Continental growth and reworking on the edge of the Columbia and Rodinia supercontinents; 1.86–0.9 Ga accretionary orogeny in southwest Fennoscandia     

Nick M.W. Roberts  Trond Slagstad 《International Geology Review》2015,57(11-12):1582-1606

Geological history from the late Palaeoproterozoic to early Neoproterozoic is dominated by the formation of the supercontinent Columbia, and its break-up and re-amalgamation into the next supercontinent, Rodinia. On a global scale, major orogenic events have been tied to the formation of either of these supercontinents, and records of extension are commonly linked to break-up events. Presented here is a synopsis of the geological evolution of southwest Fennoscandia during the ca. 1.9–0.9 Ga period. This region records a protracted history of continental growth and reworking in a long-lived accretionary orogen. Three major periods of continental growth are defined by the Transscandinavian Igneous Belt (1.86–1.66 Ga), Gothian (1.66–1.52 Ga), and Telemarkian (1.52–1.48 Ga) domains. The 1.47–1.38 Ga Hallandian–Danopolonian period featured reorganization of the subduction zone and over-riding plates, with limited evidence for continental collision. During the subsequent 1.38–1.15 Ga interval, the region is interpreted as being located inboard of a convergent margin that is not preserved today and hosted magmatism and sedimentation related to inboard extensional events. The 1.15–0.9 Ga period is host to Sveconorwegian orogenesis that marks the end of this long-lived accretionary orogen and features significant crustal deformation, metamorphism, and magmatism. Collision of an indenter, typically Amazonia, is commonly inferred for the cause of widespread Sveconorwegian orogenesis, but this remains inconclusive. An alternative is that orogenesis merely represents subduction, terrane accretion, crustal thickening, and burial and exhumation of continental crust, along an accretionary margin. During the Mesoproterozoic, southwest Fennoscandia was part of a much larger accretionary orogen that grew on the edge of the Columbia supercontinent and included Laurentia and Amazonia amongst other cratons. The chain of convergent margins along the western Pacific is the best analogue for this setting of Proterozoic crustal growth and tectonism.  相似文献   

基于广义的炮偏移方法实现地表多次波和一次波联合成像   总被引：4，自引：4，他引：0       下载免费PDF全文

郭书娟  李振春  仝兆岐  马方正  叶月明 《地球物理学报》2011,54(4):1098-1105

多次波是地下反射层的多次波反射,也蕴含了地下反射界面的信息,因此并不是绝对地只能被当做噪音来处理.为实现对地下构造的准确成像,本文基于广义概念上的炮偏移成像算法,对常规一次波偏移方法从用于向下延拓的上、下行场以及成像条件方面进行了改进,将同时含有表层多次波的炮记录与脉冲震源之和作为下行延拓的震源波场,将同时含有表层多次...  相似文献   

Determination of gravity anomaly at sea level from inversion of satellite gravity gradiometric data   总被引：1，自引：0，他引：1  

Mehdi Eshagh  Lars E. Sjberg 《Journal of Geodynamics》2011,51(5):366-377

Gravity gradients can be used to determine the local gravity field of the Earth. This paper investigates downward continuation of all elements of the disturbing gravitational tensor at satellite level using the second-order partial derivatives of the extended Stokes formula in the local-north oriented frame to determine the gravity anomaly at sea level. It considers the inversion of each gradient separately as well as their joint inversion. Numerical studies show that the gradients T_zz, T_xx, T_yy and T_xz have similar capability of being continued downward to sea level in the presence of white noise, while the gradient T_yz is considerably worse than the others. The bias-corrected joint inversion process shows the possibility of recovering the gravity anomaly with 1 mGal accuracy. Variance component estimation is also tested to update the observation weights in the joint inversion.  相似文献   

Urban spatial development and land use in Beijing: Implications from London’s experiences     

TAN Minghong  GUY M. Robinson  LI Xiubin 《地理学报》2011,21(1):49-64

Beijing is facing a huge challenge to manage the growth of its built-up area whilst also retaining both productive arable land and land for conservation purposes in order to simultaneously realize the three aims of economic development, protecting arable land and generating environmental improvements. Meanwhile, London, as a world city with more than 200 years of industrialization and urbanization, has accumulated rich theoretical and practical experiences for land use planning in a major urban area, such as the creation of Garden Cities, a designated Green Belt and New Towns. This paper firstly analyzes the main characteristics of the spatial distribution of the built-up area, arable land and conservation land in Beijing. Then, some of the key aspects of urban fringe planning in the London region are examined. Lastly, several implications from the experience of London are provided with respect to land-use planning for Beijing, concentrating on a re-appraisal of land-use functions around Beijing, measures to improve the green belt, the development of small towns to house rural-urban migrants and urban overspill, and effective implementation of land-use planning.  相似文献   

A joint distribution of significant wave height and characteristic surf parameter     

Dag Myrhaug  Sébastien Fouques 《Coastal Engineering》2010

The paper provides a joint distribution of significant wave height and characteristic surf parameter. The characteristic surf parameter is given by the ratio between the slope of a beach or a structure and the square root of the characteristic wave steepness in deep water defined in terms of the significant wave height and the spectral peak period. The characteristic surf parameter is used to characterize surf zone processes and is relevant for e.g. wave run-up on beaches and coastal structures. The paper presents statistical properties of the wave parameters as well as an example of results corresponding to typical field conditions.  相似文献   

Variable hangingwall palaeotransport during Silurian and Devonian thrusting in the western Lachlan Fold Belt: Missing gold lodes,synchronous Melbourne Trough sedimentation and Grampians Group fold interference     

J. McL. Miller  L. J. Dugdale  C. J. L. Wilson 《Australian Journal of Earth Sciences》2013,60(6):901-909

The western margin of the Lachlan Fold Belt contains early ductile and brittle structures that formed during northeast‐southwest and east‐west compression, followed by reactivation related to sinistral wrenching. At Stawell all of these structural features (and the associated gold lodes) are dismembered by a complex array of later northwest‐, north‐ and northeast‐dipping faults. Detailed underground structural analysis has identified northwest‐trending mid‐Devonian thrusts (Tabberabberan) that post‐date Early Devonian plutonism and have a top‐to‐the‐southwest transport. Deformation associated with the initial stages of dismemberment occurred along an earlier array of faults that trend southwest‐northeast (or east‐west) and dip to the northwest (or north). The initial transport of the units in the hangingwall of these fault structures was top‐to‐the‐southeast. ‘Missing’ gold lodes were discovered beneath the Magdala orebody by reconstructing a displacement history that involved a combination of transport vectors (top‐to‐the‐southeast and top‐to‐the‐southwest). Fold interference structures in the adjacent Silurian Grampians Group provide further evidence for at least two almost orthogonal shortening regimes, post the mid‐Silurian. Overprinting relationships, and correlation with synchronous sedimentation in the Melbourne Trough, indicates that the early fault structures are mid‐ to late‐Silurian in age (Ludlow: ca 420–414 Ma). These atypical southeast‐vergent structures have regional extent and separate significant northeast‐southwest shortening that occurred in the mid‐Devonian (‘Tabberabberan orogeny’) and Late Ordovician (‘Benambran orogeny’).  相似文献   

Quadrature-based approach for the efficient evaluation of surge hazard   总被引：3，自引：0，他引：3  

G.R. Toro  A.W. Niedoroda  D. Divoky 《Ocean Engineering》2010,37(1):114-124

The Joint Probability Method (JPM) has been used for hurricane surge frequency analysis for over three decades, and remains the method of choice owing to the limitations of more direct historical methods. However, use of the JPM approach in conjunction with the modern generation of complex high-resolution numerical models (used to describe winds, waves, and surge) has become highly inefficient, owing to the large number of costly storm simulations that are typically required. This paper describes a new approach to the selection of the storm simulation set that permits reduction of the JPM computational effort by about an order of magnitude (compared to a more conventional approach) while maintaining good accuracy. The method uses an integration scheme called Bayesian or Gaussian-process quadrature (together with conventional integration methods) to evaluate the multi-dimensional joint probability integral over the space of storm parameters (pressure, radius, speed, heading, and any others found to be important) as a weighted summation over a relatively small set of optimally selected nodes (synthetic storms). Examples of an application of the method are shown, drawn from the recent post-Katrina study of coastal Mississippi.  相似文献   

Structural geometry and controls on basement‐involved deformation in the northern Flinders Ranges,Adelaide Fold Belt,South Australia     

E. Paul  T. Flöttmann  M. Sandiford 《Australian Journal of Earth Sciences》2013,60(3):343-354

In the northern Flinders Ranges, Neoproterozoic and Cambrian sedimentary rocks were deformed and variably metamorphosed during the ca 500 Ma Cambro‐Ordovician Delamerian Orogeny. Balanced and restored structural sections across the northern Flinders Ranges show shortening of about 10–20%. Despite the presence of suitable evaporitic detachment horizons at the basement‐cover interface, the structural style is best interpreted to be thick‐skinned involving basement with only a minor proportion of the overall shortening accommodated along stratigraphically controlled detachments. Much of the contractional deformation was localised by the inversion of former extensional faults such as the Norwest and Paralana Faults, which both controlled the deposition of Neoproterozoic cover successions. As such, both faults represent major, long‐lived structures which effectively define the present boundaries of the northern Flinders Ranges with the Gawler Craton to the west and the Curnamona Craton to the east. The most intense deformation, which resulted in exhumation of the basement along the Paralana Fault to form the Mt Painter and Babbage Inliers, coincides with extremely high heat flows related to extraordinarily high heat‐production rates in the basement rocks. High heat flow in the northern Flinders Ranges suggests that the structural style not only reflects the pre‐Delamerian basin architecture but is also a consequence of the reactivation of thermally perturbed, weakened basement.  相似文献   

Middle to early Late Ordovician hydrothermal veining in the Molong Volcanic Belt,northeastern Lachlan Fold Belt: Sedimentological evidence     

G. H. Packham  J. B. Keene  L. M. Barron 《Australian Journal of Earth Sciences》2013,60(2):257-269

Detrital volcanic and vein quartz, accompanied by felsic volcanic debris, occur as minor constituents in the Ordovician subduction‐related mafic volcanics of the Molong Volcanic Belt. In the western province of the Molong Volcanic Belt, detrital quartz is present in the three episodes of the mafic Volcanics. Volcanic quartz occurs in allochthonous limestone blocks in the Bendigonian Hensleigh Siltstone overlying the Mitchell Formation. The second volcanic episode (the Fairbridge Volcanics) commenced after a hiatus of approximately 20 million years and lasted around 10 million years from Darriwilian to Gisbornian time. Locally derived vein quartz, volcanic quartz and felsic detritus are concentrated at the bases of autochthonous Wahringa and Yuranigh Limestone Members of the volcanics and are extensive and abundant in basal beds of the regional Eastonian limestone body that transgressed over an eroded volcanic centre at Cargo. This early Eastonian debris, deposited early in an 8 million‐year volcanic hiatus preceding the final Ordovician Bolindian volcanism, establishes a pre‐Eastonian age for mineralisation at Cargo. It is inferred that the pauses in volcanism were preceded by magmatic fractionation, intrusion and hydrothermal activity and followed by erosion, subsidence and deposition of autochthonous limestones. Minor occurrences of vein and volcanic quartz are found in Bolindian volcanogenic sediments of the third volcanic phase. It is concluded that hydrothermal vein formation (and mineralisation by inference) was associated with pauses in volcanic activity throughout the Middle to early Late Ordovician over a wide area in the western province, culminating in the mineralisation at Cargo and Copper Hill near Molong. Volcanism in the eastern province of the Molong Volcanic Belt was continuous from at least Darriwilian to latest Ordovician time. Here, detrital hydrothermal vein quartz and volcanic quartz and felsic detritus are distributed through late Middle and early Late Ordovician turbidites of the Weemalla Formation. The possible existence of cycles in the source area like those of the Fairbridge Volcanics is masked by the distal nature of these deposits. Vein formation occurred in both provinces from late Middle Ordovician to early Late Ordovician, long before the formation of the world‐class mineral deposit at Cadia associated with the latest Ordovician Cadia Monzonite.  相似文献   

Response of detrital zircon and monazite,and their U–Pb isotopic systems,to regional metamorphism and host‐rock partial melting,Cooma Complex,southeastern Australia     

I. S. Williams 《Australian Journal of Earth Sciences》2013,60(4):557-580

Progressive Early Silurian low‐pressure greenschist to granulite facies regional metamorphism of Ordovician flysch at Cooma, southeastern Australia, had different effects on detrital zircon and monazite and their U–Pb isotopic systems. Monazite began to dissolve at lower amphibolite facies, virtually disappearing by upper amphibolite facies, above which it began to regrow, becoming most coarsely grained in migmatite leucosome and the anatectic Cooma Granodiorite. Detrital monazite U–Pb ages survived through mid‐amphibolite facies, but not to higher grade. Monazite in the migmatite and granodiorite records only metamorphism and granite genesis at 432.8 ± 3.5 Ma. Detrital zircon was unaffected by metamorphism until the inception of partial melting, when platelets of new zircon precipitated in preferred orientations on the surface of the grains. These amalgamated to wholly enclose the grains in new growth, characterised by the development of {211} crystal faces, in the migmatite and granodiorite. New growth, although maximum in the leucosome, was best dated in the granodiorite at 435.2 ± 6.3 Ma. The combined best estimate for the age of metamorphism and granite genesis is 433.4 ± 3.1 Ma. Detrital zircon U–Pb ages were preserved unmodified throughout metamorphism and magma genesis and indicate derivation of the Cooma Granodiorite from Lower Palaeozoic source rocks with the same protolith as the Ordovician sediments, not Precambrian basement. Cooling of the metamorphic complex was relatively slow (average ～12°C/10⁶y from ～730 to ～170°C), more consistent with the unroofing of a regional thermal high than cooling of an igneous intrusion. The ages of detrital zircon and monazite from the Ordovician flysch (dominantly composite populations 600–500 Ma and 1.2–0.9 Ga old) indicate its derivation from a source remote from the Australian craton.  相似文献