共查询到17条相似文献,搜索用时 187 毫秒
1.
赣东北地区重要火成岩的40Ar/39Ar年龄 总被引:11,自引:0,他引:11
在赣东北蛇绿混杂岩带发现含晚古生代放射虫硅夺,测定了该带内的和带外几个关键地点的火山岩和辉长岩的^40Ar/^30Ar同位素地南年龄,获得了以下结果:火山岩的坪年龄为434.9-486.7Ma,辉长岩的坪年龄为232.5-266.3Ma,因此可以肯定赣东北地区有早生代晚期的火山活动,证实了上述火成冉不是中、新元古代的产物,它们中的一部分与晚古生代硅质岩都是蛇绿岩套的成员,属该区晚古生代洋壳的组成部 相似文献
2.
赣东北蛇绿混杂岩带中多处发现含晚古生代放射虫硅质岩 总被引:21,自引:3,他引:21
作者继1993年10月在赣东北蛇绿混杂岩带中首次发现晚古生代深水相放射虫硅质岩之后,经过1995年和1996年两次野外工作,又在该混杂岩带中及其两侧多处发现了含晚古生代放射虫的硅质岩及其深水相的沉积组合。从而为华南晚古生代或古生代—中生代洋盆的厘定,以及华南大地构造格局的再认识,提供了有力的新论据 相似文献
3.
赣东北晚古生代放射虫化石综述 总被引:12,自引:4,他引:8
首次在赣东北蛇绿混杂岩带分布的弋阳县及德兴市境内被前人定为中元古界双桥山群与下震旦统志棠组中发现了一批晚古生代放射虫化石。对樟树墩和登山两处与含放射虫硅质岩共生的岩石组合、硅质岩的岩石学、地球化学及放射虫化石属种特点进行了综合分析 ,表明它们应是一套洋盆深水环境的沉积。这一新发现不仅为研究赣东北蛇绿混杂岩带的性质、形成时代 ,也为重新厘定“板溪群”的构造属性及华南大地构造格局问题提供了科学依据 相似文献
4.
共轭伸展褶劈理夹角的定量解析 总被引:16,自引:0,他引:16
90 年代初以来,中国地质学者先后在浙、皖、赣、湘的“板溪群”及震旦系中发现了古生代的生物化石。因此,再次将“板溪群”是否是前震旦纪的一个变质地层单位、江南古陆是否存在以及华南大地构造格局是否需要重新厘定等问题提了出来。1993 年笔者于赣东北蛇绿混杂岩带内的“双桥山群”岩块中,首次发现了含晚古生代的放射虫硅质岩。1996 年又在该混杂岩带多处的“双桥山群”岩块和“下震旦统志棠组”中找到了含晚古生代的放射虫硅质岩,还首次在“登山群拔竹坑组”中发现了早古生代的几丁虫化石。经数年野外多次观察和对室内化石鉴定、岩石地球化学测试结果以及岩石学特征的综合分析表明,所发现的含晚古生代放射虫硅质岩及其岩石组合是一套洋盆深水相沉积;登山群拔竹坑组,是早古生代的一套浅水陆棚 深水陆棚 半深海相沉积。结合同行学者在邻区“板溪群”研究方面取得的新成果,笔者认为:“板溪群”不是前震旦纪的一个变质地层单位,而是一个复杂的构造岩带,江南古陆是不存在的,华南从早古生代到中生代早期还经历了一次洋盆演化过程,现在的构造格局是印支运动奠定的 相似文献
5.
赣东北构造带中的“放射虫硅质岩”主要分布于樟树墩—茅桥一带的赣东北蛇绿杂岩带之张村群中,与周边岩石地层呈断层接触关系,矿物成分和化学成分一致显示为泥质硅质岩,岩石遭受低级绿片岩相区域变质作用的改造,与泥质千枚岩、变质火山岩、蛇绿岩密切共生,含有“可疑的”晚古生代放射虫化石;茅口(孤峰)组硅质岩遍布于赣东北—皖南广大地区,整合于乐平组煤系地层之下、小江边组灰岩之上,具稳定的层位压盖关系,矿物成分和化学成分反映为纯硅质岩,岩石无变质重结晶现象,与碳质泥岩、灰岩互层,含大量的、珊瑚及腕足类化石,地层时代为二叠纪。因此,两者应分属不同的地层单位。 相似文献
6.
赣东北蛇绿混杂岩带和变质岩系中"放射虫硅质岩"的再研究 总被引:3,自引:0,他引:3
赣东北蛇绿混杂岩和变质岩中的硅质岩时代问题已成为研究华南区域构造和古地理的焦点之一,长期以来被地质学界认为属于江南古陆元古代“板溪群”的范畴。近年来,关于该构造岩系中存在晚古生代放射虫动物群的报道,导致一些学者怀疑该地区传统的构造古地理格局需要重新解释。对此,许多地学工作者提出异议。为了验证上述放射虫动物群的报道的准确性,从古生物学、构造地质学和区域地质调查等多领域进行了野外调查和样品的多次重复系统采集;同时,对已发表的资料进行了再分析。研究显示,赣东北蛇绿混杂岩和变质岩中的硅质岩和扳岩的岩石薄片和微体古生物分析样品中未产出放射虫化石,但是在部分硅质岩和板岩样品中却发现了中-新元古代的疑源类化石。有关硅质岩的主量元素、稀上元素中Ce异常值、(La/Ce)x比值和微量元素等地球化学特征显示其沉积作用与陆源物质有关,沉积环境接近大陆边缘、远离深海远洋环境。 相似文献
7.
8.
9.
东昆中断裂带中存在多期蛇绿岩组合,分别代表中元古代、新元古代-早古生代和晚古生代3次裂解成洋.断裂带中主要的3类各不相同的韧性剪切构造变形组合分别可与新元古代早期、加里东期末和晚海西期的3次碰撞缝合事件相匹配."东昆中蛇绿混杂岩带"不能仅限于东昆中断裂带,而应包括原东昆中蛇绿混杂岩带和整个东昆南单元,是一多旋回俯冲碰撞的复合蛇绿构造混杂岩带.东昆中断裂带作为统一的纵贯东昆仑造山带的线性构造变形带应形成于印支期陆内构造变形阶段,是碰撞后的陆内构造变形产物. 相似文献
10.
11.
YANG Qun WANG Yujing YIN Leiming SHU Liangshu LOU Fasheng WANG Bo Nanjing Institute of Geology Palaeontology Chinese Academy of Sciences Nanjing Jiangsu Department of Earth Sciences Nanjing University Nanjing Jiangsu Geological Survey of Jiangxi Province Nanchang Jiangxi 《《地质学报》英文版》2005,79(3):308-312
The age assignment of cherts from ophiolitic/metamorphic complexes in northeastern Jiangxi is widely regarded as one of the crucial issues in the tectonic interpretation of South China. The ophiolitic and metamorphic complexes in northeastern Jiangxi have been traditionally regarded as part of the Proterozoic “Banxi (=Penhsi) Group” of the Jiangnan Uplift. However, recent reports of Late Paleozoic radiolarians from the rock complexes have caused some researchers to question the traditional interpretation of the tectonic and paleogeographic framework in the region; but other workers are suspicious about these findings. In order to test the validity of the putative radiolarians, we, an interdisciplinary study group including micropaleontologists, tectonic specialists and regional geologists, conducted field investigations and multiple re-samplings of the localities where the reported fossils were collected. Our comprehensive study shows that the chert of the ophiolitic complex and the associated low-grade metamorphic slate yield Mesoproterozoic and Neoproterozoic acritarchs, confirming the traditional view of their age assignment (Proterozoic); on the other hand, no recognizable radiolarian fossils have been discovered therein, thus raising questions about the recently published result of Paleozoic radiolarian findings. Probable causes for the putative radiolarian findings are thus discussed herein. Geochemical characteristics indicate that the chert sedimentation most probably occurred under a continental margin setting. 相似文献
12.
对赣东北蛇绿混杂岩带相关地层的时代、沉积相和接触关系等方面认识的重大分歧,导致对华南地质演化史的不同解释。混杂岩的深成岩块体的同位素年龄数据大都在900~1000Ma之间,伴生的火山-沉积岩系(登山群)中却有古生代微体化石发现,但化石的确切年代尚难确定。古地理分析表明,赣东北地区早古生代并不存在“江南古陆”,却有深水的江南海盆。华南晚奥陶世火山碎屑沉积广泛分布,但来源不明,赣东北有可能为当时喷发中心,形成于火山岛弧环境的登山群正好与之匹配。因而,其时代可能为晚奥陶世。志留纪早期江南海盆封闭,扬子地块和华夏地块之间形成加里东褶皱带,赣东北蛇绿岩带为加里东褶皱带和华夏地块之间的接合带。这里扬子地块和华夏地块的距离最近,挤压程度高,抬升幅度大,剥蚀时间长,早古生代沉积不易保存,登山群可能是残留部分。 相似文献
13.
Paleozoic Accretion-Collision Events and Kinematics of Ductile Deformation in the Eastern Part of the Southern-Central Tianshan Belt, China 总被引:3,自引:0,他引:3
The Tianshan range could have been built by both late Early Paleozoic accretion and Late Paleozoic collision events. The late Early Paleozoic Aqqikkudug-Weiya suture is marked by Ordovician ophiolitic melange and a Silurian flysch sequence, high-pressure metamorphic relics, and mylonitized rocks. The Central Tianshan belt could principally be an Ordovician volcanic arc; whereas the South Tianshan belt, a back-arc basin. Macro- and microstructures, along with unconformities, provide some kinematic and chronological constraints on 2-phase ductile deformation. The earlier ductile deformation occurring at ca. 400 Ma was marked by north-verging ductile shearing, yielding granulite-bearing ophiolitic melange blocks and garnet-pyroxene-facies ductile deformation, and the later deformation, a dextral strike-slip tectonic process, occurred during the Late Carboniferous-Early Permian. Early Carboniferous molasses were deposited unconformably on pre-Carboniferous metamorphic and ductilely sheared rocks, implying t 相似文献
14.
大兴安岭牙克石地区新元古代与晚古生代两类岩石组合的构造属性及其地质意义 总被引:2,自引:2,他引:0
在内蒙牙克石地区发育两种不同构造属性的岩石组合:一类为乌奴耳-头道桥蛇绿混杂岩,另一类为晚古生代弧属性侵入岩。乌奴耳-头道桥蛇绿混杂岩由辉长岩、辉长辉绿岩、辉绿玢岩(岩墙?)、变玄武岩和放射虫硅质岩组成;地球化学特征显示基性岩类属于拉斑玄武岩系列,具有相似的稀土和原始地幔标准化配分模式,与N-MORB的特征类似,不具有Nb-Ta负异常,Nb/Nb~*值平均1;构造环境判别图显示该蛇绿混杂岩可能形成于扩张脊。晚古生代弧属性侵入岩出露于白井山、乌尔其汗,由中基性单元(辉长岩、辉长闪长岩和石英闪长岩)和酸性单元(花岗闪长岩和二长花岗岩)组成;地球化学特征显示中基性单元和酸性单元属于钙碱性岩系列,富集LREEs和LILEs,具有Nb-Ta负异常,高Sr、Sr/Y值,低HREEs和Y,Eu异常不明显;酸性单元显示埃达克质岩的地球化学特征。乌奴耳-头道桥蛇绿混杂岩可能形成于新元古代,与头道桥蓝片岩、吉峰蛇绿混杂岩、新林蛇绿岩构成一条重要的缝合带,暗示本区古洋盆的存在。晚古生代弧属性侵入岩中,辉长岩的结晶年龄为326±1.9Ma,花岗闪长岩的结晶年龄为323.7±1.9Ma;微量元素的组成特征显示,中基性单元和酸性单元的形成与早石炭世洋壳板片的俯冲作用有关,暗示兴安地块和松嫩地块之间洋盆的萎缩。 相似文献
15.
16.
Minella Shallo 《地学学报》1990,2(5):476-483
Ophiolitic melange and flyschoidal sediments of the Tithonian-Lower Cretaceous age are widespread in the Eastern Albanides. They lie transgressively or normally on top of the ophiolitic sequence through radiolarian cherts of the Kimmeridgian-Tithonian age, or on top of the carbonate sequence of the periphery of the ophiolites through Middle Liassic-Dogger-Malm pelagic limestones with manganese nodules and radiolarian cherts. They are overlain by conglomerates or neritic limestones of the Lower Cretaceous age. Ophiolitic melange consists of ophiolitic conglobreccias, often of homogenous composition: serpentinite melange with a ‘sedimentary’serpentinite matrix, or basaltic ‘sedimentary’tuffagglomerate. Less commonly they have a heterogeneous composition with small amounts of fine-grained matrix and marls with calpionellids. In other examples, the ophiolitic melange contains heterogeneous exotic blocks including all the members of the ophiolite suite: serpentinite, ophicalcite, gabbro, plagiogranite, diabase, basalts, dacites, amphibolite, sulphide and chromite ores as well as blocks of radiolarites, limestones etc. in the argillic matrix. They are overlain by conglomerate-sandstone-marly flyschoidal deposits with abundant ophiolitic detritus and calpionellids. These deposits are linked with Tithonian-Lower Cretaceous tectogenesis, which led to the fragmentary uplift of ophiolites and partly of their sedimentary periphery, and to the formation of the faulted topography. The presence of the ophiolitic melange and flyschoidal sediments both over the ophiolites and the associated sedimentary rocks of their periphery indicate that the latter were not the basement of an ophiolite nappe during the Late Jurassic time. 相似文献