构造变形/变质作用的精细测年及其在造山带研究中的应用

最近几年 ,增生造山过程中构造变形 /变质作用及其精细年代学研究正成为造山带研究的热点之一。造山带内部大型剪切带的运动、变形 /变质事件的精细定年对深入研究增生造山过程具有重要意义。通过把精确的测年数据与约束运动学的、变形 /变质的显微组构结合起来 ,可以比较精细地重建或复原造山带内部不同构造块体增生拼贴的精细时空过程 ,以及建立与之相一致的造山带形成的应变热模式。同时 ,近 3～ 4年的研究结果也表明 ,构造变形 /变质精确定年还存在许多难点 ,如变形矿物形成机制对其测年结果的影响、变形矿物粒度大小对定年结果的制约关系、以及构造变形 /变质过程中矿物同位素体系的变化机理对测年理论与技术质疑等。文中详细介绍了国外目前有关增生造山作用研究的一个热点———构造变形 /变质精细年代学研究的现状和意义、存在的问题和难点 ,以及新技术方法及其可行性和应用等 ,目的在于提请国内同行在进行相关研究时对此能予以重视。

DETAILED DATING OF DEFORMATION / METAMORPHISM OF SHEAR ZONES ON THE SCALE OF OROGEN AND ITS APPLICATION

Detailed dating of metamorphic and deformation events of shear zones on the scale of the orogen has been becoming one of the keys to the study of the orogen in recent years, and it is of great significance for exploring the accretion process of the mountain building. By combining ages with kinematic constraints from structures and fabrics, a palinspastic reconstruction of accretion processes of tectonic blocks constructing the orogen can be achieved, and a geodynamic model can be developed incorporating the migrating strain and the changing thermal regime as the internal parts of the orogen evolving. However, previous researches on precise timing sequences of an array of shear-deformation events in the past 4 to 5 years demonstrated that detailed dating of deformation or metamorphism also suffered from some difficulties or even paradoxes, for example, how do deformation mechanisms influence on the dating results? What are the constraints of the grain size of deformation minerals on the dating results? Are the dating techniques and theories used presently consistent with the changes of isotopic systematics in the minerals during deformation or metamorphism? The paper introduces in detail the progresses and difficulties in detailed dating of deformation or metamorphism of shear zones in the accretion process of an orogen. The authors also introduce some new techniques utilized at present to date the deformation or metamorphism of shear zones on the scale of an orogen, and discuss their feasibility and application to the study of the orogen.