碱性花岗岩的动力学氧同位素交换和流体流动几何学:交换机制和平流冷却

Oxygen isotope exchange and flow geometry of meteoric-derived water within an alkali granite pluton: exchange mechanism and advective cooling.

新疆北部乌仑古塔斯嘎克碱性花岗岩体分为主体相和北部边缘相。条纹长石广泛发育出溶 ;石英与碱性长石复杂交生。条纹长石的出溶衍生出压应力 ,造成石英的变形。大部分钠铁闪石是由霓辉石交代形成的。在 δ1 8O石英 - δ1 8O条纹长石 和δ1 8O石英 - δ1 8O钠铁闪石 协变图上 ,应用耦合的质量传输和动力学限制的同位素交换模型对样品进行了模拟。相对交换速率常数和3个矿物的显微组构特征共同指示 ,表面反应即溶解 -再沉淀和管道扩散是氧同位素交换的主要机制。大气降水从塔斯嘎克碱性花岗岩的北部边缘相往主体相发生了平流渗透。北部边缘相样品的较陡的斜率、以及石英和条纹长石较低的 1 8O亏损程度 ,被解释为是由于与同位素组成未演化的短路径大气降水在相对较短的时限内发生氧同位素交换造成的。但是 ,与同位素组成演化了的长路径大气降水在相对较长的时限内的相互作用 ,导致了主体相样品的较缓的斜率以及石英和条纹长石的较高程度的 1 8O亏损。对于一个侵入岩体的冷却来说 。

One-dimensional transport equations that include the mechanisms of advection, diffusion, hydrodynamic dispersion, and non-equilibrium exchange between water and rock were numerically solved and graphically illustrated. Two lithological groups, the northern marginal facies (NM) and the main body (MB), were distinguished within the Tasigake alkali granite pluton of Ulungur in northern Xinjiang, China. Perthite exhibits extensive exsolution with surrounding albite comb, whereas quartz grains are generally deformed. A volume increase resulting from perthite exsolution has exerted stress on the quartz grains, thus causing their deformation. Arfvedsonite grains are dominantly secondary and have been formed through metasomatism of aegirine-augite. In the delta(18)O-delta(18)O diagrams between quartz, perthite, and arfvedsonite, slopes of data trends were translated to relative exchange rates k(Quartz)/k(Perthite)/k(Arfvedsonite) ( = 1/5. 3/5. 0) that indicate surface-reaction as the oxygen isotope exchange mechanism. This, coupled with the microtextural characteristics, suggests that isotope exchange depends on mineral reactions. Application of the model of coupled mass transport and kinetically limited isotope exchange to the Tasigake pluton, established infiltration geometry of meteoric-derived water from the NM through the MB. The steep data trends and the low degrees of O-18-depletion of quartz and perthite from the NM are interpreted as resulting from interaction with an isotopically unevolved meteoric-derived water during a relatively short time-duration. However, interaction with an isotopically more evolved longer-path-length meteoric-derived water during a longer time-duration resulted in the gentle data trends and the higher degrees of O-18-depletion of quartz and perthite from the MB. This study shows that advective heat removal by circulating surface waters can be an important mechanism for cooling a granite pluton.