华南侏罗纪构造体制转换：碎屑锆石U-Pb年代学证据EI北大核心CSCD

中生代时,华南经历了从古特提斯构造域到古太平洋构造域的转换,但对转折时限的认识还存在一些差异。此外,对粤东地区晚三叠世-早中侏罗世的大地构造属性和沉积背景的工作还很缺乏。对此,本文选取粤东地区出露的早-中侏罗世碎屑岩为研究对象,运用锆石U-Pb定年方法,探究华南中生代构造体制转折的时限和构造背景。碎屑锆石测年结果显示,早侏罗世的样品中普遍出现约250 Ma的主要峰值年龄,而中侏罗世的样品则都显示约180 Ma的主要峰值年龄。研究区早侏罗世的主要物源为印支期岩浆活动产物,可能主要来自华南的南部边缘;而中侏罗世的主要物源则可能来自南岭东段中生代火山岩。研究区碎屑沉积岩的碎屑锆石主要年龄峰值的转变,及其对应的物源区转变可能表明,华南在早侏罗世末期(约180 Ma)即已经完成了从古特提斯构造域向古太平洋构造域的转变。其大地构造背景则相应地从前期总体的挤压转变为伸展作用,粤东盆地从晚三叠世-早侏罗世早期时受挤压叠合走滑作用的类前陆盆地转变为早侏罗世末期的伸展断陷盆地。     

赣东北樟树墩早侏罗世水北组碎屑锆石研究及其地质意义

赣东北樟树墩地区早侏罗世盆地处于江南造山带东南缘,揭示盆地沉积物质来源对于认识和探讨周缘早中生代造山事件和古地理格局具有重要意义。对樟树墩早侏罗世盆地开展了岩相学、碎屑锆石U-Pb年代学和Lu-Hf同位素研究。结果表明: 盆地为类磨拉石建造与内陆湖沼含煤建造,碎屑锆石年龄跨度大(2 431~263 Ma),未出现同沉积或准同沉积的碎屑锆石; 碎屑锆石年龄呈现极强的早古生代峰值(420~380 Ma,ε_Hf(t)为-10.7~-3.0, T_DM^C为2.08~1.58 Ga)、弱的新元古代峰值(858~663 Ma,ε_Hf(t)为-18.8~-6.7, T_DM^C为2.79~2.09 Ga)和晚古生代峰值(370~355 Ma),另有少量早中生代((263±5) Ma)、中—古元古代(2 431~1 224 Ma)碎屑锆石记录。碎屑锆石年龄和Hf同位素组成与华夏地块西北武夷山地区所出露地质体组成相似,而与扬子东南缘地质体组成存在显著差异,其碎屑物质主要来自陆内西北武夷山地区前寒武纪基底和古生代地质体,少量碎屑物质可能来源于浙西北地区,具有被动型大陆边缘盆地沉积特征。综合区域上早中生代盆地研究成果,认为江南造山带东段景德镇—黄山东南在早—中侏罗世并未整体隆升剥蚀,华南内陆中生代的构造-岩浆活动是其周缘多板块俯冲汇聚的构造响应,晚三叠世—早侏罗世古太平洋板块向东亚大陆的俯冲造成华南东南部隆升,使其开始为内陆盆地提供物源,至早—中侏罗世之交构造体制转换为古太平洋板块的俯冲消减。     

华北板块北缘东段柳河盆地早白垩世鹰嘴砬子组碎屑锆石U-Pb定年及其地质意义

华北板块北缘在晚中生代受到古太平洋板块西向俯冲作用的影响,发育强烈的构造变形及大规模的岩浆活动.研究区柳河盆地地处华北板块北缘,对其开展研究能够为约束华北板块北缘晚中生代构造演化阶段提供沉积方面的证据.依据对盆地早白垩世鹰嘴砬子组样品碎屑组分、岩性序列、沉积相演化特征的研究,结合碎屑锆石U-Pb年代学判断,盆地样品矿物组成具有石英含量较低,岩屑和长石含量较高的特点,显示沉积物物源主要来自岩浆弧物源区.两组碎屑锆石U-Pb年龄组成相似,以晚中生代为主,古元古代为辅.L1-B178样品（岩心）碎屑锆石存在约127Ma的主峰和约2553Ma的次峰;P303-B3样品（剖面）存在约126Ma的主峰和约2545Ma的次峰,中生代沉积物物源可能来自盆地东北侧丰富的岩浆岩.早白垩世鹰嘴砬子组最年轻碎屑锆石颗粒的U-Pb年龄限定岩层的最大沉积年龄为（125±4）Ma,介于早白垩世巴雷姆阶与阿普特阶,与层内流纹岩样品（124.3±0.7）Ma的锆石加权平均年龄吻合.通过对柳河盆地样品矿物组成特点、沉积相演化和碎屑锆石U-Pb年代学特征综合判断,盆地在（125±4）Ma已接收到古太平板块俯冲作用带来的物源...     

南岭东段早侏罗世沉积岩碎屑锆石U-Pb定年及其地质意义——以东坑盆地为例

印支造山运动是华南早中生代最重要的构造-岩浆事件,它在很大程度上影响了华南现今的地形和地貌特点。本文研究了南岭东段赣南早侏罗世东坑火山岩盆地沉积岩的碎屑锆石U-Pb年代,获得最显著的年龄峰值为196Ma、238Ma、364Ma和427Ma,表明该沉积岩并不是外来的震旦纪-寒武纪变质岩,而是早侏罗世裂谷火山盆地的沉积物。缺乏260～290Ma的锆石年龄,很可能反映物质为近源来源。通过与闽西南晚三叠世和华南内陆中-晚二叠世沉积砂岩中碎屑锆石年龄谱对比,反映华南印支早期(290～260Ma)岩浆活动主体在东南沿海地区,晚期(240～200Ma)主体发育在内陆地区。大量印支期侵入岩锆石的出现也很可能表明华南内陆印支造山带在～190Ma已经经历了相当程度的垮塌。     

桂东北恭城盆地的物源变迁:华南中生代构造体制转换的产物?

桂东北中生代恭城盆地位于南岭成矿带西段,是研究华南印支期-燕山早期构造事件动力学过程中浅表地质响应的重要窗口。盆地内上二叠统乐平组被上三叠统-下侏罗统天堂组不整合覆盖,天堂组与下侏罗统大岭组、中侏罗统石梯组为整合接触。沉积相分析表明,乐平组为海陆交互相碎屑岩,天堂组底部砾岩、含砾粗砂岩代表盆地早期山前快速堆积的冲积扇相沉积,天堂组上部、大岭组和石梯组砾岩、砂岩和泥质岩则代表河流相沉积。碎屑锆石U-Pb年龄结果显示,乐平组和天堂组底部岩屑石英砂岩均以980 Ma和～2500 Ma锆石为主,暗示晚二叠世以及晚三叠世-早侏罗世早期盆地的碎屑物主要来自南部云开地区。然而天堂组上部、大岭组和石梯组长石岩屑砂岩则以1790～1875 Ma和2370～2490 Ma锆石为主,并伴随有燕山早期(189～174Ma)锆石,指示早-中侏罗世时盆地的碎屑物主要来源于北东部武夷山-南岭地区,与古水流方向分析的结果一致。恭城盆地早-中侏罗世时沉积物源的变迁规律很好地记录了华南东南部从印支期挤压应力状态向燕山早期伸展拉张作用的转变以及区域构造机制的转换。     

华南闽西南早侏罗世梨山组碎屑锆石U-Pb定年及地质意义

对闽西南早侏罗世梨山组碎屑岩进行了碎屑锆石年代学研究,其目的是查明早侏罗世沉积物的组成及来源,揭示华南地区中生代盆地性质.梨山组上段样品(GMC12)和下段样品(GMC22)反映的主要年龄组成相似,均有一个约1 860 Ma的主峰和一个约230 Ma的次峰.但下段样品(GMC22)显示出较为简单的年龄分布,获得显著的年龄峰值为1 860 Ma和230 Ma;上部样品(GMC12)显示出多峰特征,除了主峰1 860 Ma外,还有约230 Ma、约280 Ma、约410 Ma、约490 Ma、约770 Ma和约2 540 Ma多个次峰值.由下段至上段,碎屑锆石年龄组成由简单变复杂.上段样品中较老的年龄组成比下段明显增加,而且年龄组成比下段复杂,表明物源可能发生变化.研究区早侏罗世主要物源为古元古代和晚古生代-早中生代岩浆活动产物,通过与闽西南周围不同盆地晚古生代和早中生代沉积岩碎屑锆石年龄组成对比,闽西南早侏罗世物源主要来自研究区北部和东北部.由研究区到华南内陆/南部,盆地内沉积物年龄组成发生了由复杂且相对较老到简单且年轻的变化.印支期造山运动早期到晚期,华南地区岩浆活动发生了由南部沿海向华南内陆的迁移,而华南东部沿海、东北部和北部地区岩浆活动一直较活跃.     

韩国太白山盆地古生界砂岩碎屑锆石U-Pb年代及其区域构造含义

韩国中东部的太白山盆地位于京畿、岭南两个构造单元之间。采用LA-ICP-MS方法,从太白山盆地下寒武统、中-上石炭统（下二叠统？）砂岩碎屑锆石中分别获得27个和47个U-Pb有效年龄,前者记录了1820~1945Ma、2172~2195Ma、2473~2593Ma等3期可信的构造热事件,相对概率峰值分别为1897Ma、2177Ma以及2528Ma;后者记录了288~340Ma、461~474Ma、1780~1892Ma、1941~1959Ma、2012~2050Ma等5期可信的构造热事件,其中相对概率峰值为305Ma和1867Ma的两组年龄比较集中。研究认为,太白山盆地与京畿、岭南两个地块均发育大约1850Ma的构造热事件,缺乏华南比较特征的新元古代构造热事件;进一步依据太白山盆地相应时段沉积古流向和古地理分布,说明太白山盆地至少与岭南地块之间存在密切的碎屑物源和构造属性关系,其构造热事件记录可与华北克拉通对比。另一方面,尽管中-上石炭统（下二叠统？）碎屑锆石记录了峰值为305Ma和468Ma可能发生在华北-朝鲜联合块体南缘的俯冲或构造热事件,但上述两个样品的碎屑锆石均缺乏新元古代构造热事件的年龄记录,所以亲华南的陆块至少在晚石炭世（早二叠世？）以前并未向太白山盆地提供碎屑物源。     

鄂尔多斯盆地南部二叠系砂岩碎屑锆石年代学特征及地质意义

陆源碎屑岩物质来源及变化与沉积盆地及构造演化密切相关。通过对鄂尔多斯盆地南部铜川地区晚古生代二叠系山西组、石盒子组及石千峰组砂岩样品岩石薄片鉴定、定量矿物学分析以及碎屑锆石U-Pb年代学分析,结合古流向特征,对物源进行了追溯,并讨论了盆地南部二叠系的构造—沉积过程。研究结果表明,早二叠世山西组碎屑锆石年龄具364 Ma、450 Ma、946Ma和2 446 Ma四个主要峰值;中二叠世下石盒子组碎屑锆石年龄具294 Ma、1 963.4 Ma和2 499 Ma三个主要峰值;晚二叠世石千峰组碎屑锆石年龄主要峰值出现在1 876.5 Ma,缺乏北秦岭造山带的新元古代和早古生代碎屑锆石记录。分析认为山西组主要物源区为北秦岭造山带,次要物源区为华北南缘构造带;石盒子组物源由北秦岭造山带、华北板块南缘构造带和内蒙古隆起西段共同提供;石千峰组物源区为华北南缘构造带。早二叠世山西期,华北南缘隆起幅度较低,不影响北秦岭造山带供源。石盒子期,勉略洋由被动拉张转换为主动挤压,秦岭造山带处于持续隆升状态,并造成了华北南缘构造带的不断抬升。石千峰期华北南缘强烈隆升,在为铜川地区提供物源的同时也阻挡了北秦岭造山带...     

从源到汇:大别造山带物源区与合肥盆地南缘中生代沉积耦合关系——来自碎屑锆石U-Pb年龄证据

形成于印支期的大别造山带和周缘中生代盆地构成了一级源汇系统,其中位于造山带北缘的合肥盆地中生代地层发育,且以盆地南缘出露最好,这为盆山源汇系统研究提供了理想的沉积记录。笔者从合肥盆地南缘采集了10个砂岩样品和1个砾岩样品,进行锆石U/Pb (LA-ICP-MS)定年分析,获得了742个有效年龄(置信度不小于85%),范围为113±3. 6-2983 Ma。这些碎屑锆石年龄谱可以被分为5个年龄段:113-137 Ma,峰值131 Ma; 184-273 Ma,峰值226 Ma; 274-517. 3 Ma,具有2个峰值280 Ma和474 Ma; 532-856. 6 Ma,具有3个峰值572 Ma、649 Ma和772 Ma; 1786-2600 Ma,具有2个峰值2035 Ma和2506 Ma。同时,总结了物源区大别造山带不同单元锆石U-Pb年龄特征。根据锆石U/Pb年龄和Th/U值,发现这5个年龄段比较准确地记录了物源区地质体,分别是早白垩世的岩浆岩、大别山高压—超高压变质岩、北淮阳的浅变质岩、北大别的正片麻岩和卢镇关群变质岩。根据锆石最小年龄,修正了合肥盆地南缘中生代地层格架,为源汇系统研究确立了时间框架。合肥盆地南缘中生代沉积可以分为4个演化阶段:晚三叠世瑞替期—早侏罗世辛涅缪斯期、中—晚侏罗世、早白垩世早期和早白垩世晚期,并据此确定了每个阶段主要物源区特征及其时空变化。碎屑锆石U/Pb年龄和Th/U值限定了大别造山带仅存在三叠纪的超高压变质作用,且超高压变质岩折返到地表的最早时间是晚三叠世瑞替期,大别造山带大陆岛弧发育的时间是新元古代。上述研究结果不仅为恢复大别造山带构造古地理做出了新的贡献,而且更为盆山源汇系统研究提供了一个实例。     

南盘江盆地中三叠统碎屑锆石地质年代学:物源及其地质意义

南盘江盆地的物源及其构造性质至今尚未取得较为一致的认识。目前主要的观点认为其物源主要来自盆地东南面的云开大山地区,盆地的性质为古太平洋板块俯冲所形成的前陆盆地。本文采用碎屑锆石年代学方法,首次报道该盆地中三叠统碎屑锆石年龄组成,分析了该盆地的沉积物源,并基于物源分析探讨了成盆机制和板块间动力学关系。该盆地中三叠统碎屑锆石年龄组成最主要的特征性的年龄分布在320～250Ma之间,此区间内存在280Ma和250Ma两个峰值。通过与相邻各块体锆石年龄谱对比,本研究认为:(1)南盘江盆地的主要物源区应为古特提斯北缘(华南一侧)的石炭-二叠纪岩浆弧,SongMa构造带可能是三叠纪的缝合线,而不是因Sibumasu板块增生到印支板块而导致的板内活化带;(2)该盆地三叠纪时为古特提斯闭合在华南形成的前陆盆地,与古特提斯沿SongMa带向北俯冲闭合有关,前人认为的南盘江盆地形成于古太平洋板块向西北俯冲作用的观点值得商榷。     

粤东晚三叠世小水组——早侏罗世金鸡组古气候及构造背景的矿物和地球化学记录

对揭西灰寨剖面上三叠统小水组和惠州黄洞剖面下侏罗统金鸡组采集的泥岩和砂岩样品进行了全岩分析和ICP-MS微量、稀土元素测试和矿物成分分析,根据元素含量及其比值的变化,提出了粤东揭西地区晚三叠世小水组和惠州地区早侏罗世金鸡组水体整体为还原、厌氧环境,以干燥炎热气候为主。小水组w(∑REE)较大,轻稀土富集(LREE/HREE为10.86和15.63),重稀土较稳定(w(∑HREE) 为6.09×10^-6和7.99×10^-6),Eu负异常(δEu为0.67和0.87);金鸡组轻稀土富集(LREE/HREE=7.29~10.03),重稀土较稳定(w(∑HREE)为(15.39~19.72)×10^-6),Eu负异常(δEu=0.59~0.65)。泥岩稀土元素分布模式图和源岩判别图解显示,小水组和金鸡组源岩来自上地壳的沉积岩、花岗岩和玄武岩,小水组下部样品沉积物源岩较上部要深,金鸡组上部沉积物源岩较中下部要深。Dickinson图解、K₂O/Na₂O-w(SiO₂)、Zr-Th、La-Th-Sc、Th-Co-Zr/10判别图解和稀土元素特征值显示,晚三叠世揭西地区的构造背景为弧后伸展盆地,有被动大陆边缘特性,但也有大陆岛弧(由安第斯大陆边缘弧转变而来)的特性,其物源来自火山弧造山带。早侏罗世黄洞地区为弧后挤压盆地,具有被动陆缘特性,沉积物物源来自于切割的岩浆弧。     

Sedimentary provenance of the Hengyang and Mayang basins,SE China,and implications for the Mesozoic topographic change in South China Craton: Evidence from detrital zircon geochronology

Detrital zircon U–Pb data from sedimentary rocks in the Hengyang and Mayang basins, SE China reveal a change in basin provenance during or after Early Cretaceous. The results imply a provenance of the sediment from the North China Craton and Dabie Orogen for the Upper Triassic to Middle Jurassic sandstones and from the Indosinian granitic plutons in the South China Craton for the Lower Cretaceous sandstones. The 90–120 Ma age group in the Upper Cretaceous sandstones in the Hengyang Basin is correlated with Cretaceous volcanism along the southeastern margin of South China, suggesting a coastal mountain belt have existed during the Late Cretaceous. The sediment provenance of the basins and topographic evolution revealed by the geochronological data in this study are consistent with a Mesozoic tectonic setting from Early Mesozoic intra-continental compression through late Mesozoic Pacific Plate subduction in SE China.     

鲁西隆起侏罗系碎屑主物源来自华北北缘:锆石U-Pb和Hf同位素年代学证据

鲁西隆起保存并出露比较完整的晚中生代沉积记录,是研究华北东部晚中生代构造演化的重要窗口。本文采用碎屑锆石LA-MC-ICP-MS测年方法分析鲁西隆起北缘淄川地区坊子组和三台组中的两个砂岩样品,以此探讨华北东部侏罗纪的沉积物源并约束构造古地理格架。两个砂岩样品具有近似的U-Pb年龄谱。古元古代和新太古代两组U-Pb年龄及其Hf同位素组成与广泛出露于北部的华北克拉通基底一致,根据缺乏新元古代中期(850～700 Ma)岩浆年龄和三叠纪变质年龄的事实,以此可以排除扬子板块以及现今临近于鲁西隆起东南部的苏鲁造山带物源。坊子组和三台组碎屑锆石显生宙年龄(393～256 Ma)记录的晚古生代岩浆活动均未发现于鲁西隆起及其邻近地区,而可以与大量出露于华北北缘及其北部的兴-蒙造山带的岩浆活动进行对比。此外,相当部分的显生宙碎屑锆石(183 Ma、462 Ma和324～154 Ma)具有正的ε_Hf(t)值(0.9～12.7)同位素特征,也与兴-蒙造山带特征相似,且三台组砂岩中显生宙碎屑锆石及其中ε_Hf(t)值为正值的比例较坊子组均增多。研究认为,华北北缘及其北部的兴-蒙造山带在侏罗纪时从早到晚不断抬升、剥蚀,形成相对华北克拉通内部的高地势特点,由此大量的剥蚀产物向南输运而成为鲁西隆起侏罗系的主要碎屑物源。     

漠河盆地二十二站组砂岩形成时代及物源区构造环境判别

大兴安岭北部的漠河盆地广泛发育中生界二十二站组砂岩,其形成时代一直备受争议.首次利用碎屑锆石LA-ICP-MS U-Pb法测年对其形成时代作出较为精确的限定,并结合地球化学特征对其物源区及大地构造背景进行了探讨.研究结果表明,二十二站组砂岩碎屑物磨圆度较低、分选差,表现出源区相对不稳定,快速剥蚀、搬运及沉积的特征.锆石颗粒粗大,具有清晰的震荡环带,Th/U值为0.35～1.07,为典型的岩浆锆石.测年结果显示,90个测点年龄主要分布在3个群落:152～170Ma,峰值年龄约为158Ma,这一年龄区间揭示了二十二站组沉积成岩的下限为晚侏罗世;179～193Ma,峰值年龄约为190Ma;205～214Ma,峰值年龄约为210Ma.3个年龄峰值为蒙古-鄂霍茨克洋演化过程中一系列岩浆活动的地质记录,其中210Ma与190Ma峰值年龄与盆地南缘额尔古纳地块晚三叠世、早侏罗世的岩浆事件相吻合,而158Ma峰值年龄则对应于盆地北缘晚侏罗世的岩浆事件.主、微量元素构造判别图解揭示其物源区具有活动大陆边缘的特征,同时锆石定年数据显示其没有任何前中生代的碎屑物,暗示了该3期岩浆岩均形成于额尔古纳地块北缘的中生代活动大陆边缘环境,并为二十二站组的形成提供了主要碎屑物质.由此说明,二十二站组砂岩形成于晚侏罗世蒙古-鄂霍茨克洋闭合后的造山过程中,漠河盆地南北两侧物源区快速剥蚀、快速搬运与快速沉积的环境.      

华南东部陆缘侏罗纪岩浆作用特征及其构造背景——来自浙东南毛弄组火山岩的新证据

华南东部内陆地区在侏罗纪处于陆内伸展背景已逐渐成为学术界共识,但对于该时期东部陆缘的构造环境仍存在争议。本文以浙东南毛弄组火山岩为对象,开展了岩石学、SHRIMP锆石U-Pb年代学、锆石微量元素、全岩元素地球化学和Sr-Nd同位素等研究,为认识华南东部陆缘构造背景提供制约。浙江侏罗纪火山岩以松阳毛弄剖面较具代表性,总体上是一套以英安质晶屑凝灰岩和流纹质玻屑凝灰岩为主的火山岩组合。本次研究在毛弄组下段获得的流纹质玻屑凝灰岩的SHRIMP锆石U-Pb年龄为153±2Ma。综合前人研究表明,毛弄组火山岩主要形成于180～148Ma。毛弄组火山岩属于镁质钙碱性系列,且表现出明显的轻稀土元素富集特征,其中早侏罗世毛弄英安质凝灰岩Eu负异常不明显,而晚侏罗世毛弄流纹质凝灰岩具有显著的Eu负异常;两组凝灰岩均富集K、Rb和Th等大离子亲石元素,亏损Nb、Ta、Zr和Hf等高场强元素。毛弄英安质火山岩的源区残留相组合可能为"斜长石+石榴石+角闪石",而毛弄流纹质凝灰岩则可能为"斜长石+角闪石",这一差异可能代表它们具有不同的源区深度。毛弄组火山岩的Sr-Nd-Hf同位素特征与华夏陆块古元古代基底岩体相似,其可能主要起源于基底地壳物质的部分熔融,并有少量地幔新生物质的加入。结合构造背景分析认为,毛弄组火山岩等陆缘岩浆岩形成环境为相对低温的"安第斯型"俯冲环境。通过不同时代区域岩体锆石氧逸度计算发现,早侏罗世东南海域岩浆岩的氧逸度比大陆陆缘更高,且大陆陆缘岩浆岩的氧逸度从晚三叠世至晚侏罗世不断升高,可能标志着陆缘地区俯冲流体的影响有着从东南海域向大陆陆缘扩散的趋势。综合分析认为,在侏罗纪华南东部陆缘可能发育一个与古太平洋俯冲有关的"安第斯型"陆缘岩浆弧,其时代可能最早可以追溯到早侏罗世早期,并持续扩大到中-晚侏罗世。这一时期浙闽沿海地区总体处于弧后挤压主导的构造环境,与同期内陆地区构造伸展背景形成鲜明对比。     

合肥盆地圆筒山组物源分析及其地质意义：来自碎屑锆石的证据

合肥盆地位于华北板块东南缘,形成于华南、华北板块碰撞过程中。合肥盆地形成时表现为大别造山带向北逆冲形成的前陆挠曲盆地,早白垩世在区域伸展背景下转变为断陷盆地。中侏罗统圆筒山组是合肥盆地前陆挠曲阶段的沉积地层之一,主要表现为湖泊相沉积,与下伏的防虎山组典型的河流相沉积明显不同。为了获得圆筒山组更详细的物源信息,对肥西地区出露的圆筒山组紫红色粉砂岩开展了碎屑锆石LA-ICP MS U-Pb定年。定年结果显示,两个粉砂岩样品均获得了约2.0 Ga和约770 Ma两个主要峰值以及约2.4 Ga次要峰值。该特征与扬子板块锆石年龄分布特征几乎完全一致,指示圆筒山组物源应来自扬子板块。考虑到盆地地层的物源不应来自其周边隆起区分水岭的另一侧,因而推测圆筒山组物源应来自张八岭隆起中侏罗世时地表出露岩石。在燕山运动A幕影响下,下扬子地区发生逆冲褶皱活动,张八岭隆起发生明显隆升,上部岩石被剥蚀殆尽,仅保留现今出露的新元古代张八岭群及肥东杂岩,被剥蚀的岩石搬运沉积于合肥盆地内,形成圆筒山组。     

大兴安岭北部中侏罗统漠河组砂岩LA-ICP-MS碎屑锆石U-Pb年龄:对漠河盆地源区的制约

对大兴安岭北部漠河盆地中侏罗统漠河组砂岩进行了碎屑锆石LA-ICP-MS U-Pb年龄测试,获得的碎屑锆石U-Pb年龄为1425~170 Ma,反映了中侏罗时期漠河盆地源区的复杂性。该时期漠河盆地物源主要有:中元古代变质火山岩,碎屑锆石年龄1425~1064 Ma;新元古代变质侵入岩,碎屑锆石年龄888~550 Ma;寒武—奥陶纪变质表壳岩与深成侵入岩,碎屑锆石年龄517~441 Ma;石炭—二叠纪侵入岩,碎屑锆石年龄327~252 Ma;三叠纪—中侏罗世侵入岩,碎屑锆石年龄250~170 Ma。这一测试数据与盆地现在南缘分布的地质体的时代基本对应,说明盆地的物源主要来自南部的中元古代—中侏罗世地质体,碎屑锆石中最小年龄为170 Ma,反映漠河组沉积下限不早于中侏罗世早期。这一成果对研究漠河盆地源区的物质组成、盆地沉积年代和油气成藏条件提供了新的素材。     

Petrography of Middle Jurassic to Early Cretaceous sandstones in the Kutch Basin,western India:Implications on provenance and basin evolution

This paper investigates the provenance of Middle Jurassic to Early Cretaceous sediments in the Kutch Basin, western India, on the basis of mineralogical investigations of sandstones composition(Quartz-Feldspar-Lithic(QFL)fragment), Zircon-Tourmaline-Rutile(ZTR) index, and mineral chemistry of heavy detrital minerals of the framework.The study also examines the compositional variation of the sandstone in relation to the evolution of the Kutch Basin, which originated as a rift basin during the Late Triassic and evolved into a passive margin basin by the end Cretaceous. This study analyzes sandstone samples of Jhumara, Jhuran and Bhuj Formations of Middle Jurassic,Upper Jurassic and Lower Cretaceous, respectively, in the Kutch Mainland. Sandstones record a compositional evolution from arkosic to subarkosic as the feldspar content decreases from 68% in the Jhumara Formation to 27%in the Bhuj Formation with intermediate values in the Jhuran Formation. The QFL modal composition indicates basement uplifted and transitional continental settings at source. Heavy mineral content of these sandstones reveals the occurrence of zircon, tourmaline, rutile, garnet, apatite, monazite and opaque minerals. Sub-rounded to well-rounded zircon grains indicate a polycyclic origin. ZTR indices for samples in Jhumara, Jhuran and Bhuj Formations are 25%, 30% and 50% respectively. Chemistry of opaque minerals reveals the occurrence of detrital varieties such as ilmenite, rutile, hematite/magnetite and pyrite, in a decreasing order of abundances. Chemistry of ilmenites in the Jhumara Formation reveals its derivation from dual felsic igneous and metabasic source, while those in Jhuran and Bhuj Formations indicate a metabasic derivation. Chemistry of garnet reveals predominantly Fe-rich(almandine) variety of metabasic origin. X-ray microscopic study provides the percentage of heavy minerals ranging from 3% to 5.26%. QFL detrital modes reflect the evolution of the basin from an active rift to a passive margin basin during the Mesozoic. Integration of results from QFL modal composition of the sandstones, heavy mineral analysis and mineral chemistry, suggests sediment supply from both northern and eastern highlands during the Middle Jurassic. The uplift along the Kutch Mainland Fault in the Early Cretaceous results in curtailment of sediment input from north.     

Study and geological implication of detrital zircons in Shuibei Formation of Early Jurassic in Zhangshudun of northeastern Jiangxi Province

The Early Jurassic basin in Zhangshudun of northeastern Jiangxi Province is located in the southeastern part of Jiangnan orogeny, and revealing the basin depositional source is of great importance for understanding and discussing the orogenic events and ancient geography during Early Mesozoic. The research of petrography, detrital zircons U-Pb geochronology, Lu-Hf isotope geochemistry of Early Jurassic clastic rocks was conducted in this paper. The results show that the Early Jurassic Shuibei Formation includes molasse-like deposits and fluviatile-lacustrine facies, and the detrital zircons U-Pb ages are within the wide scope of 2 431~263 Ma, with no existence of synsedimentary or pensynsedimentary detrital zircons. The detrital zircons display a very obvious peak age in Early Paleozoic of 420~380 Ma, with ε_Hf(t) values between -10.7 and -3 and T_DM^C values between 2.08 and 1.58 Ga. The weak peak ages of 370~355 Ma and 858~663 Ma are displayed in Late Paleozoic and Neoproterozoic,respectively, with ε_Hf(t) values of -18.8 to -6.7 and T_DM^C values of 2.08 to 1.58 Ga. The detrital zircons also contain a few Early Mesozoic (263 Ma) and Paleo-Meso proterozoic (2 431~1 224 Ma) ages. The detrital zircons ages and Lu-Hf isotope are similar with geological entities in northwestern Wuyi area of Cathaysia Block, while they are obviously different from the ages of the geological body in southeastern Yangtze region. The detrital materials are mainly from Early Cambrian basement and Paleozoic geological body northwestern Wuyi area. While little detrital rocks may come from northwestern Zhejiang with sedimentary characters of passive continental margin. Combined with the comprehensive regional research results of Early Mesozoic basin, the authors conclude that the southeastern Jingdezhen-Huangshan of eastern Jiangnan orogenic belt was not uplifting with erosion in Early and Middle Jurassic, and the Mesozoic structural-magmatic activities in the inland of South China were the tectonic response to the dive and influx of multiplates. The uplift in the southezstern part of South China caused by the subduction of the paleo-pacific plate to the East Asian continent from the Late Triassic to Early Jurassic can provide provenance for the inland basin, and the tectonic constitution at the turn of the Early-Middle Jurassic has been transformed into the subduction of the paleo-pacific plate.     

Jurassic uplift and erosion of the northeast Queensland continental margin: evidence from (U–Th)/He thermochronology combined with U–Pb detrital zircon age spectra

Abstract

The Jurassic–Cretaceous Great Artesian Basin is the most extensive, and largest volume, sedimentary feature of continental Australia. The source of its mud-dominated Cretaceous infill is attributed largely to contemporary magmatism along the continental margin to the east, but the source of its Jurassic infill, dominated by quartz sandstone, remains unconstrained. This paper investigates the question of a Jurassic sediment source for the northern part of the basin. Jurassic uplift and exhumation of the continental margin crustal sector to the east provided the primary Jurassic sediment source. (U–Th)/He data are presented for zircon and apatite from Pennsylvanian to mid Permian granitoids of the Kennedy Igneous Association distributed within the northern Tasmanides between the Townsville and Cairns regions and for coeval granites of the Urannha batholith from the Mount Carlton district (N Bowen Basin), also within the northern Tasmanides. The data from zircon indicate widespread Jurassic exhumation of a crustal tract located to the east of the northern Great Artesian Basin and largely occupied by rocks of the Tasmanides. Detrital zircon age spectra for samples of the Jurassic Hutton and Blantyre sandstones from the northeastern margin of the Great Artesian Basin show their derivation to be largely from rocks of the northern Tasmanides. In combination, the detrital age spectra and (U–Th)/He data from zircon indicate exhumation owing to uplift generating appreciable physiographic relief along the north Queensland continental margin during the Jurassic, shedding sediment westward into the Great Artesian Basin during its early development. A portion of (U–Th)/He data for zircon are consistent with late Permian–mid Triassic exhumation within the Tasmanides, attributable to the influence of the Hunter--Bowen Orogeny. Evidence of Cretaceous and Paleocene exhumation episodes is also indicated for some samples, mainly by apatite (U–Th)/He analysis, consistent with data previously published from fission track studies. Overall, new data from the present study reveal that the exhumation related to Jurassic regional uplift and the subsequent erosional reworking of the northeast Australian continental margin is critical for the evolution and development of the northern side of the Great Artesian Basin in eastern Australia. Apart from this, another two previously suggested Permian–Triassic and Cretaceous exhumation and uplift episodes along the northeast Australian continental margin are also confirmed by the dataset of this study.

1. KEY POINTS

2. U–Pb detrital zircon ages of sandstone samples from the northeastern Eromanga Basin reveal Paleozoic (480–280 Ma) and Proterozoic (1800–1400 Ma) age clusters.

3. (U–Th)/He zircon and apatite dating results of granitoids samples from Cairns, Townsville and the Mount Carlton districts are dominated by Jurassic (198–164 Ma) and Permian–Triassic (272–238 Ma) age clusters.

4. Combination of above two datasets proves the regional uplift-driving Jurassic exhumation episode in the northeast Australian continental is vital for the development of the northern Great Artesian Basin.