秦岭勉(县)略(阳)缝合带及南秦岭地块的变质动力学研究

将变质地质学与构造地质学的研究相结合,将造山过程与变质演化相结合,系统研究了勉(县)略(阳)缝合带的康县—高川段变质动力学特征及其与佛坪递增变质带的关系,认为该区变质作用时空演化特征表现为:不同构造环境同时出现不同类型的变质(如俯冲、拉张等),同一地带不同时期或阶段变质类型的叠加(如俯冲与碰撞),不同地段具差异抬升的历史等特征,从而导致变质类型在空间上的复杂性。这一结果也表明勉略带是一复杂的蛇绿构造混杂岩带,其内部不同的一系列构造岩片早期曾有不同的变质演化历史,后期经历了相似的变质叠加,最后在构造作用下差异抬升。该区变质作用演化可细分为4个阶段:主体发生于海西期并延续至印支早期的拉张变质作用阶段,晚海西—印支期俯冲变质作用阶段,印支晚期碰撞变质作用阶段和印支末期的热接触变质作用和动力退变质作用阶段。勉略缝合带康县—高川段不同岩片及佛坪递增变质带的PTt轨迹研究,揭示了它们不同的变质动力学演化及俯冲、碰撞、拆沉的构造演化过程和机制,也反映了缝合带是由不同层次、起源和环境的岩石经构造作用混杂而成,并经历了后期差异隆升剥蚀历史。

METAMORPHIC DYNAMICS OF THE MIAN-LUE SUTURE ZONE OF QINLING OROGENIC BELT AND THE SOUTHERN QINLING BLOCK

Synthetic methods combining tectonics to metamorphic geology were applied to study metamorphic dynamics of the Kangxian-Gaochuan sector of the Mian-Lüe suture zone and its relation to the Foping progressive metamorphic zones in the Southern Qinling Block in this paper.The metamorphic time space evolution in the suture zone showed coeval occurrence of different metamorphic types,such as subduction-type,extension type in varied tectonic settings,superposition of different metamophisms (for example,subduction-type and syn-collision-type) at different metamorphic stages in the same region.The different uplift histories of varied segments in the suture zone were revealed in the paper.All of the results in the complexity of present spatial distribution of metamorphic types indicated that the Mian-Lüe suture zone was ophiolitic tectonic melange composed of a series of tectonic slabs with different datings,varied tectonic settings and structural levels.These slabs experienced different metamorphic evolution at the early metamophic stage,similar metamorphic superimposition at the middle stage and different uplift at the later stage in the Hycinian-Indosinian orogeny.Four stages of metamorphic evolution could be recognized,namely,the extensional metamorphic stage from the Hycinian to the early Indosinian,the subductional metamorphic stage from the later Hycinian to the Indosinian,the collisional metamorphic stage in the later Indosinian and the stage of contact metamorphism and dynamic retrogressive metamorphism at the latest Indosinian.PTt paths for different slabs in the Kangxian-Gaochuan sector of the suture zone and for the Foping progressive metamorphic zones revealed that they resulted from different metamorphic dynamics,tectonic processes and mechanisms of subduction,collission and delamination,which suggested that the suture zone was a tectonic melange one,composed of slabs in different structural levels,origins and tectonic settings.Denudation or uplifting in varied segments of the suture zone might be unhomogeneous.