滇西腾冲-梁河地块早白垩世岩浆作用

滇西腾冲-梁河地区分布有大量的花岗岩。本文对梁河地区二长花岗岩进行了锆石LA-ICPMS U-Pb测年和Hf同位素分析,研究表明,锆石具有清晰的韵律环带,其Th/U值为0.34～1.65,为典型的岩浆锆石;锆石U-Pb年龄显示,花岗岩有三个年龄峰值(139.6±2.3Ma、129.7±5.2 Ma和118.8±4.2 Ma),表明该区早白垩世经历了多期岩浆作用;εHf(t)值为-20.15～-30.65,tCDM为2458～3083Ma,暗示花岗岩源自古老地壳部分熔融。该区片麻岩中具有2503Ma的碎屑锆石年龄,据此推测可能存在新太古宙基底。上述研究说明,该区早白垩世花岗岩的形成可能与班公湖-怒江洋的俯冲作用有关。     

长白山天池火山双岩浆房岩浆作用与互动式喷发

广义的长白山火山在我国境内包括天池火山、望天鹅火山、图们江火山和龙岗火山,是我国最大的第四纪火山岩分布区。长白山各个火山区的火山活动具有此起彼伏的穿时性特征,天池火山之下地壳和地幔两个岩浆房具有上下呼应、互动式喷发之特点。一方面来自地幔的钾质粗面玄武岩浆直接喷出地表,在天池火山锥体内外形成诸多小火山渣锥;另一方面钾质粗面玄武岩浆持续补给地壳岩浆房,发生岩浆分离结晶作用和混合作用,形成双峰式火山岩特征并触发千年大喷发。西太平洋板块俯冲-东北亚大陆弧后引张是长白山天池火山喷发的动力学机制。     

长白山天池火山双岩浆房的互动式喷发

天池火山的发展经历了钾质粗面玄武岩造盾、粗面岩-碱流岩造锥和全新世碱流质岩浆的爆破喷发.钾质粗面玄武岩在天池火山锥体外围呈"裙状"分布,不整合覆盖在中生代花岗岩风化壳或砾石层之上,其时代介于2.0～1.2 Ma的早更新世.造盾结束之后,约1 Ma后钾质粗面玄武岩在地壳岩浆房经历了岩浆结晶分异作用.     

长白山天池火山千年大喷发的岩浆过程

千年大喷发是长白山天池火山最近的一次大规模爆炸式喷发活动。本文在天池火口及周边的地质调查中发现,千年大喷发存在碱流质和粗面质两套堆积物,且具有岩浆混合现象。进一步岩相学与地球化学研究,证实千年大喷发应存在先后两个喷发阶段,即碱流质喷发阶段(SiO_2,~75%)和粗面质喷发阶段(SiO_2,~65%)。同时,通过微量元素和斑晶特征等分析认为两阶段的岩浆来自于两个独立的岩浆房,岩浆房平衡温度分别为743℃和862℃,相应深度约为5km和7~9km。另外,根据条带状岩浆的混合特征,认为喷发过程中碱流质与粗面质岩浆混合发生在上升通道中,排除岩浆房内混合的可能性。最后根据喷发过程和岩浆特征,综合提出了千年大喷发的岩浆过程模型。本文对千年大喷发的喷发过程和岩浆过程取得的新认识,增进了对天池火山活动习性的理解。     

由相对地热梯度推断的腾冲火山区现存岩浆囊

为利用温泉来研究和监测腾冲火山区的现今岩浆分布并探讨其活动性，提出相对地热梯度的概念：假设各热田或水热活动区的热储深度相等，则热储温度与地表温泉温度之差为该地相对地热梯度。通过对前人在该地区获得的温泉的基本要素和温泉水化学分析数据分析，选取了159个温泉计算相对地热梯度。用这159个数据，通过克里金插值方法获得了腾冲火山区的相对地热梯度平面分布。结果发现腾冲火山区有3个相对地热梯度在100℃以上的高值区域。结合其他资料，认为腾冲火山区现今存在3个岩浆囊，它们的几何尺度为19～28kin，深度为4～12km或更深，并且目前的活动性各不相同。     

滇西地区腾冲火山机构的综合地球物理解释推断

以腾冲地区1:20万区域重力调查资料为基础,结合航空磁测、人工地震、地热等资料,综合分析了腾冲地区的火山机构、喷发机制。推测在曲石-蒲川的重力高下面存在壳内浅成高位基性岩浆房。整个火山机构包括曲石-蒲川下伏的基性岩浆房和通过两侧龙川江断裂与腾冲-盈江断裂,以及通过断裂喷出地表的火山岩。     

柳河县阎家街地区早寒武世馒头组东热段英安质火山岩的发现及意义

在样子哨古生代向斜盆地东翼寒武纪馒头纽东热段地层剖面中发现一套英安质火山岩,呈薄层状夹杂于紫色含石盐假晶钙质粉砂岩中.岩石化学、稀土元素特征反映本区英安质火山岩具有非造山带陆内稳定构造区和造山带活动大陆边缘构造区过渡类型的特点.可能是华北地台北缘由被动型大陆边缘转化为活动型大陆边缘的一种陆内响应.该套火山岩的发现对研究和恢复早寒武世华北地台北缘的构造演化史具有重要意义.     

长白山火山活动历史、岩浆演化与喷发机制探讨

广义的长白山火山在我国境内包括著名的天池火山、望天鹅火山、图们江火山和龙岗火山,是我国最大的第四纪火山岩分布区。图们江火山和望天鹅火山活动都始于上新世,喷发活动分别介于上新世—中更新世（5.5~0.19 Ma）和上新世—早更新世（4.77 ~2.12 Ma）。天池火山和龙岗火山属于第四纪火山,喷发活动从早更新世（~2 Ma）持续到全新世。图们江火山岩为溢流式喷发的拉斑玄武岩,望天鹅火山、天池火山和龙岗火山母岩浆都是钾质粗面玄武岩,但经历了不同的演化过程。天池火山和望天鹅火山都经历了钾质粗面玄武岩造盾、粗面岩造锥和晚期碱性酸性岩浆（碱流岩和碱性流纹岩）的喷发;龙岗火山来自地幔的钾质粗面玄武岩浆则未经演化和混染直接喷出地表。图们江火山岩以溢流式喷发的拉斑玄武岩为主,少量玄武质粗安岩等。天池火山造盾之后,地壳岩浆房和地幔岩浆房具互动式喷发特点,来自地幔的钾质粗面玄武岩浆一方面在天池火山锥体内外形成诸多小火山渣锥,另一方面持续补给地壳岩浆房发生岩浆分离结晶作用和混合作用,分别导致双峰式火山岩分布特征和触发千年大喷发。火山岩微量元素和Sr-Nd-Pb同位素示踪揭示,长白山东（图们江火山、望天鹅火山和天池火山）、西（龙岗火山）两区显示地幔非均一性,东区岩浆源区具有软流圈地幔与富集岩石圈地幔混合特征,西区岩浆源区具有相对亏损的较原始地幔特征。西太平洋板块俯冲—东北亚大陆弧后引张是长白山火山活动的动力学机制。     

云南腾冲火山构造区马站—固东岩浆囊的地球物理模式

位于青藏高原东南边缘的云南腾冲火山构造区岩浆活动频繁强烈,火山活动规模宏大.为配合国家深部探测专项科学钻探选址,在腾冲盆地北部马站到固东、曲石乡一带进行了大地电磁测深、可控源音频大地电磁测深、反射地震和重磁测量的工作.本文依据电磁法取得的成果划分出了盆地地壳内的2个低阻低速层,其中浅部的低阻层由含水(热水)的火山岩下部、花岗岩上部与花岗砂砾岩组成,构成了腾冲盆地的地热资源的热储层,其主要层位在300到1500 m范围内;深部的低阻体是作为热源的岩浆囊,位于马站—固东—曲石乡三镇的深12~30 km,东西宽25 km以上,向南可能与腾冲北的岩浆囊相连.小空山、大空山和黑空山火山口具有典型的火山口重磁场特征,特别是由于喷发造成物质亏损形成的重力负异常与火山地形呈清晰的镜像对应关系.     

Chalcophile element constraints on magma differentiation of Quaternary volcanoes in Tengchong,SW China

The Tengchong volcanic field comprises numerous Quaternary volcanoes in SW China. The volcanic rocks are grouped into Units 1–4 from the oldest to youngest. Units 1, 3 and 4 are composed of trachybasalt, basaltic trachyandesite and trachyandesite, respectively, and Unit 2 consists of hornblende-bearing dacite. This rock assemblage resembles those of arc volcanic sequences related to oceanic slab subduction. Rocks of Units 1 and 3 contain olivine phenocrysts with Fo contents ranging from 65 to 85 mole%, indicating early fractionation of olivine and chromite prior to the eruption of magma. All the rocks from Units 1, 3 and 4 have very low PGE concentrations, with <0.05 ppb Ru and Rh, <0.2 ppb Pt and Pd, and Ir that is commonly close to, or slightly higher than detection limits (0.001 ppb). The small variations of Pt/Pd ratios (0.4–2.2) are explained by fractionation of silicate and oxide minerals. The 5-fold variations in Cu/Pd ratios (200,000–1,000,000) for the lavas at Tengchong, which do not vary systematically with fractionation, likely reflect retention of variable amounts of residual sulfide in the mantle source. In addition, all the rocks from Units 1, 3 and 4 have primitive mantle-normalized chalcophile element patterns depleted in PGE relative to Cu. Together with very low Cu/Zr ratios (0.06–0.24), these rocks are considered to have undergone variable degrees of sulfide-saturated differentiation in shallow crustal staging magma chambers. Large amounts of olivine and chromite crystallization probably triggered sulfide saturation of magma at depth for Units 1 and 3, whereas crustal contamination was responsible for sulfide saturation during ascent of magma for Unit 4.     

根据多时相夜间MODIS LST推断的腾冲地区新生代火山岩岩浆囊分布与活动特征

腾冲火山地热区位于印度板块与欧亚板块俯冲-碰撞带的弧后活动区,是我国新生代火山-地热最为活动的地区之一.本文利用MODIS夜间月平均地表温度(Land Surface Temperature,LST)数据,计算了研究区2001～2011年132个月的月平均地表温度,圈定了地温异常区;分析了异常区年内及年际间的平均地表温度变化趋势,推测了可能的地下岩浆囊分布位置及活动特征.研究结果表明,腾冲地区现今地下可能存在3个岩浆囊:第1个位于五合-新华-蒲川-团田一带,面积约为537km2,地温异常最明显;第2个位于朗蒲-热海-马鞍山地区,面积约为226km2,地温异常次之;第3个位于马站-曲石之间,面积约为28km2,地温异常较为明显.3个地温异常区在年内的地表温度变化趋势基本一致,而且周期性明显,均在5～6月份和8～9月份出现2个温度峰.其中朗蒲-热海-马鞍山异常区的地温变化波动最大,可能反映地下岩浆囊地热系统与地表地下水系统的对流交换活动性更强.MODIS夜间月平均地表温度数据得出的结果与测震、GPS形变、He同位素比值及最大相对地热梯度等方法推测的地温异常区范围具有很好的一致性,特别是地温异常区年内温度周期性变化的发现,表明卫星热红外遥感技术应用于地热异常实时监测与研究的巨大潜力.     

Crustal structure in the Tengchong volcanic area and position of the magma chambers

In this paper, we extract 1500 P receiver functions in the Tengchong volcanic area from 211 teleseismic events recorded at nine digital seismic stations. A common conversion point stacking technique is used to improve the signal-to-noise ratio and to get the time delays of the Ps, PpPs, PsPs + PpSs phases within grids of 10 km × 10 km. Finally, the crustal thickness and Poisson’s ratio are calculated. The results show that the crustal thickness ranges from 28 to 40 km and the Poisson’s ratio ranges from 0.28 to 0.36. There exist two mantle-uplifting sites each with a horizontal scale of about 30 km × 30 km, one in Mazhan–Tengchong–Maanshan and the other in Wuhe–Longjiang–Tuantian. The high Poisson’s ratio is consistently located within these two sites. Recorded shocks with Ms > 2.0 reveal that most of the shocks are distributed around the two sites and few are located at the centers. The shocks, the geothermal distribution, and the crustal structure suggest that the magma is still active, and the two mantle-uplifting sites detected may be the positions of two magma chambers in the crust.     

腾冲地块晚白垩世-古近纪富锡花岗岩成因:岩浆源区及分异演化条件SCIEI北大核心CSCD

腾冲地块锡成矿作用主要与晚白垩世-古近纪岩浆活动相关,但仅矿区花岗岩体具有较高的锡含量(平均25×10^(-6)),区域上同时代的非成矿花岗岩体并未发生锡的富集。本文通过搜集分析现有研究数据,总结了富锡成矿岩体和区域非成矿岩体在岩浆源区、演化条件和结晶分异程度的异同:区域非成矿岩体锆石ε_(Hf)(t)值(-15.1~+3.39)表明,自东北向西南幔源物质加入有升高的趋势,但区域玄武岩中低含量的Sn(1.61×10^(-6))表明幔源物质混入不利于岩浆中锡的富集。晚白垩世部分非成矿岩体与成矿岩体具有相同ε_(Hf)(t)(-9.7)值,表明其皆源于古老地壳物质的部分熔融,但岩体均表现为准铝质-弱过铝质特征,且锆石Hf同位素(t_(DM2)=1724Ma)和全岩Nd同位素(t_(DM2)=1836Ma)二阶段模式年龄基本一致,因此其源区可能并非富锡的高黎贡山群变质沉积岩,而可能是其中未经风化的变质花岗岩。根据腾冲地块地层厚度(28km)和莫霍面深度(47~35km)推断岩浆源区至少位于地下30km(8.4kbar),由于仅靠地温梯度(25℃/km)无法达到初始熔融温度(>1066℃),源区部分熔融过程很可能受地幔热的影响。根据Fe_(2)O_(3)/FeO比值,非成矿岩体(0.59)与成矿岩体(0.48)均具有较低的氧逸度,属钛铁矿系列,但成矿岩体的结晶分异程度明显高于非成矿岩体,且成矿岩体富含挥发分,高含量的挥发分降低了岩浆固结温度(650~550℃),延长了结晶分异时间,促进了锡在晚期岩浆中的富集。因此腾冲地块富锡花岗岩主要是普通岩浆在低氧逸度环境下发生高度结晶分异的结果。     

腾冲火山区壳内岩浆囊现今温度:来自温泉逸出气体 CO2、CH4间碳同位素分馏的估计

温度是岩浆囊的重要物理参数,获取温度参数并监测其变化对更好地理解岩浆囊的物理化学性质和行为、评价火山的活动性和喷发危险性具有重要的理论和现实意义.本文通过对温泉逸出气体CO2和CH4碳同位素样品的采集、分析测试,利用Horita通过实验矫正的Richet的平衡分馏系数的理论计算数据,通过拟合得到的CO2-CH4碳同位素平衡分馏方程T(K)=3880.3(10001nα(CO2-CH4))-0.5984,计算了腾冲火山区现存3个岩浆囊的温度.结果表明:在整个腾冲火山区,由CO2和CH4的碳同位素分馏值计算的气体源区平衡温度最低397℃,最高1163℃,平均615℃.腾冲火山区的3个岩浆囊中,南部五合-龙江-浦川岩浆囊的现今温度在464～1163℃,平均773℃,温度最高;中部腾冲-和顺-热海岩浆囊的现今温度在438 ～773℃间,平均达566℃,温度次之;北部马站-曲石-永安岩浆囊的现今温度在397～651℃间,平均达524℃,温度最低.我们认为,腾冲火山区地下岩浆囊顶部气体富集区目前的温度变化范围为400～ 1200℃,岩浆囊的实际温度应高于平均值615℃.3个岩浆囊的边缘温度可能在400 ～600℃间,中心温度可能在700～1200℃间.3个岩浆囊中心的现今温度已达到流纹岩浆(600～900℃)、安山岩(800 ～ 1100℃)和玄武岩浆(1000～1250℃)的形成温度,进一步说明腾冲火山区目前3个岩浆囊是客观存在的.另外,我们发现在用δ-△图解法判断CO2-CH4间碳同位素分馏平衡的过程中,在保持2条拟合直线的斜率符号相反的条件下,无论如何剔除数据点,都不能使δ13CCO2-ΔCO2-CH4拟合直线的截距bCO2和δ13 CCH4-ΔCO2-CH14拟合直线的截距bCH4之差bΔ小于0.1245,说明2条拟合直线的交点不能落于δ轴上,而这一数值与Horita方程的常数项接近,这说明CO2-CH4间碳同位素分馏方程中确实存在常数项,CO2和CH4间在再高的温度下都存在碳同位素的分馏.δ-△图解法判断CO2-CH4间碳同位素分馏平衡准则应修正为:在保持2条拟合直线的斜率符号相反的条件下,δ13 CCO2-ΔCO2-CH4拟合直线和δ13CCH4-ΔCO2-CH4拟合直线应相交于δ轴附近截距差0.1245处.     

Field evidence,mineral chemical and geochemical constraints on mafic-felsic magma interactions in a vertically zoned magma chamber from the Chotanagpur Granite Gneiss Complex of Eastern India

The Nimchak granite pluton (NGP) of Chotanagpur Granite Gneiss Complex (CGGC), Eastern India, provides ample evidence of magma interaction in a plutonic regime for the first time in this part of the Indian shield. A number of outcrop level magmatic structures reported from many mafic-felsic mixing and mingling zones worldwide, such as synplutonic dykes, mafic magmatic enclaves and hybrid rocks extensively occur in our study domain. From field observations it appears that the Nimchak pluton was a vertically zoned magma chamber that was intruded by a number of mafic dykes during the whole crystallization history of the magma chamber leading to magma mixing and mingling scenario. The lower part of the pluton is occupied by coarse-grained granodiorite (64.84–66.61?wt.% SiO₂), while the upper part is occupied by fine-grained granite (69.80–70.57?wt.% SiO₂). Field relationships along with textural and geochemical signatures of the pluton suggest that it is a well-exposed felsic magma chamber that was zoned due to fractional crystallization. The intruding mafic magma interacted differently with the upper and lower granitoids. The lower granodiorite is characterized by mafic feeder dykes and larger mafic magmatic enclaves, whereas the enclaves occurring in the upper granite are comparatively smaller and the feeder dykes could not be traced here, except two late-stage mafic dykes. The mafic enclaves occurring in the upper granite show higher degrees of hybridization with respect to those occurring in the lower granite. Furthermore, enclaves are widely distributed in the upper granite, whereas enclaves in the lower granite occur adjacent to the main feeder dykes.Geochemical signatures confirm that the intermediate rocks occurring in the Nimchak pluton are mixing products formed due to the mixing of mafic and felsic magmas. A number of important physical properties of magmas like temperature, viscosity, glass transition temperature and fragility have been used in magma mixing models to evaluate the process of magma mixing. A geodynamic model of pluton construction and evolution is presented that shows episodic replenishments of mafic magma into the crystallizing felsic magma chamber from below. Data are consistent with a model whereby mafic magma ponded at the crust-mantle boundary and melted the overlying crust to form felsic (granitic) magma. The mafic magma episodically rose, injected and interacted with an overlying felsic magma chamber that was undergoing fractional crystallization forming hybrid intermediate rocks. The intrusion of mafic magma continued after complete solidification of the magma chamber as indicated by the presence of two late-stage mafic dykes.     

长白山天池火山粗面玄武岩的喷发历史与演化

本文新提出的年代学和岩石化学结果，进一步从天池火山与区域火山活动的关系，论述了天池火山造盾、造锥历史和岩浆结晶分异转型的时间约束，早更新世早期（2Ma前）开始粗面玄武岩的造盾，早更新世晚期（约1Ma）粗面玄武岩向粗安岩、粗面岩演化，中更新世是粗面岩造锥的主阶段，到了晚更新世（约0．1Ma）粗面岩向碱流岩演化。在中-晚更新世来自地壳岩浆房的粗面岩、碱流岩造锥过程中，来自地幔的粗面玄武岩浆喷发活动始终没有间断过。由于来自地幔粗面玄武质岩浆持续向地壳岩浆房补给，所以天池火山是一座长寿命的火山。岩浆的结晶分异作用和混合作用是天池火山岩浆演化的两个最重要过程，前者形成天池火山双峰式火山岩分布特征，后者成为天池火山喷发的触发机制。天池火山在晚更新世-全新世碱流质岩浆主喷发期兼有少量玄武质粗安岩、粗安岩或粗面质岩浆的交替喷出，揭示了天池火山的地壳岩浆房熔体的分层结构特点，由于来自地幔粗面玄武质岩浆注入地壳岩浆房，导致不同层位岩浆的扰动和混合作用，触发天池火山的喷发。     

Understanding mafic-felsic magma interactions in a subvolcanic magma chamber using rapakivi feldspar: A case study from the Bathani volcano-sedimentary sequence,eastern India

The Ghansura Rhyolite Dome of the Bathani volcano-sedimentary sequence in eastern India originated from a subvolcanic felsic magma chamber that was intruded by volatile-rich basaltic magma during its evolution leading to the formation of a porphyritic andesite. The porphyritic andesite consists of rapakivi feldspars, which are characterized by phenocrysts of alkali feldspar mantled by plagioclase rims. Results presented in this work suggest that intimate mixing of the mafic and felsic magmas produced a homogeneous hybrid magma of intermediate composition. The mixing of the hot volatile-rich mafic magma with the relatively colder felsic magma halted undercooling in the subvolcanic felsic system and produced a hybrid magma rich in volatiles. Under such conditions, selective crystals in the hybrid magma underwent textural coarsening or Ostwald ripening. Rapid crystallization of anhydrous phases, like feldspars, increased the melt water content in the hybrid magma. Eventually, volatile saturation in the hybrid magma was reached that led to the sudden release of volatiles. The sudden release of volatiles or devolatilization event led to resorption of alkali feldspar phenocrysts and stabilizing plagioclase, some of which precipitated around the resorbed phenocrysts to produce rapakivi feldspars.     

松辽盆地北部徐家围子断陷下白垩统营城组火山机构类型与喷发模式研究

火山岩油气藏已成为我国东部中、新生代陆内裂谷盆地内一种重要的油气藏类型。松辽盆地北部徐家围子断陷营城组火山岩中形成大规模气藏,不同火山岩相对油气的储集性差异很大,因此探究断陷内火山机构类型和喷发模式成为天然气勘探开发的基础。徐家围子断陷发育中酸性火山岩,识别出层状火山、熔岩穹隆、破火山口等3种主要火山机构赋存类型。受区域垂向和斜向两期拉张作用控制,在断裂上盘、下盘和断裂带,火山机构分别以不同形式展布：断裂下盘的掀斜肩部火山机构发育、断裂带火山机构串珠状叠置、断裂上盘火山爆发强烈并形成大型徐东破火山口。徐东破火山口的形成说明岩浆侵位于地壳底部,形成扁平状的岩浆房。岩浆垂直上升喷发或沿断裂喷发,形成徐家围子断陷中心式-裂隙式火山喷发模式。