Alteration of hydrological processes and streamflow with juniper (Juniperus virginiana) encroachment in a mesic grassland catchment          下载免费PDF全文

Chris B. Zou  Donald J. Turton  Rodney E. Will  David M. Engle  Sam D. Fuhlendorf 《水文研究》2014,28(26):6173-6182

To understand the effect of woody plant encroachment on hydrological processes of mesic grasslands, we quantified infiltration capacity in situ, the temporal changes in soil water storage, and streamflow of a grassland catchment and a catchment heavily encroached by juniper (Juniperus virginiana, eastern redcedar) in previously cultivated, non‐karst substrate grasslands in north‐central Oklahoma for 3 years. The initial and steady‐state infiltration rates under the juniper canopy were nearly triple to that of the grassland catchment and were intermediate in the intercanopy spaces within the encroached catchment. Soil water content and soil water storage on the encroached catchment were generally lower than on the grassland catchment, especially when preceding the seasons of peak rainfall in spring and fall. Frequency and magnitude of streamflow events were reduced in the encroached catchment. Annual runoff coefficients for the encroached catchment averaged 2.1%, in contrast to 10.6% for the grassland catchment. Annual streamflow duration ranged from 80 to 250 h for the encroached catchment compared with 600 to 800 h for the grassland catchment. Our results showed that the encroachment of juniper into previously cultivated mesic grasslands fundamentally alters catchment hydrological function. Rapid transformation of mesic grassland to a woodland state with juniper encroachment, if not confined, has the potential to drastically reduce soil water, streamflow and flow duration of ephemeral streams in the Southern Great Plains. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Late Triassic E-MORB-like basalts associated with porphyry Cu-deposits in the southern Yidun continental arc,eastern Tibet: Evidence of slab-tear during subduction?     

《Ore Geology Reviews》2017

It is generally believed that andesite–dacite–rhyolite suites and contemporary porphyry Cu deposits are related to subduction in active continental margin settings. However, it is still unclear which tectonic events result in the generation of porphyry Cu deposits and whether asthenospheric mantle material is involved in this process. Widespread andesitic–dacitic felsic intrusions associated with porphyry Cu deposits and rarer basalts have been identified in the Late Triassic southern Yidun arc (SYA) of eastern Tibet. However, few geochronological and geochemical data are available for these basalts, thereby hampering the development of geodynamic models for this magmatic event and the formation of related porphyry Cu deposits in the region. Here we present the first geochemical and SIMS (secondary ion mass spectrometry) zircon U–Pb data of Xiaxiaoliu basalts in the SYA. The age of the Late Triassic Xiaxiaoliu basalts (216.1 ± 2.8 Ma) is consistent with the timing of emplacement of voluminous porphyritic intrusions and the formation of Cu deposits within the SYA (peaking at 215–217 Ma). The Xiaxiaoliu basalts have E-MORB-like trace element patterns that are free of negative Nb–Ta anomalies, and have high ¹⁴³Nd/¹⁴⁴Nd_(t) values, suggesting they were sourced from asthenospheric mantle without any arc-type influence. These observations, combined with the fact that some Late Triassic mineralized porphyritic intrusions within the SYA have adakitic affinities, suggest that the basalts and other igneous rocks and associated porphyry Cu deposits within the SYA were produced by tearing of a westward-dipping slab, triggering the upwelling of asthenospheric mantle material during subduction of the Garze–Litang Ocean crust.  相似文献   

Control of syntectonic erosion and sedimentation on kinematic evolution of a multidecollement fold and thrust zone: Analogue modeling of folding in the southern subandean of Bolivia     

《Journal of Structural Geology》2016

Several analogue modeling studies have been conducted during the past fifteen years with the aim to discuss the effects of sedimentation and erosion on Foreland Fold and Thrust Belt, among which a few have analyzed these processes at kilometric scale (Malavieille et al., 1993; Nalpas et al., 1999; Barrier et al., 2002; Pichot and Nalpas, 2009). The influence of syn-deformation sedimentation and erosion on the structural evolution of FFTB has been clearly demonstrated. Here, we propose to go further in this approach by the study of a more complex system with a double decollement level. The natural study case is the Bolivian sub-Andean thrust and fold belt, which present all the required criteria, such as the double decollement level. A set of analogue models performed under a CT-scan have been used to test the influence of several parameters on a fold and thrust belt system, among which: (i) the spatial variation of the sediment input, (ii) the spatial variation of the erosion rate, (iii) the relative distribution of sedimentation between foreland and hinterland. These experiments led to the following observations:

• 1. The upper decollement level acts as a decoupling level in case of increased sedimentation rate: it results in the verticalization of the shallower part (above the upper decollement level), while the deeper parts are not impacted.
• 2. Similarly, the increase of the erosion rate involves the uplift of the deeper part (below the upper decollement level), whereas the shallower parts are not impacted.
• 3. A high sedimentation rate in the foreland involves a fault and fold vergence reversal, followed by a back-thrusting of the shallower part.
• 4. A high sedimentation rate in the hinterland favours thrust development toward the foreland in the shallower parts.

  相似文献   

皖南晚中生代花岗闪长岩地球化学:成岩成矿制约   总被引：3，自引：2，他引：1  

谢建成  夏冬梅  方德  闫峻  杨晓勇  孙卫东  李全忠 《岩石学报》2016,32(2):439-455

皖南地区是铜、钼、金多金属成矿区,成矿与晚中生代花岗闪长岩类关系密切。近十年来,皖南花岗闪长岩的成因仍然存在分歧。本次报道了皖南花岗闪长岩全岩主、微量元素和锆石原位元素数据。皖南花岗闪长岩(Si O2=64.3%~70.8%)为高钾钙碱性、过铝质岩石,具有相似的埃达克岩特征:高Si O2、Sr/Y(17.1)和(La/Yb)N(14.9)比值,低Yb(1.72×10-6)和Y(18.4×10-6)含量。它们也具有较低Al2O3和Cr(3.40×10-6~10.0×10-6)含量、低Mg#(0.34~0.42)和Nb/Ta(9.6~13.3)值,高K2O和Ba(404×10-6)含量,高K2O/Na2O(0.89~1.55)、Th/La(0.27~0.51)和Th/U(2.79~7.49)比值。锆石原位地球化学特征显示其岩浆源区为低温(锆石Ti-in-zircon温度均值674℃)和高氧逸度(lgfO2集中在-21.4~-9.18,均值-16.4;锆石Ce4+/Ce3+平均值276)的陆壳。这些特征说明皖南花岗闪长岩可能起源于较年轻的加厚下地壳的部分熔融,并经历了斜长石、钾长石和铁镁矿物等结晶分异作用。它们可能形成于与古太平洋板块俯冲密切相关的大陆活动边缘弧至弧后拉张构造转换背景。本区大规模Cu、Mo、Au成矿作用与岩浆的高氧逸度密切相关,而锆石Ce4+/Ce3+可作为矿床勘探一个有效的指标。  相似文献   

天山南麓库车晚新生代褶皱-冲断带   总被引：2，自引：1，他引：1  

文磊  杨海军  李曰俊  彭更新  杨宪彰  黄智斌  罗俊成  张强 《岩石学报》2016,32(3):847-855

库车褶皱冲断带位于天山南麓,由近东西走向的多条构造带组成。三叠系暗色泥岩、侏罗系煤层、古近系库姆格列木组膏盐层和新近系吉迪克组膏盐层构成库车褶皱冲断带的区域性主滑脱面。褶皱冲断带底面由北向南逐渐抬高。褶皱冲断带主体发育盖层滑脱-冲断构造(薄皮构造),基底卷入型冲断构造(厚皮构造)见于北缘的根带。新生界膏盐层之上构造变形以滑脱褶皱为特色,之下以冲断构造为特色。库车褶皱冲断带是印度-亚洲碰撞远程效应下,(南)天山晚新生代造山过程的产物。褶皱冲断带构造变形的动力来源主要是造山楔向塔里木盆地推进所形成的挤压构造应力。褶皱冲断带构造变形的起始时间为约23Ma,构造变形具有阶段式加速的特点,已经识别出约23Ma、约10Ma、5~2Ma和1~0Ma共4个变形加速期。褶皱冲断带的演化过程为前展式,褶皱冲断带前锋向南推进的同时,后缘持续变形。  相似文献   

湘南荷花坪锡多金属矿床成矿年代研究   总被引：1，自引：1，他引：0  

蔡明海  张文兵  彭振安  刘虎  郭腾飞  谭泽模  唐龙飞 《岩石学报》2016,32(7):2111-2123

荷花坪锡多金属矿床是本世纪初在南岭中段湘南地区新发现的一个大型矿床,区内的锡多金属矿化产在王仙岭岩体东南内、外接触带,已发现有Ⅰ、Ⅱ、Ⅲ和Ⅳ号4个主要锡多金属矿体。其中,Ⅰ、Ⅱ和Ⅳ号矿体由早期矽卡岩型和晚期蚀变碎裂岩型矿石组成,Ⅲ号矿体则由独立产出的蚀变碎裂岩型矿石组成,且包含有部分碎裂花岗斑岩。以往研究已对Ⅳ号矿体中的矽卡岩型矿石和Ⅲ号矿体中含矿斑岩脉分别采用辉钼矿Re-Os法和锆石SHRIMP U-Pb法进行了测年,获得的年龄分别为224.0±1.9Ma和142±2Ma。本文补充了晚期蚀变碎裂岩型矿石的~(40)Ar/~(39)Ar测年,结果显示,Ⅱ号矿体中蚀变碎裂岩型矿石白云母样品和石英样品的坪年龄分别为151.88±1.58Ma和155.39±7.04Ma;Ⅳ号矿体中蚀变碎裂岩型矿石石英样品的坪年龄为156.94±1.64Ma。结合前人研究资料综合分析,认为荷花坪矿区存在印支晚期(224Ma)、燕山早期(151~156Ma)和燕山晚期(142Ma)三期成矿作用,分别与区内印支期中粗粒含电气石黑云母花岗岩、燕山早期中粗粒黑云母花岗岩和燕山晚期花岗斑岩脉有关,不同期成岩、成矿作用的构造环境均为岩石圈的拉张伸展。湘南地区印支期(205~224Ma)基性岩浆活动及荷花坪矿床印支期成岩、成矿过程中均有幔源物质的参与,它们共同指示南岭地区中生代构造体制的转换或岩石圈伸展减薄可能始于印支主期(230~244Ma)之后的224Ma左右,即晚三叠世。  相似文献   

南大洋太平洋扇区中尺度涡旋的统计特性及其变化   总被引：1，自引：0，他引：1  

段永亮  刘洪伟  于卫东  侯一筠 《海洋学报(英文版)》2016,35(11):28-34

中尺度涡旋在南大洋海洋动力学中具有重要地位,其对气候变化的响应表现也引起了海洋学家与气候学家的广泛关注。本文利用涡动动能与涡旋自动探测技术两种方法对南大洋太平洋扇区的涡旋特性及其变化进行了分析。与前人结果相一致的是,高值的涡动动能主要集中在南极极锋海区,并且自西向东逐渐减弱。在过去的20年里,涡动动能在太平洋扇区的显著增强也集中在中西部海域,这里也是南极绕极流斜压性较强的海域。涡旋统计特性揭示了涡动动能的空间分布及其年际变化主要归因于涡旋振幅与旋转速度,而并非涡旋个数或者涡旋半径。这些结果进一步确认了对应于南半球环状模正位相的绕极西风异常改变了南大洋的涡旋特性,从而表现出涡旋活跃性增强。  相似文献   

Origin of the Breno and Esino dolomites in the western Southern Alps (Italy): Implications for a volcanic influence     

《Marine and Petroleum Geology》2016

The Esino Limestone of the western Southern Alps represents a differentiated Ladinian-Lower Carnian (?) carbonate platform comprised of margin, slope and peritidal inner platform facies up to 1000 m thick. A major regional subaerial exposure event lead to coverage by another peritidal Lower Carnian carbonate platform (Breno Formation). Multiphase dolomitization affected the carbonate sediments. Petrographic examinations identified at least three main generations of dolomites (D1, D2, and D3) that occur as both replacement and fracture-filling cements. These phases have crystal-size ranges of 3–35 μm (dolomicrite D1), 40–600 μm (eu-to subhedral crystals D2), and 200 μm to 5 mm (cavity- and fracture-filling anhedral to subhedral saddle dolomite D3), respectively.The fabric retentive near-micritic grain size coupled with low mean Sr concentration (76 ± 37 ppm) and estimated δ¹⁸O of the parent dolomitizing fluids of D1 suggest formation in shallow burial setting at temperature ∼ 45–50 °C with possible contributions from volcanic-related fluids (basinal fluids circulated in volcaniclastics or related to volcanic activity), which is consistent with its abnormally high Fe (4438 ± 4393 ppm) and Mn (1219 ± 1418 ppm) contents. The larger crystal sizes, homogenization temperatures (D2, 108 ± 9 °C; D3, 111 ± 14 °C) of primary two-phase fluid inclusions, and calculated salinity estimates (D2, 23 ± 2 eq wt% NaCl; D3, 20 ± 4 eq wt% NaCl) of D2 and D3 suggest that they formed at later stages under mid-to deeper burial settings at higher temperatures from dolomitizing fluids of higher salinity, which is supported by higher estimated δ¹⁸O values of their parent dolomitizing fluids. This is also consistent with their high Fe (4462 ± 4888 ppm; and 1091 ± 1183 ppm, respectively) and Mn (556 ± 289 ppm and 1091 ± 1183 ppm) contents, and low Sr concentrations (53 ± 31 ppm and 57 ± 24 ppm, respectively).The similarity in shale-normalized (SN) REE patterns and Ce (Ce/Ce*)_SN and La (Pr/Pr*)_SN anomalies of the investigated carbonates support the genetic relationship between the dolomite generations and their calcite precursor. Positive Eu anomalies, coupled with fluid-inclusion gas ratios (N₂/Ar, CO₂/CH₄, Ar/He), high F⁻ concentration, high F/Cl and high Cl/Br molar ratios suggest an origin from diagenetic fluids circulated through volcanic rocks, which is consistent with the co-occurrence of volcaniclastic lenses in the investigated sequence.  相似文献   

青海南山地区角孔变质岩地质特征、年代学及其地质意义     

李佐臣  裴先治  李瑞保  裴磊  张永明  王旭斌  刘成军  陈有炘  王盟 《地质通报》2018,37(4):570-588

青海南山达不祖乎山北部一带的角孔变质岩系原划为早中三叠世隆务河组。通过野外实测地质剖面和路线地质调查,查明该套地层单元野外产出状态及岩石组合特征,并对其物质来源和形成时代进行分析,对进一步研究该区晚古生代-早中生代的构造演化具有重要意义。该套变质岩系为一套长石石英岩、石英岩、大理岩和黑云石英片岩组合,由下向上划分为3个岩段,叠置厚度大于3186.3m。根据碎屑锆石年龄分布特征,可大致划分为5个年龄组段,分别为250～304Ma、405～546Ma、649～1077Ma、1402～1620Ma和1861～2990Ma,其中250～304Ma可进一步划分为250～269Ma和289～304Ma两个亚组。综合前人研究资料与区域构造岩浆活动,将青海南山地区角孔变质岩的沉积时代限定为二叠纪,物源主要来自祁连造山带加里东期和晋宁期岩浆弧,柴北缘构造带海西期岩浆弧也提供了部分物质,晚古生代—早中生代经历了陆内裂陷、洋盆拉张及俯冲碰撞的构造演化过程。  相似文献   

Early Cretaceous K-rich rhyolites from the Duolong Cu–Au deposit,southern Qiangtang,China: evidence for crustal growth     

Wei Wang  Cai Li  Jian-Jun Fan  Wei Xu  Yu-Chao Dong 《International Geology Review》2018,60(9):1098-1115

We report new zircon U–Pb age, Hf isotopic, and major and trace element data for rhyolites from the Duolong Ore Concentration Area of the Southern Qiangtang Terrane. Building on previous studies, we constrain the tectonic setting and propose a model to explain the geodynamics and crustal growth during regional magmatism in the Early Cretaceous. The analysed rhyolites yield laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) zircon U–Pb ages of 115 and 118 Ma. The rocks are K-rich (K₂O = 6.66–9.93 wt.%; K₂O/Na₂O = 8.2–19.7 wt.%), alkaline and peraluminous (A/CNK = 1.02–1.46), and are characterized by high SiO₂ contents (72.8–78.8 wt.%) similar to highly fractionated I-type granites. Fractionation of Fe–Ti oxides, plagioclase, hornblende, Ti-bearing phases, apatite, monazite, allanite and zircon contributed to the variations in major and trace element chemistry. High K₂O contents are likely due to partial melting of the continental crust. The samples have positive zircon εHf(t) values ranging from +7.1 to +11.2. These features, together with young zircon Hf crustal model ages of 489–721 Ma, indicate that the K-rich rhyolites were derived from juvenile lower crust with an input of a mantle-derived component. We suggest that the Early Cretaceous K-rich rhyolites formed in a continental arc setting during northward subduction of Bangong Co–Nujiang oceanic lithosphere. Basaltic magma underplating was responsible for vertical crustal growth, triggered by slab roll-back in the Duolong Ore Concentration Area in the Early Cretaceous.  相似文献