Carbon dioxide generation and drawdown during active orogenesis of siliciclastic rocks in the Southern Alps, New Zealand
Carbon dioxide generation and drawdown during active orogenesis of siliciclastic rocks in the Southern Alps, New Zealand
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新西兰南阿尔卑斯山硅质碎屑岩活跃造山作用期间二氧化碳的产生和减少
DOI：
10.1016/j.epsl.2017.10.010
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发表时间：
2018
影响因子：
5.3
通讯作者：
Menzies C
中科院分区：
文献类型：
--
作者：
Menzies C
碰撞造山作用通过释放变质反应释放的CO2，促进机械侵蚀，进而增加大气CO2的化学风化和下降，从而影响全球碳循环。南阿尔卑斯山是一个贫碳酸盐的硅质碎屑山带，与活动的澳大利亚太平洋板块边界有关。持续不断的快速构造抬升、变质作用和热液活动正在动员碳。在这里，我们使用温泉流体和气体、变质主岩和碳酸盐脉的碳同位素测量来建立变质碳平衡。我们确定了南阿尔卑斯山CO2的三个主要来源：(1)石墨的氧化；(2)绿片岩-角闪岩相边界的变质反应消耗方解石；(3)基质和脉状方解石的溶解。阿尔卑斯断裂上形成的地幔中只有少量的CO2。温泉的HCO3−/Ca2+∼9摩尔比值明显高于方解石的溶解产物，表明深部变质作用占主导地位。估算出南阿尔卑斯山高隆起区近地表环境的总CO2通量为∼6.4×10 8m ol/a。在变质过程中，约有87%的二氧化碳来自石墨氧化(25%)和方解石浸染脱碳(62%)反应。方解石的溶解作用和地幔来源的CO2对∼和∼的贡献率分别为10%和3%。在富碳酸盐造山带中，CO2的产生以石灰岩的变质脱碳作用为主。南阿尔卑斯山温泉脱气进入大气的CO2通量为1.9~3.2×108mol/年，是近地表环境通量的30~50%。相比之下，地表化学风化的CO2降幅在2.7~20×109mol/年之间，至少比该造山带进入大气的CO2通量高一个数量级。因此，南阿尔卑斯山等硅质碎屑山脉是大气二氧化碳的净汇，而喜马拉雅等富含碳酸盐岩的造山带则是二氧化碳的净来源。
Collisional mountain building influences the global carbon cycle through release of CO 2 liberated by metamorphic reactions and promoting mechanical erosion that in turn increases chemical weathering and drawdown of atmospheric CO 2. The Southern Alps is a carbonate-poor, siliciclastic mountain belt associated with the active Australian Pacific plate boundary. On-going, rapid tectonic uplift, metamorphism and hydrothermal activity are mobilising carbon. Here we use carbon isotope measurements of hot spring fluids and gases, metamorphic host rocks, and carbonate veins to establish a metamorphic carbon budget. We identify three major sources for CO 2 within the Southern Alps:(1) the oxidation of graphite;(2) consumption of calcite by metamorphic reactions at the greenschist–amphibolite facies boundary, and (3) the dissolution of groundmass and vein-hosted calcite. There is only a minor component of mantle CO 2 arising on the Alpine Fault. Hot springs have molar HCO 3−/Ca 2+∼ 9, which is substantially higher than produced by the dissolution of calcite indicating that deeper metamorphic processes must dominate. The total CO 2 flux to the near surface environment in the high uplift region of the Southern Alps is estimated to be∼ 6.4× 10 8 mol/yr. Approximately 87% of this CO 2 is sourced from coupled graphite oxidation (25%) and disseminated calcite decarbonation (62%) reactions during prograde metamorphism. Dissolution of calcite and mantle-derived CO 2 contribute∼ 10% and∼ 3% respectively. In carbonate-rich orogens CO 2 production is dominated by metamorphic decarbonation of limestones. The CO 2 flux to the atmosphere from degassing of hot springs in the Southern Alps is 1.9 to 3.2× 10 8 mol/yr, which is 30–50% of the flux to the near surface environment. By contrast, the drawdown of CO 2 through surficial chemical weathering ranges between 2.7 and 20× 10 9 mol/yr, at least an order of magnitude greater than the CO 2 flux to the atmosphere from this orogenic belt. Thus, siliciclastic mountain belts like the Southern Alps are net sinks for atmospheric CO 2, in contrast to orogens involving abundant carbonate rocks, such as the Himalaya, that are net CO 2 sources.
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