Hydromagnesite precipitation in the Alkaline Lake Dujiali, central Qinghai-Tibetan Plateau: Constraints on hydromagnesite precipitation from hydrochemistry and stable isotopes
Hydromagnesite precipitation in the Alkaline Lake Dujiali, central Qinghai-Tibetan Plateau: Constraints on hydromagnesite precipitation from hydrochemistry and stable isotopes
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青藏高原中部杜家丽碱性湖水菱镁矿降水：水化学和稳定同位素对水菱镁矿降水的制约
DOI：
10.1016/j.apgeochem.2016.12.020
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发表时间：
2017-03-01
影响因子：
3.4
通讯作者：
Ye, Chuanyong
中科院分区：
文献类型：
--
作者：
Lin, Yongjie;Zheng, Mianping;Ye, Chuanyong
矿物水菱镁矿，Mg-5(CO3)(4)(OH)(2)中心点4H(2)O，是碱性湖中水合碳酸镁的常见形式，但其形成过程尚不清楚。本研究重点关注青藏高原中部的杜家丽湖，该湖是地球表面少数发生大量全新世水菱镁矿沉淀的环境之一。对地表水的水文地球化学以及水菱镁矿矿床的矿物学、稳定同位素（δ C-13 和 δ O-18）和放射性同位素含量进行了分析，以研究形成机制。杜家里湖周围地表水的化学成分由于蒸发作用由T1岩石风化型水（Ca-Mg-HCO3水型）演变为浓度较高的T2（Na-SO4-Cl水型）水。 XRD结果表明，样品的矿物成分为纯水菱镁矿。对水菱镁矿中氧同位素的分析表明，蒸发水自生碳酸盐结晶的表生形成是主要的沉淀过程。碳-氧同位素联合分析表明大气中的二氧化碳为水菱镁矿的沉淀提供了碳源。这些发现表明，杜家丽湖的水菱镁矿降水本质上主要是无机的，温室气体二氧化碳直接从大气中被捕获并储存在水菱镁矿中。样品的 AMS 放射性碳测年表明，杜家里湖水菱镁矿矿床中二氧化碳被封存在 5845 +/- 30 至 6090 +/- 25 cal a BP 之间。这项研究有助于提高对现代和古代普拉亚水菱镁矿形成的了解。 (C) 2016 Elsevier Ltd. 保留所有权利。
The mineral hydromagnesite, Mg-5(CO3)(4)(OH)(2)center dot 4H(2)O, is a common form of hydrated Mg-carbonate in alkaline lakes, yet the processes involved in its formation are not well understood. This study focuses on Dujiali Lake, in the central Qinghai-Tibetan Plateau (QTP), which is one of the few environments on the earth's surface with extensive Holocene precipitation of hydromagnesite. The hydrogeochemistry of surface waters, and the mineralogical, stable isotope (delta C-13 and delta O-18), and radiogenic isotope content of hydromagnesite deposits were analyzed to investigate fortnation mechanisms. The chemical composition of surface water around Dujiali Lake evolved from the rock-weathering-type waters of T1 (Ca-Mg-HCO3 water type) to more concentrated sodic waters of T2 (Na-SO4-Cl water type) due to evaporation. XRD results show that the mineralogical composition of samples is pure hydromagnesite. Analysis of oxygen isotopes in the hydromagnesite indicates that supergene formation with authigenic carbonate crystallization from evaporation water is the dominant precipitation process. Combined carbon-oxygen isotope analysis suggests atmospheric CO2 provided a carbon source for the precipitation of hydromagnesite. These findings suggest that hydromagnesite precipitation at Lake Dujiali is mainly inorganic in nature, and the greenhouse gas, CO2, is trapped and stored in the hydromagnesite directly from the atmosphere. AMS radiocarbon dating of samples indicates CO2 was sequestered betWeen 5845 +/- 30 to 6090 +/- 25 cal a BP in the Dujiali Lake hydromagnesite deposit. The study contributes to improved understanding of hydromagnesite formation in modern and ancient playas. (C) 2016 Elsevier Ltd. All rights reserved.