念青唐古拉山扎当冰川冰储量估算及冰下地形特征分析

冰川体积估算对水资源以及冰川变化研究具有重要的意义. 但是实测的冰川厚度数据十分稀少,限制了冰川体积的估算. 2011年5月对念青唐古拉山北坡扎当冰川进行了雷达测厚工作,获取了该冰川的厚度分布状况. 基于该冰川的厚度数据,测量点的GPS数据,1970年的地形图和2010年Landsat TM影像,在ArcGIS技术的支持下,采用简单Kriging插值方法对冰川非测厚区域的厚度进行了插值计算,绘制出了冰川厚度等值线图并估算了冰川的冰储量. 结果表明：冰川最大厚度出现于海拔约5 748 m靠近主流线的位置,最大冰厚度为108 m,冰川平均厚度为38.1 m,2010年冰川面积为1.73 km²,扎当冰川的冰储量为0.066 km³. 将扎当冰川表面DEM与冰川厚度分布图相结合,绘制出了该冰川的冰床地形图. 结果显示,在冰川厚度大的区域,冰床地形呈现近V字形分布,这与其相对平缓的冰面地形形成明显对比;同时,在冰表地形较陡区域,冰川厚度不大,冰床地形呈现U形分布.     

Denudation history of the Kiso Range,central Japan,and its tectonic implications: Constraints from low‐temperature thermochronology

Fission‐track (FT) and (U–Th–Sm)/He (He) analyses are used to constrain the denudation pattern and history of the Kiso Range, a Japanese fault‐block mountain range which has been uplifted since ca 0.8 Ma. We obtained nine zircon FT ages ranging 59.3–42.1 Ma, 18 apatite FT ages ranging 81.9–2.3 Ma, and 13 apatite He ages ranging 36.7–2.2 Ma. The apatite FT and He ages are divided into an older group comparable to the zircon FT age range and a younger group of <18 Ma. The younger ages are interpreted as a reflection of uplift of the Kiso Range because they were obtained only to the east of the Seinaiji‐touge Fault, and the event age estimated from apatite FT data is consistent with the timing of the onset of the Kiso Range uplift. On the basis of the distribution of the younger ages, we propose westward tilting uplift of the Kiso Range between the boundary fault of the Inadani Fault Zone and Seinaiji‐touge Fault, which implies a model of bedrock uplift that is intermediate between two existing models: a pop‐up model in which the Kiso Range is squeezed upward between the two faults and a tilted uplift model which assumes that the Kiso Range is uplifted and tilted to the west by the Inadani Fault Zone. The original land surface before the onset of uplift/denudation of the Kiso Range is estimated to have been uplifted to an elevation of 2700–4900 m. We estimated denudation rates at 1.3–4.0 mm/y and maximum bedrock uplift rates at 3.4–6.1 mm/y since ca 0.8 Ma. The Seinaiji‐touge fault is interpreted as a back thrust of the west‐dipping Inadani Fault Zone. The older group of apatite FT and He ages is interpreted to reflect long‐term peneplanation with a probable denudation rate of <0.1 mm/y.     

Petrogenesis and geodynamic significance of the Ganhe Formation lavas,eastern Great Xing'an Range,China: Evidence from geochemistry and geochronology

Mesozoic volcanic rocks are widespread throughout the Great Xing'an Range of northeastern China. However, there has been limited investigation into the age and petrogenesis of the Mesozoic volcanics in the eastern Great Xing'an Range. According to our research, the volcanic rocks of the Dayangshu Basin, eastern Great Xing'an Range are composed mainly of trachybasalt, basaltic andesite, and basaltic trachyandesite, with minor intermediate–basic pyroclastic rocks. In this study, the geochemistry and geochronology of the Mesozoic volcanic rocks are presented in order to discuss the petrogenesis and tectonic setting of the Ganhe Formation in the Dayangshu Basin. Zircon U–Pb dating by laser ablation inductively coupled plasma–mass spectrometry indicates that the Mesozoic lavas formed during the late Early Cretaceous (114.3–108.8 Ma). This suite of rocks exhibits a range of geochemical signatures indicating subduction‐related genesis, including: (i) calc‐alkaline to high‐K calc‐alkaline major element compositions; (ii) enrichment of large ion lithophile elements (e.g. Rb, Ba, K) and light rare earth elements (LREEs/HREEs =7.33–9.85); and (iii) weak depletion in high field strength elements (e.g. Nb, Ta, Ti). Furthermore, Sr–Nd–Pb isotopic data yield initial ⁸⁷Sr/⁸⁶Sr values of 0.70450–0.70463, positive ε_Nd(t) values of +1.8 to +3.3, and a mantle‐derived lead isotope composition. Combined with the regional tectonic evolution, the results of this study suggest that the Ganhe Group lavas are derived from decompression melting of a metasomatized (enriched) lithospheric mantle, related to asthenospheric upwelling, which resulted from lithospheric mantle delamination and produced extension of the continental margin following the subduction of the Paleo‐Pacific Plate.     

Constraining the links between the Himalayan belt and the Central Myanmar Basins during the Cenozoic:An integrated multi-proxy detrital geochronology and trace-element geochemistry study

Geological and tectonic analysis of the Eastern Himalayan basins has given rise to a decade-long debate on the geodynamic evolution of the Burmese terrane and on the extent of reorganization of the main SE Asia drainage systems.However,the influence of the Himalayan belt on the Central Myanmar Basin(CMB)system remains poorly documented,although it is key to providing more accurate models for the evolution of the Himalayan-Burmese orogen.In this contribution,we present geochronological,isotopic and geochemical analysis from 2500 zircon,1700 titanite,700 rutile and 850 apatite detrital grains from fifteen Cenozoic siliciclastic samples and one Cretaceous igneous rock.The samples were collected within the fore-and back-arc basins of the Central Myanmar Basin domain(CMB)to constrain the provenance,maximum depositional ages,and depositional environments of the west Burma terrane.Nine key lithological units,the Sadwingyi,Ketpanda,Wabo Chaung,Gwegon,Minwun,Padaung,Okmintaung and Irrawaddy formations have detrital age spectra spanning from the Miocene to Paleoarchean.The entire data set has common age peaks at ca.20,40,60,90,100 Ma,with about 80%of the U–Pb ages younger than ca.140 Ma and only ca.1%of the grains predating ca.3.0 Ga.Our results shed light on the current ambiguities on the transport pathways of Himalayan detritus in the CMB.They show that the fore-arc basin was open to the trench and fed by the unroofing of both the Wuntho Popa volcanic arc to the east and possibly from the Burmese basement and/or from Himalayan-derived Bengal Fan detritus to the west during the Eocene,from at least ca.44 Ma to before ca.39 Ma.We show that the west Burma Terrane was partitioned into pull-apart basins such as the Minwun Basin,which during the Oligocene recorded the first evidence of a new source contribution into the CMB at ca.27 Ma.This new source is characterized by detritus highly compatible with the SE Asia basement rocks,which we suggest corresponds to the initiation of the palaeo–Irrawaddy River.This geodynamic evolution does not require any Yarlung Tsangpo-Irrawaddy-Brahmaputra paleodrainage reorganization,since from the Oligocene to the Early Miocene,the Irrawaddy River fed an internally drained basin,and from the Late Miocene onwards,the Yarlung drained into the Brahmaputra in the Bengal Basin.     

念青唐古拉花岗岩热演化历史和山脉隆升过程的热年代学分析

念青唐古拉山是青藏高原内部的重要山脉,主体由黑云母二长花岗岩组成,岩体内部发育不同类型的变质岩包体如Lgn、Ygn片麻岩和元古代（Pt）变质岩,岩体东西两侧发育伸展型韧性剪切带。对念青唐古拉黑云母二长花岗岩进行矿物对热年代学分析,良好地揭示了岩浆热演化历史和山脉隆升过程。通过单颗粒锆石离子探针测年,发现65．0～55．0Ma发生早期岩浆侵位事件,形成Lgn、Ygn花岗片麻岩包体;在18．3～11．1Ma期间,在约11km深度的Lgn、Ygn下方发生大规模岩浆侵位和结晶成岩事件,形成念青唐古拉黑云母二长花岗岩（NG）。在11．1～9．3Ma期间,念青唐古拉花岗岩发生快速冷却和隆升过程,平均降温速度约222．2℃／Ma,对应的平均差异隆升速率为5．56mm／a;在9．3～8．6Ma期间,念青唐古拉花岗岩继续发生差异隆升和快速降温,平均降温速率为142．8℃／Ma,对应的差异隆升速率为3．57mm／a;在8．0～5．0Ma期间,念青唐古拉山区发生伸展型韧性剪切变形,导致念青唐古拉花岗岩快速隆升,平均差异隆升速率为3．50mm／a;在5．0～3．7Ma期间,念青唐古拉花岗岩继续发生构造隆升,平均降温速率约92．3℃／Ma,对应的平均差异隆升速率为2．31mm／a。自3．7Ma以来念青唐古拉花岗岩平均降温速度达27．0℃／Ma,平均抬升速度达0．68mm／a。念青唐古拉岩浆集聚、NG花岗岩侵位与INDEPTH-Ⅱ地震深反射亮点揭示的地壳局部熔融存在动力学成因联系,导致上地壳伸展构造变形、NG花岗岩缓慢冷却和念青唐古拉山脉快速隆升。     

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秦岭北缘仙游寺粘土(膨胀土)的发现及初步研究

首次在秦岭北缘周至县马召镇仙游寺一带发现了中更新世厚层褐色粘土,命名为“仙游寺粘土”。它们是中更新世晚期湿润(半湿热)气候环境下形成的坡面流堆积,其物质来源为秦岭山地表层的褐色古风化壳。室内土工试验结果表明：仙游寺粘土是一种典型的富含膨胀性粘土矿物(伊利石／蒙脱石混层矿物)的膨胀土,是以往渭河盆地没有发现的膨胀土新类型。仙游寺粘土不良的工程特性导致仙游寺周边和108国道秦岭北缘一带的天然斜坡和人工边坡都很不稳定,在强降雨作用下,大量土体滑坡频繁发生。基于野外调查和室内试验测试结果,着重介绍了仙游寺粘土的发育特征、成因时代及其工程地质特性,这不仅有助于北秦岭山地第四纪古气候的恢复及对北秦岭和渭河盆地第四纪以来地质环境演化的认识,而且对于认识秦岭北缘土体滑坡的成灾机理并指导地质灾害的防治具有重要的意义。     

Clockwise exhumation path of granulitized eclogites from the Ama Drime range (Eastern Himalayas)

The metamorphic evolution of a granulitized eclogite from the Phung Chu Valley (Eastern Himalaya) was reconstructed combining microstructural observations, conventional thermobarometry and quantitative pseudosection analysis. The granulitized eclogite consists of clinopyroxene, plagioclase, garnet, brown amphibole, and minor orthopyroxene, biotite, ilmenite and quartz. On the basis of microstructural observations and mineral relationships, four metamorphic stages and related mineral assemblages have been recognized: (i) M1 eclogite‐facies assemblage, consisting of garnet, omphacite (now replaced by a clinopyroxene + plagioclase symplectite) and phengite (replaced by biotite +plagioclase symplectite); (ii) M2 granulite‐facies assemblage, represented by clinopyroxene, orthopyroxene, garnet, plagioclase and accessory ilmenite; (iii) M3 plagioclase + orthopyroxene corona developed around garnet, and (iv) M4 brown amphibole + plagioclase assemblage in the rock matrix. Because of the nearly complete lack of eclogitic mineral relics, M1 conditions can be only loosely constrained at >1.5 GPa and >580 °C. In contrast, assemblage M2 tightly constrains the peak granulitic stage at 0.8–1.0 GPa and >750 °C. The second granulitic assemblage M3, represented by the plagioclase + orthopyroxene corona, formed at lower pressures (～0.4 GPa and ～750 °C). During the subsequent exhumation, the granulitized eclogite experienced significant cooling to nearly 700 °C, marked by the appearance of brown amphibole and plagioclase (M4) in the rock matrix. U‐Pb SHRIMP analyses on low‐U rims of zircon from an eclogite of the same locality suggest an age of 13–14 Ma for the M3 stage. The resulting decompressional clockwise P–T path of the Ama Drime eclogite is characterized by nearly isothermal decompression from >1.5 GPa to ～0.4 GPa, followed by nearly isobaric cooling from ～775 °C to ～710 °C. Modelling of phase equilibria by a calculated petrogenetic grid and conventional thermobarometry on a biotite‐garnet‐sillimanite metapelite hosted in the country rock granitic orthogneiss extends the inferred P–T trajectory down to ～630 °C and ～0.3 GPa.     

南岭东段早侏罗世沉积岩碎屑锆石U-Pb定年及其地质意义——以东坑盆地为例

印支造山运动是华南早中生代最重要的构造-岩浆事件,它在很大程度上影响了华南现今的地形和地貌特点。本文研究了南岭东段赣南早侏罗世东坑火山岩盆地沉积岩的碎屑锆石U-Pb年代,获得最显著的年龄峰值为196Ma、238Ma、364Ma和427Ma,表明该沉积岩并不是外来的震旦纪-寒武纪变质岩,而是早侏罗世裂谷火山盆地的沉积物。缺乏260～290Ma的锆石年龄,很可能反映物质为近源来源。通过与闽西南晚三叠世和华南内陆中-晚二叠世沉积砂岩中碎屑锆石年龄谱对比,反映华南印支早期(290～260Ma)岩浆活动主体在东南沿海地区,晚期(240～200Ma)主体发育在内陆地区。大量印支期侵入岩锆石的出现也很可能表明华南内陆印支造山带在～190Ma已经经历了相当程度的垮塌。     

小兴安岭西北部早——中侏罗世TTG花岗岩年代学、地球化学特征及构造意义

通过对出露于小兴安岭西北部白石砬子地区中生代花岗岩的研究,查明该地区存在一套由英云闪长岩-花岗闪长岩-石英闪长岩和少量闪长岩为组合的花岗岩,锆石U-Pb LA-ICP-MS测年分别获得(171.1±1.3)、(173.9±3.9)、(178.3±1.5)和(169.1±6.2)Ma的岩体侵位年龄,证明其形成于早—中侏罗世。通过岩石地球化学方法判别该花岗岩组合具有高Al_2O_3型T_1T_2G_1花岗岩特征,整体具有富硅、富铝,钠质,贫铁、镁、钛,属于偏铝质-弱过铝质钙碱性系列,富集轻稀土,相对亏损重稀土,富集Rb、Ba、Th、U、Sr等大离子亲石元素,相对亏损Nb、Ta、Zr、Hf等高场强元素,Eu具有轻微负异常的特点,与安第斯I型花岗岩具有相似性。其低Sr/Y值、(La/Yb)N值,弱或无负δEu异常等特征反映源区残留相矿物以角闪石、辉石为主,有少量斜长石,石榴石可能有少量残留。岩体露头有闪长质岩浆与英云(花岗)闪长质岩浆两种不完全机械混合的现象,反映可能存在两个以上的不同源区。另外,岩体不规则侵入元古宙地层(兴华渡口群和落马湖群)和岩浆中残留有大量早期捕获锆石,说明在岩浆上升侵位过程中与围岩发生同化混染作用。综合研究认为,该早—中侏罗世TTG岩浆形成与蒙古—鄂霍茨克洋的闭合作用密切相关,反映侏罗纪蒙古—鄂霍茨克洋存在向南侧微陆块的俯冲作用。