矽卡岩化作用排碳到大气中的途径

Pathways of carbon emissions to atmosphere due to skarnification

鉴于大陆岩浆弧上盘广泛分布有碳酸盐岩,岩体上升侵位过程使其碳通量明显的高于洋内岛弧,从而有可能影响着地质历史长时间尺度(百万年)的气候变化。陆弧碳的排放可分为两部分,一部分是与喷出岩相关的火山作用,另一部分是与侵入岩相关的脱碳过程。侵入岩的体量一般是喷出岩体量的10倍以上,由此与侵入岩有关的脱碳作用释放的碳通量不可忽视,可能类似与喷出岩有关的火山作用释放的碳通量甚至更大。火山作用能够将气体直接排入大气中,因此在以往的工作中研究较为充分。但与侵入岩相关的脱碳过程如:矽卡岩化,发生在地下,关于地下脱碳过程如何将碳释放到大气中还缺少详细的工作。本文,通过对比研究火山地区和非火山地区与侵入岩相关的深部脱碳过程,发现深部碳可以通过区域断层系统、地下水系统和热泉、火山通道、隐爆角砾岩筒、高频率的岩浆热液事件等途径瞬时地释放进入大气。通过初步估算,发现单个矽卡岩矿化事件所产生的二氧化碳通量(0.02~0.2Mt/yr)能够与目前地球绝大部分的普通单个火山的碳通量(<0.5Mt/yr)类比。因此岩浆深部脱碳过程对大气的影响至少与火山相当,其对气候的影响不可忽视。

Continental arcs have been recently hypothesized to release more carbon dioxide than island arc,because magmas can interact with carbonate wall rocks which store in continent margin during its ascent through the continental arcs.Hence,the variation of continental arc magmatism might drive long-term(>1 Myr)climate events.The emission of continental arc carbon can be divided into two parts:one is the volcanism related to extrusive rocks;the other is the decarbonation process related to intrusive rocks.And the volume of intrusion is much larger than that of extrusion.Thus,the carbon fluxes released by decarbonation process associated with intrusion are similar to,even larger than those released by volcanism associated with extrusion.Among them,volcanism can eject gases directly into the atmosphere,but decarbonation processes associated with intrusion,such as skarnification,take place underground.There is a lack of detailed work on how the decarbonation processes that take place in the underground release carbon into the atmosphere.In this paper,we investigate how decarbonation process associated with intrusion in different volcanic and non-volcanic regions release carbon into atmosphere.And we find that the carbon dioxide produced by skarnification can be released through fault systems,groundwater systems and hot spring,volcanic channels,and high-frequency magmatic-hydrothermal events.We find that the carbon dioxide flux(0.02~0.2 Mt/yr)produced by a single skarn deposit due to skarnification can be on the same order as the carbon flux(<0.5 Mt/yr)liberated from most of single volcano on the earth.Thus,its impact on the atmosphere should be comparable to that of most volcanoes.