塔里木盆地南缘历史时期气候环境变化的过程与特征   总被引：2，自引：9，他引：2  

钟巍  塔西甫拉提·特依甫  王立国  李偲 《中国沙漠》2004,24(3):261-267

根据塔里木盆地南缘具较高分辨率的湖沼相沉积物碳酸盐δ^13C和粒度等记录，恢复出2162-850BC期间为一相对稳定的温暖干旱时期，之后迅速转冷湿，湿润程度呈持续、阶段式增加，50 BC至500 AD期间呈现的显著冷湿特征于550 AD之后突变转暖干而结束。550 AD和1000 AD前后的具突变性质的气候事件在南疆地区近2．0ka的气候变化中具有重要意义，反映气候状况有过重大调整。850—1300AD期间(相当于中世纪温暖期)冷暖、干湿多变，但温暖特征并不明显。特别是1100—1200AD期间气候快速、频繁变化之后，奠定了本地区现代稳定干旱环境特征。区域对比表明，尼雅剖面记录的气候变化具有广泛的区域一致性。  相似文献   

A deep seismic transect from Hovgård Ridge to northwestern Svalbard across the continental-ocean transition: A sheared margin study     

O. Ritzmann  W. Jokat  W. Czuba  A. Guterch  R. Mjelde  Y. Nishimura 《Geophysical Journal International》2004,157(2):683-702

  相似文献   

Magma flow in the East Greenland dyke swarm inferred from study of anisotropy of magnetic susceptibility: magmatic growth of a volcanic margin   总被引：2，自引：0，他引：2  

Jean-Paul Callot  Laurent Geoffroy 《Geophysical Journal International》2004,159(2):816-830

  相似文献   

Estimating the effective elastic thickness of the lithosphere of the Iberian peninsula based on multitaper spectral analysis   总被引：1，自引：0，他引：1  

D. Gómez-Ortiz  R. Tejero  J. Ruiz  R. Babín-Vich  J. M. González-Casado 《Geophysical Journal International》2005,160(2):729-735

  相似文献   

The crustal structure of central East Greenland—I: From the Caledonian orogen to the Tertiary igneous province     

Mechita C. Schmidt-Aursch  Wilfried Jokat 《Geophysical Journal International》2005,160(2):736-752

  相似文献   

Crustal structure of the Lofoten–Vesterålen continental margin, off Norway     

Filippos Tsikalas  Olav Eldholm  Jan Inge Faleide   《Tectonophysics》2005,404(3-4):151-174

By compiling wide-angle seismic velocity profiles along the 400-km-long Lofoten–Vesterålen continental margin off Norway, and integrating them with an extensive seismic reflection data set and crustal-scale two-dimensional gravity modelling, we outline the crustal margin structure. The structure is illustrated by across-margin regional transects and by contour maps of depth to Moho, thickness of the crystalline crust, and thickness of the 7+ km/s lower crustal body. The data reveal a normal thickness oceanic crust seaward of anomaly 23 and an increase in thickness towards the continent–ocean boundary associated with breakup magmatism. The southern boundary of the Lofoten–Vesterålen margin, the Bivrost Fracture Zone and its landward prolongation, appears as a major across-margin magmatic and structural crustal feature that governed the evolution of the margin. In particular, a steeply dipping and relatively narrow, 10–40-km-wide, Moho-gradient zone exists within a continent–ocean transition, which decreases in width northward along the Lofoten–Vesterålen margin. To the south, the zone continues along the Vøring margin, however it is offset 70–80 km to the northwest along the Bivrost Fracture Zone/Lineament. Here, the Moho-gradient zone corresponds to a distinct, 25-km-wide, zone of rapid landward increase in crustal thickness that defines the transition between the Lofoten platform and the Vøring Basin. The continental crust on the Lofoten–Vesterålen margin reaches a thickness of 26 km and appears to have experienced only moderate extension, contrasting with the greatly extended crust in the Vøring Basin farther south. There are also distinct differences between the Lofoten and Vesterålen margin segments as revealed by changes in structural style and crustal thickness as well as in the extent of elongate potential-field anomalies. These changes may be related to transfer zones. Gravity modelling shows that the prominent belt of shelf-edge gravity anomalies results from a shallow basement structural relief, while the elongate Lofoten Islands belt requires increased lower crustal densities along the entire area of crustal thinning beneath the islands. Furthermore, gravity modelling offers a robust diagnostic tool for the existence of the lower crustal body. From modelling results and previous studies on- and off-shore mid-Norway, we postulate that the development of a core complex in the middle to lower crust in the Lofoten Islands region, which has been exhumed along detachments during large-scale extension, brought high-grade, lower crustal rocks, possibly including accreted decompressional melts, to shallower levels.  相似文献   

佳木斯地块西缘金矿带构造效应与壳幔作用--以鹤岗隆起为例     

徐受民赵海滨  于荣文 《华东地质学院学报》2005,28(4):325-328

佳木斯地块西缘金矿带的形成受左行走滑断裂带和深部流体控制，壳-幔作用和地球动力体制转换是成矿物质活化→运移→聚集→成矿的基本动力学保障，构造应力场转换是其重要表现形式。深切地幔牡丹江岩石圈断裂的活动发生了深熔作用，使成矿物质得以活化、运移的重要驱动力，是成岩成矿作用发生的根本原因之一。地幔流体通过壳-幔相互作用形成了含矿流体，为流体成矿作用提供了矿源，并沿深断裂运移到更高的层位，在物理化学条件发生改变时沉积成矿。佳木斯地块西缘金矿带是受深断裂控制的，矿床之间是相互联系的，是在一个构造应力体制下完成它们的成矿作用的。北北东向和伴生的北西西向断裂，并有中生代浅成-超浅成岩体或脉岩侵位是今后找矿的方向。  相似文献   

Structure de socle,sismostratigraphie et héritage structural au cours du rifting au niveau de la marge d'Ifni/Tan-Tan (Maroc sud-occidental)     

Naïma AbouAli  Mohamad Hafid  El Hassane Chellaï  Mohamed Nahim  Mahmoud Zizi 《Comptes Rendus Geoscience》2005,337(14):1267-1276

Seismic reflection profiles from the Ifni/Tan-Tan Atlantic margin of southern Morocco, interpreted in the light of well data and field geology from the Western Anti-Atlas, allowed us to establish the seismostratigraphic framework of the syn-rift series and to reveal (i) a compressional structural style in the pre-Triassic basement similar to that established in the adjacent outcropping onshore basement but with an opposed western vergence, (ii) the importance of inherited anterior structures in the formation of Triassic-Liassic rift structures and (iii) an east–west propagation of these rift structures. To cite this article: N. AbouAli et al., C. R. Geoscience 337 (2005).  相似文献   

Constraints from Thorium/Lanthanum on Sediment Recycling at Subduction Zones and the Evolution of the Continents   总被引：20，自引：3，他引：20  

PLANK  T. 《Journal of Petrology》2005,46(5):921-944

Arc magmas and the continental crust share many chemical features,but a major question remains as to whether these features arecreated by subduction or are recycled from subducting sediment.This question is explored here using Th/La, which is low inoceanic basalts (<0·2), elevated in the continents(>0·25) and varies in arc basalts and marine sediments(0·09–0·34). Volcanic arcs form linear mixingarrays between mantle and sediment in plots of Th/La vs Sm/La.The mantle end-member for different arcs varies between highlydepleted and enriched compositions. The sedimentary end-memberis typically the same as local trench sediment. Thus, arc magmasinherit their Th/La from subducting sediment and high Th/Lais not newly created during subduction (or by intraplate, adakiteor Archaean magmatism). Instead, there is a large fractionationin Th/La within the continental crust, caused by the preferentialpartitioning of La over Th in mafic and accessory minerals.These observations suggest a mechanism of ‘fractionation& foundering’, whereby continents differentiate intoa granitic upper crust and restite-cumulate lower crust, whichperiodically founders into the mantle. The bulk continentalcrust can reach its current elevated Th/La if arc crust differentiatesand loses 25–60% of its mafic residues to foundering. KEY WORDS: arc magmatism; continental crust; delamination; thorium; sediment subduction  相似文献   

Age of Gimli beach of Lake Agassiz based on new OSL dating     

James T. Teller  Lewis A. Owen 《第四纪科学杂志》2021,36(1):56-65

Gimli beach in Manitoba is one of the lowest elevation beaches in the southern Lake Agassiz basin, and is a distinct ridge composed of bedded sand and gravel that rises above the lake plain and extends for more than 40 km. Ten new optically stimulated luminescence (OSL) ages from Gimli beach yield ages mostly ranging from 9.7 ± 0.7 to 10.5 ± 0.8 ka (average 10.3 ± 0.5 ka), which is older by 0.6 to >1.0 ka than age estimates of previous researchers. Two of our new OSL ages are notably older than the others, dating to ~11.3 ± 0.8 and 13.9 ± 1.0 ka, which we attribute to poorly bleached sands. We ascribe an age of about 10 ka to Gimli beach, which is several centuries before overflow from Lake Agassiz and its vast drainage basin shifted from the western Great Lakes to glacial Lake Ojibway and the St. Lawrence Valley.  相似文献