西藏班公湖-怒江缝合带中段A-型花岗岩的岩浆源区与板片断离

近年来地质调查在班公湖怒江缝合带中段发现了一批A-型花岗岩,岩体呈大小几百平方米的岩株产出,岩性上分为黑云母花岗岩和花岗闪长斑岩两种,侵入白垩系地层中.全岩元素地球化学分析显示这些A型花岗岩相对富硅,SiO2含量在68.62％～75.36％之间,全碱(K2O+Na2O=8.03％～9.37％)和全铁(Fe2 O3T＝0.86％～5.39％)含量偏高,Al2O3(12.76％～15.54％)偏低,显示弱过铝质和亚铝质特征.微量元素中大离子亲石元素(LILE)Rb、Th、U、K、Pb明显富集,Ba、Sr明显亏损;同样在高场强元素(HFSE)中Nb、Ta、Ti亏损明显,但Zr、Hf相对富集,这些与岛弧型花岗岩都是明显不同的,显示出了A-型花岗岩的特征.岩体稀土元素含量总体较高(∑REE=122.37×106～291.19×10-6,平均为201.31×10-6),相对富集轻稀土元素(LREE/HREE=4.89～9.58,平均为5.93),负Eu异常明显(δ Eu=0.14～0.54,平均为0.34),造成分配曲线呈向右缓倾的V型分布型式.Nd、Sr、Pb同位素分析显示班公湖-怒江缝合带中段的这些A型花岗岩富集放射成因同位素,其中87Sr/86Sr、87Rb/86 Sr及Isr比值分别在0.719842～0.786395、6.7171～48.8063和0.706900～0.710378之间;143 Nb/144 Nb和147 Sm/144 Nd比值分别在0.512123～0.512392和0.0853～0.2847之间,εNd为较大的负值(在-3.37～-10.34之间),显示出地壳组分的重要影响.206 pb/204 Pb、207pb/204Pb和208 pb/204 Pb比值分别在18.703～19.070、15.680～15.732、和39.121～39.576之间,在Zartman等(1981)的Pb构造模式图上位于上地壳线和造山带演化线之上,显示出异常高的富集组分.分析表明班公湖-怒江缝合带中段的A-型花岗岩是岩石圈地幔在洋壳俯冲过程中受到沉积物熔体的交代富集,之后早白垩世晚期(110Ma±)在碰撞后伸展阶段由于俯冲的洋壳板层断离形成了“板片窗”,软流圈物质借此上涌,引起富集的岩石圈地幔(接近EMⅡ)发生部分熔融形成的.     

基于钢筋拉压力传递的预制空心板残余抗震性能研究

为提升建筑质量,分析在循环往复荷载作用下预制空心板整体抗震性能,研究基于钢筋拉、压应力传递的预制空心板残余抗震性能.制备不含钢筋预制空心板结构试件:不含钢筋试件、未使用钢筋拉压力传递间接搭接试件、使用钢筋拉、压应力传递灌孔构造边缘构建试件,对各试件循环施加地震荷载,记录各试件性能变化情况.试验结果表明,相比于压剪破坏的...     

缅甸弧及邻区的壳幔S波速度结构与动力学过程

用适配滤波频时分析技术处理了锡龙（SHIO）、清迈（CHTO）、昆明（KMI）和拉萨LSA）台记录的长周期数字化面波记录,获取了穿过缅甸弧及周边地区的530条路径的Rayleigh波频散,这些频散的周期范围为10.45～105.03 s.在此基础上,以分格频散反演方法从混合路径频散中提取了1°×1°网格内的纯路径频散,并且由网格内的纯路径频散反演出深达200 km的S波速度结构,最后重建了缅甸弧及周边地区的S波速度三维结构.所得结果表明：大致以实皆断裂为分界,其东部地壳波速较低,其西部地壳波速较高.印度-缅甸地区岩石圈厚度为110～130 km,上地幔顶部S波速度为43～4.4 km/s;而缅甸弧东侧的滇缅泰地块下方为一低速地幔柱上涌区,其宽度为150～200 km左右,这里的岩石圈厚度为70～80 km,上地幔顶部S波速度为41～4.2 km/s.另外,S波速度结构还反映出这一构造格局呈南北向的空间展布,并且与该区地震震源分布、断裂走向、火山分布有很好的对应关系.     

板片深部俯冲动力学研究的新进展

高精度的层析成像结果显示了全球范围内形态各异的俯冲板片,这充分表明地球动力学过程的复杂性.本文简单回顾了影响板片俯冲的主要因素和对俯冲板片有关的,如对地震、火山、弧后变形等地球物理现象的各种合理解释.讨论中国东北新生代火山的地球动力学背景可能是不同于一般俯冲带火山的成因.     

对结构设计中几个问题的浅见

作者对结构设计中一些规范不太明确的问题,如什么是短肢剪力墙较多、地震等级与地震烈度的关系、如何对抗震设防区预制板楼盖加强其整体性等问题,查阅和分析了现有的资料,并提出了自己的看法,可供同行参考。     

Exhumation of eclogite and blueschist (Cyclades,Greece): Pressure–temperature evolution determined by thermobarometry and garnet equilibrium modelling

High‐P rocks such as eclogite and blueschist are metamorphic markers of palaeo‐subduction zones, and their formation at high‐P and low‐T (HP–LT) conditions is relatively well understood since it has been the focus of numerous petrological investigations in the past 40 years. The tectonic mechanisms controlling their exhumation back to the surface are, however, diverse, complex and still actively debated. Although the Cycladic Blueschist Unit (CBU, Greece) is among the best worldwide examples for the preservation of eclogite and blueschist, the proposed P–T evolution followed by this unit within the Hellenic subduction zone is quite different from one study to another, hindering the comprehension of exhumation processes. In this study, we present an extensive petrological data set that permits refinement of the shape of the P–T trajectory for different subunits of the CBU on Syros. High‐resolution quantitative compositional mapping has been applied to support the thermobarometric investigations, which involve semi‐empirical thermobarometry, garnet equilibrium modelling and P–T isochemical phase diagrams. The thermodynamic models highlight the powerful use of reactive bulk compositions approximated from local bulk compositions. The results are also combined with Raman spectrometry of carbonaceous material (RSCM) to retrieve the metamorphic peak temperature distribution at the scale of the island. A major result of this study is the good agreement between all the independent thermobarometric methods, permitting reconstruction of the prograde and retrograde P–T trajectories. Garnet compositional zoning was used to retrieve prograde, peak and retrograde growth stages in line with the results of the P–T isochemical phase diagrams, RSCM temperature and peak‐pressure crystallization of the garnet–omphacite–phengite assemblage. Our results are consistent with previous thermobarometric estimates from other occurrences of CBU rocks (Tinos, Andros), suggesting a multistage exhumation process with (1) early syn‐orogenic exhumation within the subduction channel, (2) isobaric heating at mid‐crustal depths (~10–12 kbar) following thermal re‐equilibration of the lithosphere from a cold syn‐orogenic regime in the subduction zone to a warmer post‐orogenic regime in the back‐arc domain and (3) exhumation and cooling related to a post‐orogenic phase of extension following slab retreat. Expanding to the general aspects of subduction zones, we suggest that such metamorphic evolution of HP–LT units should be regarded as a characteristic feature of exhumation driven by slab rollback.     

基于PDA平台的高铁轨道板检测技术的研究

CRTS II型板是我国引进国外板型改进后的无砟轨道板,文章主要介绍基于PDA平台的3维工业测量的CRTS II型板制板检测系统。CRTS II型板制板检测系统采用索佳高端NET 05电子全站仪建立空间3维坐标系统并对各个目标点进行高精度3维坐标测量,依据空间解析几何、最小二乘法等数学计算方法,根据全站仪测量的有关坐标...     

Crustal structure of the Central Precordillera of San Juan,Argentina (31°S) using teleseismic receiver functions

The subduction of the Nazca plate under the South American plate around 31°S is characterized by flat slab geometry. The (Chilean) Pampean flat slab of Argentina associated with the subduction of the Juan Fernandez ridge lies in a region of a series of foreland uplifts corresponding to the thin-skinned Precordillera and basement cored Sierras Pampeanas ranges. The SIEMBRA project deployed 40 broadband stations in 2008–2009 in both the Precordillera and the Sierras Pampeanas with the aim to foster the understanding of the entire central Andean flat slab region. One of the SIEMBRA station (DOCA) located on the western flank of Sierra de la Invernada in the Central Precordillera appears particularly appropriate to study the crustal structure and eventually detect discontinuities related to terranes establishment. We thus performed a receiver function analysis using teleseismic data recorded at the DOCA station during the SIEMBRA project and from October 2011 to June 2012 using a broadband UNSJ (National University of San Juan) seismic station with the purpose to obtain crustal images with details of the intracrustal structure consistent with a mechanism that could explains both the observed earthquake depths and the uplift pattern in the Central Precordillera. Our results show that the Moho beneath the Precordillera lies at a depth of about 66 km. The Moho signal appears diminished and behaves irregularly as a function of azimuthal orientations. Although this observation could be the result of an irregular geometry it also correlates with the hypothesis of partial eclogitisation in the lower crust. Two mid-crustal discontinuities have also been revealed. The shallower one could correspond to a décollement level between the Precordilleran strata and the Cuyania basement at 21 km depth. The deeper one which the presence has been matched with a sharp decrease of the crustal seismic activity drove us to the hypothesis of a major change in crustal composition at 36 km. Finally the flat portion of the subducted slab has been imaged lying at about 100 km depth.     

Structure of the Soresat Metamorphic Complex,North Sanandaj–Sirjan Zone,northwest Iran

The metasedimentary and granitoid rocks of the Soresat Metamorphic Complex occur along the northern margin of the Sanandaj–Sirjan Zone in northwest Iran. Four different deformational events (D1–D4) are recorded in the Soresat Metamorphic Complex. The D1 and D2 progressive deformation events resulted from north-northeast–south-southwest regional horizontal shortening due to the subduction of Neo-Tethys oceanic lithosphere beneath the Sanandaj–Sirjan Zone. Post-suturing convergence between Arabia and Iran, which resulted in a right lateral-reverse displacement along the suture caused the north-northwest–south-southeast horizontal shortening of D3. D4 is recorded by normal faulting. Andalusite, cordierite and sillimanite (fibrolite) record the thermal peak (with a geothermal gradient >30°C/km). Field and microscopic studies of intruded granitoid rocks in the Soresat Metamorphic Complex divide them into three major groups: (i) syn-deformation (syn-D2) granitic gneiss; (ii) late- to post-deformation (late- to post-D2) granites and granodiorites; and (iii) post-deformation (post-D2) alkali granites.