晋冀内蒙交界区下地壳流变性质的实验研究及其构造演化意义

EXPERIMENTAL RESEARCH ON RHEOLOGICAL BEHAVIORS OF LOWER CRUST AND ITS SIGNIFICANCE OF TECTONIC EVOLUTION IN THE JUNCTURE AREA OF SHANXI, HEBEI AND INNER MONGOLIA PROVINCES, CHINA

酸性和基性麻粒岩的高温高压实验表明，基稳态流动律分别为：ε＝２０．７ｅｘｐ（－２８８／ＲＴ）·Δσ３．０和ε＝１０６．５９ｅｘｐ（－４２５／ＲＴ）·Δσ３．０２，并可与加拿大地盾的麻粒岩流动律相比。在下地壳的温度７００℃～１０００℃、压力１．０Ｇｐａ～１．２ＧＰａ和应变率１０－４／ｓ～１０－７／ｓ条件下，岩石变形以韧性变形为主，并发育韧性剪切带，其中辉石和斜长石极易发生动态重结晶及定向排列成线理，石英则已静态恢复，此结果与野外观察的吻合。下地壳的宏观流变模型显示，增厚型下地壳存在一厚的低蠕变强度层，减薄型地壳则上地幔也出现低强度层。大陆下地壳这种低蠕变强度层的流变性质有助于岩石圈增厚和减薄的发生。

Highpressure and high temperature experiments on basic and acid granulites sampled from the juncture area of Shanxi and Hebei and Inner Mongolia provinces show that, steadystate flow law obtained from these two kinds of granulites are ε=20.7exp(-288/RT)·Δσ3.0 and ε=106.59 exp(-425/RT)·Δσ3.02 respectively, and can be correlated with those from granulites exposed in Canadian continental shield. Under the condition of temperature at 700～1000℃ and confining pressure at 10～12GPa and strain rate at 10-14S-1 concerning lower crust, experimental rocks deformed in mainly ductility and ductile shear zones developed in some rocks. Pyroxene and feldspar are subject to undergoing dynamic recrystallization and oriented in lineation, while quartz was in static recovery. The result above can match with that observed from the field. The macrorheologymodels of lower crust show that one or more thicker lowercreepstrengthlayers exist in lower crust with regard to thicked lithosphere as well as in upper mantle with regard to thinned one. Rheological behaviors of continental lower crust characteristic of lowercreepstrength layer of this kind can help lead to thicking and thinning of lithosphere.