微陆块属性厘定的依据OA北大核心CSTPCD

Many Precambrian geological units remained in the orogenic belt;some of them were considered as the Precambrian basements for discussing the tectonic affinities of the microcontinents they belonged to.Because the nature of the microcontinents is of great significance to the architecture and evolution of the orogenic belt,and the Precambrian geological units discussed contain information about the early evolution history of Earth,the definition of the nature of the microcontinent has become one of the key and difficult issues in the study of the orogenic belt.This study takes the microcontinents of the middle segment of the southern Central Asian Orogenic Belt as an example to summarize and sort out the criteria for defining the nature of microcontinents:rock assemblages,metamorphism and deformation,the age feature of provenance revealed by detrital zircon spectra,geological event sequences,the Precambrian crustal evolution characteristic indicated by Hf or Nd isotopes,deep crust information denoted by inherited zircons or zircon xenocrysts and the isotopic composition of Paleozoic igneous rocks,and geophysical characteristics.The different criteria for defining the nature of microcontinents,even the same criterion,lead to huge controversies over it,which affects the understanding of the tectonics and evolution of orogenic belts.Based on the above reasons,this paper suggests that the discussion on the affinity of the Precambrian basement should not only focus on the rock assemblages and formation age but also pay attention to the comprehensive comparative analysis of its metamorphism and deformation characteristics,contact relationships,provenance age characteristics,rock genesis and tectonic setting,crustal accretion information,and deep crustal information on the basis of elaborate field anatomy and high-resolution geochronology,so as to obtain more comprehensive criteria and explore its tectonic affinity.When a series of information of Precambrian geological units are obtained,they can be compared with the same tectonic unit first and then with other units.When the characteristics are different,it is necessary to split the tectonic unit or consider the possibility of structural emplacement(including but not limited to thrusted,strike slipped allochthons,and subduction scraped tectonic slices);When the characteristics are similar,it may indicate that the same microcontinent has been broken up or different microcontinents have experienced similar Precambrian history.