the ancient Pacific Plate.  相似文献   

11.
在天山造山带觉罗塔格山系东段的中天山地块内,新识别出一套侵位于长城系星星峡群变质岩中的片麻状花岗质岩体,岩石组合为片麻状闪长岩+片麻状花岗闪长岩+片麻状二长花岗岩+片麻状钾长花岗岩,锆石SHRIM PU-Pb测年表明这套侵入岩的结晶年龄为(1 453±15)~(1 458±40)Ma(207Pb/206Pb表面年龄),是中元古代晚期的产物。岩石学及地球化学特征显示为高钾钙碱性系列,具I型花岗岩组合特征,形成于板块汇聚的环境。这套花岗质侵入岩的厘定,对于可能存在于元古宙的天山洋的闭合事件,从岩浆作用上提供了重要信息,同时对中天山星星峡群的地层时代提供了一个很好的上限。另外,还发现了一颗形成年龄为(2 991±22)Ma的残留锆石,指示该区可能存在太古宙的古老基底。  相似文献   

12.
蒙山主峰龟蒙顶为片麻状花岗闪长岩,原划为新太古代早期侵入岩。根据新测的2件样品锆石SHRIMP U-Pb年龄分别为（2 539±17）Ma,（2 544±15）Ma,其形成时代确定为新太古代晚期。蒙山北部云蒙峰为中粒二长花岗岩,锆石SHRIMP U-Pb年龄为（2 534±8）Ma,其侵入龟蒙顶岩体片麻状花岗闪长岩。龟蒙顶岩体属峄山岩套TTG质花岗岩,是地幔岩浆侵入混入地壳物质形成的。云蒙峰岩体属傲徕山岩套二长花岗岩,为上地壳物质重熔（深熔）作用形成。  相似文献   

13.
朱永峰 《岩石学报》2012,28(7):2113-2120
在新疆西南天山科桑溶洞地区,新厘定出一套斜长角闪岩-花岗岩地质单元:侵入斜长角闪岩中的新元古代白云母花岗岩(片麻状构造)、以及侵入上述古老岩石单元的早奥陶世花岗岩(块状构造)。片麻状白云母花岗岩中锆石具有热液锆石边、岩浆锆石幔和碎屑锆石核(边-幔-核结构),剔除被热液锆石和碎屑锆石混染的SHRIMP测点,获得岩浆锆石幔的加权平均年龄752.3±5.1Ma(MSWD=0.95),代表岩浆的结晶年龄。块状花岗岩的锆石具有边-核结构,热液锆石边的U-Pb年龄(419.5±5.7Ma)明显偏低。剔除热液锆石和碎屑锆石,获得岩浆锆石的平均U-Pb年龄481.1±4.4Ma(MSWD=0.88),代表花岗岩的结晶年龄。早奥陶世早期,岩浆侵入新元古代片麻状白云母花岗岩中。在晚志留世或者更晚时期,两类花岗岩共同经受了变质热液改造,变质流体交代岩浆锆石,导致锆石溶蚀再生长。  相似文献   

14.
山东鲁山地区新太古代壳源花岗岩主要包括粗粒钾长花岗岩、中-粗粒二长花岗岩和斑状二长花岗岩。根据SHRIMP锆石U—Pb定年．其形成时代分别为2525Ma±13Ma、2517Ma±13Ma和2508Ma±20Ma,且常有残余锆石核存在。它们的形成与华北克拉通新太古代晚期（2．5～2．55Ga）强烈的构造热事件有关,标志着鲁西和华北古陆块克拉通化完成。  相似文献   

15.
洪涛  游军  吴楚  徐兴旺 《岩石学报》2015,31(9):2583-2596
扬子板块西缘滇西地区是否存在古老基底一直存在争议。本文对滇西桃花地区花岗斑岩进行了岩石学、地球化学和锆石SHRIMP U-Pb年代学研究。形成于晚造山-后碰撞背景的桃花花岗斑岩具岛弧花岗岩地球化学特征,其成因可能与:1)俯冲拆离的洋壳俯冲拆离的洋壳或富集地幔重熔作用;2)加厚的地壳部分熔融。花岗斑岩中的继承锆石有两种类型:一类是发育具有密集振荡环带的岩浆锆石;另一类是次浑圆状锆石。测年结果显示,花岗斑岩的岩浆锆石年龄为36.35±0.35Ma,环带发育的继承锆石年龄介于167~891Ma之间;而次浑圆状继承锆石可以分为两组,其207Pb/206Pb加权平均年龄分别为1851±22Ma与2499±32Ma。新的锆石测年结果表明着滇西桃花地区不仅存在古金沙江洋东向俯冲形成的晚古生代弧岩浆记录,还发现新元古代岩浆活动信息,及早古元古代和新太古代的锆石记录。推测1.8Ga与2.5Ga锆石可能是捕获自地壳或围岩(石鼓片岩),表明滇西地区可能存在古老基底。  相似文献   

16.
吉林通化地区光华岩群出露于太古宙TTG片麻岩之中,其形成时代一直存在争议.利用SHRIMP与LA-ICPMS技术,对其代表性岩石样品开展了锆石U-Pb定年分析,包括石榴黑云片岩、黑云二长片麻岩、石榴角闪片岩和侵入光华岩群底部的钾长花岗岩.结果显示,光华岩群4件变质岩石样品尽管位置不同,但碎屑锆石年龄非常接近,207Pb/206Pb谐和年龄集中在2.6~2.5 Ga之间,加权平均值分别为2 529±7 Ma、2 568±4 Ma、2 526±11 Ma和2 530±6 Ma,表明其成岩物质来源于新太古代地体.部分变质岩石记录了2 525±10 Ma、1 926±40 Ma和1 878±16 Ma的变质锆石年龄,表明其既经历了太古代末期的构造热事件改造,又遭受了古元古代晚期碰撞造山事件的扰动.确定侵入光华岩群底部的钾长花岗岩的侵位年龄为2 154±7 Ma,岩石未遭受变形改造,其成因可能与陆内裂谷发育过程有关.   相似文献   

17.
刘福来  许志琴  宋彪 《地质学报》2003,77(2):229-237
锆石微区矿物包体的激光拉曼和阴极发光测试以及相应的SHRIMP U-Pb定年结果表明,苏鲁地体片麻岩锆石微区记录了十分复杂的年代学信息。其中副片麻岩锆石核部记录了345～743 Ma的继承性锆石年龄,标志着原岩碎屑锆石来源的复杂性;含柯石英的锆石微区记录了220～234 Ma的超高压变质年龄;而含石英包体的边部则记录了202～219 Ma的退变质年龄。正片麻岩继承性锆石核部所记录的年龄为574～680 Ma,表明原岩锆石曾经历了部分Pb丢失,原岩的形成年龄应大于680 Ma;含柯石英锆石微区所记录的超高压变质年龄为224～242 Ma;而锆石边部所记录的退变质年龄为209～219 Ma。两类片麻岩锆石微区所隐藏的超高压变质和退变质年龄信息十分相近,平均值分别为229±4Ma和211±4Ma,标志着苏鲁地体超高压变质时代应为印支期,相应的构造抬升速率约5.6 km/Ma。该项成果不仅确定了苏鲁地体超高压变质和退变质时代,而且对于深入探讨苏鲁地体快速折返过程中的动力学机制有着重要的科学意义。  相似文献   

18.
赵苗  杨竹森  张洪瑞 《地球科学》2019,44(6):2187-2196
伊朗乌尔米耶-达克塔尔弧岩浆带(Urumieh-Dokhtar magmatic arc,UDMA)是特提斯域最重要的斑岩铜矿省,发育大量中新世大型超-大型斑岩铜矿床;同时,该带也发育大量同时代无矿岩体,但控制岩体成矿潜力的关键因素尚不清楚.为此,选择该带中段、成矿及无矿岩体同时发育的大理矿区,针对成矿及无矿岩体开展了系统的锆石岩相学、年代学、微量元素地球化学及Hf同位素地球化学对比.结果显示,无矿闪长岩(锆石U-Pb年龄:17.4±0.3 Ma)比成矿石英闪长斑岩(锆石U-Pb年龄:15.6±0.1 Ma)形成略早,但近乎同期;闪长岩εHf(t)值变化介于+2^+4,石英闪长斑岩εHf(t)值变化介于+2^+5,两者具有类似的Hf同位素组成;闪长岩中锆石常含老的继承核(172~920 Ma),石英闪长斑岩则不发育继承锆石;闪长岩及石英闪长斑岩中的中新世锆石具有类似的稀土配分模式,且Eu负异常不明显,而闪长岩中的锆石继承核则显示出明显的Eu负异常,配分模式与中新世锆石不同.基于上述结果,我们提出大理矿区的两套中新世岩体具有相同的岩浆源区,但经历了不同的地壳演化过程,成矿的石英闪长斑岩浆形成后,与古老地壳没有明显交互,而无矿的闪长岩浆,在上升过程中与地壳物质、特别是古老还原性物质发生了交互,交互过程中岩浆氧逸度降低,是该套岩浆不成矿的主要原因.进而我们提出UDMA带中段斑岩成矿与否不仅与前人所认为的受岩浆源区控制,也与岩浆演化过程密不可分.  相似文献   

19.
中国东北地区佳木斯地块南部麻山杂岩正、副片麻岩 7个样品的锆石 SHRIMP年龄数据首次明确地表明 ,东北地区存在 500 Ma的晚泛非期高级变质作用事件。峰期麻粒岩相变质导致柳毛地区 (502± 10)Ma (2σ )深熔花岗岩的形成。正、副片麻岩变质年龄的一致性表明它们已在变质前发生了构造叠置。西麻山副片麻岩中含有在后期麻粒岩相变质过程中未重结晶的碎屑锆石，由此形成从协和一致的 550 Ma到弱不一致 1 900 Ma的较大 207Pb/206Pb年龄变化范围，表明其原岩具有从新元古代到中元古代-古元古代的年龄。柳毛地区变质的片麻状闪长岩中所含的古老锆石的 207Pb/206Pb年龄为 546～ 1 460 Ma表明，该闪长岩大约在 1 400 Ma就位，并受到 500 Ma变质事件的影响，从而说明柳毛地区存在中元古代基底。然而，与以前的认识相反，麻山杂岩不存在具有太古宙基底的同位素证据。晚泛非期变质事件年龄的确定对重塑晚前寒武纪-显生宙早期麻山杂岩和佳木斯地块的古地理位置具有重要意义。根据目前获得的有关证据，认为佳木斯地块可能曾经位于冈瓦纳大陆北缘的华北克拉通附近。  相似文献   

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