燕山地区早侏罗世岩浆活动热供给的数值模拟

摘要/Abstract

摘要： 燕山地区燕山期发育大量的岩浆岩, 如此大规模的岩浆活动(热)的来源一直是一个谜。本文利用有限元的热传导模拟反演可能的热供给。模型假设温度1250 ℃、面积905.86 km²半圆面形玄武岩浆底侵到36.6~50 km深的陆壳底部, 陆壳的地温梯度随着克拉通的破坏而逐渐升高。数值模拟的主要结论: ① 早侏罗世时期的地温曲线表明, 要使围岩发生熔融, 所需要的底侵玄武岩岩浆量是非常大的, 基于燕山地区实际产出的早侏罗世时期的酸性岩, 反演产生81 km²的花岗岩需要的最少底侵玄武岩岩浆量为1053 km²; ② 早侏罗世(J₁)的模型温度场表明, 随着时间的演化, 在40～50 km处水平方向的围岩温度升高明显, 形成很明显的一条高温带或熔融带, 该高温带或者熔融带可能成为后期的构造薄弱面, 加上榴辉岩相变造成的密度增加引起下坠, 达到临界值时, 就会出现垮落, 因此本文从数值模拟的角度, 支持拆沉作用的发生。

关键词: 岩浆活动, 早侏罗世, 拆沉, 数值模拟, 燕山地区

Abstract: Massive Yanshanian magmatic rocks were developed in the Yanshan area of North China. These large-scale magmatic rocks were formed in a short time. However, the heat source of these massive magmatic activities remains unknown. This paper attempts to invert the source of magma with the heat conduct problem by finite element simulation. It is hypothesized that a piece of round-shaped basaltic magma of 905.86 km², underplated into deep crust between 36.6 km and 50 km at the temperature of 1250℃, the geothermal gradient of the crust rose gradually with the evolution of North China craton. The main conclusions of this numerical simulation are as follows: (1) The geothermal temperature curves of J1 reveal that, to make the wall rock melt, the volume of underplating basaltic magma should be considerably huge. Based on the actual output of the acid rock during J1 period in Yanshan area, the amount of underplating basaltic magma required by inversion is 1053 km² to produce 86 km² granites (J1). (2) The temperature field of J1 model shows, the temperature of wall rock at the level of 40~50 km in the horizontal direction was increased significantly and formed a high-temperature zone or melting zone which might be the later tectonic weak surface. And when it transformed into eclogite facies, the density would be greatly increased. The high-density residue fell until caving occurred, as it reached a critical value. This paper supports the occurrence of delamination from the perspective of numerical simulation.

Key words: Magma-heating Supply, Early Jurassic (J1), Delamination, Numerical Simulation, Yanshan Area

中图分类号:

P315

刘翠, 石耀霖, 乔彦超, 邓晋福, 李宁, 段培新. 燕山地区早侏罗世岩浆活动热供给的数值模拟[J]. 地震, 2013, 33(4): 257-268.

LIU Cui, SHI Yao-lin, QIAO Yan-chao, DENG Jin-fu, LI Ning, DUAN Pei-xin. Numeric Simulation of Early Jurassic Magma-heating Supply in the Yanshan Area[J]. EARTHQUAKE, 2013, 33(4): 257-268.

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