Indosinian Tectonic Setting of the Southern Yidun Arc： Constraints from SHRIMP Zircon Chronology and Geochemistry of Dioritic Porphyries and Granites   总被引：2，自引：0，他引：2  

LIU Shuwen  WANG Zongqi  YAN Quanren  LI Qiugen  ZHANG Dehui  WANG Jianguo  YANG Bin  GU Libing  ZHAO Fengshan The Key Laboratory of Orogenic Belts  Crustal Evolution  Ministry of Education  School of Earth  Space Sciences  Peking University  Beijing 《《地质学报》英文版》2006,80(3):387-399

A mass of granitoid and dioritic intrusions are distributed in the southern Yidun Arc, among which the representative Indosinian intrusions include the Dongco and Maxionggou granitoid intrusions in Daocheng County and hypabyssal intrusions intruding into arc volcanic rocks near the Xiangcheng town. The Dongco and Maxionggou granitoid intrusions consist mainly of porphyraceous monzogranites, megacryst monzogranites and aplite granites. The Xiangcheng hypabyssal intrusions are composed dominantly of dioritic porphyries. SHRIMP zircon ages of 224±3 Ma and 222±3 Ma have been obtained for the Dongco granitoid intrusion and the Xiangcheng dioritic porphyries, respectively. The Xiongcheng dioritic porphyries show a cak-alkaline geochemical feature, and are characterized by higher Sr/Y ratios, depletive Nb, Ta, P and Ti, enriched LILEs, and lower εNd (t) (= -3.27), suggesting that they might be derived from mantle source magmas that were obviously contaminated by continent crustal materials. However, the Dongco and Maxionggou granitoids belong to high-potassium calc alkaline series with a per-metaluminous feature, and are characterized by higher CaO/(∑FeO+MgO) and Al2O3/(∑FeO+ MgO) ratios, lower (La/Yb)n and Sr/Y ratios, depletive Nb, Ta, Sr, P and Ti, enriched LILEs, and very low εNd (t) (= -8.10), indicating that the granitoids might be derived from partial melting of continental crust materials mainly of graywacke. Petrogenesis of Dongco and Maxionggou granitoids implies that there was an oceanic crust between the Zongza continental block (ZCB) and western margin of the Yangtze Craton (WMYZC). And the oceanic crust slab subducted westward during the Indosinian Epoch, producing an Andes-type continent marginal arc and a back arc basin at the WMSCC. Then the oceanic basin closed and a sinistrally lateral collision occurred at ca. 224 Ma-222 Ma between the ZCB and the WMYZC, causing partial melting of sediments in the back-arc basin to generate granitoid magmas of the Dongco and Maxionggou intrusions.  相似文献   

Waterpoint management system in central district with ArcView GIS     

FU Guo-bin 《地理学报(英文版)》1999,(1)

1StudyAreaCentralDistrictisthelargestdialectinBotSWana.Itcoversanareaof146531kin',whichisroughlyonequarterofBotswana.ThedistrictborderstheRepublicofSouthcocainthesouthandeast,andZimbabweinthenorth-east.ItalsobordersNorthEastDistricttotheeast.ThenorthernboundalofthedistrictissharedfaiththeChobeDistrictandNgdrilandDistrict.Inthet"estandthesouth-u'estaledistrictbordersNgndland.Ghanzi.KwenengandKgahengDistrictS.ThedistlictisdiyridedintofiveadlnjnistrahvesubdistrictsfBobirwa.Serowemalapy…  相似文献   

A 100 m.y. record of volcanic arc evolution in Nicaragua     

Kennet E. Flores  Esteban Gazel 《Island Arc》2020,29(1)

The processes that result in arc magmas are critical to understanding element recycling in subduction zones, yet little is known about how these systems evolve with time. Nicaragua provides an opportunity to reconstruct the history of a volcanic arc since the Cretaceous. Here we present the stratigraphy of the Cretaceous–Eocene volcanic units in Nicaragua and their relationship to the different tectonic units where the arc developed. We discovered an evolution from an arc‐dominated by calc‐alkaline compositions in the Cretaceous–Eocene, to transitional compositions in the Oligocene–Miocene, to finally tholeiitic magmas common in the modern volcanic front. Our petrographic studies confirm that in the Cretaceous–Eocene the olivine + clinopyroxene cotectic was followed by clinopyroxene + plagioclase ± amphibole. Given the abundance of amphibole and the lack of this mineral in the modern volcanic front, the Cretaceous–Eocene Arc melts were likely more water‐rich than modern Nicaragua, suppressing the crystallization of plagioclase after olivine. We also found temporal changes in element ratios that are sensitive to variations in sediment input. The Cretaceous–Eocene Arc is characterized by a lower Ba/Th compared to the Oligocene–Miocene and modern volcanic front samples, suggesting that the sediment input was lower in Ba, possibly analogous to old deep siliceous sediment subducting in the western Pacific. Both U/Th and U/La are higher in the modern volcanics, reflecting higher U/Th in the subducting sediments following the 'Carbonate Crash'. Finally, we found that the orientation of the arc axis also changed, from northeast‐southwest in the Cretaceous–Eocene to northwest‐southeast after the Oligocene. This change probably records variations in the location of the subduction zone as this region shaped into its current geographic configuration.  相似文献   

Estimating the thickness of a faulted mechanical layer based on fault spacing: An example from Miyako‐jima Island,southern Ryukyu Arc,Japan     

Sumire Maeda  Makoto Otsubo  Daisuke Asahina  Yuki Furuno 《Island Arc》2020,29(1)

The thickness of the mechanical layer that hosts a group of faults can be estimated from the spacing of saturated faults (i.e. the constant spacing between faults when the fault system is fully developed and has attained its final fault density). We measured fault spacing for a group of saturated active normal faults on Miyako‐jima Island (southern Ryukyu Arc, Japan) and estimated the thickness of the faulted mechanical layer. The measured fault spacing is 1.30 ±0.14 km, and the thickness of the mechanical layer is < 3 km, which is the upper limit of the seismogenic zone. This faulted mechanical layer corresponds to a sedimentary layer in which earthquakes cannot occur. Results indicate that the shallow (< 3 km depth) normal faults on Miyako‐jima Island do not have the potential to cause medium‐size earthquakes as individual faults. The origin of the shallow normal faults might be related to the presence of a larger‐scale, deeper fault. The results indicate that fault spacing provides important information on the potential magnitude of earthquakes associated with active faults.  相似文献   

山东黄县弧形断裂带断层泥铁元素化学种分布特征及其地震地质意义     

王华林  郑国东  王纪强  付海清  马向贤  胡超 《中国地震》2017,33(2):248-259

本文利用德国Wissel公司生产的新型穆斯堡尔谱仪(Bench-MB500)对山东龙口常庄子村北黄县弧形断裂断层剖面上的多种断层泥样品进行了穆斯堡尔谱测试分析,讨论了该断层剖面上铁元素地球化学分布特征及其地震地质意义。结果显示,该断裂中央部分比较年轻的断层泥相对富集para-Fe~(2+),而两侧较老的断层泥基本由para-Fe~(3+)组成;剖面断层泥样品中铁元素的地球化学特征与断层的活动演化历史密切相关,显示了断裂带内存在复杂的水岩相互作用。  相似文献   

东印度洋近20 ka以来的生物硅记录及其古生产力意义     

徐勇航  王亮  赖志坤  徐晓辉  王凤  刘升发  石学法  TROA Rainer Arief  ZURAIDA Rin  TRIARSO Eko  HENDRIZAN Marfasran 《海洋学报(英文版)》2019,38(1):78-84

通过对东印度洋钻孔CJ01-185的生物硅来探讨东印度洋古生产力的变化和古气候演化的响应。CJ01-185钻孔的生物硅含量在末次冰期最低,为0.86%;而到了全新世晚期生物硅含量达到1.89%。全新世晚期生物硅的堆积速率明显大于末次冰期。随着全新世海平面的快速上升,巽他海峡贯通,来自爪哇海的陆源物质输入到东印度洋,导致全新世的生物硅含量和生物硅的堆积速率增加。研究表明：巽他海峡贯通前,研究区的古生产力主要受东南季风变化和上升流的活动影响;而巽他海峡贯通后,古生产力很明显受到陆源物质输入的控制,东南季风变化和上升流的影响较弱。  相似文献   

Early to mid-Paleozoic magmatic and sedimentary records in the Bainaimiao Arc: An advancing subduction-induced terrane accretion along the northern margin of the North China Craton     

《Gondwana Research》2020

The early to mid-Paleozoic subduction-induced terrane accretion along the northern margin of the North China Craton is not well understood. To address this issue, we investigate the magmatic and sedimentary records, including both new and previously published geochemical, Sr–Nd isotopic, and zircon U–Pb–Hf isotopic data from the Bainaimiao Arc. The collected gabbro–diorites and granitoids have been dated to 431–453 Ma. The gabbro–diorites have high Mg/(Mg + Fe) molar ratios (44.41–73.39); depleted Nb, Ta and Ti; and negative ε_Nd(t) values (-9.43–-6.80). They were derived from a mantle wedge metasomatized by subduction-derived fluids with crustal contamination. The granitoids are characterized by high silica, low to high K, low Fe and Mg contents, strong fractionation of rare earth elements, and positive ε_Hf(t) values (+1.42–+8.19). They were derived from crustal melts with juvenile additions. The clastic rocks from the Baoerhantu Group and Xibiehe Formation are dominated by early Paleozoic zircons, whereas those from the Bainaimiao Group are dominated by early Paleozoic and Precambrian zircons. Detrital zircon geochronology and field geology confirm their deposition in early to mid-Paleozoic. The U–Pb ages and petrographic and geochemical analyses indicate that the clastic rocks were deposited in arc-related basins with felsic sources from the Bainaimiao Arc. The xenocrystic and detrital zircons in the magmatic and clastic rocks, respectively, imply a Precambrian basement for the Bainaimiao Arc. The early Paleozoic magmatic rocks of the Bainaimiao Arc show secular changes with decreasing age: increasing K₂O contents and Sr/Y ratios and decreasing Fe₂O₃^T + MgO contents and ε_Hf(t) and ε_Nd(t) values. This is likely in response to advancing subduction and related crustal thickening. Accordingly, the following tectono-paleogeographic model was proposed for the Bainaimiao Arc: (a) ∼500–455 Ma initial subduction and juvenile arc development, (b) ∼455–415 Ma continuous subduction with mature arc development, and (c) ∼415–400 Ma accretion to the North China Craton.  相似文献   

Constructing the latest Neoproterozoic to Early Paleozoic multiple crust-mantle interactions in western Bainaimiao arc terrane,southeastern Central Asian Orogenic Belt     

《地学前缘(英文版)》2020,11(5):1727-1742

Identifying the crust-mantle interactions in association with the evolution of the Precambrian microcontinents provides critical constraints on the accretionary evolution in the Central Asian Orogenic Belt(CAOB).The Bainaimiao arc terrane(BAT) is one of the most important Precambrian microcontinents in southeastern CAOB,however,few studies have paid attention to the types and the evolving processes of the crust-mantle interactions that occurred before its final accretion onto the northern North China Craton.This study presents an integrated study of geochronology,zircon Hf isotope and whole-rock geochemistry on the latest Neoproterozoic diabases and the Early Paleozoic arc intrusions in the western BAT.The latest Neoproterozoic(ca.546 Ma) diabases display low SiO_2(46.52-49.24 wt.%) with high MgO(8.23-14.41 wt.%),Cr(66-542 ppm) and Ni(50-129 ppm),consisting with mantle origin.Their highly negative zircon ε_(Hf)(t)(-12.0 to-24.7) and high Fe/Mn ratios(62.1-81.7)further indicate a significantly enriched mantle source.Considering that the BAT maybe initially separated from the Tarim Craton with a thickened crustal root,we propose that these diabases were generated through partial melting of an enriched lithospheric mantle source that had been hybridized by lower-crustal eclogites during foundering of the BAT lower crust.The Early Paleozoic(ca.475-417 Ma) arc intrusions in western BAT can be divided into Periods Ⅰ and Ⅱ at approximately 450 Ma.The Period Ⅰ(450 Ma) intrusions contain abundant mafic minerals like hornblende and pyroxene,and show positive zircon ε_(Hf)(t)(+1.5 to+10.9).They are predominantly medium-K calc-alkaline with broad correlations of SiO2 versus various major and trace elements,which correlate well with the experimental melts produced by the fractional crystallization of primitive hydrous arc magmas at 7 kbar.We assume they were formed through mid-crustal differentiation of the mantle wedge-derived hydrous basaltic melts.By contrast,the Period Ⅱ(≤450 Ma) intrusions are characterized by variable zircon e_(Hf)(t)(-15.0 to+11.5) with irregular variations in most major and trace elements,which are more akin to the arc magmas generated in an open system.The general occurrence of elder inherited zircons,along with the relatively high Mg#(45) of some samples,call upon a derivation from the reworking of the previously subduction-modified BAT lower crust with the input of mantle-derived mafic components.In combination with the Early Paleozoic tectonic melanges flanking western BAT,we infer that the compositional transition from Period Ⅰ to Ⅱ can be attributed to the tectonic transition from south-dipping subduction of Solonker ocean to north-dipping subduction of South Bainaimiao ocean in southeastern CAOB.The above results shed light not only on the latest Neoproterozoic to Early Paleozoic multiple crust-mantle interactions in western BAT,but also on the associated crustal construction processes before the final arc-continent accretion.  相似文献   

动态分段思想在公路地理信息系统中的实现   总被引：7，自引：0，他引：7  

李军利  查良松  王中 《测绘与空间地理信息》2006,29(1):67-70

动态分段是一种全新的线性特征的动态分析技术,可以有效地解决公路线性特征的动态分析问题,实现公路图形和属性数据间的双向动态可视化查询。文章以Arc/Info为代表,分析了动态分段技术的原理,结合VB6.0、MapObjects2.2和Access,初步介绍了公路GIS中动态分段的数据结构与算法,并探讨了如何实现公路GIS的过程。  相似文献   

Origin of high field strength element enrichment in volcanic arcs: Geochemical evidence from the Sulu Arc, southern Philippines   总被引：1，自引：0，他引：1  

P.R. Castillo  S.J. Rigby  R.U. Solidum   《Lithos》2007,97(3-4):271-288

Lavas from the Sulu Arc, southern Philippines, exhibit an enrichment in high field strength elements (HFSE) that represents a departure from the typical volcanic arc geochemical signature. It has been postulated that this relative enrichment arises from metasomatism of mantle wedge peridotites by melts derived from the subducting oceanic lithosphere, through formation of amphibole which subsequently breaks down and enriches the mantle source of parental arc magmas in HFSE. Divergent chemical and isotopic characteristics between Sulu Arc HFSE-enriched lavas and the Sulu Sea crust being subducted—the presumed source of slab-derived melts—render it unlikely, however, that HFSE enrichment arises from the influence of such melts. New geochemical data suggest that the varying degrees of HFSE enrichment in Sulu Arc lavas are instead the result of variable amounts of mixing between enriched and depleted mantle end-components—the sources of South China Sea intraplate lavas and Sulu seafloor basalts, respectively—within a compositionally heterogeneous mantle wedge.  相似文献