The hercynian chain in Sardinia (Italy)     

Luigi Carmignani  Rodolfo Carosi  Anselmo Di Pisa  Marco Gattiglio  Giovanni Musumeci  Giacomo Oggiano 《Geodinamica Acta》2013,26(1):31-47

Abstract

A new geodynamic model for the Sardinian segment of the Hercynian chain is presented. The improvement of knowledge regarding several geological, metamorphic, magmatic and geochronological aspects of the Sardinian Palaeozoic basement, mainly achieved in the last few years, allows us to propose a more complete picture of its evolution.

The occurrence of remnants of an oceanic suture along a major tectonic lineament in northern Sardinia, as well as the products of Ordovician calc-alkaline magmatism, testifies to the presence, during the Lower Paleozoic, of an ancient (Precambrian- Cambrian) oceanic domain and its consumption along an Andean- type subduction zone. The following Carboniferous continental collision caused crustal stacking with Barrovian metamorphism and southward-migrating deformation from the suture zone toward the foreland.

Early Carboniferous Culm-type facies sediments, deposited in the outermost zone of the chain, imply that continental collision took place earlier in the internal zone, from Late Devonian or Early Carboniferous.

The collisional orogenic wedge experienced ductile extension during the Late Carhoniferous as a result of gravitational collapse of the thickened continental crust.

Extensional tectonism enhanced the uplift of the chain and some regions underwent tectonic denudation or LP/HT metamorphism and somewhere anatexis. The emplacement of calc-alkaline batholiths and the development of Late Carboniferous - Early Permian molasse basins occurred during extension that prolonged throughout the Permian.  相似文献   

Syn-convergence exhumation of the Central Alps     

Olivier Merle 《Geodinamica Acta》2013,26(3):129-138

Abstract

The exhumation of rocks in a plate convergence setting is commonly related to erosion and/or tectonic denudation accompanied by isostatic adjustment. Isostatic compensation is the physical response to denudation. It leads to unroofing of deep levels of the crust. A new model for producing topographic relief is proposed which explains well the rapid exhumation of high-temperature rocks in the Central Alps via erosion and tectonic denudation (i.e. gravitational collapse and normal faulting). It is shown that the forward motion of the cold and rigid Adriatic indenter into the European crust is twofold. Firstly, horizontal compression led to the vertical extrusion of the deepest ductile European basement into shallower levels. This tectonic process induced heat transfer through the southern steep belt as well as heat advection together with the extruded material, resulting in the metamorphic aureole observed in the Central Alps. Secondly, the lower part of the Adriatic crust protruded into the warm European crust as a result of continuous forward motion. Geophysical data suggest that the isostatic response to indentation (i.e. deepening of the alpine root) has been inhibited by the mechanical strength of the cold and rigid Adriatic crust. Then, the indentation process induced a deviation from isostatic equilibrium by creating a tremendous topographic relief. This relief disappeared rapidly, possibly as fast as it forms, by enhanced erosion and tectonic denudation leading to rapid exhumation of the metamorphic dome.  相似文献   

Structural Characteristics of the Basement beneath Qiangtang Basin in Qinghai-Tibet Plateau: Results of Interaction Interpretation from Seismic Reflection/Refraction Data     

LI Qiusheng  GAO Rui  FENG Shaoying  LU Zhanwu  HOU Hesheng  GUAN Ye  LI Pengwu  WANG Haiyan  YE Zhuo  XIONG Xiaosong  LIU Jinkai  HE Rizheng 《《地质学报》英文版》2013,87(2):358-377

The studies on configuration, character/property of the basement of Qiangtang basin is helpful for evaluating petroleum and nature gas resources as well as understanding the basin evolvement. Recently a moderate to high-grade metamorphic gneiss rock was found underlying beneath very low metamorphic Ordovician strata in Mayer Kangri to the north of the central uplift. That fact actually proved existence of the crystalline basement just the distribution and structures of pre-Paleozoic crystalline basement still remain puzzle. In recent years a number of active sources deep seismic profiling, to aim at lithospheric structure of northern Tibet and petroleum resources of the Qiangtang basin, had been conducted that make it possible to image the structure of the basement of the Qiangtang. Near vertical reflection profiles, included those acquired previously and those during 2004 to 2008, have been utilized in this study. By through the interaction process and interpretation between the reflection profiles and the wide-angle profile, a model with the detailed structure and velocity distribution from surface to the depth of 20 km of Qiangtang basin has been imaged.Based on the results and discussions of this study, the preliminary conclusions are as follows: (1) The velocity structure section (~20 km) that is interactively constrained by the refraction and reflection seismic data reveals that the sedimentary stratum gently lie until 10 km in the south Qiangtang basin. (2) The basement consists of fold basement (the upper) and crystalline basement (the lower).The fold basement buried at the average depth of 6 km with a velocity of 5.2–5.8 km/s. The shallowest appear at range of the central uplift. The crystalline basement is underlying beneath the fold basement at the average depth of 10 km with a velocity of 5.9–6.0 km/s except near Bangong-Nujiang suture. (3) The high-velocity body at the depth range of 3–6 km of the central uplift is considered as a fragment of the crystalline basement that perhaps was raised by Thermal or deformation. (4) The lower-consolidated fold basement show more affinity of Yangtze block but the crystalline basement seems more approximate to Lhasa terrene in geophysical nature. We have attempted to improve the resolution and reliability by interaction of the active seismic data and prove it effective to image complex basement structure. It will be a potential to process the piggy-back acquisition data and has wide prospects.  相似文献   

Late Miocene-Quaternary Synchronous-But-Magnitude- Differentiated Episodic Rapid Uplifts of The NE Tibetan Plateau: A Synthesis From Flexural Basins     

FANG Xiaomin  LI Jijin  SONG Chunhui  YAN Maodu 《《地质学报》英文版》2013,87(Z1):207-209

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GPS Measurements of Present-day Vertical Motions of Tibet     

YANG Shaomin  WANG Qi  Jeff FREYMUELLER  QIAO Xuejun 《《地质学报》英文版》2013,87(Z1):84-84

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准噶尔盆地车排子凸起沙湾组二段油气成藏特征及其主控因素     

马立驰 《现代地质》2013,(5)

通过准噶尔盆地车排子凸起沙湾组二段油藏的油源条件、沉积储层特征、输导通道及其时空配置等成藏要素解剖,油藏和失利圈闭多项地质参数的对比分析,明确了油气成藏机制及主控因素。研究区油气主要来自昌吉凹陷侏罗系和二叠系烃源岩;扇三角洲水下分支水道侧翼上倾尖灭砂岩和滨浅湖滩坝砂体构成了主要的储集层类型;稳定分布的沙湾组一段毯砂、红车断裂、浅部调整断层构成了网毯式输导格架。成藏要素时空上的良好配置,为研究区“缓坡远源、厚砂侧向输导、中低充注”奠定了基础。储层岩性物性控制了油气充注程度;浅层调整断层倾角、圈闭砂体与沙湾组一段毯砂距离以及两者之间泥岩累计厚度三者共同控制了油气的输导效率和圈闭含油概率。  相似文献   

Peri-Gondwanan Ordovician crustal fragments in the high-grade basement of the Eastern Rhodope Massif,Bulgaria: evidence from U-Pb LA-ICP-MS zircon geochronology and geochemistry     

Nikolay Bonev  Maria Ovtcharova-Schaltegger  Robert Moritz  Peter Marchev  Alexey Ulianov 《Geodinamica Acta》2013,26(3-4):207-229

Field, geochemical, and geochronologic data of high-grade basement metamafic and evolved rocks are used to identify the nature and timing of pre-Alpine crustal growth of the Rhodope Massif. These rocks occur intrusive into clastic-carbonate metasedimentary succession. Petrography and mineral chemistry show compositions consistent with Alpine amphibolite-facies metamorphism that obliterated the original igneous textures of the protoliths. Bulk-rock geochemistry identifies low-Ti tholeiitic to calc-alkaline gabbroic-basaltic and plagiogranite precursors, with MORB-IAT supra-subduction zone signature and trace elements comparable to modern back-arc basalts. The U-Pb zircon dating revealed a mean age of 455 Ma for the magmatic crystallization of the protoliths that contain inherited Cambrian (528–534 Ma) zircons. Carboniferous, Jurassic, and Eocene metamorphic events overprinted the Ordovician protoliths. The radiometric results of the metamorphic rocks demonstrate that Ordovician oceanic crust was involved in the build-up of the Rhodope high-grade basement. Dating of Eocene-Oligocene volcanic rocks overlying or cross-cutting the metamorphic rocks supplied Neoproterozoic, Ordovician and Permo-Carboniferous xenocrystic zircons that were sampled en route to the surface from the basement. The volcanic rocks thus confirm sub-regionally present Neoproterozoic and Paleozoic igneous and metamorphic basement. We interpret the origin of the Middle-Late Ordovician oceanic magmatism in a back-arc rift-spreading center propagating along peri-Gondwanan Cadomian basement terrane related to the Rheic Ocean widening. The results highlight the presence of elements of Cadomian northern Gondwana margin in the high-grade basement and record of Rheic Ocean evolution. The eastern Rhodope Massif high-grade basement compared to adjacent terranes with Neoproterozoic and Cambro-Ordovician evolution shares analogous tectono-magmatic record providing a linkage among basement terranes incorporated in the Alpine belt of the north Aegean region.  相似文献   

Quaternary and Holocene coastal uplift in Ikaria Island,Aegean Sea     

《Geodinamica Acta》2013,26(3-4):123-131

Abstract

Geomorphological, biological and AMS radiocarbon dating provide evidence of an about lm high elevated palaeo-shoreline at the NE coast of Ikaria Island,Aegean Sea, and to a seismic uplift which occurred after AD950-1150 and was probably responsible for damage in an ancient tower. These data are important for several reasons. They provide evidence for a strong earthquake in an island usually assumed aseismic, coastal uplifts and coastal fauna are scarce in this region, while the Late Holocene uplift correlates with a flight of marine terraces of probably Quaternary age, at least up to 40m high. Long-term uplift is not observed at the footwall of a fault bounding a major graben north of Ikaria, it represents a structural puzzle and it may help to shed some light to the evolution of various extensional terranes.  相似文献   

The denudation history of the Argentera Alpine External Crystalline Massif (Western Alps,France-Italy): an overview from the analysis of fission tracks in apatites and zircons     

《Geodinamica Acta》2013,26(6):455-473

Apatite/zircon fission track (FT) records of the Argentera external crystalline massif (Western Alps) show three tectonic pulses, respectively at 22 Ma (zircons), 6 and 3.5 Ma (apatites). The first pulse is consistent with the basement exhumation and initiation of the major deformation recorded in the foreland of the belt from Middle to early Upper Miocene. The two others might be respectively local expressions of the syncollisional extension mainly controlled by a westward sedimentary cover detachment and a Plio-Quaternary uplift acceleration. Zircon ages of 50-80 Ma in a limited NW area and evidence of an uplift elsewhere show that in a large fraction of the massif, temperatures in post-Variscan times never reached 320°C. Finally, FT data show that the Argentera massif did not behave as a single block during its denudation. First, in the NW of the massif, a small fault-limited block was already separated since the Cretaceous and later on recorded the 6 Ma denudation event, the 22 Ma pulse being recorded only in the remaining part of the massif. Second, less than 3.5 Ma ago, the northeastern part of the massif overthrust the southwestern block along the Bersézio-Veillos fault zone.  相似文献   

内蒙古武川西乌兰不浪地区早前寒武纪变质基底锆石SHRIMP定年及Hf同位素组成   总被引：19，自引：16，他引：3  

马铭株  徐仲元  张连昌  董春艳  董晓杰  刘守偈  刘敦一  万渝生 《岩石学报》2013,29(2):501-516

本文报道了华北克拉通西部武川西乌兰不浪地区太古宙变质基底的锆石SHRIMP年龄和Hf同位素组成。一个片麻状奥长花岗岩样品的锆石具核边结构,核部岩浆锆石和边部变质锆石的207Pb/206Pb加权平均年龄分别为2692±17Ma和2528±16Ma。对9个样品进行了锆石Hf同位素分析。新太古代早期(2692～2697Ma)片麻状奥长花岗岩(2个样品)的岩浆锆石的εHf(t)、tDM1(Hf)和tDM2(Hf)分别为4.78～8.83、2646～2780Ma和2632～2845Ma;新太古代二辉麻粒岩(2个样品)中的捕获锆石的εHf(t)、tDM1(Hf)和tDM2(Hf)分别为-2.30～8.62、2543～2954Ma和2529～3189Ma;新太古代变质深成岩(4个样品)的岩浆锆石的εHf(t)、tDM1(Hf)和tDM2(Hf)分别为-2.60～8.09、2529～2880Ma和2538～3089Ma;古元古代蓝晶石榴长英质片麻岩(1个样品)的碎屑锆石的εHf(t)、tDM1(Hf)和tDM2(Hf)分别为1.52～6.59、2432～2774Ma和2498～2925Ma。结合前人研究结果,可得出如下结论和认识:1)该区存在新太古代早期片麻状奥长花岗岩,太古宙岩石在新太古代晚期普遍遭受高级变质作用影响;2)新太古代早期为该区地壳形成主要时期,新太古代晚期则主要表现为陆壳物质再循环;3)作为阴山地块的典型代表,固阳-武川地区与华北克拉通东部太古宙基底十分类似,可能表明华北克拉通在新太古代晚期已成为统一的整体。  相似文献