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首页> 外文期刊>American Journal of Science >MODELING METAMORPHISM IN COLLISIONAL OROGENS INTRUDED BY MAGMAS: II. FLUID FLOW AND IMPLICATIONS FOR BARROVIAN AND BUCHAN METAMORPHISM, SCOTLAND
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MODELING METAMORPHISM IN COLLISIONAL OROGENS INTRUDED BY MAGMAS: II. FLUID FLOW AND IMPLICATIONS FOR BARROVIAN AND BUCHAN METAMORPHISM, SCOTLAND

机译：MAGMAS引入的碰撞造山带中的变质模拟：II。流体流动及其对苏格兰巴罗文和布昌变质的意义

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This paper presents the results of two-dimensional numerical modeling of crustal fluid flow in a collisional overthrust setting during emplacement of synmetamorphic mafic sills. An important feature of the fluid flow in the presence of magmatic intrusions is the long-lived prograde up-temperature (up-T) flow of fluid. This upward flow is driven by dehydration reactions in the rocks underlying the intrusions and upward is the consequence of the inverted thermal profile that appears within the depth range of magmatism. If magma is intruded at mid-crustal depths following crustal collision, the up-T flow regime may persist for as much as 5 Myr. Such long-lived up-T fluid flow is not observed in models without magmatism. Strong retrograde reactions in rocks surrounding intrusions may give rise to downward up-temperature flow into the heated but rapidly cooling areas of the crust during exhumation, but the fluid fluxes in these areas are typically small. The total timeintegrated fluid fluxes produced by magmatism and crustal overthickening in the middle and deep crust are substantial, in some cases reaching 3,000 m~3 m~(-2) over 35 Myr. Early magmatic events may give rise to fluid fluxes exceeding 1,000 m~3 m~(-2) in only 1 Myr. The strong dehydration that accompanies the emplacement of hot magma into the relatively low-temperature wall rock leads to hydrofracturing of large volumes of crustal rocks surrounding intrusions. The fractured rock region may extend over tens of kilometers from the zone of magma emplacement. More hydrofracturing is predicted for the middle and deep crust than for the shallow crust because of the exponential decrease of crustal permeability with depth that is assumed in our models.Endothermic dehydration, exothermic retrograde hydration, and the latent heat of wall rock fusion can all influence thermal budgets. In the final part of the paper we integrate the results of the fluid flow modeling presented here, the reconstructions of thermal evolution presented in Part I, and field-based data for the type locality of Barrovian and Buchan metamorphism in Scotland. Many key phenomena predicted by our numerical models are observed in the Scottish Dalradian, including the very short thermal peaks attained over a relatively narrow time span across a broad range of metamorphic zones; penecontemporaneous Barrovian, Buchan, and granulite facies metamorphism; steep Metamorphic Field Temperature Gradients (MFTGs) in the vicinity of intrusions; and petrological evidence consistent with up-temperature fluid flow. Our results suggest that some controversial aspects of regional metamorphism in the Scottish Dalradian, including heat transfer processes and the steep MFTGs, may be plausibly explained by the effects of plutonism.
机译：本文介绍了在同形变质镁铁窗台安置期间冲撞上冲环境中地壳流体流动的二维数值模拟结果。在存在岩浆侵入的情况下，流体流动的一个重要特征是流体的长寿命提升高温（up-T）流动。这种向上的流动是由侵入岩下面的岩石中的脱水反应驱动的，而向上的流动是在岩浆作用深度范围内出现的反向热剖面的结果。如果岩浆在地壳碰撞后侵入地壳中部深度，则向上T流动状态可能会持续长达5 Myr。在没有岩浆作用的模型中没有观察到这种长寿命的向上T流体流动。掘进过程中，侵入体周围岩石中强烈的逆行反应可能导致向下的高温流流入地壳的加热但迅速冷却的区域，但是这些区域中的流体通量通常很小。在中，深地壳中，由岩浆作用和地壳超厚产生的总时间积分流体通量很大，在某些情况下超过35 Myr达到3,000 m〜3 m〜（-2）。早期岩浆事件可能仅在1 Myr内就产生超过1000 m〜3 m〜（-2）的流体通量。伴随着热岩浆进入温度相对较低的围岩，强烈的脱水作用导致侵入岩周围大量地壳岩石的水力压裂。破碎的岩石区域可能从岩浆侵袭区延伸数十公里。由于我们模型中假设的地壳渗透率随深度呈指数下降，因此预测中，深地壳的水力压裂将比浅地壳的水压裂化更多。吸热脱水，放热逆行水化和围岩熔合潜热均可影响热预算。在本文的最后部分中，我们整合了此处介绍的流体流动模型的结果，第一部分中介绍的热演化重构以及苏格兰Barrovian和Buchan变质类型类型的基于现场的数据。由我们的数值模型预测的许多关键现象都在苏格兰的达拉丹中观察到，包括在很宽的变质带范围内相对较短的时间范围内获得的非常短的热峰。准当代Barrovian，Buchan和花岗石相变质作用;侵入体附近的陡峭的变质场温度梯度（MFTG）;和岩石学证据与高温流体流动相一致。我们的研究结果表明，苏格兰达拉丹地区一些有争议的方面，包括传热过程和陡峭的MFTG，可能是由重子现象的影响合理解释的。

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