Late Variscan “Basin and Range” magmatism and tectonics in the Central Alps: evidence from U-Pb geochronology     

Urs Schaltegger  Fernando Corfu 《Geodinamica Acta》2013,26(2):82-98

Abstract

Towards the end of the Variscan orogeny, volcano-sedimentary basins were formed within the mountain hell. U-Pb age determinations on zircons of volcanic and plutonic rocks from intramontane basins of the Central Alps allows us to define the age of two volcano-sedimentary units: The former one was dated older than 333 Ma (probably Visean), the younger one was deposited in a short time span between 303 and 298 Ma (Stephanien). The latter contains tuffs (303 ± 4 Ma), ignimbrites and microgranites (299 ± 2 Ma) and intrusive rhyolites (300 ± 2 Ma) that are all coeval within analytical precision. Granitoid rocks intruded into the volcano-sedimentary rocks at 333 ± 2 Ma, 310 ± 3 Ma and 298 ± 2 Ma. An angular unconformity between the older and the younger units in the Tö di area (Aar massif) indicates uplift and erosion between 310 and 303 Ma.

Our results suggest the existence of two periods of late Variscan extension (or transtension) in the Alpine realm, both combined with magmatic activity. The extensional event of Stephaniun age is characterized by a short duration of only a few million years, between 303 and 298 Ma, comprising tectonic activity, volcanism and plutonism. The plutonic rocks are characterized by a dominant lithospheric mantle component, which was contaminated by different amounts of crostai material and might have been increasingly influenced by aslhcnos-pherie mantle melts in the course of crostai thinning. The ealc-alkaline geochemical characteristics of the granites may be explained as an inherited source feature.

The overall tectonic style and the mode of magmatism resembles the situation of the Basin-and-Kange Province (eastern USA). Consequently there is no need to invoke a late-Variscan Andean-type subduction to explain the geochemical composition of the magmatic rocks. We conclude that late-orogenic extension is an important tectonic stage of the Variscan orogeny, which lasted for some 50 million years. The extension led to thinning of the crust and upwelling of hot mantle, causing high heat flow, intrusion of mantle melts and formation of huge volumes of acid melts.  相似文献   

Evidence of two-stage extensional tectonics from the northern edge of the Edremit Graben,NW Turkey     

《Geodinamica Acta》2013,26(3-4):283-297

Western Turkey is a place of active continental extension, characterized by the occurrence of several WNW-ESE-trending major grabens. The central part of the northern edge of the Edremit Graben is delineated by various geological units, namely the metamorphic Kazda? Massif, the Mid-Cretaceous Çetmi mélange, the sedimentary Küçükkuyu formation, and loose Plio-Quaternary deposits. Detailed structural and sedimentological study suggests a two-stage extensional evolution of the area, separated by a short break in the tectonic regime. The first stage, possibly related to back-arc extension and/or orogenic collapse, is marked by the activity of a newly described low-angle detachment fault, the ?elale detachment fault, from the latest Oligocene onward. The fault plane, separating the mylonitized rocks of the Kazda? Massif in the footwall from the unmetamorphosed Çetmi mélange and Küçükkuyu formation in the hanging wall, must have played a significant role in the initial exhumation processes of the Kazda? Massif at that time. The Lower Miocene syntectonic Küçükkuyu formation has recorded the initiation and filling up of a small basin, which has developed in a typical supra-detachment basin, above the detachment fault. After a short phase of possible compression and erosion, the second stage—which marks the onset of neotectonic activity—is marked by the development of Plio-Quaternary step-like normal faults, which cut through all the previous units. Coarse, loose sediments were deposited following the fault activity. These local results are extrapolated to apply to the entire Edremit Graben. In that case, its evolution is seen as the succession of two extensional stages, characterized by distinct structural and sedimentological patterns, and possibly separated by a short compressional phase.  相似文献   

数字化测绘技术在公路改扩建中的应用   总被引：1，自引：0，他引：1  

孙莉  刘琦 《地理空间信息》2010,8(3):25-26

主要对现有公路改扩建中的数字化勘测及数字化设计进行了探讨,首先概述了湖南梅城公路改扩建项目背景,然后对数字摄影测量、GPS-RTK三维路基数据获取以及数字路基模型及与地面模型叠加等方面进行了论述,最后指出了生成1:2000三维数字地形图用于纸上定线和建立数字地面模型,能够达到公路改扩建带状图绘测精度的要求。  相似文献   

Sapphirine in SW Sweden: a record of Sveconorwegian (–Grenvillian) late-orogenic tectonic exhumation     

MÖller 《Journal of Metamorphic Geology》1999,17(1):127-141

In the Sveconorwegian granulite region of SW Sweden, sapphirine occurs in reaction coronas in Mg- and Al-rich kyanite eclogites which form parts of mafic complexes. Aluminous to peraluminous sapphirine forms symplectitic intergrowths with plagioclase±corundum±spinel after kyanite. Kyanite and omphacite were the main reactants in the formation of sapphirine. The sapphirine formed during decompression from the eclogite facies ( P >15  kbar) through the high- to medium-pressure granulite and upper amphibolite facies at c. 750  °C. Preserved growth zoning in garnet, frozen-in reaction textures, and chemical disequilibrium suggest a rapid tectonic exhumation. Ductile deformation in the surrounding gneisses and parts of the mafic complex is characterized by foliation development, WNW–ESE stretching and dynamic recrystallization under granulite to upper amphibolite facies conditions, simultaneous with the sapphirine formation. This decompression, high-grade re-equilibration and associated deformation took place during the exhumation of the Sveconorwegian eclogites, bracketed between 969±14 and 956±7  Ma. Probable tectonic causes are late-orogenic gravitational collapse and/or plate divergence following the Sveconorwegian–Grenvillian continent–continent collision. There are no indications of metastability of aluminous and peraluminous sapphirine in the decompressed kyanite eclogites; sapphirine is stable in amphibole-poor and amphibolitized varieties, including rocks that have undergone dynamic recrystallization. Close similarities between rocks from different parts of the world with respect to reaction textures suggests that sapphirine+plagioclase-forming reactions are a universal feature in high-temperature decompressed kyanite eclogites.  相似文献   

Comparison of the ‘strike‐slip’ versus the ‘episodic rift‐sag’ models for the origin of the Isa Superbasin     

P. G. Betts  G. S. Lister 《Australian Journal of Earth Sciences》2013,60(2):265-280

In this paper we assess two competing tectonic models for the development of the Isa Superbasin (ca 1725–1590 Ma) in the Western Fold Belt of the Mt Isa terrane. In the ‘episodic rift‐sag’ tectonic model the basin architecture is envisaged as similar to that of a Basin and Range province characterised by widespread half‐graben development. According to this model, the Isa Superbasin evolved during three stages of the Mt Isa Rift Event. Stage I involved intracontinental extension, half‐graben development, the emergence of fault scarps and tilt‐blocks, and bimodal volcanism. Stage II involved episodic rifting and sag during intervening periods of tectonic quiescence. Stage III was dominated by thermal relaxation of the lithosphere with transient episodes of extension. Sedimentation was controlled by the development of arrays of half‐grabens bounded by intrabasinal transverse or transfer faults. The competing ‘strike‐slip’ model was developed for the Gun Supersequence stratigraphic interval of the Isa Superbasin (during stage II and the beginning of stage III). According to this model, sinistral movements along north‐northeast‐orientated strike‐slip faults took place, with oblique movements along northwest‐orientated faults. This resulted in the deposition of southeast‐thickening ramp sequences with local sub‐basin depocentres forming to the west and north of north‐northeast‐ and northwest‐trending faults, respectively. It is proposed that dilation zones focused magmatism (e.g. Sybella Granite) and transfer of strike‐slip movement resulted in transient uplift along the western margin of the Mt Gordon Arch. Our analysis supports the ‘episodic rift‐sag’ model. We find that the inferred architecture for the strike‐slip model correlates poorly with the observed structural elements. Interpretation is made difficult because there has been significant modification and reorientation of fault geometry during the Isan Orogeny and these effects need to be removed before any assertion as to the basin structure is made. Strike‐slip faulting does not explain the regional‐scale pattern of basin subsidence. The ‘episodic rift‐sag’ model explains the macroscopic geometry of the Isa Superbasin and is consistent with the detailed sedimentological analysis of basin facies architecture, and the structural history and geometry.  相似文献   

利用复测水准资料寻求反映地壳纯形变的定量指标     

崔笃信 《大地测量与地球动力学》1994,(1)

地壳纯变形分为剪切变形和扩张变形。在前人研究的基础上提出了仅利用复测水准资料求出描述地壳剪切变形和扩张变形指标的方法和步骤，所得的定量指标不受基准的影响，受测量累积误差的影响亦很小，能客观地反映地壳变形的特征。通过理论和实例证明：以一点周围变形分量的最大值代表该点周围垂直面的变形程度比其平均值更能突出变形信息。最后根据实例计算结果分析了剪切变形分量、扩张变形分量与形变速率、构造地震的关系。  相似文献   

Submarine canyons on the north of Chiwei Island:influenced by recent extension of the southern Okinawa Trough     

ZHAO Yuexi  LIU Baohu  LI Xishuang  LIU Chenguang  WU Jinlong  WANG Kuiyang 《海洋学报(英文版)》2008,27(4):63-72

Based on new multibeam bathymetric data and about 300 km long single seismic profiles, three topographic units were identified： the canyons, fractural valley and submarine terrace on the north of Chiwei Island where is a structural transition zone between the southern trough and the middle trough. The Chiwei Canyon and the North Chiwei Canyon are two of the largest canyons in the East China Sea （ECS） slope. Topographic features and architectures of them are described. The study shows that both of them are originated along faults. The evolution and spatial distribution of topographic units in the study area are controlled mainly by three groups of faults which were formed and reactive in the recent extensional phase of Okinawa Trough. The Chiwei Canyon was initia- ted during the middle Pleistocene and guided by F4 that is a N--S trending fault on the slope and F1, a large NW--SE trending fault on the trough. The pathway migration from the remnant channel to the present one of Chiwei Canyon is the result of uplift of tilted fault block that is coupled to the recent extension movements of the southern trough. The submarine terrace is detached from the ECS slope by the NEE -trending fault. The North Chiwei Canyon, developing during the late Pleistocene, is guided by FS, a N-S trending fault, diverted and blocked by the submarine terrace.  相似文献   

Application of matter-element model in soil nutrient evaluation of ecological fragile region     

Jie Tang  Chenye Wang  Nianfeng Lin  Zhaoyang Li  Haiyi Li  Zilong Mao 《中国地理科学(英文版)》2009,19(2):168-176

On the basis of the soil environment investigation in Da'an City, Jilin Province, China, 40 soil samples from main land use types were obtained and tested by standard method. Soil organic matter (SOM), total N (TN), total P (TP), total K (TK), available N (AN), available P (AP) and available K (AK) were chosen as the evaluation factors. A regional soil nutrient evaluation model was developed based on the matter-element model. The results show that the soil samples with nutrient grade Ⅱ-Ⅴ respectively account for 10%, 30%, 32.5% and 27.5%, and those with grade Ⅳ and Ⅴ account for 60% in all samples. The relationship between soil nutrients and land types indicates that the nutrients of farmland are relatively good, with 41.7% of soil samples with the nutrient grade Ⅳ and Ⅴ. The nutrients of saline-alkali land and sandy land are the worst, with 100% of soil samples with the nutrient grade Ⅳ and Ⅴ. And the ratios of soil samples grade Ⅳ and Ⅴ in grassland and wasteland are respectively 62.5 % and 54.55%. Generally speaking, the soil nutrients status in Da'an City is poor, 60% of soil samples are in poor and extremely poor conditions, indicating that the soil has been severely eroded. Being a relatively superior evaluation method with more accurate resuits and spatial distribution consistency, matter-element analysis is more suitable for regional soil nutrient evaluation than previous models.  相似文献   

自定义空间数据格式的扩展与应用     

陈振  陈荣国  谢炯  张明波 《测绘学院学报》2011,(2)

针对商业GIS软件缺乏对自定义空间数据格式的支持能力,提出了利用OGR自定义数据源来实现GIS软件对自定义空间数据格式支持。并以ArcGIS平台为例,将OGR数据模型在数据组织、几何模型、属性信息和空间参考信息等方面转换为ArcGIS软件空间数据模型,使ArcGIS具备了访问OGR自定义空间数据格式的能力,实现了自定义空间数据格式的扩展与应用,体现了开源GIS软件和商业GIS软件协同工作能力。  相似文献   

Growth by extension,and reworking,of a south‐western Kalahari linear dune     

Matt W. Telfer 《地球表面变化过程与地形》2011,36(8):1125-1135

Optically stimulated luminescence (OSL) dating studies of linear (longitudinal) dunes have been used extensively to elucidate late Quaternary environments and climates in arid or formerly arid regions, yet understanding of the development of such dunes is incomplete. In particular, conflicting opinions have been presented regarding the propensity of linear dunes to migrate laterally, the degree to which they rework their own sediment during accumulation and whether they form primarily by extension, as opposed to lateral sand movement from adjacent interdunes. This study focuses on this last point, although the importance of the other controversies is discussed in context. A simple linear dune in the south‐western Kalahari, which has a prominent termination on a pan (playa) surface, provides an opportunity to directly test hypotheses of dune extension. Chronostratigraphy along a ~600 m transect along the crest of the dune, constrained by 42 OSL ages, reveals that the dune grew by extension on occasions in the late Pleistocene and early Holocene, but has also been subject to reworking along its length, which has continued until recent times. Dune development by extensional growth is suggested to operate under environmental conditions more conducive to net accumulation, whereas reworking is largely independent of conditions throughout the last ~18 ka, and may represent seasonal fluctuations in the position of the dune crest. The relative significance of these two modes of development is suggested to be a key control on the efficacy of linear dunes as archives of environmental and climatic change. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献