Jamtveit Bjørn, Moulas Evangelos, Andersen Torgeir B, Austrheim Håkon, Corfu Fernando, Petley-Ragan Arianne, Schmalholz Stefan M
Physics of Geological Processes (PGP), The Njord Centre, Department of Geosciences, University of Oslo, P.O. Box 1048 Blindern, N-0316, Oslo, Norway.
Institute of Earth Sciences, University of Lausanne, Geopolis, CH-1015, Lausanne, Switzerland.
Sci Rep. 2018 Nov 19;8(1):17011. doi: 10.1038/s41598-018-35200-1.
Studies of mineral equilibria in metamorphic rocks have given valuable insights into the tectonic processes operating at convergent plate margins during an orogeny. Geodynamic models simulating orogenesis and crustal thickening have been constrained by temperature and pressure estimates inferred from the mineral assemblages of the various lithologies involved along with age constrains from increasingly precise geochronological techniques. During such studies it is assumed that the pressure experienced by a given rock is uniquely related to its depth of burial. This assumption has been challenged by recent studies of high pressure (HP) and ultrahigh pressure (UHP) rocks. Here, we describe an example of Caledonian HP metamorphism from the Bergen Arcs in western Norway, and show that the associated formation of Caledonian eclogites at the expense of Proterozoic granulites was related to local pressure perturbations rather than burial, and that the HP metamorphism resulted from fluid-induced weakening of an initially dry and highly stressed lower crust when thrust upon the hyperextended margin of the Baltic shield.
对变质岩中矿物平衡的研究为造山运动期间汇聚板块边缘发生的构造过程提供了宝贵的见解。模拟造山作用和地壳增厚的地球动力学模型受到了温度和压力估计值的限制，这些估计值是根据所涉及的各种岩性的矿物组合推断出来的，同时也受到日益精确的地质年代学技术所提供的年龄限制。在这些研究过程中，假定给定岩石所承受的压力与其埋藏深度具有唯一的相关性。最近对高压（HP）和超高压（UHP）岩石的研究对这一假设提出了挑战。在此，我们描述了挪威西部卑尔根弧中加里东期高压变质作用的一个实例，并表明以元古代麻粒岩为代价形成加里东期榴辉岩与局部压力扰动而非埋藏有关，且高压变质作用是由于流体导致最初干燥且高度应力的下地壳在逆冲到波罗的地盾超伸展边缘时弱化所致。
