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蚌类在湿地生态系统元素的富集与转化过程中发挥重要作用.以巢湖常见扭蚌（Arconaia lanceolata）、三角帆蚌（Hyriopsis cumingii）、褶纹冠蚌（Cristaria plicata）和圆顶珠蚌（Unio douglasiae）为对象,分析其内脏团、外套膜（包含鳃,下同）和斧足中5种微量元素（Cu、Zn、As、Cd、Pb）的含量.结果表明：5种元素在4种蚌体内均有检出,除Zn在圆顶珠蚌组织间表现为外套膜>内脏团>斧足外,4种蚌体组织间5种微量元素含量均表现为内脏团 > 外套膜 > 斧足;4种蚌类各微量元素平均含量均表现为Zn > Cu > As > Pb > Cd;Cu和Pb在4种蚌类中的平均含量表现为扭蚌 > 褶纹冠蚌 > 圆顶珠蚌 > 三角帆蚌,扭蚌各组织中Pb含量是其他3种蚌类的2.62~6.99倍,Zn的各平均含量表现为圆顶珠蚌 > 扭蚌 > 三角帆蚌 > 褶纹冠蚌,As表现为圆顶珠蚌 > 三角帆蚌 > 褶纹冠蚌 > 扭蚌,Cd表现为扭蚌 > 圆顶珠蚌 > 三角帆蚌 > 褶纹冠蚌,Cd在圆顶珠蚌和扭蚌中的含量是三角帆蚌和褶纹冠蚌的2.75~6.08倍.不同种类之间微量元素含量的差异大于同一种类微量元素含量的空间差异.微量元素污染较重的河口区蚌体组织具有较高的微量元素含量,污染较轻的河口中蚌体组织各微量元素含量也相对较低,表明蚌类可作为巢湖水体微量元素污染监测的指示生物.4种蚌类中Pb、Cd、As含量均未超出国家食品安全标准的限定值. 相似文献
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太湖蚌类现存量及空间分布格局 总被引：1，自引：1，他引：0
于2016年10月和2017年10月对太湖全湖8个湖区129个样点的蚌类进行调查,分析蚌类的物种组成、现存量、空间分布及历史变化.共采集到蚌类704个个体,隶属8属14种.全湖蚌类平均生物量和密度分别为4.169±9.337 g/m2和0.164±0.386 ind./m2;各湖区蚌类平均生物量和密度差异较大,东部沿岸区生物量和密度最高,分别为14.975±16.743 g/m2和0.577±0.758 ind./m2;湖心区生物量和密度最低,仅为0.727±1.622 g/m2和0.029±0.071 ind./m2.扭蚌（Arconaia lanceolata）、圆顶珠蚌（Unio douglasiae）和背角无齿蚌（Anodonta woodiana woodiana）为太湖现阶段的优势种.基于蚌类平均密度的聚类分析,8个湖区分为3类.与历史数据相比,太湖蚌类资源呈明显衰退趋势,现状不容乐观,需加强对太湖蚌类的保护和资源的有效管理. 相似文献
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鄱阳湖流域蚌类环境DNA宏条形码引物的筛选验证 总被引：1，自引：0，他引：1
环境DNA技术是一种非侵入、高灵敏、高效率且对环境无破坏性,对生物体无损伤的调查工具.为了筛选适合于蚌类环境DNA生物多样性研究的宏条形码引物,本研究通过对鄱阳湖流域24种常见蚌的基因组DNA进行普通扩增和高通量测序筛选了11对引物(设计了9对通用引物及从相关文献中引用了2对引物),结果显示引物cyt b和16S rRNA具有良好的扩增效果和高辨别度.进一步用环境样本(n=6)并结合传统采样技术对这2对引物进行验证,结果表明:使用引物16S rRNA共注释到蚌科物种6属8种,蚌科物种序列占总序列数的26.69%;而使用引物cyt b共注释到蚌科物种4属6种,蚌科物种序列占总序列数的6.60%.引物16S rRNA更适合用于蚌类环境DNA生物多样性研究的宏条形码引物.在生物多样性监测中环境DNA技术可以作为传统方法的有效补充,且同时使用多对引物,可增加可信度和检测率. 相似文献
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富营养化浅水湖泊生态修复中背角无齿蚌(Anodonta woodiana)对水质改善的影响 总被引：2，自引：0，他引：2
滤水速率的快慢是决定滤食性河蚌对水质改善与否的关键,但受蚌龄大小、食物多少和季节变化的影响.以背角无齿蚌（Anodonta woodiana）为研究对象,设置幼龄蚌组、成年蚌组和无蚌对照组,在惠州西湖生态修复后的清水态和未修复的富营养化水体同时进行中型系统原位实验,测定了各处理组水层中氮、磷、总悬浮物（TSS）浓度和浮游藻类生物量（用叶绿素a（Chl.a）浓度表示）的季节变化,以研究蚌龄、食物和季节变化对背角无齿蚌水质改善的影响.结果表明,与对照组相比,背角无齿蚌提高了清水态水体总磷（TP）和铵态氮浓度,但对总氮（TN）、TSS和浮游藻类Chl.a浓度的影响不显著,表明其不能有效改善清水态水体水质;富营养化水体中,背角无齿蚌虽对水中TN浓度影响不显著,但显著降低了TP浓度、浮游藻类Chl.a浓度和TSS浓度;表明背角无齿蚌可改善富营养化水体水质;且富营养化水体中幼龄蚌的滤水速率显著高于成年蚌;幼龄蚌的滤水速率春季最大（0.132±0.018 L/（g·h））,夏季最小.因此,在富营养化水体修复前期,可通过放养本地滤食性河蚌,如背角无齿蚌,以改善水质,春季放养幼龄蚌更佳,为接下来的修复创造有利条件;而在生态修复后期的清水态水体中,单独的河蚌对水质改善效果不明显.本研究可为水生态系统保护和富营养化水体生态修复提供参考. 相似文献
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水位洪枯变化对菜子湖江湖过渡带鱼类物种和功能多样性的影响 总被引：1，自引：1，他引：0
水位的洪枯变化通过江湖连通影响泛滥平原湖泊鱼类的组成和分布,因而江湖过渡带是反映泛滥平原生态系统鱼类交流和多样性变动的关键区域.尽管如此,针对江湖过渡带鱼类群落随水位洪枯变化的研究十分匮乏.本研究以菜子湖江湖过渡带为例,分别在洪水和枯水期选取包括静水和流水生境的样点对鱼类群落进行系统的调查采样,探讨水位洪枯变化对菜子湖江湖过渡带鱼类物种和功能多样性的影响.共采集到鱼类6目12科37属52种,其中,洪水期和枯水期物种数差异显著,分别采集到鱼类50和42种,而静水生境和流水生境物种数差异不明显,分别采集到鱼类47和48种.与洪水期相比,枯水期山溪河流性鱼类的物种数、重量、尾数和优势度百分比分别减少了7.3%、6.3%、14.4%和12.0%;与静水生境相比,流水生境山溪河流性鱼类的物种数、重量、尾数和优势度百分比分别增加了5.3%、14.6%、18.0%和22.3%.SIMPER分析结果显示,麦穗鱼（Pseudorasbora parva）、蛇鮈（Saurogobio dabryi）、（Hemiculter leucisculus）、鲤（Cyprinus carpio）、鲫（Carassius auratus）、短颌鲚（Coilia brachygnathus）、似鳊（Pseudobrama simoni）、翘嘴鲌（Culter ilishaeformis）、达氏鲌（Culter dabryi）、光唇蛇鮈（Saurogobio gymnocheilus）和无须鱊（Acheilognathus gracilis）是引起水位洪枯变化以及不同生境类型鱼类群落结构差异的主要物种.优势度分析结果表明枯水期和静水生境的优势种鱼类相似,重要值较高的优势种鱼类为鲤、鲫、和似鳊;而洪水期和流水生境的优势种鱼类同样相似,重要值较高的优势种鱼类为麦穗鱼、蛇鮈、光唇蛇鮈和短颌鲚.通过双因素方差分析解析了水位洪枯变化和不同生境类型对鱼类物种和功能多样性的影响.发现洪枯水位变化仅对物种多样性指数中的物种数（Richness）产生显著差异,而对功能多样性的3个指数（功能丰富度指数（FRic）、功能离散指数（FDiv）和功能分散指数（FDis））均有显著影响.洪水期鱼类的Richness、FRic、FDiv和FDis指数均显著高于枯水期.同时,静水生境条件下的FRic指数要显著高于流水生境.本研究发现,与传统的物种多样性相比,基于功能性状的功能多样性对水位的洪枯变动更为敏感,河流周期性洪泛是泛滥平原生态系统中鱼类功能补充的重要方式. 相似文献
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洪泽湖鱼类群落结构及其资源变化 总被引：6，自引：1，他引：5
根据2017-2018年在洪泽湖湖心、成子湖湾、保护区湖湾和淮河入湖口进行的鱼类资源调查,结合历年渔业捕捞统计数据,分析了该水域的鱼类群落结构及资源变化趋势.调查共采获鱼类51种,隶属10目16科41属,其中鲤形目种类最多,占总数的62.7%;群落优势种为鳙（Aristichthys nobilis）、（Hemiculter leucisculus）、鲫（Carassius auratus）、刀鲚（Coilia nasus）等7种,鱼类群落的丰富度指数、多样性指数和均匀度指数处于一般至较丰富水平.不同类型湖区间鱼类种类及优势种组成存在一定差异,其中湖心、淮河入湖口的生物多样性指数整体高于成子湖湾、保护区湖湾.与历史资料相比,洪泽湖鱼类的物种数量下降,鱼类资源组成结构发生较大变化,鱼类个体小型化趋势明显,捕捞强度过大、水位波动和水质污染是洪泽湖渔业资源衰退的主要因素. 相似文献
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基于2006-2016年近10年的长期监测数据,对乌江下游两座高坝的修建对底栖动物群落结构的影响效应进行研究.结果表明：大坝蓄水前后底栖动物群落结构发生显著变化,不同时期的群落结构差异明显.蜉蝣目稚虫对生境的剧烈变动不适应,软体动物田螺科和觹螺科的一些种类对生境的剧烈扰动较为适应,生活史较短的机会主义物种在水库淹没区和坝下河段逐渐定殖下来.建坝以及大坝的运行调度对乌江下游底栖动物的群落结构产生了重大影响,底栖动物群落结构随着时间发生一定程度的演替.在底栖动物所有类群中,软体动物对栖息地的丧失以及流量的剧烈波动具有较高的耐受性,水生昆虫相对较不耐受环境的剧烈变化,而甲壳动物的适应性极强.百分比模式相似性指数（Percent Model Affinity,PMA）的变动趋势可有效地反映大坝对底栖动物群落的影响效应,其均值随离坝距离的增加而呈现逐步增加的趋势,表明大坝调度对水生态造成的负面影响会随着离坝距离的增加而逐步弱化,这与河流不连续体理论（Serial Discontinuity Concept,SDC）的预测趋势基本一致.根据长期监测成果,蜉蝣目扁蜉科、四节蜉科、细裳蜉科以及毛翅目纹石蛾科的种群恢复状况以及PMA指数可作为评估大坝不利影响减缓措施效果的依据. 相似文献
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为了解青藏高原湿地浮游植物在时空不同维度上的分布特征,本文选取西藏四大国际湿地之一的麦地卡湿地作为研究地点,于2019年7月和10月在麦地卡湿地主要水系——麦地藏布及其支流和湖泊,设置了14个样点,采集了2个水情期（丰水期和枯水期）浮游植物的水样共252个.通过活体观察和固定染色方法鉴定浮游藻类物种,使用直接计数法统计浮游藻类的数量.计算麦地卡湿地浮游植物优势种的优势度指数（Y）、更替率（r）、生态位宽度（Bi）、生态位重叠值（Oik）和生态响应速率（R）,运用生态位分化的方法,对麦地卡湿地浮游植物优势种的生态位进行了不同时空维度的研究.结果表明：本研究中鉴定出浮游植物优势种（Y>0.02）共8种,其中克洛脆杆藻（Fragilaria crotomensis）和窗格平板藻（Tabellaria fenestrata）是2个水情期的共有优势种.生态位宽度值差异较大,可分为三大生态位类群,且优势度指数与生态位宽度值呈极显著正相关.总体上浮游植物优势物种的生态位重叠值高,在时间、空间和时空三个维度上Oik>0.6的分别占89.29%、60.71%和28.57%.生态响应速率之和在时间维度上为负数,在空间和时空维度上为正数,说明该湿地浮游植物群落处于发展阶段.冗余分析表明,酸碱度、溶解氧、总氮和浊度是影响麦地卡湿地浮游植物优势种分布的重要因素,浮游植物优势种在这些环境因子上存在明显的生态分化现象. 相似文献
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The Late Mesozoic-Cenozoic volcanism of the Tugnui-Khilok sector in the western Transbaikalia rift area is related to the development of the Tugnui, Tsolgin, Margentui, and Khilok grabens and is characterized by a north-south migration of magmatic centers. In these grabens, the igneous associations are composed of high-alkaline rocks: alkaline and subalkaline basalts, tephrites, phonolites, trachytes, trachyrhyolites, comendites and pantellerites, alkaline syenites and alkaline gabbroids. These associations are known to have formed during 10 stages: Late Jurassic (150–158 Ma), Late Jurassic-Early Cretaceous (139–147 Ma), the beginning of the Early Cretaceous (133–145 Ma), mid-Early Cretaceous (115–134Ma), the end of the Early Cretaceous (104–114 Ma), the end of the Early-beginning of Late Cretaceous (99–102 Ma), Late Cretaceous (72–90 Ma), Eocene (38–48 Ma), Early Oligocene (30–35 Ma), and Late Oligocene (25–27 Ma). The composition of igneous associations was changing in such a way that the relative amount of salic rocks gradually decreased (occasionally even disappeared completely) in the later developmental stages. As well, the content of SiO2 in basic rocks also decreased with increasing Nb and Ta contents, and depletion occurred in the lithophylic elements Rb, K, Ba, Sr, and in light rare-earths relative to heavy ones. The geochemical and isotope-geochemical parameters of basaltoids change through time, probably due to successive changes in the mantle sources of magmatism. During Mesozoic time, the source composition was consistent, with OIB-EM-II sources enriched in radiogenic strontium, but since the second half of the Cretaceous, the isotope composition began to be modified toward moderately depleted sources of the OIB-PREMA type. 相似文献
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报道了米仓山-汉南穹窿一带磷灰石裂变径迹分析结果,以制约该区白垩纪以来的剥蚀-演化历史.露头样品磷灰石裂变径迹年龄分布显示从汉南穹窿南部的核部地区向南至四川盆地北部裂变径迹的年龄逐渐变新,这与米仓山地区逆冲断裂以背驮式扩展的构造样式从汉南穹窿向南经米仓山褶皱-逆冲带发育到四川盆地北缘的构造模式相吻合.热模拟的结果显示米仓山-汉南穹窿经历了两期快速的剥蚀,其分别发生在白垩纪（约90 Ma之前）和15 Ma以来.研究区白垩纪的快速剥蚀反映了秦岭-大别造山带白垩纪的区域性剥蚀事件,这可能是对临区诸多构造事件（如西伯利亚-蒙古-中朝板块的碰撞,拉萨-羌塘-思茅-印支块体的碰撞,太平洋板块向欧亚板块的俯冲及其相关的岩浆活动）远场效应的响应;约15 Ma以来的快速剥蚀是对青藏高原隆升向东北方向传递的响应. 相似文献
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通过对河南南阳西峡盆地含恐龙蛋化石的阳域-丹水剖面的岩石磁学与古地磁学研究表明,该陆相沉积地层的特征剩磁载体以赤铁矿与磁铁矿为主,特征剩磁通过了倒转检验,表明其很可能为岩石形成时期获得的原生剩磁.结合该剖面古生物资料,磁性地层学结果表明,剖面上部2973~3023 m处年代为83~79 Ma;该剖面蛋化石所在最高层位年龄不晚于83 Ma,暗示该地区大型爬行动物的绝灭可能与西峡地区当时的气候、环境变化有关.此外,自晚白垩世以来,该剖面所处位置相对华北和华南地块发生了约18°的顺时针旋转,可能由该地区的局部构造活动引起. 相似文献
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Global correlation for strontium isotope curve in the Late Cretaceous of Tibet and dating marine sediments 总被引：7，自引：0，他引：7
HUANG Sijing SHI He SHEN Licheng ZHANG Meng & WU Wenhui State Key Laboratory of Oil/Gas Reservoir Geology Exploitation College of Geoscience Chengdu University of Technology Chengdu China 《中国科学D辑(英文版)》2005,48(2):199-209
87Sr/86Sr ratios of marine carbonate samples collected from a sedimentary section of the Late Cretaceous in the south of Tibet were measured. Based on the absence of cathodo-luminescence and a very low Mn/Sr ratio (average 0.06) of the samples, it is thought that they contain information on the original seawater strontium isotope composition. The strontium isotope evolution curve of the Late Cretaceous in Tibet we established here, is consistent with other coeval curves from Europe, North America and Antarctica, supports the notion that the strontium isotope composition of seawater is governed by global events, which provides a new approach for the inter-continental and inter-basinal correlations of Late Cretaceous in the area and is a complementarity for biostratigraphy. In addition, we attempt to determine the age of the boundaries for Campanian/Santonian and Maastrichtian/Campanian by 87Sr/86Sr ratios for Gamba section in southern Tibet. The two boundaries are located in the thickness of 217 m (83.5 M 相似文献
15.
Modelling of low-temperature exhumation rate in Dabie Mountain based on (U-Th)/He and fission-track thermochronological data 总被引：1，自引：0，他引：1
While the high-temperature exhumation process in the Dabie Mountain has been well documented, the low-temperature exhumation of this area since Cretaceous, especially since Late Cretaceous, is relatively less studied. Low-temperature thermochronology provides one of the important approaches to solve this problem. Based on the data of fission track and (U-Th)/He analysis of apaptites and zircons from the granitoid and metamorphic rocks in the Dabie Mountain, this paper applies Mancktelow’s and Braun’s methods to estimating the exhumation rates and to drawing the regional differential exhumation pattern since Cretaceous, especially since Late Cretaceous by taking into consideration factors such as heat transport, heat advection, topography and heat production, which could influence geothermal field in the shallow crust. Since Cretaceous, the exhumation rate (0.08-0.10 km/Ma) in the region around Tiantangzhai and in the south of Tanlu fault zone is larger than the rate (0.04-0.07 km/Ma) in other areas of the Dabie Mountain. The regional differential exhumation pattern might be related to the push-up effect caused by differential strike-slip movement along NNE-trending faults. 相似文献
16.
为进一步确定拉萨地块白垩纪-古近纪的古地理位置,我们对青藏高原拉萨地块措勤地区林子宗火山岩18个采点进行了古地磁研究.结果表明高温(高场)特征剩磁分量主要为亚铁磁性的磁铁矿所携带,特征剩磁分量在95%置信水平下通过了褶皱检验. 倾斜校正后采点平均的特征剩磁方向为D/I=16.2°/17.7°, α95=5.6°,对应古地磁极位置为63.1°N,224.6°E,A95=5.1°. 另一方面,Ar-Ar年代学结果表明采样剖面的林子宗火山岩形成年龄为~99-93 Ma, 与拉萨地块林周盆地的林子宗群火山岩的形成年龄存在较大差异.由此我们得到晚白垩世拉萨地块中部措勤地区的古纬度为8.5°±6.9°N,与林周盆地古近纪林子宗群典中组和年波组所揭示出的古纬度相当,进一步表明亚洲大陆最南缘的拉萨地块在晚白垩世-古近世期间位于北半球~10°N的低纬度地区.结合最新的特提斯海相地层古地磁结果,晚白垩世-古近世拉萨地块的古地理位置限定了印度与欧亚大陆的初始碰撞时间不晚于60.5 Ma;~93 Ma以来,拉萨地块和单一刚性欧亚大陆之间存在~1900 km的构造缩短. 相似文献
17.
Koji Wakita Kazuhiro Miyazaki Iskandar Zulkarnain Jan Sopaheluwakan & Prihardjo Sanyoto 《Island Arc》1998,7(1-2):202-222
Cretaceous subduction complexes surround the southeastern margin of Sundaland in Indonesia. They are widely exposed in several localities, such as Bantimala (South Sulawesi), Karangsambung (Central Java) and Meratus (South Kalimantan).
The Meratus Complex of South Kalimantan consists mainly of mélange, chert, siliceous shale, limestone, basalt, ultramafic rocks and schists. The complex is uncomformably covered with Late Cretaceous sedimentary-volcanic formations, such as the Pitap and Haruyan Formations.
Well-preserved radiolarians were extracted from 14 samples of siliceous sedimentary rocks, and K–Ar age dating was performed on muscovite from 6 samples of schist of the Meratus Complex. The radiolarian assemblage from the chert of the complex is assigned to the early Middle Jurassic to early Late Cretaceous. The K–Ar age data from schist range from 110 Ma to 180 Ma. Three samples from the Pitap Formation, which unconformably covers the Meratus Complex, yield Cretaceous radiolarians of Cenomanian or older.
These chronological data as well as field observation and petrology yield the following constraints on the tectonic setting of the Meratus Complex.
(1) The mélange of the Meratus Complex was caused by the subduction of an oceanic plate covered by radiolarian chert ranging in age from early Middle Jurassic to late Early Cretaceous.
(2) The Haruyan Schist of 110–119 Ma was affected by metamorphism of a high pressure–low temperature type caused by oceanic plate subduction. Some of the protoliths were high alluminous continental cover or margin sediments. Intermediate pressure type metamorphic rocks of 165 and 180 Ma were discovered for the first time along the northern margin of the Haruyan Schist.
(3) The Haruyan Formation, a product of submarine volcanism in an immature island arc setting, is locally contemporaneous with the formation of the mélange of the Meratus Complex. 相似文献
The Meratus Complex of South Kalimantan consists mainly of mélange, chert, siliceous shale, limestone, basalt, ultramafic rocks and schists. The complex is uncomformably covered with Late Cretaceous sedimentary-volcanic formations, such as the Pitap and Haruyan Formations.
Well-preserved radiolarians were extracted from 14 samples of siliceous sedimentary rocks, and K–Ar age dating was performed on muscovite from 6 samples of schist of the Meratus Complex. The radiolarian assemblage from the chert of the complex is assigned to the early Middle Jurassic to early Late Cretaceous. The K–Ar age data from schist range from 110 Ma to 180 Ma. Three samples from the Pitap Formation, which unconformably covers the Meratus Complex, yield Cretaceous radiolarians of Cenomanian or older.
These chronological data as well as field observation and petrology yield the following constraints on the tectonic setting of the Meratus Complex.
(1) The mélange of the Meratus Complex was caused by the subduction of an oceanic plate covered by radiolarian chert ranging in age from early Middle Jurassic to late Early Cretaceous.
(2) The Haruyan Schist of 110–119 Ma was affected by metamorphism of a high pressure–low temperature type caused by oceanic plate subduction. Some of the protoliths were high alluminous continental cover or margin sediments. Intermediate pressure type metamorphic rocks of 165 and 180 Ma were discovered for the first time along the northern margin of the Haruyan Schist.
(3) The Haruyan Formation, a product of submarine volcanism in an immature island arc setting, is locally contemporaneous with the formation of the mélange of the Meratus Complex. 相似文献
18.
The ages of polarity chrons in previous M-sequence magnetic polarity time scales were interpolated using basal sediment ages in suitably drilled DSDP holes. This method is subject to several sources of error, including often large paleontological age ranges. Magnetostratigraphic results have now tied the Early Cretaceous and Late Jurassic paleontological stage boundaries to the M-sequence of magnetic polarity. The numeric ages of most of these boundaries are inadequately known and some have been determined largely by intuition. An examination of relevant data suggests that 114 Ma, 136 Ma and 146 Ma are optimum estimates for the ages of the Aptian/Barremian, Cretaceous/Jurassic and Kimmeridgian/Oxfordian stage boundaries, respectively. Each of these boundaries has a good correlation to the M-sequence of magnetic reversals. The magnetostratigraphic tie-level ages are linearly related to the spreading distance and have been used to calculate a new magnetic polarity time scale for the Early Cretaceous and Late Jurassic. All stage boundaries in this time interval were correlated by magnetic stratigraphy to the proposed new time scale which was then used to estimate their numeric ages. These are, with the approximate relative errors of placement within the M-sequence:The absolute errors of these interpolated stage boundary ages depend on the accuracy of the tie-level ages. 相似文献
19.
Late Cretaceous uplift history of the Cretaceous volcanic arc in Southwest Japan: Provenance analysis of the Yuasa–Aridagawa basin based on U–Pb zircon ages 
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下载免费PDF全文 The Ryoke Metamorphic complex has undergone low‐P/T metamorphism and was intruded by granitic magmas around 100 Ma. Subsequently, the belt was uplifted and exposed by the time deposition of the Izumi Group began. The tectonic history of uplift, such as the timing and processes, are poorly known despite being important for understanding the spatiotemporal evolution of the Ryoke Metamorphic Belt. U–Pb zircon ages from sedimentary rocks in the forearc and backarc basins are useful for constraining uplift and magmatism in the provenance. U–Pb dating of detrital zircons from 12 samples (four sandstones and eight granitic clasts) in the Yuasa–Aridagawa basin, a Cretaceous forearc basin in the Chichibu Belt of Southwest Japan, gave mostly ages of 60–110 Ma. Granitic clasts contained in conglomerate suggest that granitic intrusions predate the formation of Coniacian and Maastrichtian conglomerate. Emplacement ages of granitic bodies originated from granitic clasts in Coniacian conglomerate are (110.2 ±1.3) Ma, (106.1 ±1.8) Ma, (101.8+5.8–3.8) Ma, and (95.3 ±1.4) Ma; for granitic clasts in Maastrichtian conglomerate, (89.6 ±1.8) Ma, (87.3+2.4–1.8) Ma, (85.7 ±1.2) Ma, and (82.7 ±1.2) Ma. The results suggest that detrital zircons in the sandstones were mainly derived from volcanic eruptions contemporaneous with depositional age, and plutonic rocks of the Ryoke Metamorphic Belt. Zircon ages of the granitic clast samples also indicate that uplift in the provenance began after Albian and occurred at least during the Coniacian to Maastrichtian. Our results, together with the difference of provenance between backarc and forearc basins suggest that the southern marginal zone of the Ryoke Metamorphic Belt was uplifted and supplied a large amount of clastic materials to the forearc basins during the Late Cretaceous. 相似文献
20.
Thrust and nappe tectonics have affected the eastern Jiaodong Peninsula, the easternmost terminal of the Sulu Ultra-high Pressure Metamorphic Belt. Four nappes have been mapped, named respectively the Shidao, Rongcheng, Mishan and Mouping nappes. The methods used included multi-scale struc- tural analysis and structural chronology analysis. These nappes define four deep level slip-thrust shear zones that were mainly active in the Mesozoic. The amount of ductile deformation decreases from the Shidao to Rongcheng to Mouping to Mishan shear zones, and shows an inverse relationship with temperature. 40Ar/39Ar chronological analysis and the chronological results of former workers reveal four movement steps defined by the development of thrusts and nappes in the late Triassic (210-180 Ma), extensional movement from the Jurassic to early Cretaceous (180-130 Ma), slip-thrust movement in the Early Cretaceous (130-120 Ma), and extensional movement since the Late Cretaceous (120 Ma). The order of boundary shear zone motion in the period of slip-thrust movement during the Early Cre- taceous (130-120 Ma) was along the Shidao, Rongcheng, Mouping and finally the Mishan shear zone. This resulted in clockwise rotation of the nappes relative to block west to the Tan-Lu Faults. Because of the similar evolutionary history of the Tan-Lu Faults and the thrust and nappe structure in the eastern Jiaodong Peninsula, slip dislocation along the Tan-Lu Faults might have been absorbed by thrust and nappe tectonics in the Jiaodong area in the Mesozoic era, resulting in much less dislocation on the Tan-Lu faults in North Eastern China than that in south along the Jiaodong Peninsula. 相似文献