冀东新太古代晚期界岭口闪长岩成因:U-Pb-Nd-Hf-O同位素研究   总被引：2，自引：1，他引：1  

董春艳  王晨  颉颃强  白文倩  万渝生 《岩石学报》2018,34(9):2793-2810

本文报道了华北克拉通东部冀东地区界岭口闪长岩及其中基性岩包体的锆石定年结果和地球化学组成。界岭口闪长岩是华北克拉通规模最大的太古宙闪长质侵入体,总面积约650km2。界岭口闪长岩由闪长岩和石英闪长岩组成,两者渐变过渡。在界岭口闪长岩中存在基性岩包体,包括辉绿岩、细粒辉长岩和辉长岩,一些基性岩包体边部存在冷凝边。石英闪长岩和细粒辉长岩包体的岩浆锆石年龄分别为2533±5Ma和2534±8Ma。闪长岩和石英闪长岩元素组成类似(13个样品),主要区别是后者SiO_2相对较高一些。它们稀土总量较高(TREE=93. 0×10~(-6)~234. 2×10~(-6)),轻重稀土分异程度不强((La/Yb)N=10. 4～23. 9),无明显铕异常(Eu/Eu*=0. 80～1. 05)。在MORB标准化的微量元素图解上,大离子亲石元素相对富集,高场强元素相对亏损。全岩εNd(t)和tDM1(Nd)分别为-1. 20～2. 13和2. 73～2. 95Ga(7个样品),岩浆锆石εHf(t)和tDM1(Hf)分别为1. 66～4. 37和2. 60～2. 78Ga(13个数据点),δ~(18)O值为5. 00‰～6. 83‰(13个数据点)。相对于闪长岩-石英闪长岩,基性岩包体(3个样品)的MgO和CaO含量明显增高。岩石稀土总量偏低(TREE=82. 4×10~(-6)～155. 7×10~(-6)),轻重稀土分离不强((La/Yb)N=3. 3～6. 0),出现较弱的负铕异常(Eu/Eu*=0. 71～0. 88),在MORB标准化的微量元素图解上,大离子亲石元素相对富集,高场强元素相对亏损。全岩εNd(t)和tDM1(Nd)分别为-0. 70和2. 97Ga(1个样品),岩浆锆石εHf(t)和tDM1(Hf)分别为0. 52～4. 72和2. 66～2. 82Ga(16个数据点),δ~(18)O值为4. 88‰～6. 72‰(13个数据点)。结合前人研究,可得出如下结论:1)界岭口闪长岩是基性岩浆结晶分异和陆壳物质影响双重作用的产物,而陆壳物质参与可能起了更重要的作用; 2)界岭口闪长岩形成于新太古代晚期总体上仍处于挤压的岛弧构造环境; 3)在华北克拉通,至少一部分具有中太古代晚期-新太古代早期Nd-Hf模式年龄的新太古代晚期TTG岩石形成与新太古代晚期富集地幔添加有关或是新太古代晚期亏损地幔添加与陆壳物质影响共同作用的结果。  相似文献   

西准噶尔巴音达拉地区卡拉岗组火山岩锆石U-Pb年代学、地球化学及其地质意义   总被引：1，自引：1，他引：0       下载免费PDF全文

刘阁  舍建忠  杨文龙  王庆军  贾健  邸晓辰 《中国地质》2018,45(6):1241-1250

西准噶尔巴音达拉地区发育一套酸性火山岩,被称为卡拉岗组,岩石组合以流纹岩、英安岩、流纹质熔结凝灰岩等酸性火山岩为主。本文对卡拉岗组火山岩进行高精度锆石LA-ICP-MS U-Pb测年,获得英安岩和流纹岩的加权平均²⁰⁶Pb/²³⁸U年龄分别为（294.4±1.3）Ma（n=9,MSWD=0.8）和（298.4±2.5）Ma（n=9,MSWD=3.4）,其形成于早二叠世。岩石地球化学特征表明,卡拉岗组火山岩岩具有高硅（66.69%~75.21%）,富碱（Na₂O+K₂O：6.98%~8.35%）,低MgO（0.18%~1.32%）,贫钙（0.24%~2.49%）的特征,均属过铝质（A/CNK：1.14~1.33）及高钾钙碱性系列。微量元素数据显示,稀土总量为∑REE为83.82×10^-6~197.61×10^-6,（La/Yb）_N=3.15~12.50,轻、重稀土元素分馏比较明显,轻稀土元素（LREE）较为富集,重稀土元素分布相对平坦,球粒陨石标准化配分模式为右倾型。微量元素富集大离子亲石元素（LILE）Rb、Th、U、K,并亏损高场强元素（HFSE）_Nb、Ta、P、Ti。综合最新区域资料及本文研究成果,文章认为研究区早二叠世卡拉岗组火山岩岩浆来源于壳源物质不同程度的部分熔融,残留相中有少量斜长石和角闪石,为后碰撞伸展阶段的产物。  相似文献   

新疆准噶尔古生代洋盆闭合时限——来自卡拉麦里地区石炭纪碎屑锆石U-Pb年代学的约束   总被引：4，自引：0，他引：4  

白建科  陈隽璐  唐卓  张越 《地质通报》2018,37(1):26-38

新疆准噶尔古生代洋盆闭合时限对中亚造山带古生代构造格局及演化研究具有重要意义。东准噶尔卡拉麦里断裂带南缘广泛出露石炭纪陆相粗碎屑岩系,沉积相分析表明其形成于扇三角洲沉积环境。依据区域地层对比、岩石组合特征及地层接触关系,将其重新厘定为山梁砾石组。选择西段滴水泉和东段双井子2个地区的山梁砾石组剖面进行地层对比,并在2个剖面底部采集粗砂岩样品进行LA-ICP-MS锆石U-Pb年龄测定,获得最年轻的碎屑锆石年龄分别为349±4Ma和355±3Ma,代表山梁砾石组沉积时代晚于349Ma,应为早石炭世早期。碎屑锆石年龄分布特征及砾石成分表明,其物源主要来自断裂带北侧的泥盆纪火山岩。在分析前人资料的基础上,认为山梁砾石组碎屑岩系是卡拉麦里造山带强烈隆升造山过程的沉积学响应,形成于前陆盆地,限定了准噶尔古生代洋盆闭合时限在早石炭世早期之前。  相似文献   

Upper mantle anisotropy inferred from shear wave splitting beneath the Eastern Indian Shield region     

《地学前缘(英文版)》2018,9(6):1911-1920

We estimate the shear wave splitting parameters vis-à-vis the thicknesses of the continental lithosphere beneath the two permanent seismic broadband stations located at Dhanbad (DHN) and Bokaro (BOKR) in the Eastern Indian Shield region. Broadband seismic data of 146 and 131 teleseismic earthquake events recorded at DHN and BOKR stations during 2007–2014 were analyzed for the present measurements. The study is carried out using rotation-correlation and transverse component minimization methods. We retain our “Good”, “Fair” and “Null” measurements, and estimate the splitting parameters using 13 “Good” results for DHN and 10 “Good” results for BOKR stations. The average splitting parameters (ϕ, δt) for DHN and BOKR stations are found to be 50.76°±5.46° and 0.82 ± 0.2 s and 56.30°±5.07° and 0.95 ± 0.17 s, and the estimated average thicknesses of the anisotropic layers beneath these two stations are ∼ 94 and ∼109 km, respectively. The measured deviation of azimuth of the fast axis direction (ϕ) from the absolute motion of the Indian plate ranges from ∼8° to 14°. The measured deviation of azimuth of the fast axis direction (ϕ) from the absolute motion of the Indian plate ranges from ∼8° to 14°. The eastward deviation of the fast axis azimuths from absolute plate motion direction is interpreted to be caused by induced outflow from the asthenosphere. Further, the delay time found in the present analysis is close to the global average for continental shield areas, and also coherent with other studies for Indian shield regions. The five “Null” results and the lower delay time of ∼0.5–0.6 s might be indicating multilayer anisotropy existing in the mantle lithosphere beneath the study area.  相似文献   

The effect of sea-level rise in the 21st century on marine structures along the Mediterranean coast of Israel: An evaluation of physical damage and adaptation cost     

《Applied geography (Sevenoaks, England)》2015

This study presents estimates of the impact adaptation costs due to damage to coastal and marine structures located along the Mediterranean coast of Israel caused by sea-level rise in the 21st century. The study examines the effects on various types of constructions, including seaports, power plants, marinas, desalination plants, sea walls, detached breakwaters, and bathing beach infrastructures for sea-level rises of 0.5 m and 1 m. To this end, we conduct an analysis of hydrodynamic forces on the structures and an uncertainty analysis of their occurrence. The study find that the impact of wave overtopping of breakwaters can lead to extensive damage to port infrastructure and to the vessels moored inside. Adaptation costs are computed as the corrective measures to be taken to maintain the functionality of the structures.  相似文献   

从清代新疆屯垦政策角度谈屯田与生态环境的关系——以天山北路东部屯垦为中心     

刘超建 《干旱区地理》2015,38(2)

近年来,清代新疆屯田与生态环境的关系已成为研究热点。但多数只是从经济史或社会史的角度,作为研究的出发点,只注重了屯田对环境所造成的负面影响,对其正面影响多无涉及,得出屯田是造成土地沙漠化扩大的主要因素。事实上,这样的结论并不符合历史事实。为此,选取清代天山北路东部屯垦作为研究对象,运用历史农业地理的理论与方法,在小尺度的范围内,探求屯垦政策下所进行的农业开发与生态环境变化之间的互动性,以求对二者之间关系有个正确的定位。其主旨不是就清代屯田对生态环境影响进行的重新研究,而是从屯垦政策的角度,通过对清代移民人口、屯田规模、农业技术选择、土地权属及在屯田过程中所形成相关人文要素进行探讨,并由此所引起的屯田与生态环境的关系进行分析。结果表明屯田对生态环境影响主要表现在其积极的方面上,即戈壁变为绿洲,而不是所说的屯田引起沙漠化扩大,也就是说,其负面影响并不突出。这样就为我们能够正确认识清代新疆地区环境变迁提供了理论及事实上的支持。从而得出,自然本身、战争等其它要素,应该是环境变迁的主要因素。  相似文献   

Structural evolution of the Irtysh Shear Zone (northwestern China) and implications for the amalgamation of arc systems in the Central Asian Orogenic Belt     

《Journal of Structural Geology》2015

The NW–SE Irtysh Shear Zone is a major tectonic boundary in the Central Asian Orogenic Belt (CAOB), which supposedly records the amalgamation history between the peri-Siberian orogenic system and the Kazakhstan/south Mongolia orogenic system. However, the tectonic evolution of the Irtysh Shear Zone is not fully understood. Here we present new structural and geochronological data, which together with other constraints on the timing of deformation suggests that the Irtysh Shear Zone was subjected to three phases of deformation in the late Paleozoic. D₁ is locally recognized as folded foliations in low strain areas and as an internal fabric within garnet porphyroblasts. D₂ is represented by a shallowly dipping fabric and related ∼ NW–SE stretching lineations oriented sub-parallel to the strike of the orogen. D₂ foliations are folded by ∼ NW–SE folds (F₃) that are bounded by a series of mylonite zones with evidence for sinistral/reverse kinematics. These fold and shear structures are kinematically compatible, and thus interpreted to result from a transpressional deformation phase (D₃). Two samples of mica schists yielded youngest detrital zircon peaks at ∼322 Ma, placing a maximum constraint on the timing of D₁–D₃ deformation. A ∼ NE–SW granitic dyke swarm (∼252 Ma) crosscuts D₃ fold structures and mylonitic fabrics in the central part of the shear zone, but is displaced by a mylonite zone that represents the southern boundary of the Irtysh Shear Zone. This observation indicates that the major phase of D₃ transpressional deformation took place prior to ∼252 Ma, although later phases of reactivation in the Mesozoic and Cenozoic are likely. The late Paleozoic deformation (D₁–D₃ at ∼322–252 Ma) overlaps in time with the collision between the Chinese Altai and the intra-oceanic arc system of the East Junggar. We therefore interpret that three episodes of late Paleozoic deformation represent orogenic thickening (D₁), collapse (D₂), and transpressional deformation (D₃) during the convergence between the Chinese Altai and the East Junggar. On a larger scale, late Paleozoic sinistral shearing (D₃), together with dextral shearing farther south, accommodated the eastward migration of internal segments of the western CAOB, possibly associated with the amalgamation of multiple arc systems and continental blocks during the late Paleozoic.  相似文献   

东秦岭火山岩的壳幔热动力状态及造山模式     

何瑞芳  段联合 《地球科学与环境学报》1993,(3)

根据火山岩、沉积岩、变质作用与花岗岩成岩和形成环境的综合研究,本文确认熊耳群玄武粗安岩-英安流纹岩组合、大红口组粗面岩组合具低级壳幔热动力状态,形成于大陆裂谷环境;秦岭群、宽坪群变拉斑玄武岩建造具中级壳幔热动力状态,形成于海槽环境;二郎坪群、丹凤群细碧岩-石英角斑岩建造发育于高级壳幔热动力状态的海盆环境,具有下地幔岩石圈拆离导致的A型俯冲造山模式。  相似文献   

Topographic signatures of progressive glacial landscape transformation     

Moritz Liebl  Jörg Robl  David Lundbek Egholm  Günther Prasicek  Kurt Stüwe  Gerit Gradwohl  Stefan Hergarten 《地球表面变化过程与地形》2021,46(10):1964-1980

The Pleistocene glaciations left a distinct topographic footprint in mountain ranges worldwide. The geometric signature of glacial topography has been quantified in various ways, but the temporal development of landscape metrics has not been traced in a landscape evolution model so far. However, such information is needed to interpret the degree of glacial imprint in terms of the integrated signal of temporal and spatial variations in erosion as a function of glacial occupation time. We apply a surface process model for cold-climate conditions to an initially fluvial mountain range. By exploring evolving topographic patterns in model time series, we determine locations where topographic changes reach a maximum and where the initial landscape persists. The signal of glacial erosion, expressed by the overdeepening of valleys and the steepening of valley flanks, develops first at the glacier front and migrates upstream with ongoing glacial erosion. This leads to an increase of mean channel slope and its variance. Above steep flanks and head-walls, however, the observed mean channel slope remains similar to the mean channel slope of the initial fluvial topography. This leads to a characteristic turning point in the channel slope–elevation distribution above the equilibrium line altitude, where a transition from increasing to decreasing channel slope with elevation occurs. We identify this turning point and a high channel slope variance as diagnostic features to quantify glacial imprint. Such features are abundant in glacially imprinted mid-latitude mountain ranges such as the Eastern Alps. By analysing differently glaciated parts of the mountain range, we observe a decreasing clarity of this diagnostic morphometric property with decreasing glacial occupation. However, catchments of the unglaciated eastern fringe of the Alps also feature turning points in their channel slope–elevation distributions, but in contrast to the glaciated domain, the variance of channel slope is small at all elevation levels.  相似文献   

Archean Granitoids at the Contact of Eastern Ghat Granulite Belt and Singhbhum-Orissa Craton, in Bhuban-Rengali Sector, Orissa, India     

S. Misra  S. Moitra  S. Bhattacharya  T.V. Sivaraman 《Gondwana Research》2000,3(2):205

The small granite plutons occurring at the contact of the Singhbhum-Orissa Iron Ore craton (IOC) to the north and the Eastern Ghat Granulite Belt (EGGB) to the south in eastern Indian shield are characterised by the presence of enclaves of the granulites of EGGB and the greenschist facies rocks of IOC. These granites also bear the imprints of later cataclastic deformation which is present at the contact of the IOC and the EGGB. In situ Pb-Pb zircon dating of these granites gives minimum age of their formation 2.80 Ga. A whole-rock three point Rb-Sr isochron age of this rock is found to be 2.90 Ga. Therefore, the true age of formation of these granites will be around 2.90–2.80 Ga. These granitic rocks also contain xenocrystic zircon components of 3.50 Ga and show a later metasomatic or metamorphic effect 2.48 Ga obtained from the analyses on overgrowths developed on 2.80 Ga old zircon cores. The presence of granulitic enclaves within these contact zone granite indicates that the granulite facies metamorphism of the EGGB is 2.80 Ga or still older in age. The cataclastic deformations observed at the contact zone of the two adjacent cratons is definitely younger than 2.80 Ga and possibly related to 2.48 Ga event observed from the overgrowths. As 2.80 Ga granite plutons of small dimensions are also observed at the western margin of the IOC; it can be concluded that a geologic event occurred 2.80 Ga over the IOC when small granite bodies evolved at the marginal part of this craton after its stabilisation at 3.09 Ga.  相似文献