Bayesian Markov-Chain Monte Carlo Inversion of Low-Temperature Thermochronology Around Two 8 − 10 m Wide Columbia River Flood Basalt Dikes
Bayesian Markov-Chain Monte Carlo Inversion of Low-Temperature Thermochronology Around Two 8 − 10 m Wide Columbia River Flood Basalt Dikes
复制标题
两个 8~10 m 宽哥伦比亚河洪水玄武岩堤周围低温年代学的贝叶斯马尔可夫链蒙特卡罗反演
DOI：
--
复制
发表时间：
2019
影响因子：
2.9
通讯作者：
P. Reiners
中科院分区：
文献类型：
--
作者：
L. Karlstrom;Kendra E. Murray;P. Reiners
洪流玄武岩火山作用涉及在地质时间尺度较短的情况下，大量岩浆侵入地壳和地表环境。洪流玄武岩侵位的机制，包括地壳岩浆运移系统的动力学以及单次喷发的节奏，都没有得到很好的限定。在此，我们研究了美国俄勒冈州东北部哥伦比亚河洪流玄武岩省的两条出露的岩脉，利用磷灰石和锆石（U - Th）/He热年代学来确定岩脉侵位的历史。垂直于岩脉边缘的样本剖面记录了花岗岩围岩的瞬时加热情况。我们将加热模拟为由于岩脉侵位所致，考虑了一个针对玄武质岩浆和花岗岩围岩具有不同熔体分数 - 温度关系的热模型，以及岩脉内非稳定流的参数化。我们通过考虑球形颗粒中He扩散作为对岩脉加热的响应来模拟热年代计的部分重置。采用贝叶斯马尔可夫链蒙特卡罗框架来联合反演与岩脉侵位和颗粒尺度He扩散相关的六个参数。我们发现，尽管在露头尺度上这两条岩脉尺寸相似，但在远离岩脉处热年代计部分重置的空间模式不同。这些模式导致了不同的预测侵位历史。我们扩展了之前对俄勒冈州东北部沃洛瓦山脉麦克斯韦湖假定的补给岩脉的建模，发现后验概率分布函数（PDFs）预测在1 - 6年期间由于持续的岩浆流动而稳定加热，以及远场围岩温度升高。这表明麦克斯韦湖附近存在区域尺度的加热，这可能是由附近的侵入体引起的。另一条位于科努科皮亚子群内的岩脉，预计其热活动寿命为1 - 4年，加热速率不稳定，这表明与麦克斯韦湖相比，其岩浆流动速率较低，且处于较冷的近地表热环境中。在这两种情况下，模型对近岩脉处热年代计部分重置的不匹配表明，要么是通过围岩中的流体平流进行热传递，要么是岩脉中岩浆的脉冲式流动。我们的研究结果凸显了哥伦比亚河洪流玄武岩省内岩脉侵位历史的多样性，以及贝叶斯反演方法在量化热模型中的参数权衡和不确定性方面的能力。
Flood basalt volcanism involves large volumes of magma emplaced into the crust and surface environment on geologically short timescales. The mechanics of flood basalt emplacement, including dynamics of the crustal magma transport system and the tempo of individual eruptions, are not well constrained. Here we study two exhumed dikes from the Columbia River Flood Basalt province in northeast Oregon, USA, using apatite and zircon (U-Th)/He thermochronology to constrain dike emplacement histories. Sample transects perpendicular to the dike margins document transient heating of granitic host rocks. We model heating as due to dike emplacement, considering a thermal model with distinct melt-fraction temperature relationships for basaltic magma and granitic wallrock, and a parameterization of unsteady flow within the dike. We model partial resetting of thermochronometers by considering He diffusion in spherical grains as a response to dike heating. A Bayesian Markov-Chain Monte Carlo framework is used to jointly invert for six parameters related to dike emplacement and grain-scale He diffusion. We find that the two dikes, despite similar dimensions on an outcrop scale, exhibit different spatial patterns of thermochronometer partial resetting away from the dike. These patterns result in distinct predicted emplacement histories. We extend previous modeling of a presumed feeder dike at Maxwell Lake in the Wallowa Mountains of northeastern Oregon, finding posterior probability distribution functions (PDFs) that predict steady heating from sustained magma flow over $1-6$ years and elevated farfield host rock temperatures. This suggests regional-scale heating in the vicinity of Maxwell Lake, which might arise from nearby intrusions. The other dike, within the Cornucopia subswarm, is predicted to have a $1-4$ year thermally active lifespan with an unsteady heating rate suggestive of magma low flow rate compared to Maxwell Lake, in a cool near-surface thermal environment. In both cases, misfit of near-dike partial resetting of thermochronometers by models suggests either heat transfer via fluid advection in host rocks or pulsed magma flow in the dikes. Our results highlight the diversity of dike emplacement histories within the Columbia River Flood Basalt province and the power of Bayesian inversion methods for quantifying parameter trade-offs and uncertainty in thermal models.