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中国东北与俄罗斯远东富CO2矿泉成因研究
中文摘要

全球CO₂气体释放点(或气藏)分布广泛,同时富CO₂泉也广泛分布。CO₂有多种无机和有机来源,但富CO₂泉主要分布在造山带、板块碰撞带、板块俯冲消减带和活火山区,与CO₂的无机来源密切相关,这些地区一般也是高地热值区,故大多数富CO₂泉为温(和/或)热泉。中国东北五大连池和俄罗斯远东地区发育大量富CO₂冷矿泉,泉水含有丰富的微量元素和溶解性CO₂气体,是优质的天然饮用矿泉水资源,同时具有广泛的医疗用途。 本次研究基于太平洋板块俯冲影响带深大断裂和岩浆活动强烈的构造背景研究,结合地质和水文地质条件分析,应用元素地球化学、同位素地球化学、地球化学模拟(PHREEQC)方法,确定中国东北和俄罗斯远东地区富CO₂矿泉水化学特征和气体来源,研究深部流体的运移和CO₂-水-岩相互作用,探讨活火山区富CO₂矿泉的形成机制。 本文得出以下结论: 1.中国东北五大连池与远东Primorye地区出露泉水为低温、微酸、HCO₃型、富含Si、 Fe、Sr和CO₂气体的综合优质饮用矿泉水;长白山天池出露泉水为高温、中性—微碱、HCO₃型、富含Si和CO₂气体的优质热矿泉水。 五大连池和Primorye泉水温都在20℃以下,矿化度超过1000㎎/L;长白山天池泉水大部分温度高于40℃,矿化度大多在1000㎎/L左右。所有泉水中都逸出CO₂气体。冷泉的pH值都小于7,显示出弱酸性;长白山天池的长白泉群pH值在7.5~7.7,显示出中性—微碱性。五大连池、长白山泉与俄罗斯远东泉基本为重碳酸泉,泉水为HCO₃型水。五大连池、长白山天池和远东各泉的H₂SiO₃含量都大于50 ㎎/L,达到偏硅酸矿泉水标准,可以作为医疗和饮用偏硅酸矿泉水;五大连池和远东各泉的Fe含量基本上都大于10 ㎎/L,达到铁矿泉水标准,可以作为医疗和饮用铁矿泉水;五大连池和远东各泉的Sr含量基本上都大于0.2㎎/L,达到锶矿泉水标准,可以作为饮用锶矿泉水。 2.所有泉水中的气体以CO₂为主,其次含有少量的N₂和O₂。碳同位素和惰性气体同位素标识了CO₂气体的上地幔岩浆无机来源。 各泉中气体基本由CO₂、N₂和O₂组成,以CO₂为主。CO₂的δ¹³C值变化范围明显包含了大洋玄武岩及包体CO₂的范围(即MORB),也部分包括了活动构造深源和变质CO₂。 CO₂/³He与δ¹³C关系图上,五大连池泉逸出气落在MORB范围内,溶解气部分落在日本岛弧热泉范围内,长白山泉逸出气体主要落在日本岛弧热泉范围内,部分泉落在MORB范围内;远东泉落在靠近MORB的正下方,反映这些泉中气体的MORB来源。CO₂气体来源于上地幔岩浆。 五大连池、长白山天池与俄罗斯远东各地泉中气体He具有典型的地幔来源特征。各泉中气体R值都大于1 Ra,五大连池泉逸出气2.64~3.87 R〓;五大连池泉溶解气1.18~3.30 R〓;长白山泉逸出气2.29~5.71 R〓;远东泉溶解气2.32~4.66R〓。五大连池逸出气体中惰性气体有30.69~45.06%来源于地幔,平均为37.89%;54.94~69.31%来源于地壳,平均为62.11%:而长白山天池逸出气体中惰性气体有26.66~66.55%来源于地幔,平均为51.97%;33.45~ 73.34%来源于地壳,平均为48.03%。 3.五大连池、长白山天池与俄罗斯远东各地泉具有相似而不同的成因模式,超临界流体是泉水出露的主要驱动力之一,CO₂-H₂O-花岗岩不断相互作用是泉水矿化成分的主要来源,五大连池泉水中有明显的“岩浆水”来源。 中国东北和俄罗斯远东地处太平洋板块俯冲带,上地幔岩浆房发育,上地幔岩浆沿岩浆通道上升过程中结晶分异产生大量CO₂,形成H₂O+CO₂混合超临界流体,沿岩浆通道和深大断裂上升。在五大连池形成一定含量的“岩浆水”和CO₂超临界流体、长白山天池形成CO₂超临界流体、俄罗斯远东形成少量的“岩浆水”和CO₂超临界流体继续上升,成为泉水出露的主要驱动力之一。 五大连池地下深度1750m处,温度60.04℃,地下水与上涌的“岩浆水”和CO₂超临界流体混合,不断与围岩花岗岩相互作用,形成矿泉的主要水化学成分;长白山天池地下深度2021m处,温度129.65℃,地下水与上涌的CO₂超临界流体混合,不断与围岩花岗岩相互作用,形成矿泉的主要水化学成分;俄罗斯远东地下深度2235m处,温度75.3℃,地下水与上涌的少量“岩浆水”和CO₂超临界流体混合,不断与围岩花岗岩相互作用,形成矿泉的主要水化学成分。 流体不断与围岩相互作用,沿深大断裂上升过程中不断降压降温,在五大连池地下深度784m处,超临界CO₂形成气体逸出;在长白山天池地下深度753m处,超临界CO₂形成气体逸出;在俄罗斯远东地下深度760m处,超临界CO₂形成气体逸出。大量CO₂气体-H₂O花岗岩不断相互作用,并与浅层地下水不断混合,在断裂带上出露成富CO₂矿泉。 论文中采用“分步式”溶解平衡,基于惰性气体同位素,计算了五大连池泉水中惰性气体的MORB-CRUST-ASW三相来源份额;在五大连池富CO₂冷矿泉中发现明显的“岩浆水”,泉水的“氧漂移”进一步证实了其存在:提出超临界流体是泉水出露的主要驱动力之一,并首次给出了五大连池、长白山天池与俄罗斯远东各地泉具有相似而不同的成因模式。 开展富CO₂矿泉的研究,具有重要的科学意义和实用价值:(1)富CO₂冷矿泉中CO₂为深部无机来源,是地幔岩浆活动良好的指示剂和信息载体,富CO₂冷矿泉中CO₂的研究揭示了俯冲带岩浆活动与深部流体之间的关系。(2)富CO₂矿泉中的CO₂深部以超临界流体形式存在,地下水与CO₂超临界流体的自然混合过程为CO₂地质处置和封存提供了天然实验依据。(3)CO₂-H₂O-花岗岩体系中的相互作用是一个复杂过程,随着温度和压力的变化,CO₂和H₂O都会以不同状态和溶蚀能力存在,富CO₂矿泉水化学成分来源的研究丰富了水—岩相互作用的研究内容。(4)深部流体是矿泉出露的主要驱动力之一,不同于传统的水头差(或水力梯度)驱动的认识,提出与深部流体相关的富CO₂矿泉形成模式,丰富和发展了水文地质理论。 关键词:富CO₂矿泉;水化学;气体来源;成因;中国东北;俄罗斯远东

英文摘要

CO₂-rich mineral springs are widely distributed close to areas of hot spots of CO₂ gas releasing (or CO₂ reservoir) in the world. Although CO₂ has a variety of inorganic and organic sources, CO₂-rich mineral springs mainly occur in orogenic belts and zones of plate collision, plate subduction and active volcanism, and are related to inorganic origin and high geothermal areas. Cold mineral springs from Wudalianchi, northeast China and the Far East Russia are enriched in trace elements and have high solubility of CO₂, and are good natural mineral water resources for drinking and medical purposes. Based on analysis of the tectonic background of impact zones of the Pacific plate subduction, deep fault and magma activities as well as geological and hydrogeological settings, genesis of CO₂-rich mineral springs of NE China and the Far East Russia was studies in detail using approaches of element geochemistry, isotope geochemistry and geochemical modeling (PHREEQC). The chemistry of CO₂-rich mineral springs was characterized so as to understand the origin of CO₂ gas, deep fluid migration, CO₂ - water - rock interaction, and the origin of CO₂-rich mineral water. Some conclusions were obtained as follows. 1.CO₂-rich mineral springs from Wudalianchi and Primorye are high quality drinking water with the characteristics of low temperature, slightly acidic, HCO₃ type, rich in Si, Fe, Sr and CO₂ gas, different to that of Changbaishan Tianchi springs with higher temperature, neutral to slight-alkali, HCO₃ type, and rich in Si and CO₂ gas. The Wudalianchi and Primorye springs have temperatures below 20℃, and salinity more than 1000 ㎎/L; but the Changbaishan Tianchi springs have temperature higher than 40℃, and mostly salinity about 1000 ㎎/L or so. All springs are escaping CO₂ gas. Wudalianchi and Primorye springs are slightly acidic with pH less than 7, while Changbaishan Tianchi springs are neutral to slight-alkali with pH from 7.5 to 7.7. They are all soda springs with HCO₃ water type. For those with concentration of H₂SiO₃ higher than 50 ㎎/L, they can be used as medical and drinking H₂SiO₃ mineral water. For the concentration of Fe higher than 10 ㎎/L of Wudalianchi and Primorye springs, they can be used as medical and drinking Fe mineral water, so as to Sr with concentration higher than 0.2 ㎎/L of Wudalianchi and Primorye springs. 2.The gas composition is predominantly CO₂ with a small amount of N₂ and O₂ in all of the springs. CO₂ originates from mantle magma degassing according to carbon isotope and inert gas isotope. Escaped and dissolved gases of all spring mainly consist of CO₂, N₂ and O₂, and the content of CO₂ is much higher than those of other gases. The δ¹³C value of CO₂ is in the range of ocean basalt and its inclusions, also include the source of deep active tectonic and metamorphic CO₂. In the figure of relationship between CO₂/³He to δ¹³C, Wudalianchi escaped gas samples fall in MORB area, while some of dissolved gas fall in Japanese island arc hot spring area. Some of Changbaishan Tianchi escaped gas samples fall in Japanese island arc hot spring area, others fall in MORB area. Primorye is close and under to MORB area. So the origin of CO₂ is upper mantle magma degassing. Helium has typical characteristics of mantle source from Wudalianchi, Changbaishan Tianchi, and Primorye springs because the R value s is greater than 1 R〓. The R value of escaped gas from Wudalianchi is 2.64 ~ 3.87 R〓, while that of its dissolved gas 1.18 ~ 3.30 R〓. The R value of Changbaishan Tianchi escaped gas 2.29 ~ 5.71 R〓, and Primorye dissolved gas 2.32 ~ 4.66 R〓. The inert gas of Wudalianchi escaped gas has 30.69 ~ 45.06% from the mantle with an average of 37.89%, 54.94 ~ 69.31% from the crust with an average of 62.11%. While that of Changbaishan Tianchi escaped gas has 26.66 ~ 66.55% from the mantle with an average of 51.97%, and 33.45 ~ 73.34% from the crust, with an average of 48.03%. 3.Comparing Wudalianchi, Changbaishan Tianchi and Primorye springs, they have almost similar genesis pattern: supercritical fluid is one of the main driving force, CO₂-H₂O-granite continuous interaction resulted in increase of groundwater TDS of the mineral spring, and "magmatic water" may have been mixed in Wudalianchi spring. Northeast China and the Far East Russia are close to Pacific plate subduction and upper mantle magma chamber developed. A large amount of CO₂ was produced for magma crystallization differentiation when the mantle magma intruded upwards, and mixed H₂O and CO₂ supercritical fluid rose along the magma intrusion channel and deep fault zones. There was certain concentration of "magmatic water" and CO₂ supercritical fluid in Wudalianchi,; only CO₂ supercritical fluid in Changbaishan Tianchi; and few "magmatic water" and CO₂ supercritical fluid in Primorye. In Wudalianchi, at 1750 m underground, the temperature is 60.04℃, groundwater mixed with upwelling "magmatic water" and CO₂ supercritical fluid, the mixture interacted with granite and formed major mineral components of spring water. Similar conditions exist in Changbaishan Tianchi and Primorye, but the depth is 2021m and the temperature is 129.65℃ in Changbaishan Tianchi, the depth is 2235 m and the temperature is 75.3℃ in Primorye. The pressure and temperature of deep fluid decreased gradually during its upfloe along deep faults and interaction with surrounding rocks. The supercritical CO₂ turned into gas and escaped with groundwater in the depth of 784 m in Wudalianchi, 753m in Changbaishan Tianchi, and 760 m in Primorye respectively. Abundant CO₂ gas-H₂O-granite interacted and continuously mixed with shallow groundwater, to form CO₂-rich mineral springs along fault zones. The inert gas share of MORB-CRUST-ASW of Wudalianchi springs was calculated with "step-by-step" dissolution balance based on isotopes. "Magmatic water" was found obviously in Wudalianchi CO₂-rich cold mineral springs, approved further by oxygen shift of spring water. We for the first time proposed in this thesis that supercritical fluid be one of main driving forces in the genesis of CO₂-rich mineral springs from northeast China and the Far East Russia.. The study on CO₂-rich mineral springs has important scientific significance and practical value. (1) Deep inorganic CO₂ of CO₂-rich cold mineral springs is a good indicator of magmatic activities, and it can reflect the relationship between magmatic activity and deep fluid in subduction zone. (2) As supercritical fluid of CO₂ at depth, CO₂-rich mineral springs are a natural analogue about the mixing process of groundwater and supercritical CO₂ during CO₂ geological disposal. (3) CO₂-H₂O-granite is a complex interacting system, CO₂ and H₂O are in different stations with different dissolution capacity when the temperature and pressure change. So this study can supply additional information about water- rock interaction. (4) Deep fluid is one of the main driving forces for spring, as different from traditional models of gravity-driven flow, and therefore studying for the genesis of mineral springs related to deep fluids provides new insights into hydrogeological theories. Key Words: CO₂-rich mineral spring; water chemistry; gas origin; genesis; northeast China; the Far East Russia

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