大别山超高压变质带p-T-t轨迹数值模拟

p T t PATH NUMERICAL MODELING OF UHP METAMORPHIC BELT IN DABIE OROGEN

模拟设计了拆沉底辟模型、叠瓦俯冲纯剪切伸展模型二组共９种模型。拆沉底辟模型，第一阶段ｐＴｔ轨迹在地幔热影响下都为降压增温过程，第二阶段ｐＴｔ轨迹明显不同，快速折返速率下为近等温降压，从深部抬升到岩石圈底为显著的降压升温、近等温降压过程，从岩石圈底部经过地壳出露地表为降温降压过程。慢速抬升速率下，为降温降压。模拟比较了底辟上升俯冲板片形态不变与板片形态改变模型，陆壳与陆壳俯冲碰撞和陆壳与洋壳俯冲碰撞，在岩石圈深度范围内ｐＴｔ轨迹形态基本相似，首先是等温降压然后降温降压。叠瓦俯冲纯剪切伸展模型，快速伸展速率下ｐＴｔ轨迹表现出３个不同的阶段：从降温降压到近等温降压，然后再降温降压。慢速伸展速率下ｐＴｔ轨迹为开阔弧形形态，首先为降压增温，然后为降压降温。

Nine models belonging to two groups are assumed. These are the delamination diapir model and the pure shear model following the imbricate subduction. During the first phase of them the p T t paths are characterized by decrease in p and increase in T because of the mantle thermal effect. While in the second phase the p T t paths are different. At the faster exhumation rate, the p T t paths are characterized first by increase in p and T , second by isothermal decompression. At the slower exhumation rate the p T t paths are characterized by decrease in p and T . All the p T t paths from the bottom to the surface of the lithosphere are wholly characterized by decrease in p and T . The models compare the difference between the deformed and undeformed plate shapes during their exhumation. The models also compare the model of the continents subducting to ocean plates with the model of the continents subducting to continents. Their p T t paths are similar. Concerning to the pure shear model following the imbricate subduction, the p T t paths are of difference at different exhumation rates. At the faster extensional rate the p T t paths are shown to have 3 different phase, first decreasing in T and p , second isothermal decompression, final decreasing in T and p . At the slower extension rate the p T t paths show as an open arc, first decreasing in p and increasing in T , second decreasing in p and T .