北极斯瓦尔巴、高亚洲和阿尔卑斯山冰川物质平衡对比研究     

何海迪  李忠勤  叶万花  梁鹏斌  牟建新  张明军 《冰川冻土》2018,40(2):205-213

基于冰川物质平衡和平衡线高度数据,对北极斯瓦尔巴、高亚洲和阿尔卑斯山的冰川物质平衡变化和平衡线高度空间分布特征进行了对比分析,得出以下结论：（1）阿尔卑斯山冰川年均负物质平衡值最大,为-907 mm;斯瓦尔巴为-431 mm;高亚洲最小,为-264 mm。（2）高亚洲和斯瓦尔巴冰川物质平衡年振幅较小,年际变化较小;阿尔卑斯山冰川物质平衡年振幅较大,年际变化较大。斯瓦尔巴冰川物质平衡趋向正平衡,阿尔卑斯山和高亚洲冰川物质平衡趋向负平衡。（3）斯瓦尔巴内陆的冰川平衡线高度高于沿海地区,高亚洲冰川平衡线高度呈纬向地带性、经向地带性和区域地带性的分布规律,阿尔卑斯山的冰川平衡线高度主要受冰川所处海拔的影响。  相似文献   

福贡地区石炭系地层可能属于拉萨地块:来自碎屑锆石年龄谱的指示   总被引：1，自引：1，他引：0  

信迪  杨天南  薛传东  廖程  韩雪  梁明娟  李晓天 《岩石学报》2018,34(5):1335-1346

欧亚与印度大陆的碰撞使得印度大陆的北东角强烈挤入欧亚大陆内部,形成东构造结,其引发的强烈变形将南羌塘地块、北羌塘地块、拉萨地块、保山地块、兰坪-思茅地块以及地块之间的缝合带挤压于很窄的范围内,造成青藏高原腹地与其东南缘之间构造单元划分、对比困难。滇西福贡地区位于青藏高原东南缘,东构造结影响范围内,是三江造山带及青藏高原相关地块的汇聚处。福贡地区石炭系岩石组合表明其形成于较为稳定的浅海相沉积环境中,具有被动大陆边缘沉积特征。三件石炭系二云母石英片岩碎屑锆石表面年龄数据(194个有效分析点)形成五个主要年龄区间:2550~2400Ma、1800~1550Ma、1200~1080Ma、1000~850Ma和600~480Ma,峰值分别为~2502Ma、~1724Ma、~1120Ma、~886Ma和~512Ma。对比其他地块同时代地层的碎屑锆石年龄谱表明,福贡地区石炭系可能是拉萨地块的一部分,与腾冲地块一样,属于其南延部分。结合中新生代岩浆岩带的构造连续性,我们认为,印度板块东北角向北、北东方向的强烈挤压导致拉萨地块及冈底斯岩浆岩带弯曲、缩颈、并发生分离与旋转。  相似文献   

Late Quaternary Slip Rate of the Xiugou Segment,Eastern Kunlun Fault Zone   总被引：1，自引：0，他引：1  

Feipeng Huang  Junjie Ren  Yanwu Lü  Junxiang Zhao 《地球科学进展》2018,33(3):321-332

The Eastern Kunlun fault zone (EKLF) is a large left-lateral strike-slip fault, whose slip rate is meaningful to seismic hazard assessment and geodynamics of the Tibetan Plateau. Previous studies suggested that the late Quaternary average slip rate was stable and uniform (10~13 mm/a) in the central and western segment of the EKLF. But there were a few researches of accurate slip rate in the central segment on the EKLF. Therefore, we focused on an offset and well preserved alluvial fan from Xiugou basin, located in the east of Xidatan-Dongdatan, to make it clear. Moreover, we used high-resolution satellite images and digital elevation model extracted from SPOT7 stereo image pairs to restore the offset alluvial fan, and combined terrestrial cosmogenic nuclides method, including 13 quartz-rich samples from this fan surface, 1 quartz-rich sample from the main active channel bed and 1 ¹⁰Be depth profile from this fan edge to eliminate the ¹⁰Be concentration of inheritance accurately, with 1 optically stimulated luminescence sample to obtain the reliable age of this alluvial fan together. Referring to field observations, this alluvial fan was offset left-laterally by (1 862±103) m, and its age is (76.55±3.20)~(106.37±3.38) ka which can be determined through the actual geologic setting and improving chi-square test. Thus, we used the Monte Carlo method to obtain a left-lateral slip rate of (20.3+3.5/-2.3) mm/a with 68% confidence envelopes since the late Pleistocene in the Xiugou basin. As a result, combining with the results of previous studies, the left-lateral slip rate indicated that the obviously decreasing activity transferred from late Pleistocene to Holocene on the central segment of the EKLF.  相似文献   

Advances and Issues in Luminescence Dating of Loess Deposits in Arid Central Asia   总被引：1，自引：1，他引：0  

Leibin Wang  Haitao Wei  Jia Jia  Guoqiang Li  Fahu Chen 《地球科学进展》2018,33(1):93-102

High-resolution loess deposits are widely distributed in Arid Central Asia (ACA) and provide important records associated with dust transportation, paleoenvironmental and paleoclimatic evolution. The chronology is the foundation of the research into loess deposits as an environmental archive. In recent decades, the gradually developed optical dating method has been increasingly matured and become an important approach to establishing the loess-paleosol sequences. Here, we summarized and discussed previous work on loess chronology mainly based on optical dating approach in ACA. The following understandings have been listed: ① In comparison with optical dating method, the suitable material for ¹⁴C dating is uncommon in ACA. However, the dating range of luminescence dating is more extensive, and the dating materials are accessible. Thus, the optical dating is widely applicable in the establishment of loess framework in this area. ② Until now, the quartz Single Aliquot Regeneration (SAR) method can be applied to the establishment of loess-paleosol sequence since last glacial period. But several issues remain unaddressed. For example, the Optically Stimulated Luminescence (OSL) signal sensitivity of quartz grains are low in some areas. Furthermore, the results of OSL dating of different grain sizes within a single sample are inconsistent in some areas. The solution of these problems still requires more methodological research. ③ The post-IR IRSL (pIRIR) and multiple elevated temperature stimulation (MET-pIRIR) protoCols of feldspar have basically overcome the anomalous fading issue in the traditional IRSL dating process. In ACA, the framework since MIS 7 can be established with K-feldspar luminescence dating method. Compared with quartz luminescence characteristics, the K-feldspar luminescence signals are more sensitive and exhibit a high saturation level. In specific applications, it is necessary to establish the age frame according to the luminescence sensitivity, the age of samples or other factors.  相似文献   

新疆乌鲁木齐东部早二叠世枕状玄武岩火山岩系的发现及大地构造意义     

钟建华  倪良田  邵珠福  孙宁亮  李旭平  刘选  郝兵  刘闯  杨冠群  葛毓柱  陈彬  罗可  黄雷桐  曲俊利  范莉红  王韶洁  王雅琳 《地质学报》2018,92(4):638-664

新疆乌鲁木齐东部野生动物园附近的下二叠统下部发育了一套以枕状玄武岩为代表的火山岩系。该玄武岩在公路上发育有两层,上部一层较厚,可达7～8m,下部一层2～3m。岩枕近圆形、肾状、枕状、条带状或蠕虫状等,多呈顶突底凹。岩枕长轴平行排列,长轴基本顺层面分布;有的岩枕中含大量海百合茎、珊瑚及腕足等生物化石。在TAS图中大部分样品位于玄武粗安岩,而在K_2O-SiO_2图上主要落在低K拉斑玄武岩区间。MnOTiO_2-P_2O_5图解显示以岛弧为主,常量元素的特征总体上更接近岛弧玄武岩。在Hf/3-Th-Ta图解上也以岛弧为主;在Zr/4-2Nb-Y图解显示以火山弧为主,常量元素的特点总体上更接近岛弧玄武岩。微量元素原始地幔标准化蛛网图表明为同源岩浆产物,具高度相似的演化过程,多种微量元素判别图揭示岛弧-弧后盆地环境;稀土总量明显较低,在稀土元素球粒陨石标准化图解上,其稀土分布曲线一致性较好,呈轻稀土富集右倾型,Eu为负异常,揭示了乌东玄武岩岩浆有一定分异。稀土元素配分曲线与弧后盆地玄武岩(BABB)具有很好的一致性。U-Pb和谐年龄为283±8Ma,结合地层及古生物资料推测乌东玄武岩喷发的时间为早二叠世早期。乌东枕状玄武岩-灰岩之下有一套(磨拉石)底砾岩,初定为石炭-二叠系的界限。底砾岩之下为下石炭统的中厚层灰岩,具有明显的喀斯特化,为不整合接触,揭示在两者之间发生了造山作用。通过对新疆乌东早二叠世早期的枕状玄武岩的地质特征、地球化学特征、形成环境和时代的研究,表明乌东一带早二叠世主要为一个岛弧和弧后盆地环境,进一步揭示了北天山北缘石炭-二叠世碰撞闭合造山之后又发生了松弛扩张形成了弧后盆地,海水再度大规模入侵。最终的闭合碰撞造山的时间最早可能在晚二叠世。由于乌东枕状玄武岩在喷出地表后受到了生物化石和陆源碎屑的污染,再加上侵入过程中地壳的污染,使其具有非常复杂的地球化学特点和多解性。乌东玄武岩的研究对于了解博格达山、甚至天山中段在晚古生代的构造沉积演化及造山作用具有重要意义,同时对准噶尔盆地、吐哈盆地及三塘湖盆地油气资源的形成与分布具有重要意义。  相似文献   

辽东半岛大金山花岗岩体SHRIMP U-Pb年龄、元素地球化学和Hf同位素特征及地质意义     

杨佳林  顾玉超  杨凤超  李东涛  鞠楠  贾宏翔 《地质论评》2018,64(6):1541-1556

辽东半岛早白垩世时期受到强烈的构造—岩浆作用使岩石圈构造环境由挤压造山向伸展减薄转变,前人对其成因有所争议。本文通过锆石SHRIMP U- Pb测年、原位Lu- Hf同位素和主量、微量、稀土元素测试对辽东半岛大金山花岗岩体进行了系统研究,结果显示：大金山花岗岩体结晶年龄为~ 124Ma,侵位于早白垩世岩浆活动的高峰期。岩石地球化学特征显示大金山花岗岩属弱过铝质~过铝质岩石,经历了高程度的结晶分异过程,富集Rb、Th、U、K等大离子亲石元素（LILE）,亏损P、Ti等高场强元素（HFSE）,中等Eu负异常,为I型花岗岩。TW003样品εHf(t)值为-25.8~ -14.2,tDM2为2093~2805Ma,岩浆物质来源于新太古代—古元古代下地壳火成岩的部分熔融。根据年代学和岩石地球化学研究认为大金山花岗岩是古太平洋板块向欧亚大陆板块俯冲所形成的活动大陆边缘弧花岗岩,辽东半岛早白垩世的伸展环境是受板块俯冲造山后伸展作用和下地壳拆沉作用的联合制约。  相似文献   

末次间冰期以来源自中亚的粉尘记录的对比   总被引：1，自引：0，他引：1  

邬光剑  姚檀栋 《冰川冻土》2005,27(1):80-87

中亚干旱区是全球重要的粉尘源区, 粉尘经过不同的大气环流系统的搬运和具体的沉积条件, 在其传输路径上沉积于不同的介质中, 如冰芯、黄土、湖泊和深海. 在前人所做工作的基础上, 以古里雅冰芯、宝鸡黄土剖面、琵琶湖风尘沉积、北太平洋风尘沉积和格陵兰冰芯等记录进行对比, 初步讨论近130 ka BP以来上述记录所反映的中亚粉尘的产生、搬运和沉积. 这些记录既表现出一致性, 也存在某些差异, 显示了搬运过程、沉积过程以及区域性因素对粉尘记录的影响.  相似文献   

Surface water and aerosol spatiotemporal dynamics and influence mechanisms over drylands     

《地学前缘(英文版)》2023,14(2):101524

Under the background of global warming and excessive human activities, much surface water in drylands is experiencing rapid degradation or shrinkage in recent years. The shrinkage of surface water, especially the degradation of lakes and their adjacent wetlands in drylands, may lead to the emergence of new salt dust storm hotspots, which causes greater danger. In this paper, based on high spatial resolution global surface water (GSW) and multiangle implementation of atmospheric correction (MAIAC) AOD data, we systematically analyze the dynamic characteristics of surface water and aerosols in typical drylands (Central Asia, CA) between 2000 and 2018. Simultaneously, combined with auxiliary environment variables, we explore the driving mechanisms of surface water on the regional salt/sand aerosols on different spatial scales. The results show that the seasonal surface water features an increasing trend, especially a more dramatic increase after 2015, and the permanent surface water indicates an overall decrease, with nearly 54.367 % at risk of receding and drying up. In typical lakes (Aral Sea and Ebinur Lake), the interannual change feature of the surface water area (WA) is that a continuous decrease during the study period occurs in Aral Sea area, yet a significant improvement has occurred in Ebinur Lake after 2015, and the degradation of Ebinur Lake takes place later and its recovery earlier than Aral Sea. The aerosol optical depth (AOD) in CA shows obvious seasonal variation, with the largest in spring (0.192 ± 0173), next in summer (0.169 ± 0.106), and the smallest in autumn (0.123 ± 0.065). The interannual variation of AOD exhibits an increase from 2000 to 2018 in CA, with high AOD areas mainly concentrated in the Taklamakan Desert and some lake beds resulting from lake degradation, including Aral Sea and Ebinur Lake. The AOD holds a similar trend between Aral Sea and Ebinur Lake on an interannual scale. And the AOD over Ebinur Lake is lower than that over Aral Sea in magnitude and lags behind in reaching the peak compared with Aral Sea. The WA change can significantly affect aerosol variation directly or indirectly on the aerosol load or mode size, but there are obvious differences in the driving mechanisms, acting paths, and influence magnitude of WA on aerosols on different spatial scales. In addition, the increase of WA can significantly directly suppress the increase of Ångström exponent (AE), and the effects of WA on AOD are realized majorly by an indirect approach. From the typical lake perspective, the effects of WA on aerosol in Aral Sea are achieved via an indirect path; and the decrease of WA can indirectly promote the AOD rise, and directly stimulate the AE growth in Ebinur Lake.  相似文献   

Geochronology and geochemistry of lithium-rich tuffs in the Sichuan basin,western Yangtze: Implication for the magmatic origin and final closure of eastern Paleo-Tethys     

《地学前缘(英文版)》2023,14(1):101480

The felsic volcanogenic tuffs named “green-bean rocks” (GBRs), characterized by a green or yellowish green color, are widely distributed in the western Yangtze platform and have a high lithium content (286–957 ppm). This paper studies the ages, origin and tectonic setting of the GBRs in the Sichuan basin on the western margin of the Yangtze platform through the whole-rock geochemistry and zircon trace elements by using U–Pb dating and Hf–O isotopes. The GBR samples from the Quxian and Beibei sections yielded zircon U–Pb ages of 245.5 ± 1.8 Ma and 244.8 ± 2.2 Ma. These samples can be used as the isochronous stratigraphic marker of the Early–Middle Triassic boundary (EMTB) for regional correlation. The whole-rock and zircon geochemistry, and zircon Hf–O isotopes exhibited S-type geochemical affinities with high positive δ¹⁸O values (9.28‰–11.98‰), low negative ε_Hf(t) values (?13.87 to ? 6.79), and T_DM² ages of 2150–1703 Ma, indicating that the lithium-rich GBRs were generated by the remelting of the pre-existing ancient Paleoproterozoic layer without mantle source contamination in the arc-related/orogenic tectonic setting. The results of this study demonstrate that the lithium-rich GBRs in the western Yangtze platform were derived from arc volcanic eruptions along the Sanjiang orogen, triggered by the closure of the eastern Paleo-Tethys Ocean and the syn-collision between the continental Indochina and Yangtze blocks at ca. 247 Ma. This was marked by a major shift from I-type magmas with intermediate ε_Hf(t) values to S-type magmas with low negative ε_Hf(t) values. Collectively, our results provide new insights into the origin of the GBRs and decodes the closure of the eastern Paleo-Tethys.  相似文献   

Trace element and Nd isotope analyses of apatite in granitoids and metamorphosed granitoids from the eastern Central Asian Orogenic Belt: Implications for petrogenesis and post-magmatic alteration     

《地学前缘(英文版)》2023,14(2):101517

We present in situ trace element and Nd isotopic data of apatites from metamorphosed and metasomatized (i.e., altered) and unaltered granitoids in the Songnen and Jiamusi massifs in the eastern Central Asian Orogenic Belt, with the aim of fingerprinting granitoid petrogenesis, including both the magmatic and post-magmatic evolution processes. Apatites from altered granitoids (AG) and unaltered granitoids (UG) are characterized by distinct textures and geochemical compositions. Apatites from AG have irregular rim overgrowths and complex internal textures, along with low contents of rare earth elements (REEs), suggesting the re-precipitation of apatite during epidote crystallization and/or leaching of REEs from apatite by metasomatic fluids. ε_Nd(t) values of the these apatites are decoupled from zircon ε_Hf(t) values for most samples, which can be attributed to the higher mobility of Nd as compared to Sm in certain fluids. Apatites from UG are of igneous origin based on their homogeneous or concentric zoned textures and coupled Nd-Hf isotopic compositions. Trace element variations in igneous apatite are controlled primarily by the geochemical composition of the parental melt, fractional crystallization of other REE-bearing minerals, and changes in partition coefficients. Sr contents and Eu/Eu* values of apatites from UG correlate with whole-rock Sr and SiO₂ contents, highlighting the effects of plagioclase fractionation during magma evolution. Apatites from UG can be subdivided into four groups based on REE contents. Group 1 apatites have REE patterns similar to the host granitoids, but are slightly enriched in middle REEs, reflecting the influence of the parental melt composition and REE partitioning. Group 2 apatites exhibit strong light REE depletions, whereas Group 3 apatites are depleted in middle and heavy REEs, indicative of the crystallization of epidote-group minerals and hornblende before and/or during apatite crystallization, respectively. Group 4 apatites are depleted in heavy REEs, but enriched in Sr, which are features of adakites. Some unusual geochemical features of the apatites, including the REE patterns, Sr contents, Eu anomalies, and Nd isotopic compositions, indicate that inherited apatites are likely to retain the geochemical features of their parental magmas, and thus provide a record of small-scale crustal assimilation during magma evolution that is not evident from the whole-rock geochemistry.  相似文献