Constraints of REE and trace elements of high-pressure-veins and host rocks in western Tianshan on origin of deep fluids in paleosubduction zones

The western Tianshan high-pressure(HP) metamorphic belt represents the paleosubduction mélange of paleozoic south Tianshan ocean between the Yili-central Tianshan and Tarim plates. High-pressure veins are extensively developed in this HP belt. Compared with normal mid-ocean ridge basalt(N-MORB), the high-pressure veins and host rocks are enriched in light rare earth elements(LREE) and incompatible elements. But high-pressure veins show a larger variation than host rocks in total REE abundance. On the trace element spidergram, all the samples are enriched in incompatible elements and show strong positive Pb anomaly relative to N-MORB. The array tendency lines of plots of the HP rocks have apparent slopes on diagram of m(Sr) vs m(Sr)/m(Zr), m(Li) vs m(Li)/m(Y) and (m(Ce)) vs m(Ce)/m(Pb), which indicates that the enrichment in LREE and incompatible elements relative to N-MORB of the HP-metamorphic rocks from western Tianshan is not attributed to magma evolution process of the protolith. High field strength elements, such as Nb, Ta, Ti, Zr and Hf, do not show negative anomaly relative to N-MORB, which is dissimilar to that of island arc basalts. Therefore, the enrichment in LREE and incompatible elements of the HP rocks is not attributed to the enrichment of the source of the protolith. The mass ratios of Rb to Ba, Ce to Pb, Nb to U and Ta to U of high-pressure veins and host rocks are intermediate of mid-ocean ridge basalt or oceanic island basalt and continental crust. The fluids in western Tianshan paleosubduction zones are mixtures of two sources, dehydration or devolatilization of host rocks and of subducted sediments.

Fluid flow on centimeter-scale in deep paleosubduction zones in western Tianshan,China:Evidence from high-pressure veins

High-pressure(HP)veins were extensively developed in western Tianshan high-pressure(HP)metamorphic belt.The HP vein and host-rocks were analyzed by electronic microprobe to trace the origin of vein-forming fluids.Analytical data show that the immediately adjacent host-rocks of the studied HP vein are eclogites and gradually turned into blueschist as the distance from the veins increases,which indicates that the vein-forming fluid was derived from adjacent host-rocks;the boundaries between the vein and the host-rocks are sharp,which indicates that the fracture of the host-rocks is brittle during the vein-forming process.It is suggested that this type of HP veins is precipitated from the liquid formed by the dehydration of the host-rocks during the prograde metamorphism from blueschist to eclogite facies,which results in hydrofracturing of the rocks and provides the space for the vein to precipitate.The width of the eclogite-facies host-rocks is usually 1-2 cm,which provides the direct evidence that the fluid flow is on centimeter-scale.

Application of high-pressure water jet technology and the theory of rock burst control in roadway

This paper puts forward using high-pressure water jet technology to control rock burst in roadway, and analyzes the theory of controlling rock burst in roadway by the weak structure zone model. The weak structure zone is formed by using high-pressure water jet to cut the coal wall in a continuous and rotational way. In order to study the influence law of weak structure zone in surrounding rock, this paper numerically analyzed the influence law of weak structure zone, and the disturbance law of coal wall and floor under dynamic and static combined load. The results show that when the distance between high-pressure water jet drillings is 3 m and the diameter of drilling is 300 mm, continuous stress superposition zone can be formed. The weak structure zone can transfer and reduce the concentrated static load in surrounding rock, and then form distressed zone. The longer the high-pressure water jet drilling is, the larger the distressed zone is. The stress change and displacement change of non-distressed zone in coal wall and floor are significantly greater than that of distressed zone under dynamic and static combined load. And it shows that the distressed zone can effectively control rock burst in roadway under dynamic and static combined load. High-pressure water jet technology was applied in the haulage gate of 250203 working face in Yanbei Coal Mine, and had gained good effect. The study conclusions provide theoretical foundation and a new guidance for controlling rock burst in roadway.

Blueschist:A window into high-pressure/low-temperature metamorphism and subduction zone dynamics

Blueschist is a regional metamorphic rock formed under high-pressure(HP)low-temperature(LT)conditions.It is formed in the subduction zone environment with low geothermal gradients(4-14℃km^(−1)),and is characterized by the presence of HP/LT index minerals like glaucophane,lawsonite,aragonite,jadeite,and deerite.In general,blueschist-facies rocks are stable in subduction zones at depths of 30-60 km,and transform to eclogite-facies rocks at greater depths.The preservation of blueschists requires a fast exhumation rate.Based on protolith and tectonic setting,blueschists can be grouped into Type-A and Type-B,but some metasomatic blueschists also occur.Blueschist belts distribute mainly as bands along the margins of orogenic belts,and their occurrences within cratons are very limited.Precambrian blueschists,of which the oldest ones are about 800-700 Ma in age,are rare;most of the exposed blueschist terranes are of post-Paleozoic metamorphic age.As diagnostic evidence of ancient subduction zones,blueschist plays an important role in understanding plate tectonics.Blueschist-eclogite transition at cold subduction zones involves dehydration reactions and fluid release,which are of great importance in facilitating slab-mantle wedge water and element recycling,generating arc magmatism,and triggering intermediate-depth earthquakes in the subducting slab.Metamorphic P-T paths of blueschists and associated rocks provide key information on constraining the onset of the subduction initiation and subsequent geodynamic evolution.As a cold geothermal indicator,the emergence of blueschist offers robust evidence for the start of modern plate tectonics on the Earth.Blueschist-facies metamorphism still represents an important research direction in metamorphic geology,which requires further investigations on determining the beginning of plate tectonics,constraining phase-transition processes,and constructing a global blueschist database.

High-pressure experimental verification of rutile-ilmenite oxybarometer: Implications for the redox state of the subduction zone

The more oxidized mantle peridotites above subducting slabs than stable continental areas have been attributed to the infiltration of some oxidizing fluids released from the subducting slabs. However, knowledge for the redox states of the slabs itself is very limited. Until now, few oxybarometers can be directly used to constrain the redox states of the subducting slabs.The rutile-ilmenite oxybarometer was proposed and successfully applied to constrain the oxygen fugacity of mantle assemblages.However, its application to rocks equilibrated at crustal P-T conditions has been hampered by some uncertainties in an early solid solution model of ilmenite. With a newly-released solid solution model for the ilmenite, we have conducted high-P experiments(at 3 and 5 GPa, and 900–1300°C) to test the accuracy of this oxybarometer. The experiments were performed with their oxygen fugacities controlled by the CCO buffer(i.e., C+O_2=CO_2). We demonstrated that the oxygen fugacities calculated for our high-P experimental products by using the rutile-ilmenite oxybarometer were in excellent agreement with the fO_2 dictated by the CCO buffer, suggesting a wide applicability of this oxybarometer to crust rocks. As examples, the rutile-ilmenite oxybarometer has been used to constrain the oxygen fugacities of some metamorphic rocks such as eclogite, granulite and amphibolite usually observed from the subduction zones.

侏罗系煤田弱胶结岩层水砂涌出机制研究与危险性评价

我国西部侏罗系煤田由于成煤时代相对较晚,岩层特征表现出胶结性差、强度低、遇水易软化崩解的特点,导致工作面回采期间易发生弱胶结岩层水砂涌出事件,因此,查明水砂涌出机制是制定相应防治措施的关键。以新疆某矿为研究对象,通过测试岩石力学强度、软化系数等参数,判定侏罗系砂岩为典型的易软化崩解弱胶结软岩地层;根据该矿首采工作面导水裂隙带发育高度、含水层水位变化、涌水水质分析结果,得出了工作面充水水源,查明水砂涌出形成机制为顶板弱胶结砂岩水沿裂隙带形成的导水通道进行渗流;同时,由于垮落带也贯通了直接顶泥岩发育至砂岩层,以及工作面长期停采导致裂隙进一步扩大,最终水携带崩解的弱胶结砂岩进入采动空间,通过结合弱胶结岩含水层富水性和煤层直接顶泥岩隔水层受垮落带破坏程度,对弱胶结岩层水砂涌出进行危险性分区评价。

瞬变电磁法在探测导水通道中的应用

采用瞬变电磁勘探技术,查明了地表水涌入矿井的三条通道,划出了L6、L7灰岩的岩溶裂隙富水区及其二者的水力联系,从而有的放矢地实施帷幕注浆截流治水工程,同时在七矿的注浆工程实践中也充分验证了瞬变电磁勘探成果的准确性。

瞬变电磁法在矿井水害治理工作中的应用

平煤集团七矿属大水矿井,每年仅排水一项就耗资巨大,给煤矿的经济发展和安全生产带来了极大的风险。为了彻底治理矿井水害,七矿采用瞬变电磁勘探技术,查明了地表水涌入矿井的三条通道,划出了L6、L7灰岩的岩溶裂隙富水区及其二者的水力联系,从而有的放矢地实施帷幕注浆截流治水工程。七矿的注浆工程实践充分验证了瞬变电磁勘探成果的准确性。

焦作矿区底板注浆加固工作面富水性分区及加固效果分析

以焦作矿区8个发生突水的底板注浆加固工作面为背景,依据底板钻孔涌水量对工作面进行了富水性分区,研究了工作面底板注浆加固体的空间分布特征,分析了底板突水的机理。研究结果表明:底板突水主要发生在富水区,并受断层带、基本顶来压等多个因素影响。注浆加固有效地降低了大水工作面的突水危险,表明对工作面的富水区、断层带、基本顶来压等特殊位置加大注浆工程量是十分必要的。

富水覆岩特厚煤层综放开采相似材料模拟研究

为研究综放工作面在不同采高情况下富水覆岩破坏特征,以胡家河矿首采401101工作面为工程背景,采用物理相似模拟实验的方法,通过三次不同采高(10m、8m、6m)的实验,研究当工作面推进到180m时上覆岩层在不同采高下的破坏状况,导水裂隙带高度能否到达含水层。在此基础上,分析了采动岩体的周期破断和裂隙发展过程,以及支承压力分布的变化。结论可以为胡家河矿首采面提供可靠的采高参照,以避免发生大范围的顶板透水灾害。

瞬变电磁法在煤矿水害防治中的应用

煤层附近的富水区(带)严重威胁着煤矿的生产安全,探明地下煤层附近富水区的赋存和断层、裂隙的发育情况,可以有效地指导煤矿水害的防治工作。对于含水地层及富水区,瞬变电磁法在多测道剖面上具有典型响应特征,据此可以查明地下水分布情况。在山东某煤田和河南某矿,应用瞬变电磁勘探,准确地查明了煤层顶底板富水区。

综合物探技术在煤矿水害防治中的应用

金凤煤矿为保证安全生产,需查明18煤顶板主要含水层空间分布规律及工作面内隐伏断层、小构造等地质异常体。结合井田内地质勘查及矿井开拓资料,运用音频电透视法和"三图-双预测"评价法,分析了工程范围内水文地质条件与充水特征,对含水层富水性及煤层开采时的突水危险性进行了预测;运用无线电波坑道透视法,对工作面内的隐伏地质情况进行了探测,为工作面过断层提供了技术支撑,确保了工作面安全高效开采。

高盖山隧道高压富水区超前帷幕注浆设计

针对向莆铁路高盖山隧道掌子面的突水突泥情况,采用挡碴墙对掌子面堆积体进行加固,并在堆积体上设计三级止浆墙,采用在上半断面钻孔辐射至洞身全断面的帷幕注浆方案进行加固。设计了超前帷幕注浆孔位置及轮廓线,并确定注浆长度为30 m,扩散半径为5 m,注浆压力4-6 MPa,针对开挖后可能的渗水情况提出了径向补强注浆设计方案,注浆效果及注浆质量符合设计要求。

矿井瞬变电磁法在煤矿采空积水区的应用研究

为了排除某矿首采工作面的水害隐患,本文对该矿首采工作面进行矿井瞬变电磁探测,查明上覆煤层采空积水情况、该矿工作面内的钻孔封闭情况和富水情况。通过矿井瞬变电磁法探测,结合钻孔结果分析,验证了瞬变电磁方法的准确性。

Partial Melting and Its Implications for Understanding the Seismic Velocity Structure within the Southern Tibetan Crust

In order to constrain the crustal wave velocity structure in the southernTibetan crust and provide insight into the contribution of crustal composition, geothermal gradientand partial melting to the velocity structure, which is characterized by low average crustalvelocities and widespread presence of low-velocity zone(s), the authors model the crustal velocityand density as functions of depth corresponding to various heat flow values in light of velocitymeasurements at high temperature and high pressure. The modeled velocity and density are regarded ascomparison standards. The comparison of the standards with seismic observations in southern Tibetimplies that the predominantly felsic composition at high heat flow cannot explain the observedvelocity structure there. Hence, the authors are in favor of attributing low average crustalvelocities and low-velocity zone(s) observed in southern Tibet mainly to partial melting. Modelingbased on the experimental results suggests that a melting percentage of 7-12 could account for thelow-velocity zone(s).

瞬变电磁法在煤矿水害探测中的应用研究

煤层附近的富水区和采空区积水严重威胁着煤矿的生产安全,传统的地球物理方法在煤矿水害勘查工作中得到应用的同时,新的更先进的物探方法不断涌现,本文通过实例阐述了瞬变电磁法在探测采空区积水和煤层顶底板富水区中的实用性和有效性。

High-Pressure Eclogite-Blueschist Metamorphic Belt and Closure of Paleo-Tethys Ocean in Central Qiangtang, Qinghai-Tibet Plateau

The high-pressure metamorphic belt （HPMB） of eclogite-blueschist in Central Qiangtang （羌塘） lies in the Longmu Co （龙木错）-Shuanghu （双湖） suture zone. To the west, the HPMB extends 500 km from Hongjishan （红脊山） to Caiduochaka （才多茶卡）, east of Shuanghu; to the east it extends to Baqing （巴青） and Jitang （吉塘） in Qamdo （昌都）, and then bends southward to Yunnan （云南） Province. Including the Lancangjiang （澜沧江） blueschist belt, the entire HPMB is about 2 000 km long. In Central Qiangtang, the belt is mainly composed of blueschist and eclogite, whereas in West Yunnan it contains only blueschist. The Baqing-Jitang segment is dominated by garnet phengite schist. 40Ar-39Ar dating of glaucophane and phengite from the blueschists yielded plateau ages ranging from 223 to 215 Ma, whereas SHRIMP U-Pb dating of zircon from the eclogites gives metamorphic ages of 243-217 Ma. The calculated metamorphic conditions for the blueschists are 410-460 ℃ and 0.67-0.75 GPa, and for the eclogites, 〈500℃ and 1.56-2.35 GPa. The metamorphic ages suggest that the Longmu Co-Shuanghu suture closed in the Late Triassic. The region south of the Longmu Co-Shuanghu- Lancang suture consists of the pan-African basement overlain by Condwana sedimentary and metasedimentary rocks, whereas the region north of the suture is dominated by the Jinning （晋宁） basement and Yangtze sedimentary and metasedimentary rocks. The Qiangtang HPMB marks the closure of the paleo-Tethys Ocean.

矿井瞬变电磁法在煤层顶板富水异常区探测中的应用

一直以来,煤层顶板水害对红柳林煤矿安全生产构成了严重威胁,为保证5号煤层工作面安全回采,必须在开采前期查明顶板基岩层导、含水构造及其富水性。基于此,文章结合矿井瞬变电磁法对低电阻率地层有反应敏感、分辨率高及探测深度大等优点,查明了红柳林矿15204工作面顶板导、含水构造,圈定了富水异常区,并在工作面回采前,通过对15204工作面顶板基岩存在的富水异常区1和异常区2打钻放水验证可知,该次矿井瞬变电磁法所取得的成果与现场实际水文地质情况相符,对该矿区今后顶板水害防治技术提供了科学依据,具有一定的指导意义。

南京市地下水资源评价

本文论述了南京地区水文地质条件，深层地下水富水规律及可开采量，并对深层地下水水质特征进行了分析，为今后南京地区工业布局和深层地下水开发利用提供了可靠的依据。

断层破碎带及富水基岩井筒施工方案选择及井壁结构设计

唐口煤矿采用立井开拓方式,分区开拓,分区通风。因主通风机通风阻力逐渐增大,通风负压达到3 564.6Pa,在井田南部需开凿进风井、回风井各1个。两井筒均穿过第四系、侏罗系F2断层破碎带及富水基岩,涌水量较大,决定第四系和侏罗系破碎带段采用冻结法施工;基岩富含水层段采用钻孔泄水,普通法施工,双层素混凝土井壁结构,确保井筒安全高效施工。