中国大陆新生代典型火山区温室气体释放的规模及其成因

火山活动能够将地球深部的碳输送到大气圈,是地质碳排放和深部碳循环的重要形式.火山作用不仅在喷发期能够释放大量温室气体,而且在休眠期也能释放巨量的温室气体.在全球变暖的背景下,定量化地研究火山活动对大气圈温室气体含量增加的贡献具有至关重要的意义.本文利用密闭气室法等该领域国际先进的测试技术,测量并计算了长白山、腾冲、五大连池及青藏高原南部的羊八井等典型火山区的温室气体释放规模.结果显示,我国大陆新生代典型火山区向大气圈输送的温室气体总通量约为8.13×10⁶t·a^-1,接近10⁷t·a^-1级别,相当于全球火山活动导致的温室气体(主要为CO₂)释放总量的6%左右.太平洋构造域火山区的温室气体在释放通量与总量方面均低于特提斯构造域,并且太平洋构造域火山气体的地壳混染程度较低,显示出大洋俯冲带与大陆俯冲带火山区温室气体释放的成因差异.     

腾冲火山区的现代幔源氦释放:构造和岩浆活动意义

深地震测深(DSS)和大地电磁测深(MT)都表明腾冲火山区现今仍存在壳内岩浆囊,但对其数量和空间分布还存在分歧并缺乏全貌性认识。MT探测认为腾冲火山区是一个软流圈上涌和岩石圈减薄区,但对这一减薄区的空间范围还缺乏充分的约束。通过对腾冲火山区及外围大范围温泉逸出气体的分析测试,我们共获得了75个温泉逸出气体的氦同位素³He/⁴He比值数据(部分为前人资料)。利用氦同位素示踪原理,我们研究了腾冲火山区幔源氦释放强度空间分布和时间变化特征,结果发现:腾冲火山区的幔源挥发份释放呈1带3区分布。以³He/⁴He≥1 Ra,幔源氦比例≥15%为界,腾冲火山区的幔源挥发份释放异常区呈整片分布,为一南北走向的条带,南北长100km,东西宽50km。在整片异常区的内部,腾冲火山区的幔源挥发份释放又有强度不同的3个区域:① 中部腾冲县城-热海一带,³He/⁴He比值达到5.5 Ra以上,幔源氦比例达到70%以上,释放强度最强。② 北部曲石一带,³He/⁴He比值达4.5 Ra以上,幔源氦比例达到50%以上,释放强度次之。③ 南部五合-蒲川-新华一带,³He/⁴He比值达2Ra以上,幔源氦比例达到25%以上,释放强度最弱;腾冲火山区幔源挥发份释放强度在不断升高,其中第3个释放区的³He/⁴He比值(Ra)升高速率比前两者明显要大。我们认为:腾冲火山区现今幔源挥发份释放强度的空间分布图象就是该地区软流圈上涌和岩石圈减薄区空间尺度和上涌强度的最直接反映,上涌区(减薄区)的大小大致为南北长100km,东西宽50km;腾冲火山区现今存在3个壳内岩浆囊。第1个岩浆囊位于腾冲县城-热海一带,第2个岩浆囊位于马站-曲石一带,第3个岩浆囊位于五合-龙江-团田-蒲川-新华一带;腾冲火山区3个岩浆囊都在不断受到幔源岩浆的持续补充;第1个岩浆囊集幔源挥发份释放、相对地热梯度、地壳形变和地震活动等异常于一身,活动性最强,是未来腾冲火山最可能喷发的地点,需重点监视。第2个岩浆囊的幔源挥发份释放强度也引人注目,需加强监测。第3个岩浆囊规模大,埋深较浅,幔源挥发份释放增加较快,需引起注意。     

长白山火山区温泉温室气体排放通量研究

温泉是深部岩浆活动在地表的直接表现,并且向大气圈排放大量的温室气体.然而,国内尚无火山区温泉排放的温室气体通量研究报道.我国长白山火山区水热活动强烈,主要有湖滨温泉带、聚龙温泉群、锦江温泉以及火山口外围的十八道沟温泉.本文利用数字皂膜流量计测量温泉气体排放通量,并结合前人对长白山火山区温泉气体成分的研究成果,估算了研究区温泉所排放的温室气体通量.结果表明,长白山火山区温泉排放的CO2通量为6.9×104t·a-1,CH4排放通量为428.44t·a-1,与意大利Pantelleria Island火山区温泉排放的温室气体通量规模相当.本文的测试结果表明:数字皂膜流量计在火山区温室气体排放通量估算研究中的应用是可行的.     

腾冲新生代火山区CO2气体释放通量及其成因

许多研究结果表明,休眠期火山主要通过喷气孔、温泉以及土壤微渗漏三种方式向大气圈释放温室气体。腾冲是我国重要的新生代火山区之一,同时也是主要的水热活动区,但是关于温室气体释放通量的研究却鲜有报道。本文首次估算了该地区土壤微渗漏和温泉水的CO2释放通量,并根据气体成分的分析结果探讨了这些温室气体的来源。2012~2013年连续两年使用密闭气室法现场测量了土壤微渗漏CO2通量,结果表明,马站、热海-黄瓜箐和五合-蒲川-团田三个地区通量较高,其中,热海-黄瓜箐地区平均通量最高,马站次之,五合-蒲川-团田地区最低。较高的土壤微渗漏CO2释放地区同前人推断的岩浆囊的分布在空间上具有较好的一致性;三个地区气体的3He/4He比值较高,三端元模拟结果表明,它们均有较高含量的幔源He释放;根据气体CO2/3He与δ13CCO,CO2模拟计算,CO2主要来源于碳酸盐矿物的脱碳作用和岩浆脱气。由此推断2的释放同深部的岩浆囊具有重要的成因联系,它为碳酸盐矿物的脱碳作用提供了主要的热源,同时也是重要的物质来源。根据土壤微渗漏CO2平均通量及火山、地热异常区的分布面积估算出三个地区土壤微渗漏CO2的释放通量分别为1.8×106t/a(马站),3.2×106t/a(热海-黄瓜箐)和2.0×106t/a(五合-蒲川-团田)。腾冲新生代火山区每年通过土壤微渗漏向大气圈释放CO2的量至少可达7.0×106t,为意大利Etna火山区释放CO2通量(1.4×107t/a)的二分之一。通过水岩相互作用计算温泉水中CO2气体的释放通量为4.9×104t/a。腾冲温泉气泡及温泉水向大气圈释放CO2气体的总通量为5.3×104t/a,远高于意大利Vulcano火山区温泉释放的CO2总通量(3.7×103t/a)。     

火山温室气体释放通量与观测的研究进展

火山活动是地球深部碳循环的重要环节,火山区不仅在火山喷发期能够释放温室气体,而且在休眠期也能向大气圈中释放大量的温室气体。在当前全球温室气体减排的背景下,定量化地研究火山区对大气圈温室气体含量增加的贡献,对于识别自然因素和人类因素碳排放的相对规模、为国际碳排放谈判积累基础数据等均具有至关重要的科学价值和现实意义。本文对火山区温室气体的排放方式与特征、温室气体释放通量与成因的研究方法进行了简要概括,并综述了中国新生代典型火山区温室气体释放通量与成因的研究成果。结合国外温室气体排放研究现状,指出深入研究活火山(包括休眠火山)区的温室气体释放通量与成因对于估算火山来源温室气体的释放规模、建立火山未来喷发预测-预警体系、深入理解岩浆脱气过程与机制等问题均具有至关重要的现实意义和科学价值。     

火山区温室气体排放研究进展

火山活动是地球深部脱气的重要途径之一,它在大气圈温室气体浓度变化及全球碳排放研究中具有重要的作用。以国外火山气体研究成果为基础,概述火山气体的研究内容、研究方法（包括样品采集、实验室测试）,并重点探讨国外间歇期火山区土壤脱气、温泉脱气及喷气孔脱气的温室气体排放通量估算方法及其相应规模。结果表明,全球范围内火山间歇期土壤...     

中国东部CO2气地球化学特征及其气藏分布

中国东部CO₂气田(藏)发育广泛,分布复杂。本文对中国东部松辽、渤海湾、苏北、三水、东海、珠江口、莺琼、北部湾等盆地和内蒙古商都地区以及部分现代构造岩浆活动区CO₂气田(藏)和气苗中CO₂的地球化学特征进行了分析和研究,探讨了中国东部CO₂气的成因、来源及分布。中国东部CO₂气的含量主要分布区间为0~10%,其次为90%~100%,呈现典型的U字型。δ¹³C_CO2值则呈现典型的单峰式分布,峰值区间为-6‰~-4‰。CO₂含量、δ¹³C_CO2值和R/Ra值综合表明,中国东部高含CO₂气以幔源无机成因为主,混有部分有机成因气和(或)壳源无机气。中国东部已发现的36个无机成因CO₂气田(藏)在空间分布上与新近纪及第四纪北西西向玄武岩活动带展布一致,深大断裂和岩浆活动是无机成因CO₂富集、运移和分布最重要、最直接的两大主控因素。     

土壤温室气体昼夜变化及其环境影响因素研究

通过对北京东灵山草地和桦树林土壤气体CO₂,N₂O和CH₄浓度及其排放通量的昼夜连续观测,探讨了生长季节草地和森林土壤温室气体昼夜变化及其环境影响因素。研究表明:1)土壤CO₂排放通量昼高夜低,N₂O排放通量有明显小时尺度波动,但昼夜变化不突出;土壤CO₂和N₂O浓度昼夜变化不明显,且与排放通量波动不一致;土壤是大气CH₄的一个汇,相对厌氧的环境可能有利于土壤吸收CH₄。2)无雨时气温昼夜变化通过影响土壤表层的气体扩散和CO₂产生过程,来影响土壤CO₂和N₂O的地表排放通量,而对土壤10cm以下CO₂和N₂O的产生影响不大。小时尺度的土壤CO₂和N₂O浓度波动则可能还有其他影响因素或机制。3)降雨时土壤渗水引起的土壤空气对流取代气体浓度扩散成为土壤与大气空气交换的主要方式,导致土壤CO₂和N₂O排放通量的同步波动。降雨渗水较多时,较多的溶解氧随着雨水进入土壤内,会促进土壤CO₂的生成和抑制N₂O的产生。4)土壤CO₂与N₂O浓度存在显著的正相关关系,反映出土壤CO₂和N₂O有相对稳定的产率比。土壤有效碳可能是造成土壤CO₂与N₂O浓度正相关的主要原因,土壤空气的氧分压则可能是造成土壤CO₂和N₂O浓度波动不一致的重要因素。     

植物——大气N2O的一个潜在排放源

N₂₂和CH₄的重要温室气体。目前,全球N₂₂₂O不仅是一个普遍存在的自然现象,而且其排放量可达到与土壤排放相比较的水平,因而植物可能是未知的大气N₂O的一个重要排放源;植物排放N₂O受植物的种类、生长发育阶段、养分供给、光照强度及CO₂浓度等因素的影响。     

火山区CO_2气体释放研究进展

不同构造域的火山释放CO_2气体的方式、机制和规模具有明显的差异。在全球变暖的大背景下,定量化研究不同类型火山区CO_2气体的释放通量、模拟及计算火山气体的来源演化,对于估算地质源温室气体释放对大气圈温室气体增加的贡献,以及理解地球的深部碳循环过程具有重要意义。近年来,全球火山区CO_2气体释放研究取得了显著进展,尤其在定量研究火山区CO_2气体释放通量的方法、气体源区与地球动力学背景的判定以及不同构造背景的火山区CO_2气体释放特征等领域取得了重大成果。本文综述了不同构造域火山区CO_2气体释放研究的最新成果,详细介绍了我国新生代典型火山地热区的CO_2气体释放研究进展。     

Subduction-related hot spring-type gold mineralization in the central Tengchong block,southwestern China

Numerous present-day hot springs and associated ancient Lianghe gold deposit occur in the central Tengchong block, SW China, associated with oceanic crust subduction. From the center outwards, the alteration zones in the hot spring of the Rehai consist of alunite and silica in a breccia zone, a kaolinite and illite zone, and a chlorite, illite, kaolinite zone. The gas phase in the hot spring is dominated by CO₂ with δ¹³C ranging from −4.5‰ to −7.2‰. These features indicate a major magmatic origin of the hot spring gas. The ³He/⁴He ratios in the gas from central Tengchong vary from 1.56 to 5.88, approaching to those of the MORB. This is probably related to the ongoing subduction of the Indian plate beneath the Tengchong block. The hot spring waters in the central Tengchong block have much higher content of Au and other elements, e.g., Ag, As, Sb, and Tl, than other typical hot springs, such as Hasbrouck, Sulfer, etc. in the world. The hot springs with more mantle gas contribution and higher water temperature show more elevated Au contents, which implies that the metal in the hot spring was most likely contributed from the magmatic gas. The compiled D-O isotopes of the hot spring waters from previous studies suggest that they are primarily derived from meteoric water. A genetic model for the hot spring system in the central of Tengchong has been tentatively established. The gold-charged hot spring is genetically connected to an active magma chamber, which was produced by subduction of oceanic crust. The chamber is driving long-term surface meteoric circulation and constantly releasing magmatic volatiles enriched with metals. As hot spring water mixed with magmatic volatiles, causing decompression-boiling and forming hydraulic fractures to penetrate the roof of siliceous sinter, which induced the continuing metal deposition and formed the Lianghe hot spring.     

云南腾冲热海高温地热水中汞的地球化学异常及其指示意义

汞是环境中典型有害组分,深部地热系统可能是环境中汞的重要来源之一,但当前地热成因汞的研究程度很低。本文以腾冲火山带热海水热区为研究区,开展了热泉中汞的水文地球化学研究。热海水热区内排泄的中性热泉含有异常高浓度的汞,但酸性热泉则绝大多数未检出汞。热海热泉中的汞与典型的岩浆来源组分氯相同,均主要来源于岩浆流体的混合。在中性热泉中,Hg(II)是汞的占优势地位的价态,Hg²⁺与不同形态硫化物的配合则是决定Hg(II)的形态分布的直接因素,但pH可通过控制水中硫化物的形态分布来影响Hg(II)的形态分布。Hg(II)不易挥发,故中性热泉中汞含量普遍较高;但酸性热泉中的汞受泉口氧化还原电位较高的影响,以Hg(0)为主要价态,且因Hg(0)易挥发而导致总汞含量极低。就中性热泉而言,其汞含量对水热区断裂分布有重要指示作用,原因为沿不同断裂上升的中性地热水经历的冷却方式不同,最终导致热泉汞含量也表现出显著差异。热泉汞含量对水热系统结构研究有借鉴意义。     

Mantle-derived CO_2 in Hot Springs of the Rehai Geothermal Field,Tengchong,China

Gas concentrations and isotopic compositions of He and CO2 were determined on free gas samples from ten hot springs of the Rehai geothermal field, Tengchong, China. The results showed that hot-spring CO2 gas, together with He,was derived mainly from the mantle, indicating the accumulation of mantle-derived volatiles beneath the survey area. The δ^13C values of CO2, higher than those of the typical mantle-derived carbon and the isotopic composition of hot-spring-free CO2 in unequilibrium with dissolved CO2, are recognized only in the Rehai geothermal field, suggesting that there seems to be a still-degassing magmatic intrusion at depths, which provides mantle-derived volatiles to the hydrothermal system above. The accumulation of those volatiles has probably played an important role in triggering earthquakes in this region.In addition, the isotopic characteristics of He and C also indicate that the magmatic intrusion seems to have been derived from the MORB source, and could be contaminated by crustal materials during its upwelling through the continental crust.     

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。     

青藏高原南部及邻区深部碳释放规模与成因

不同构造背景下的深部碳释放通量与机制研究对于深刻理解长时间尺度的气候变化具有重要意义,以往的相关研究多集中在洋中脊、大洋俯冲带和大陆裂谷等地质单元,缺少对大陆碰撞带深部碳释放规模与机理的关注,从而制约了对大陆碰撞带深部碳循环过程及其气候环境效应的进一步认识。青藏高原起源于印度和欧亚大陆的碰撞,是研究大陆碰撞带深部碳循环的理想地区。为此,在近年来青藏高原温室气体释放野外观测与研究的基础上,本文估算了高原南部及邻区火山-地热区的CO₂释放规模并探讨了其释放模式。气体He-C同位素地球化学与温泉水热活动特征等显示,青藏高原南部及邻区的深部碳释放主要受深部岩浆房、断裂和浅部水热系统等因素的控制。依据深部流体源区和上升运移控制因素的差异,可以将青藏高原南部及邻区的深部碳释放划分为三大类：(1)以壳内水热系统脱碳为主的藏南地区;(2)深大断裂控制的以水热系统脱碳为主的川西地区;(3)深部岩浆房和浅部水热系统共同控制的滇西南地区。青藏高原南部土壤微渗漏CO₂释放通量介于18.7～52.3Mt/yr之间,温泉溶解无机碳释放通量约为0.13Mt/yr;高原邻区...     

Influence of the Chuxiong Yao’an Earthquake on the Mineralization of Hot Springs in the Tengchong Geothermal Area, Southwestern China

<正>The Tengchong geothermal area,an active tectonic region with frequent earthquakes,is located in Yunnan Province of southwestern China.This area contains abundant active hot springs, which often display high metal concentrations and obvious mineralization phenomena.At 19:19 on 9 July 2009,an earthquake occurred in Yao'an,Chuxiong,Yunnan Province,which is 300 km to the northeast of the Tengchong geothermal area.We sampled water in the hot springs in the Tengchong area from 4 July to 9 July 2009 and from 10 July to 15 July 2009 to study the changes of elemental concentrations before and after the earthquake and discuss the influence of the earthquake on the mineralization of the hot springs.The concentrations of most trace elements increased slightly,but the concentration of REE(rare earth elements) decreased by 50%after the earthquake in the hot springs around a NS-trending fault.The elemental concentrations remained unchanged in Longtan and Suanshuigou,which are related to an inactive crater.The elemental concentrations in other springs controlled by superficial and small-scale faults decreased after the earthquake.The earthquake can stimulate the activity of deep faults and magma chambers,as is responsible for the increase of metal concentrations in the hot springs along the NS-trending deep fault;whereas it can decrease the porosity of permeable rocks,resulting in the decline of the flux of ore-bearing fluids and the corresponding mineralization in the hot springs related to superficial faults.     

Geochemical constraint on origin and evolution of solutes in geothermal springs in western Yunnan,China

Geothermal resources are very rich in Yunnan, China. However, source of dissolved solutes in geothermal water and chemical evolution processes remain unclear. Geochemical and isotopic studies on geothermal springs and river waters were conducted in different petrological-tectonic units of western Yunnan, China. Geothermal waters contain Ca–HCO₃, Na–HCO₃, and Na (Ca)–SO₄ type, and demonstrate strong rock-related trace elemental distributions. Enhanced water–rock interaction increases the concentration of major and trace elements of geothermal waters. The chemical compositions of geothermal waters in the Rehai geothermal field are very complicated and different because of the magma chamber developed at the shallow depth in this area. In this geothermal field, neutral-alkaline geothermal waters with high Cl, B, Li, Rb Cs, As, Sb, and Tl contents and acid–sulfate waters with high Al, Mn, Fe, and Pb contents are both controlled by magma degassing and water–rock interaction. Geothermal waters from metamorphic, granite, and sedimentary regions (except in the Rehai area) exhibit varying B contents ranging from 3.31 mg/L to 4.49 mg/L, 0.23 mg/L to 1.24 mg/L, and <0.07 mg/L, respectively, and their corresponding δ¹¹B values range from −4.95‰ to −9.45‰, −2.57‰ to −8.85‰, and −4.02‰ to +0.06‰. The B contents of these geothermal waters are mainly controlled by leaching host rocks in the reservoir, and their δ¹¹B values usually decrease and achieve further equilibrium with its surrounding rocks, which can also be proven by the positive δ¹⁸O-shift. In addition to fluid–rock reactions, the geothermal waters from Rehai hot springs exhibit higher δ¹¹B values (−3.43‰ to +1.54‰) than those yielded from other areas because mixing with the magmatic fluids from the shallow magma. The highest δ¹¹B of steam–heated waters (pH 3.25) from the Zhenzhu spring in Rehai is caused by the fractionation induced by pH and the phase separation of coexisting steam and fluids. Given the strong water–rock interaction, some geothermal springs in western Yunnan show reservoir temperatures higher than 180 °C, which demonstrate potential for electricity generation and direct-use applications. The most potential geothermal field in western Yunnan is located in the Rehai area because of the heat transfer from the shallow magma chamber.     

腾冲热海地热田高温热泉中的硫代砷化物及其地球化学成因

以我国大陆范围内典型的岩浆热源型水热系统——云南腾冲热海为研究区,在国内首次对热泉中硫代砷化物含量及其地球化学成因进行了分析.研究采用的在野外对富硫化物水样进行快速冷冻处理、而后在实验室进行砷的形态分离和测试的方法明显优于当前通用的水样砷含量及其形态分析的预处理和测试方法.主要原因为后者在采样现场对水样的酸化处理可使样品中三硫代砷酸盐以非定形态硫砷化合物的形式沉淀,且用常规阴离子交换柱在野外无法实现硫代砷酸盐的完全回收及其与砷酸盐的分离.受岩浆流体输入和热储内高温条件下强烈流体-岩石相互作用的控制,热海水热系统排泄的中性-偏碱性热泉中富集硫化物和砷,为热泉中硫代砷化物的形成提供了必要条件.热海热泉中检出的硫代砷化物包括一硫代砷酸盐、二硫代砷酸盐和三硫代砷酸盐,在总砷中所占比例最高分别可达26.7%、43.3%和33.7%.热海地热田的2个子区(硫磺塘和澡塘河) 的热泉沿不同断裂带出露,地热水升流过程中经历的冷却方式也不同,使硫磺塘热泉具有相对较高的总硫化物含量和总砷含量,并导致其中各类硫代砷酸盐具有更高的含量范围.