东秦岭216.8Ma前7.0级隐爆成因大地震的震源遗迹  

Source Remains of a Ms 7 Cryptoexplosive Earthquake Occuring before 21.8Ma in East Qinling Mountains

作　　者：陈志耕[1] 

机构地区：[1]河北地质学院地球动力与应用研究所,石家庄050031

出　　处：《地质学报》2015年第8期1495-1529,共35页Acta Geologica Sinica

摘　　要：地震预测是公认的世界性科学难题，而地震成因问题又是地震预测的基础与关键。由于人们不能进入因而不能直接观察和研究发生地震的震源，使得认识地震的成因非常困难。本文依据地质勘查、地球物理探测和工程揭露等事实，在东秦岭熊耳山南麓发现一个形成于216.8±4.0Ma（等时线年龄227±8.4Ma）前古地震的震源遗迹。通过隐爆角砾岩体、隐爆系列角砾岩、岩石地球化学、同位素示踪、同位素测年、稀土元素、多相包裹体、角砾岩微观破碎特征等分析表明，该震源遗迹是一个在杨子板块与华北板块碰撞对接的印支-燕山主造山阶段晚期，上地幔或下地壳经深熔形成的I型造山带花岗质母岩浆结晶分异产生高温高压气液流体乃至超临界流体，沿断裂等薄弱部位上升到局部硅化封闭空间内积聚，产生高温高压气液流体膨胀压力并逐渐积累，当积累的巨大压力超过其所处深度的静岩压力与围岩破裂强度可承受的压力之和时，便在深部产生剧烈的隐蔽爆炸即隐爆所形成。根据上覆地层厚度、临近可参照深成岩体的侵位时代与深度、现代相对高度比较、震源遗迹主震的现代地表尺度并参照地下核爆炸试验相关数据等估算，东秦岭熊耳山震源遗迹的隐爆深度位于当时地表约10km之下，形成震源遗迹隐爆主震的隐爆总能量约为1.55×10^17J，相应的主震面波震级Ms为7.0。同理得知中国印支-燕山期19个典型隐爆角砾岩型多金属矿床隐爆所产生地震的强度为Ms5.1-7.6级之间，据此统计分析得到它们产生地震的等效球状隐爆地质体的压碎区半径R与面波震级Ms的经验关系为Ms=1.40＋0.95ln（R）。与一般“地震遗迹”不同，东秦岭熊耳山南麓地震遗迹不仅是一个震源的实体遗迹即“震源遗迹”，而且是一个震源深度、发生年代、地震强度等地震要素完整、一致且现Earthquake prediction is a worldwide recognized scientific challenge, and the causes of earthquakes is the basis and key of earthquake prediction. Because it can not be directly observed and studied, it is hard to knowledge the causes and mechanism of the earthquake. Based on the fact of field geological and geophysical probe etc, a ancient remnant of earthquake source formed at in 216.8±4Ma （isochron age is 227±8.4M） has been found in the north of Xiong＇ er mountain of the eastern Qinling China. Combined with the characteristics analysis of cryptoexplosion pipes and cryptoexplosion breccia, rock geochemistry, isotope tracer, isotopic dating, REE, gas-liquid inclusions, and the macroscopic and microscopic crushing characteristics of breccia show that the remnant of earthquake has been formed by a strong hidden explosion in the deep crust on the collision and docking of late Indosinian orogeny between Yangtze plate and north China Plate, the upper mantle or lower crust form I-type granites magma by the depth melt of orogeny squeeze, in upwelling process generated high temperature and pressure gas-liquid-supercritical fluid by the crystallization differentiation and reduced pressure boiling, the supercritieal fluid and expansion pressure accumulate in weak parts of the enclosed silicified space such as fracture or cracks ect, when the enormous expansion pressure of supercritical fluid exceeds bearing pressure of the depths of static pressure and broken rock strength. According to the thickness of the overlying strata, eruption ages and depth of the referenced plutonic rock, modern relative height contraction, modern outcrops scale of main remnant earthquake, and the experimental data of underground nuclear explosions suggest that the cryptoexplosion depth of the remnant of earthquake is about 10km below the surface, with the major cryptoexplosion energy earthqukes being about 1.55×10^17J, corresponding main earthquake＇s surface wave magnitude Ms of about 7.0. Thus it can be infered that 20 typical crypto

关 键 词：东秦岭熊耳山 隐爆成因地震 地震成因 隐爆系列岩 硅化封闭 古地震遗迹 震源遗迹 

分 类 号：P315.33[天文地球—地震学]