浙西北中生代火山岩Rb-Sr同位素地质年龄研究

浙西北火山杂岩系原划为侏罗系上统建德群,分为劳村组、黄尖组、寿昌组和横山组。作者在浙西北火山岩带劳村组、黄尖组、寿昌组酸性火山岩中获得了132Ma,107Ma和93Ma的全岩等时线年龄值。这表明,劳村组、黄尖组应划归早白垩世,寿昌组应划归晚白垩世。而这些岩组的火山岩锶同位素初始比值(~(87)Sr/(86)Sr)_0为0.70561—0.71434,火山岩应属硅铝壳中下部物质深熔的产物,个别样品(~(87)Sr/~(86)Sr)_0值表明,抑或有上地幔物质的干扰。     

新疆萨热阔布金矿黑云母~(40)Ar/~(39)Ar年龄及矿床成因启示

新疆萨热阔布金矿位于阿尔泰造山带南缘克兰盆地内,矿体呈脉状产于康布铁堡组火山岩地层中。为准确厘定其成矿时代,对矿区含矿石英脉中的云母进行了年龄测定,1件黑云母样品的40Ar/39Ar坪年龄为(213.5±2.3)Ma,相应的等时线年龄为(212.4±2.2)Ma,反等时线年龄为(212.5±2.2)Ma,与坪年龄在误差范围内一致。据此,萨热阔布金矿成矿作用发生于约213 Ma,成矿年龄晚于成岩年龄(~400 Ma)约180 Ma。因此,萨热阔布金矿为后生矿床。成矿年龄略晚于区域变质作用(~250 Ma)约37 Ma,推测成矿与阿尔泰造山带碰撞造山作用有关。结合矿床地质特征和流体包裹体特征,认为萨热阔布金矿为碰撞造山体制下形成的造山型金矿。     

新疆博格达造山带东段二叠纪流纹岩地球化学特征及地质意义

二叠纪火山岩主要由酸性火山岩及其火山碎屑岩组成,其中流纹岩Rb-Sr同位素等时线年龄为278±2 Ma;具有高Si低Al,富K贫Na,强不相容元素和LREE相对富集,Nb-Ta呈负异常,特别是Sr,P,Ti为强烈的负异常,以及δEu负异常明显等特点.流纹岩(w(~(87)Sr)/w(~(86)Sr))_I=0.7068～0.707 1,δ~(18)O_(SNOW)=11.97‰.因此,总体地球化学特征揭示了二叠纪酸性火山岩是中基性物质发生部分熔融的结果,斜长石可能是源区的主要残留相或在岩浆作用过程中经历过低压分离结晶作用,形成于后造山隆升的伸展构造背景下.     

浙江翼龙化石层的K-Ar年龄及地质意义

在浙江省临海市上盘镇岙里村北首次发现浙江翼龙化石的地层剖面上,共采集了8块火山碎屑岩石标本。在系统薄片观察的基础上,经过特殊处理,分选出其中的长石单矿物,用K-Ar同位素稀释技术定年。其表观年龄值域自76.5Ma至83.3Ma,中值为81.1Ma。~(40)Ar/~(36)Ar-~(40)K/~(36)Ar等时线年龄在相关系数为0.9990时是81.5 Ma。这一年龄在国际地层表中当属晚白垩,该年龄值既是浙江翼龙的年龄,又是该化石所赋存的塘上组火山沉积岩的形成时代。浙江翼龙的进化特征和产出时代可与北美洲的相对比。     

大垅铅锌矿床硫化物Rb-Sr同位素和主微量成分特征及矿床成因

大垅铅锌矿床位于湘东邓阜仙复式岩体北端,其赋矿围岩为二云母花岗岩,矿体产于南北向硅化破碎带中。对闪锌矿的Rb-Sr同位素进行分析,对矿床地质特征及硫化物电子探针主微量成分进行分析。研究结果表明:本区有3种矿化形式,分别对应3个成矿阶段,即石英—多金属硫化物阶段、石英—黄铁矿—闪锌矿阶段和石英—萤石—闪锌矿阶段,其初始~(87)Sr与~(86)Sr质量分数之比即w(~(87)Sr)/w(~(86)Sr)=0.709 9±0.009 7,与八团岩体的相近,Rb-Sr等时线成矿年龄为(154±8.0)Ma,与成岩年龄(159.2±4.6)Ma一致,反映成矿与燕山期岩浆活动具有密切的成因联系;成矿作用以岩浆热液为主;黄铜矿—黄铁矿微量元素温度计、矿物对硫同位素温度计以及绿泥石温度计显示成矿温度为161~229℃,属中低温范畴。矿床成因属于与燕山期中酸性岩浆侵入作用有关的中低温岩浆热液型铅锌矿床。     

江西广丰碱性橄榄玄武岩的成因:SHRIMP锆石U-Pb年龄和元素、Sr-Nd-Pb同位素制约

广丰盆地红色沉积岩系下部夹有一层玄武岩,玄武岩的锆石具有明显的环带结构,显示岩浆成因的特征;SHRIMP锆石U-Th-Pb分析结果显示:Th/U=0.28~1.28,13个分析点的206Pb/238U年龄变化为88.5~102.5 Ma,加权平均年龄为(99.0±0.7)Ma,MSWD=1.3,地质时代属晚白垩世早期。在Si O2-(K2O+Na2O)和Nb/Y-Zr/Ti O2图解上均落入碱性玄武岩范围,显示碱性系列的特征,在TFe O/Mg O-Si O2图解上显示拉斑系列的特征,属典型的碱性橄榄玄武岩。较低的Nb/Th(=2.21~4.98,平均3.43)、Ti/Yb(=3 125~5 753,平均3975),较高的Nb/U(=6.63~25.82,平均16.24)和δ18O值(=8‰~9.6‰,平均值为8.9‰),指示碱性橄榄玄武岩有地壳物质的成分。(87Sr/86Sr)i-Si O2,εNd(t)-Si O2,(87Sr/86Sr)i-10 000/Sr和εNd(t)-100/Nd图解显示,地壳物质的加入主要是源区混合的结果。在(143Nd/144Nd)i-(206Pb/204Pb)i,(87Sr/86Sr)i-(206Pb/204Pb)i和(143Nd/144Nd)i-(87Sr/86Sr)i图解上,碱性橄榄玄武岩均显示是由亏损地幔(DMM)和岩石圈富集地幔(EMⅡ)端元混合而成,且亏损地幔成分所占比例高于浙东玄武岩,与浙西玄武岩相近。     

豫西栾川中鱼库锌(铅)矿床闪锌矿Rb-Sr年龄及其地质意义

中鱼库矽卡岩型锌(铅)矿床位于华北陆块南缘河南省西部栾川Mo-W-Pb-Zn-Ag多金属矿集区南部,矿体呈层状-似层状赋存于新元古界栾川群三川组碎屑岩、碳酸盐岩地层中.因缺乏精确的成矿年代学研究,对该矿床成因的争议较大.本文在矿床地质背景和岩石矿物学研究的基础上,对13件矿石样品中的闪锌矿进行Rb-Sr同位素年代学研究.闪锌矿87 Rb/86 Sr和87 Sr/86 Sr同位素比值分别集中在0.802～18.98和0.713 359～0.748 684,二者具有良好的线性关系;其等时线年龄为(136.4士0.8) Ma (2σ,MSWD=3.6),(87 St/86 Sr)t=0.711 913士0.000 074.Rb-Sr同位素年龄反映该矿床形成于早白垩世,稍晚于研究区内的斑岩-矽卡岩型Mo-W矿床(146士2 MaB.P.),与区内最后一阶段花岗质岩浆活动(142～136MaB.P.)有关,属于栾川Mo-W-Pb-Zn-Ag多金属成矿系统.结合区域资料,认为该矿床形成于中生代陆-陆碰撞过程中由挤压向伸展转变的阶段,或碰撞后造山的局部伸展背景.     

排山楼金矿床~(40)Ar-~(39)Ar年龄及其地质意义

采用Ar-Ar同位素测年法对辽宁排山楼金矿床矿化阶段形成的钾长石和似斑状花岗岩中的钾长石进行了测试,获得矿化阶段形成钾长石40Ar-39Ar坪年龄为(116.69±1.15)Ma,等时线年龄为(116.97±1.39)Ma,以及似斑状花岗岩中原生钾长石40Ar-39Ar坪年龄为(126.71±2.03)Ma,等时线年龄为(124.00±4.32)Ma的数据.前者代表了该矿床的形成年龄,即该矿床形成于早白垩世,后者表明金矿化不早于(126.71±2.03)Ma.这一成矿年龄与华北陆块北缘大部分金矿床的成矿年龄一致,表明华北陆块北缘绝大多数金矿床形成于中国东部中生代动力学体制发生转折的时期.     

江西会昌盆地埃达克质粗面岩年代学、地球化学与成因研究

江西是华南白垩纪红色碎屑沉积岩系最发育的地区之一,且常夹有火山岩层。会昌岽背村一带红色沉积岩系底部的火山岩具有较高Si O2和Al2O3,较低的Mg O,Si O2=59.0%~64.6%(平均61.9%),Al2O3=15.5%~18.9(平均17.7%),Mg O=0.28%~0.92%(平均0.55%);富碱和钠,(Na2O+K2O)=7.19%~10.1%(平均9.70%),Na2O=6.50%~7.70%(平均7.03%),在Si O2-(Na2O+K2O)图解上落入碱性系列粗面岩或粗面英安岩范围;CIPW计算结果显示,标准矿物Ab=57.2%~65.7(平均60.5%),Q=6.07%~14.7%(平均9.95%),小于20%,属粗面岩。稀土总量较低,轻稀土明显富集,重稀土强烈亏损,Eu负异常不明显,∑REE=114×10-6~168×10-6,∑LREE=101×10-6~148×10-6,∑HREE=14.9×10-6~19.6×10-6,∑LREE/∑HREE=6.54~7.52,(La/Yb)N=24.9~34.2(平均27.4),δEu=0.81~1.10(平均0.98%),在稀土曲线图上呈明显的右倾,具高压型粗面岩的特征。较低的Y和Yb含量,较高的Sr含量和Sr/Y比值,Y=8.99×10-6~11.7×10-6(平均10.8×10-6),Yb=0.55×10-6~0.82×10-6(平均0.7×10-6),Sr=329×10-6~836×10-6(平均498×10-6),Sr/Y=36.5~71.8(平均48.2),具有埃达克岩的特征;在不相容元素蛛网图上显示富集大离子亲石元素(Cs,Rb,Ba,K等元素),强烈亏损高场强元素(Ta、Nd),具壳源的特征。较低的(87Sr/86Sr)i值、较高的εNd(t)和较小的TDM2值,(87Sr/86Sr)i=0.7074~0.7082(平均0.7077),εNd(t)=-1.99~-2.60(平均-2.29),TDM2=1 071 Ma~1 120 Ma(平均1094 Ma),具年轻下地壳部分熔融产物的特征。SHRIMP锆石U-Pb测年结果显示,14个分析点的206Pb/238U年龄变化范围为(114~108)Ma,加权平均年龄为(110.7±1.0)Ma,MSWD=0.47,指示地质时代属早白垩世晚期。上述特征显示,会昌岽背村一带红色沉积岩系底部的火山岩为早白垩世晚期加厚地壳背景下年轻下地壳部分熔融形成的埃达克质粗面岩。     

福建李坊重晶石矿床锶同位素组成及成因意义

通过对李坊重晶石矿床重晶石的Sr同位素分析,探讨钡的物质来源.结果显示,重晶石的Rb含量为2.70×10~(-6)～13.41×10~(-6), Sr含量为520.40×10~(-6)～2 166.00×10~(-6),~(87)Rb/~(86)Sr比值低,~(87)Sr/~(86)Sr比值介于0.710 81～0.711 80之间,平均值为0.711 26,高于同时期海水锶的~(87)Sr/~(86)Sr比值,低于壳源锶的~(87)Sr/~(86)Sr平均值,表明重晶石的锶来自海水锶与壳源锶的混合.示踪结果显示重晶石的钡主要来源于下伏地层,并暗示基底属于大陆型地壳.     

K-Ar dating of late Mesozoic volcanism and geochemistry of volcanic gravels in the North Huaiyang Belt, Dabie orogen: Constraints on the stratigraphic framework and exhumation of the northern Dabie orthogneiss complex

Two eruption episodes are identified through systematic field investigations and K-Ar dating of the lateMesozoic volcanic rocks in the North Huaiyang belt (NHB),Dabie orogenic belt, of which the earlier volcanic suitetermed Maotanchang Fm. (Fm.) occurring at Jinzhai,Xianhualing and Maotanchang, etc., was erupted from 149Ma to 138 Ma. The other named Xiaotian Fm. mainly dis-tributed at Xiaotian, Shucheng, etc., was formed between132 Ma and 116 Ma. During the eruption gap of the two vol-canic suites deposited a volcano-sedimentary conglomeratelayer, which are composed of the multi-compositional gravels, including the North Dabie orthogneiss complex (NDOC),volcanic gravels, etc. These volcanic gravels in the con-glomerate layer show identical geochemical and isotopic compositions (87Sr/86Sr(t) =0.7084-0.7092, (Nd (t) = 21.8-24.4) to the Maotanchang Fm. volcanic rocks (87Sr/86Sr = 0.7086-0.7102, (Nd = 19.2-24.4), but significantly distinct from those of Xiaotian Fm. (87Sr/86Sr = 0.7076-0.7084, (Nd = 17.2 - 19.2). K-Ar dating results of its underlying andoverlying volcanic sequences indicate that the conglomerate layers were deposite d at ~135 Ma. This suggests that the NDOC was rapidly exhumed to the surface dur ing or shortly before ~135 Ma and became the important provenance of the late Me sozoic volcano-sedimentary basins in the NHB. In combination with the regional v olcano-sedimentary correlation, we divided the Mesozoic stratigraphic sequence i n the NHB from base to top into Fanghushan Fm. (>160 Ma), Yuantongshan Fm. (/mid dle- lower segment of Sanjianpu Fm.) (160-149 Ma), Maotanchang Fm. (/Zhougongsh an Fm./upper segment of Sanjianpu Fm./Fenghuangtai Fm.) (149-135 Ma) and Xiaoti an Fm. (/Baidafan Fm./Heshidu Fm.) (135-116 Ma).     

阿尔泰地区霍热木德克花岗岩体年代学、地球化学特征及构造意义

中阿尔泰构造带出露大面积晚三叠世花岗岩,对其进行详细研究是了解阿尔泰造山带构造演化和陆壳增生过程的重要途径。本文对霍热木德克岩体进行详细的岩石学、锆石U-Pb年代学、岩石地球化学及Sr-Nd同位素研究。霍热木德克花岗岩体主要有粗粒二长花岗岩、细粒二长花岗岩和正长花岗岩。LA-ICP-MS锆石U-Pb年代学研究结果表明,其结晶年龄为(222.3±1.8)Ma(MSWD=1.6),为晚三叠世岩浆活动产物。地球化学研究表明,岩石具有高SiO_2、Al_2O_3、ALK,低TiO_2、MnO、MgO、P_2O_5的特征,轻稀土富集、轻重稀土分馏明显,具有Eu的负异常(δEu=0.37~0.50),富集大离子亲石元素、相对亏损高场强元素,显示出强过铝质S型花岗岩的特征,花岗岩具有负的εNd(t)(-3.7~-2.7)和较老的二阶段模式(T2DM)年龄(1.2~1.3Ga)。综合分析认为,霍热木德克花岗岩由富含白云母和黑云母的变泥质岩经历部分熔融形成,其源区有富钙斜长石、钛铁矿的残留,为同碰撞造山阶段挤压环境下地壳加厚而发生部分熔融的产物,形成于同碰撞构造环境。     

Petrogenesis of Aoyougou high-silica adakite in the North Qilian orogen, NW China: Evidence for decompression melting of oceanic slab

A trondhjemitic body occurs in the Aoyougou area,the western part of the North Qilian orogen.It is geochemically characterized by high SiO 2,Na 2 O (high Na/K),elevated Sr/Y and (La/Yb) N,positive Sr anomaly,relatively enriched large ion lithophile elements (LILEs) and light rare earth elements (LREEs),and depleted Nb,Ta,Ti,resembling the high-silica adakite.Zircon U-Pb SHRIMP dating yields a weighted mean age of 438±3 Ma.This age is significantly younger than eclogitization ages of 460-490 Ma in the North Qilian orogen,suggesting that formation of the adakite postdates the subduction of oceanic crust in association with closure of the ancient Qilian Ocean.Whole-rock Sr and Nd isotopic analyses give initial ratios of I Sr =0.7044 0.7047 and Nd (t)=3.0 4.1,indicating that they are derived from partial melting of the juvenile oceanic crust.In view of the tectonic evolution of the North Qilian orogen,the high-silica adakite was probably derived from decompression melting of the exhumed eclogite at the depth of ～60 km.     

LA-ICPMS zircon U-Pb geochronological constraints on the tectonothermal evolution of the Early Paleoproterozoic Dakendaban Group in the Quanji Block,NW China

The Quanji Block, situated between the northern margin of the Qaidam Block and the South Qilian orogenic belt in the NE Qinghai-Tibet Plateau, China, is thought to represent a remnant continental crust. In this study, LA-ICPMS U-Pb analyses of detrital zircon grains from two mesosomes in the migmatitic Dakendaban Group yield ages of 2467＋28/-26 Ma and 2474＋66/-52 Ma, respectively. Zircon grains from a leucosome give two distinct ages of 2471＋18/-16 Ma and 1924＋14/-15 Ma. Zircon from a granitic pegmatite that intruded into the Dakendaban Group yields an age of 2427＋44/-38 Ma. These data suggest that the Early Paleoproterozoic Dakendaban Group deposited between -2.43 to -2.47 Ga and has been subject to an intrusive event at 2.43Ga, and regional metamorphism-anatexis at 1.92 Ga. The common lower intercept age of -0.9 Ga probably records a significant Early Neoproterozoic event in the Quanji Block.     

南兴安岭晚中生代火山岩的岩石成因(II):Pb同位素制约

 对南兴安岭地区晚中生代火山岩的Pb同位素进行了分析,结合其主微量元素和Sr-Nd同位素地球化学特征,探讨了火山岩的岩石成因。满克头鄂博组低钾拉斑-钙碱性玄武安山岩表现出富集LILE、LREE和HFSE亏损元素地球化学特征以及稍高放射性成因Sr、Pb (⁸⁷Sr/⁸⁶Sr=0.704 88～0.704 99; ²⁰⁶Pb/²⁰⁴Pb=18.18～18.23)和弱相对亏损至弱富集的Nd同位素组成(ε_Nd((t)=-0.12～+0.68),其来源于俯冲沉积物参与改造富集地幔熔融源区。该组的英安岩-流纹岩较基性岩浆具有稍高放射性成因Sr、Pb (⁸⁷Sr/⁸⁶Sr=0.705 22～0.707 09; ²⁰⁶Pb/²⁰⁴Pb=18.16～18.33)和低Nd同位素组成 (ε_Nd(t))=-1.5～-0.4), 且在空间上与玄武岩共生,为玄武质岩浆结晶分异,并同化混染作用 (AFC)的产物。玛尼吐组英安岩具有与现代俯冲带adakite岩石相似的特征;在Sr-Nd-Pb同位素组成上,它们较同期或近期玄武安山岩更低Sr、Pb (⁸⁷Sr/⁸⁶Sr=0.704 09~0.704 25;²⁰⁶Pb/²⁰⁴Pb=18.15~18.17)和高Nd同位素比值(ε_Nd((t))=+0.9~+2.1),为造山带下地壳镁铁质岩石的部分熔融产物。     

Zircon U-Pb age of granitic gneiss on Duku highway in western Tianshan of China and its geological implications

Granitic gneiss on Duku highway in western Tianshan has been dated by the U-Pb zircon method. When plotted on the concordia diagram, the results give linear data array and the upper intercept age of (882 ± 33)Ma, and the age was considered as the crystallization age of the protolith. Granitic gneiss has high ASI value (1.09), high LILE and LREE contents, significantly negative Eu depletion, distinctly negative Ba, Sr, P, Ti and Nb anomalies and indicate continental crust parentage, which is consistent with high initial⁸⁷Sr/⁸⁶Sr ratios value (0.7170) and very negative ε_Nd(t)=-14.1. The protolith magma is interpreted as a product of partial melting of the basement rocks of older basement crust.     

大兴安岭柴河白音高老组流纹岩锆石U-Pb定年及成因探讨

为了研究大兴安岭中段柴河地区白音高老组流纹岩的形成时代和岩石成因,进行了锆石U-Pb同位素年龄测试和地球化学研究.LA-ICP-MS锆石U-Pb定年结果显示,白音高老组流纹岩形成于年龄为129~137 Ma的早白垩世.岩石地球化学研究表明,白音高老组流纹岩具有高硅富碱、贫钙镁的特征;稀土丰度总量m(∑REE)=121.35×10-6~194.92×10-6,轻重稀土分馏明显,m(La)/m(Yb)N=12.2~21.7,Eu负异常(δ_(Eu)=0.39~0.61),微量元素以富集Rb,Ba,Th,K,亏损Nb,Sr,P,Ti为特征;白音高老组流纹岩原始岩浆来源于上地壳岩石的部分熔融.     

Potash-rich volcanic rocks and lamprophyres in western Shandong Province: 40Ar39Ar dating and source tracing

Highly precise 40Ar39Ar dating results demonstrate that the ages of potash-rich volcanic rocks in western Shandong Province are 114.7-124.3 Ma, and that of the lamprophyres is 119.6 Ma. The potash-rich volcanic rocks have relatively high (87Sr/86Sr)i ratios ( 0.708715-0.711418)and distinctly negative εNd values ( -11.47 - -17.54), and are enriched in radiogenic lead (206Pb/204pb=17.341-17.622,207pb/204Pb=15.525-15.538, 208Pb/204pb = 37.563-37.684).Similarly, the lamprophyres also have quite low εNd values ( -11.57 - -19.64). Based on the fact that the Sr, Nd and Pb isotopic compositions of potash-rich volcanic rocks are very consistent with that of the clinopyroxene separates, and by integrating comprehensive analyses of their tectonic settings,and extensive comparisons of the Sr, Nd isotopic compositions with that of the related simultaneous rocks, it is concluded that the potash-rich volcanic rocks and lamprophyres in western Shandong Province were most possibly derived from the partial melting of enriched mantle which was caused by source contamination and metasomatism of subducted continental crustal materials.``     

Zircon SHRIMP U-Pb dating for the Cangshuipu volcanic rocks and its implications for the lower boundary age of the Nanhua strata in South China

Continental volcanic rocks and volcaniclastic sedi-mentary conglomerates of the Cangshuipu Formation oc- cur as wedge-shaped Neoproterozoic strata in the Yiyang region, Hunan Province. They overlie with a high-angle unconformity the Lengjiaxi Group of the Upper Meso- proterozoic Eonothem. The wedge-shaped Neoproterozoic strata of the continental clastic rocks and the Mesopro-terozoic deep marine flysch turbidites of the Lengjiaxi Group represent two distinct stages of basin-tectonic evo-…