| 秦岭和华北地区地壳低速层的成因探讨──岩石高温高压波速实验证据 |
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| 引用本文： | 赵志丹,高山.秦岭和华北地区地壳低速层的成因探讨──岩石高温高压波速实验证据[J].地球物理学报,1996,39(5):642-652. |
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| 作者姓名： | 赵志丹 高山 |
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| 作者单位： | 1. 中国科学院地球化学研究所，贵阳 550002;2.中国地质大学地球化学研究所，武汉 430074 |
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| 基金项目： | 国家自然科学基金,地质矿产部“八五”重点基础地质研究基金 |
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| 摘 要： | 对秦岭和华北地区地壳主要岩类１３８个样品进行高温高压实验，测量其纵波速度的结果表明，其中５４个样品出现了纵波低速现象．对出现该现象的样品的实验产物所做的肉眼和镜下观察、电子探针分析以及综合对比显示，微裂隙不是产生低速现象的决定因素，而主要是含水矿物（角闪石、黑云母等）的脱水相交和由之引发的岩石部分熔融导致岩石出现纵波低速现象．通过实验条件与中、下地壳的温度和压力等条件的类比揭示，秦岭和华北地区中、下地壳存在的低速（高导）层也可能是由含水矿物的脱水相变或岩石部分熔融引起的．
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| 关 键 词： | 地壳低速层 岩石波速 矿物脱水相变 部分熔融 秦岭和华北 |
| 收稿时间： | 1994-11-17 |
ORIGIN OF THE CRUSTAL LOW VELOCITY LAYER OF QINLING AND NORTH CHINA EVIDENCE FROM LABORATORY MEASUREMENT OF P-WAVE VELOCITY IN ROCKS AT HIGH PT CONDITIONS |
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| ZHAO ZHI-DAN,GAO SHAN,LUO TING-CHUAN,ZHANG BEN-REN,XIE HONG-SEN, ZHANG YUE-MING,XU HUI-GANG.ORIGIN OF THE CRUSTAL LOW VELOCITY LAYER OF QINLING AND NORTH CHINA EVIDENCE FROM LABORATORY MEASUREMENT OF P-WAVE VELOCITY IN ROCKS AT HIGH PT CONDITIONS[J].Chinese Journal of Geophysics,1996,39(5):642-652. |
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| Authors: | ZHAO ZHI-DAN GAO SHAN LUO TING-CHUAN ZHANG BEN-REN XIE HONG-SEN ZHANG YUE-MING XU HUI-GANG |
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| Institution: | 1. Institute of Geochemistry, Academia Sinica, Guiyang 550002, China;
2. Institute of Geochemistry, China University of Geosciences, Wuhan 430074, China |
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| Abstract: | The crustal low-velocity layers（CLVL） occuring in the middle andlower crust have been found in many regions around the world and correspond mostly to tectonically or seismically active belts with high heat flow.The origin of CLVL has been explained in different ways. In our research, the compressional wave velocity （Vp） of 138 rock samples of the Precambrian basement and intrusions of various ages from the Qinling Orogenic Belt and North China Craton were measured under high temperatures（up to 1500℃） and high pressures（up to 3 GPa）simultaneously according to the relationship of Pand T given by the geotherm of e regions. The exPerimental products have been examlned by microscope and EPMA.54 samples show the characteristic phenomenon of Vp decrease with increasing depth. Vp increases rapidly with depth in the range between 0 and 10km, slowly increase in the range between 10 and 30 km ,and reaches the maximum at 750-920 ℃ and 0.630.90 GPa（corresponding to 21 -30km）. Then it gradually decreases to the minimum at 1100-1200℃ and 0.99-1.50 GPa（30-50km）. The greatest differences between the maximum and minimum is 1.6 km/s or 21 %. Mineral constitutions and textures of experimental products indicate that the dehydration, phase n and partial melt of water-bearing minerals, such as hornblende and biotite, are responsible for tha Vp decrease ,This would induce the increase in electrical conductivity simultaneously. The results suggest that dehydration melting of hydrous minerals might be an important mechanism for CLVL observed in the continental crust of the study area and probably other parts of the world. |
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| Keywords: | Crustal lower-velocity layers Seismic velocity in rocks Dehydration and phase transition Partial melt The Qinling Orogenic Belt and North China Craton |
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