Experimental study of gold activation-transportation in the process of potash metasomatism-alteration——North China platform gold deposit taken as an example

Chemical reactions of plagioclase, biotite and their singleminerals, as well as a mineral mixture of (plagioclase +biotite+quartz), with KCl and (KCl+KHCO3) solutions were carried out at 150400℃ and 5080 MPa. Experiments show that alkaline fluid promotes plagioclase’s changing into potash feldspar, while acid fluid helps plagioclase, potash feldspar and biotite alteration form chlorite and sericite. After chemical reaction the acidity-alkalinity of solutions often changes reversely. It was observed that gold dissolved from the tube wall and recrystallized on the surfaces of biotite and pyrite. Therefore the transportation and enrichment of gold are related to the elementary effect of the fluid-mineral interfaces. Fe3+-Fe2+, as an oxidition-reduction agent, and volatile components Cl? and CO2 play important roles in the reaction process.     

青藏高原东南缘南段现今变形特征研究

本文以青藏高原东南缘南段1999—2017年的GPS速度场为主,结合小震分布、历史地震和活断层探测等资料,首先,基于Okada断层位错模型反演了研究区域主要活断层的滑动速率;其次,以断层滑动速率和GPS速度场观测资料作为约束,利用DEFNODE负位错方法反演了研究区域的块体内部变形及主要活断层的闭锁程度和滑动亏损;最后,计算研究区域现今应变率场,并结合Pms和XKS剪切波分裂结果,探讨分析了青藏高原东南缘的动力学特征.研究结果表明：（1）红河断裂带现今滑动速率明显低于南华—楚雄—建水断裂和无量山断裂;（2）红河断裂带的元江—元阳段、鹤庆—洱源段和小江断裂带北段处于强闭锁状态,南华—楚雄—建水断裂带和无量山断裂带中—北段的闭锁程度强于南段;（3）青藏高原东南缘南段现今地壳变形表现为近E-W向的拉张和近N-S向的挤压,最大剪切方向与Pms和XKS剪切波分裂的快波方向呈一定角度,表明地壳与地幔处于完全解耦状态,而中-下地壳低速层可能是壳幔解耦的主要原因之一;（4）青藏高原东南缘的整体变形受控于印度板块的推挤、印缅俯冲带的深源俯冲以及缅甸微板块与巽他板块的后撤/回退的共同作用.

     

青藏高原东南缘的地壳结构与动力学模式研究综述

青藏高原东南缘的川滇地区壳幔变形特征及地球动力学模式一直是研究的热点问题之一,多年来一直受到各国地球科学家的高度关注.青藏高原演变的"下地壳流模型"模拟得到的地表速度和变形场与GPS观测具有很好的一致性,该模型在当前国际地学界很流行,因而寻找下地壳流存在与否的证据,是深部地球物理学必须面对的一个科学问题.本文综合了川滇地区GPS观测、震源机制解和Pms相分裂的结果,旨在探讨川滇地区地壳演变模式的合理性;另外,从层析成像、接收函数反演和大地电磁测深结果分析,认为川滇地壳内存在大范围的低速层,但分布的几何形态较复杂.在云南地区,这一壳内低速区似乎被小江断裂和金沙江-红河断裂限制在特定的区域内.     

藏北高原地壳及上地幔导电性结构——超宽频带大地电磁测深研究结果

为了研究西藏中、北部壳、幔导电性结构,讨论高原中、北部岩石圈热状态,1998年和1999年（INDEPTH（Ⅲ） MT）在西藏中、北部完成了德庆—龙尾错（500线）和那曲—格尔木（600线）超宽频带大地电磁深探测剖面的研究.研究结果表明,西藏中、北部以昆仑山断裂为界,其南北壳、幔电性结构有很大差异.昆仑山断裂以北地壳和上地幔为高阻区.而昆仑山以南,地壳和上地幔的导电性有明显的分层结构：地壳上部以不连续的高阻体为主,夹有局部低阻异常体,沿南北方向上地壳的电性结构复杂,具有不连续、分块的特点;但中、下地壳为大范围的高导异常区,区内发育有大规模、不相连续、产状各异的高导体,其电阻率均小于4Ωm;在班公—怒江和金沙江缝合带之下,壳内高导体都具有向上地幔延伸的趋势,存在连通壳、幔的低阻通道.根据西藏高原中、北部壳、幔电性结构的研究推断：如同藏南一样,这里也普遍存在部分熔融体和热流体,它们的成因主要与班公—怒江和金沙江缝合带的壳-幔热交换、热活动有关,这是两期形成的壳-幔热交换通道.其中,班公—怒江缝合带的壳-幔热交换通道形成时间比金沙江缝合带早.因此,研究区壳、幔的热活动是从南边和西边开始,向北、向东扩展,导致现今西藏中、北部地壳和上地幔的热流分布由西向东、由南向北增大.     

Deep structure and lithospheric shear faults in the East Kunlun-Qiangtang region,northern Tibetan Plateau

The Cenozoic magmatic rocks of shoshonitic series in the eastern Qinghai-Tibet Plateau include potassic alkaline plutonic rocks, volcanic rocks, lamprophyres and acidic porphyries. Analytical results show that these different lithological rocks are extremely similar in Sr, Nd and Pb isotopic compositions with the range of 0.705 187– 0.707 254 for⁸⁷Sr/⁸⁶Sr, 0.512 305–0.512 630 for¹⁴³Nd/¹⁴⁴Nd, 18.53–18.97 for²⁰⁶Pb/²⁰⁴Pb, 15.51–15.72 for²⁰⁷Pb/²⁰⁴Pb and 38.38–39.24 for²⁰⁸Pb/²⁰⁴Pb. They are isotopically similar to the EMII end-member. This indicates that mantle metasomatism must have taken place in their source region. The formation of these particular rocks is related to crustal thinning and mantle upwelling in a large-scale strike-slip and pull-apart fault zone at about 40 Ma in northern and eastern Qinghai-Tibet Plateau     

青藏高原现代地壳运动与活动断裂带关系的模拟实验

本文以GPS观测、大地热流测量、较高精度地形数据、全球板块相对运动的REVEL模型为基础,建立了以青藏高原现代构造活动为主要研究对象的东亚地区构造形变场有限元模型.数值模拟结果显示,青藏高原内部和周边地区走滑断裂带的活动对东亚地区地壳运动速率和方向有较大的影响,特别是对青藏高原物质向东南方向运动有显著影响;不同构造块体岩石圈强度的差异直接影响了川滇菱形地块边界断层错动性质.在考虑青藏高原地形附加重力作用和周边板块汇聚作用对现今大型断裂带运动特征控制作用的同时,岩石圈之下的橄榄岩软流圈至转换带物质对流对岩石圈的拖曳力也是必须考虑的底部边界条件.     

Deep structure and lithospheric shear faults in the East Kunlun-Qiangtang region,northern Tibetan Plateau

An integrated study of earthquake seismic tomography in the Golmud-Tanggula Pass (west) and Gonghe-Yushu (east) with profiles traversing the East Kunlun-Qiangtang region of the northern Tibetan Plateau shows that the deep structure of the study region has the following characteristics: (1) from south to north the crustal thickness decreases from 70–75 km to 55–66 km, and the variation range of thickness (10 km) in the western part is smaller than that in the eastern part (20 km); (2) the crust has a sandwich-like structure and the middle crust has a lens-shaped low-velocity layer; (3) above 150 km in depth, the physical states of various terranes are marked by alternation of high-velocity and low-velocity bodies; and (4) the discontinuity of the lithospheric structure reveals the existence of three lithospheric shear faults on the the East Kunlun-Qiangtang region—the South Kunlun-A’nyêmaqên lithospheric shear fault, the Jinsha River lithospheric shear fault and the Xianshui River lithospheric shear fault. It is inferred that the easternward extrusion of northern Tibetan Plateau occurred in the lithospheric range.

     

青藏高原东北缘祁连山中部精细地壳结构研究

现今的青藏高原东北缘祁连山地区是在早古生代构造格架的基础之上,于新生代在欧亚大陆与印度大陆碰撞拼合的远程影响下,重新活化进而隆起成为高原的组成部分.因此,该区域地壳结构的揭示不仅可以获得高原地壳变形方式的关键信息,而且也能对该区域早古生代晚期北祁连洋闭合时的相关构造演化提供重要证据.本文以一条穿过青藏高原东北缘祁连山中部地区的深地震反射剖面为基础,结合前人地质、地球物理资料,通过细致的地质构造解译,获得了青藏高原东北缘祁连山中部地区的精细地壳结构.反射剖面图像揭示了海原断裂西段的深部延伸形态、中地壳的双重构造、以及中下地壳的祁连逆冲断裂系等精细的深部构造.结合前人的地质以及地球物理资料,我们提出早古生代晚期北祁连闭合时的南向俯冲以及新生代以来祁连山地区两次陆内俯冲作用可能造就了现今的祁连山.

     

剪切波分裂揭示的青藏高原上地壳地震各向异性基本特征

青藏高原整体隆升,构造运动与介质变形强烈,然而由于地震观测数据不足,青藏高原内部上地壳各向异性研究一直是一个空白.本研究使用西藏地区的地震台网（2009年5月—2017年5月）的观测资料,利用剪切波分裂研究青藏高原上地壳地震各向异性特征.由于青藏高原固定地震台站分布稀疏,可用于进行剪切波分裂研究的近场地震事件记录稀少,本研究采用地震事件的单台定位技术,对公开的地震目录里没有震源深度数据的地震事件进行震源位置约束,并引入微震模板匹配定位方法,对连续地震波形进行检索,识别出地震目录里遗漏的新的微震（小地震）事件波形.微震识别获得的新地震事件记录是地震目录里报告的地震事件记录的大约6倍,用于补充研究区的剪切波分裂数据分析.通过数据分析,对比快波偏振方向,证实微震识别获得的数据极大地增加了有效数据的数量,提高了结果的可靠性.研究结果表明,雅鲁藏布江缝合带与班公—怒江缝合带之间的拉萨地块东部地区,台站的快剪切波（快波）偏振方向主要受区域应力场影响,快波偏振方向主要是NS或NNE方向,表明了区域最大主压应力方向;但个别地震台站（当雄台）快波偏振方向受原地主压应力影响,其快波偏振方向既不平行于断裂走向也不平行于区域主压应力方向,揭示出地壳介质的局部变形导致的局部应力方向不同于青藏块体里的其他地区.研究区西部的改则、普兰和研究区北部的双湖,快波偏振方向显示与断裂等构造走向一致的特点.研究区东部的昌都和察隅,快波偏振方向除了与断裂走向（或构造线）一致,还与地表运动的方向相同,揭示了青藏块体东部的深部物质可能的运移方向.这个现象虽然还需更多的研究证实,但这个发现的重要启示是,地震各向异性结合地表变形可用于探讨地壳深部物质的运动.

     

Sampling strategy and climatic implications of tree-ring stable isotopes on the southeast Tibetan Plateau

We explore the potential of tree-ring cellulose δ¹⁸O and δ¹³C records for reconstructing climate variability in the southeast Tibetan Plateau. Our sampling strategy was designed to investigate intra and inter-tree variability, and the effects of the age of tree on δ¹⁸O variation. We show that intra-tree δ¹³C and δ¹⁸O variability is negligible, and inter-tree coherence is sufficient to build robust tree-ring δ¹⁸O or δ¹³C chronologies based on only four trees. There is no evidence of an age effect regarding δ¹⁸O, in contrast with tree-ring width. In our warm and moist sampling site, young tree δ¹³C is not clearly correlated with monthly mean meteorological data. Tree-ring δ¹⁸O appears significantly anti-correlated with summer precipitation amount, regional cloud cover, and relative humidity. Simulations conducted with the ORCHIDEE land surface model confirm the observed contribution of relative humidity to tree cellulose δ¹⁸O, and explain the weak correlation of δ¹³C with climate by the non-linear integration linked with photosynthesis. Altogether, the tree-ring cellulose δ¹⁸O is shown to be a promising proxy to reconstruct regional summer moisture variability prior to the instrumental period.     

藏北高原主要断裂带电性结构特征

对600线的部分测点及2100线的全部测点构成的五道梁—绿草山大地电磁深探测剖面进行了二维非线性共轭梯度反演,得到青藏高原中北部二维电性结构模型.根据该电性结构模型,结合研究区域重、磁及区域地质资料推断了青藏高原中北部主要断裂的位置、产状和切割深度等信息.研究结果表明,青藏高原中北部发育有F1—F16一系列深断裂.其中,F1(苟鲁山克错—囊谦断裂带)和F9(乌兰乌拉湖—玉树断裂带)共同构成金沙江缝合带的北界,是松潘—甘孜—可可西里地块与羌塘—唐古拉地块的分界线;F4、F10—F12共同构成昆仑断裂带,F4(阿尼玛卿断裂带)是南部松潘—甘孜—可可西里地体和北部北昆仑-柴达木地体的分界线;F6、F13—F16为柴北缘断裂带,由南倾的岩石圈深断裂F6和一系列产状相背、北倾的逆冲断裂F13—F16所构成;F7和F8可能反映岩石圈内产状平缓、隐伏的滑脱构造形迹.     

青藏高原东北缘地壳各向异性的构造含义

青藏高原东北缘记录了印度-欧亚大陆板块碰撞和汇聚的远场效应,且仍正处于侧向生长阶段.而地壳各向异性则反映了高原地壳的形变特征.为此,本文主要利用甘肃数字地震台网(2001年1月-2010年10月)波形记录资料,采用SAM方法进行剪切波分裂研究,得到青藏高原东北缘地壳各向异性的平均剪切波分裂参数及剩余地震各向异性参数,两个参数分别反映了区域构造和应力场特征及局部构造和局部断裂特征.研究结果表明:快剪切波2个优势偏振方向分别为NE47.72°±21.83°和121.65°±22.07°,慢剪切波平均时间延迟为2.63±1.31 ms·km-1.快剪切波平均偏振方向反映了该区域的水平主压应力方向,快剪切波偏振方向的第二优势取向揭示了NWW的局部构造意义,表明应力环境受本区NWW深大断裂带的影响.各个台站的剩余快剪切波偏振方向的优势取向与断裂走向一致,表明活动断裂控制着剩余快剪切波偏振方向.剩余慢剪切波时间延迟变化反映了断裂引起地震各向异性程度,形变具有区域特征.     

松辽盆地深部地壳构造特征与无机油气生成模式

松辽盆地中地壳有一低速-高导层(也称塑性层),中地壳的塑性层与松辽盆地的成因以及盆山耦合系统有关.盆地地幔流体活动有下列表现:(1)高热流、高地温场;(2)深大断裂与火山岩喷溢;(3)碱交代作用(如钠长石化、伊利石化);(4)Mg2 交代作用(如白云石化)等等.地球化学省与地球化学急变带控制了大油气田的分布并显示了盆地发生的壳-幔相互作用.中地壳的低速-高导层不是岩浆岩,而是一充满地幔流体的地质体,它们富含氢、碱金属(K 、Na )、卤素(F-、Cl-)、碳(甲烷、CO、CO2)、氮、硫等.在中地壳的温度压力条件下,在Fe、Ni等催化荆的参与下,H2与CO(CO2)可发生费-托合成烃的反应.实验表明:这个反应不仅可生成气态烃还可生成液态烃,并将发生碳同位素分馏作用.松辽盆地的U形运移模型受到质疑.按照石油无机生成的模型,松辽盆地的深部将会有更多的石油与天然气,庆深气田的发现便是一个明证.     

Coupling Between Seismic Activity and Hydrogeochemistry at the Shillong Plateau, Northeastern India

Transient hydrogeochemical anomalies were detected in a granite-hosted aquifer, which is located at a depth of 110 m, north of the Shillong Plateau, Assam, India, where groundwater chemistry is mainly buffered by feldspar alteration to kaolinite. Their onsets preceded moderate earthquakes on December 9, 2004 (M_W = 5.3) and February 15, 2005 (M_W = 5.0), respectively, 206 and 213 km from the aquifer. The ratios [Na+K]/Si, Na/K and [Na+K]/Ca, conductivity, alkalinity and chloride concentration began increasing 3–5 weeks before the M_W = 5.3 earthquake. By comparison with field, experimental and theoretical studies, we interpret a transient switchover between source aquifers, which induced an influx of groundwater from a second aquifer, where groundwater chemistry was dominantly buffered by the alteration of feldspar to smectite. This could have occurred in response to fracturing of a hydrological barrier. The ratio Ba/Sr began decreasing 3–6 days before the M_W = 5.0 earthquake. We interpret a transient switchover to anorthite dissolution caused by exposure of fresh plagioclase to groundwater interaction. This could have been induced by microfracturing, locally within the main aquifer. By comparison with experimental studies of feldspar dissolution, we interpret that hydrogeochemical recovery was facilitated by groundwater interaction and clay mineralization, which could have been coupled with fracture sealing. The coincidence in timing of these two hydrogeochemical events with the only two M_W ≥ 5 earthquakes in the study area argues in favor of cause-and-effect seismic-hydrogeochemical coupling. However, reasons for ambiguity include the lack of similar hydrogeochemical anomalies coupled with smaller seismic events near the monitoring station, the >200 km length scale of inferred seismic-hydrogeochemical coupling, and the potential for far-field effects related to the Great Sumatra–Andaman Islands Earthquake of December 26, 2004.     

Oceanic crust and Moho of the Pacific Plate in the eastern Ogasawara Plateau region

Abstract   To show the structure of oceanic crust and Moho around the eastern Ogasawara Plateau, we have analyzed industry-standard two-dimensional multichannel seismic reflection data. To obtain improved velocity models, phase information of seismic signals was used for velocity analysis and velocity models for oceanic crust above Moho were determined. We apply this velocity analysis technique to seismic reflection data around the eastern Ogasawara Plateau, with the result of clear images of structures within oceanic crust and Moho. South of the Ogasawara Plateau, Moho deepens proximal to the Plateau. Moho distal to the Plateau is ca 7 km below sea floor (bsf), whereas it is ca 10 km bsf near the Plateau. The characters of oceanic crust and Moho differ significantly north and south of the Plateau. To the north, the structure of oceanic crust is ambiguous, the sea floor is shallower and less smooth, and Moho is discontinuous. To the south, structures within oceanic crust and Moho are imaged clearly, and the sea floor is deeper. A strong Moho reflection south of the Plateau might represent a sharp boundary between layered gabbro and peridotite. However, discontinuous Moho reflections north of the Plateau might represent rough topography because of intensive magmatism or a gradual downward increase in velocity within a thick Moho transition zone. A fracture zone north of the Plateau also appears to separate oceanic crust and Moho of different characters, suggesting vigorous magmatism between the Plateau and the fracture zone, and that the Ogasawara Plateau and the fracture zone influenced the genesis of oceanic crust and upper mantle. Differences in acoustic characteristics to the north and south of the Plateau are apparent in profiles illuminated by seismic attributes.     

Water isotopes and hydrograph separation in different glacial catchments in the southeast margin of the Tibetan Plateau

Snow and glaciers are known to be important sources for freshwater; nevertheless, our understanding of the hydrological functioning of glacial catchments remains limited when compared with lower altitude catchments. In this study, a temperate glacial region located in the southeast margin of the Tibetan Plateau is selected to analyse the characteristics of δ¹⁸O and δD in different water sources and the contribution of glacier–snow meltwater to streamflow. The results indicate that the δ¹⁸O of river water ranges from ?16.2‰ to ?10.2‰ with a mean of ?14.1‰ and that the δD values range from ?117.0‰ to ?68.0‰ with a mean of ?103.1‰. These values are more negative than those of glacier–snow meltwater but less negative than those of precipitation. The d ‐excess values are found to decrease from meltwater to river to lake/reservoir water as a result of evaporation. On the basis of hydrograph separation, glacier–snow meltwater accounts for 51.5% of river water in the Baishui catchment in the melting season. In the Yanggong catchment, snow meltwater contributes 47.9% to river water in the premonsoon period, and glacier meltwater contributes only 6.8% in the monsoon period. The uncertainty in hydrograph separation is sensitive to the variation of tracer concentrations of streamflow components. The input of meltwater to a water system varies with local climate and glacier changes. The results confirm that hydrograph separation using water isotopes is valuable for evaluating the recharge sources of rivers, especially in ungauged glacial regions. This study provides insights into the hydrological processes of glacial catchments on the Tibetan Plateau, which is important for water resource management.     

The P and S wave velocity structures of the crust and upper mantle beneath Tibetan Plateau

Using the P-and S-wave arrivals from the 150 earthquakes distributed in Tibetan Plateau and its neighboring areas, recorded by Tibetan seismic network, Sichuan seismic network, WWSSN and the mobile network situated in Tibetan Plateau, we have obtained the average P-and S-wave velocity models of the crust and upper mantle for this region:

苏门答腊俯冲带地区壳内密度结构研究

俯冲带上覆板片密度特征是认识俯冲及其引发深部岩浆过程的一个窗口.本文以苏门答腊俯冲带空间重力异常数据为基础,在2.5D密度结构剖面约束下,通过3D密度反演,获得了研究区3D密度结构分布.反演结果表明,俯冲板片角度和下倾极限深度均从研究区西北向东南方向逐渐增加;研究区上覆板片下地壳存在低密度异常,主要集中在东南部,分布范围也随深度而增加.分析认为这有可能是俯冲引发的洋壳脱水对上覆板片下地壳侵染所造成.此外,研究区东南部存在的地幔板片撕裂可能是造成该区下地壳低密度异常最为显著的另一个原因.3D密度切片揭示出下地壳密度异常具有沿NE方向延伸迹象,推断应与印澳板块在苏门答腊地区的斜向俯冲作用有关.本文还对研究区的地震分布特征进行了讨论.大部分的浅源地震集中在下倾极限附近,为脆性破裂或摩擦滑移所引发.震源深度大于200 km的地震基本分布在研究区中部和东南部,震源深度从西北向东南方向逐渐加大,这从另一角度为研究区东南部地幔存在板片撕裂的观点提供了佐证.

     

青藏高原地壳高导层的成因及动力学意义探讨——大地电磁探测提供的证据

大地电磁探测结果显示,青藏高原的中下地壳普遍存在大规模的高导层,其电阻率低于10 Ωm,远低于稳定构造区地壳的平均电阻率值.通过对可能形成地壳内大规模低阻异常地质原因的分析认为,青藏高原地壳中的高导层不可能是由金属矿、石墨层或者单纯的含盐水流体引起的,而很可能是由于地壳岩石的部分熔融或者是部分熔融与含盐水流体共同导致的.这些高导层的形成是与板块运动等动力学过程密切相关的.地壳内的高导层可能是印度板块和亚洲板块俯冲的电性痕迹,其成因与板块俯冲过程中由于摩擦生热导致的岩石部分熔融和脱水作用有关,也可能与岩石圈拆沉造成幔源物质上涌有关.沿高原内主要缝合带均存在东西向连续分布的大规模高导体,有可能是青藏高原下地壳物质向东"逃逸"的证据;其中班公—怒江缝合带可能是最重要的物质运移"通道".     

Crustal structure across the Altyn Tagh Range at the northern margin of the Tibetan Plateau and tectonic implications

We present new seismic refraction/wide-angle-reflection data across the Altyn Tagh Range and its adjacent basins. We find that the crustal velocity structure, and by inference, the composition of the crust changes abruptly beneath the Cherchen fault, i.e., ∼100 km north of the northern margin of the Tibetan plateau. North of the Cherchen fault, beneath the Tarim basin, a platform-type crust is evident. In contrast, south the Cherchen fault the crust is characterized by a missing high-velocity lower-crustal layer. Our seismic model indicates that the high topography (∼3 km) of the Altyn Tagh Range is supported by a wedge-shaped region with a seismic velocity of 7.6–7.8 km/s that we interpret as a zone of crust–mantle mix. We infer that the Altyn Tagh Range formed by crustal-scale strike-slip motion along the North Altyn Tagh fault and northeast–southwest contraction over the range. The contraction is accommodated by (1) crustal thickening via upper-crustal thrusting and lower-crustal flow (i.e., creep), and (2) slip-parallel (SW-directed) underthrusting of only the lower crust and mantle of the eastern Tarim basin beneath the Altyn Tagh Range.