| In xishankou of Kuruktag.The leucoleptite in the Xinditage Group has generally affected by the metamorphism with in amphibolite-granulite facies in Early Proterozoic.In this area,the leucoleptite group,gneiss group and the metamorphic granitic rocks were symbiotic and this phenomeno considered to be evidence of anatexis of the ancient crust.I address,1)the evidence in macroscopic of the anatexis effect in field,2)the recovery of the primary rock of the leucoleptite group,3)the comparison of the rare earth elements of the residual granulites and the melt,4)the evidence in microscopic of the anatexis,5)the study of zircon U-Pb chronology,6)Estimation of temperature and pressure for metamorphism in anatexis 7)Discussion on tectonic setting of metamorphic granitic rock.Through these points I aim to restrain the time when the anatexis happend and the extent of anatexis in Kuruktag region on Paleoproterozoic.And compared with the precambrian block which in the same period of orogenic belt around in Tarim craton,and the global orogenic events,conclude that the anatexis in Kurukhtag region is the responed to the event of Colombian continental polymerization on 1.9Ga around.In the group of leucoleptite,especially in the folds of the layer,there are a large number of melt in the shape of lenticular,sausage and metamorphic diorite exist.The evidence of leucoleptite group shows the residual bedding and the mineral particles in the specific parts are obviously enlarged and the typical fused silica.the peak of the metamorphic mineral assemblage is Pl + K + Bi + Gr + Q,it shows the low amphibolite facies at least(T: 575 °-700 ° P: 4-8Kb),then,the biotite and garnet et al were replaced by sericite,Shown as a greenschist facies.The restoration of the original rock shows that the primary rock is a lithologic group of miscellaneous sandstone and marble interlayer.Its zircon is generally remelted,its age in core can be regarded as the time of anatexis issue(measured :1950 ± 30Ma).The zircons of metamorphic diorite have obvious characteristics of magmatic zircon(1893 ± 15Ma),and the predecessor's geochemical characteristics are discriminated,which is characterized by plate-edge convergence volcanic arc granite.By comparing the rare earth elementdistribution patterns of the two,it is found that the enrichment of Eu in the feldspar-plagioclase leucoleptite in the leucoleptite group shows that there is no sufficient plagioclase or potassium feldspar in the anatexis process,The extend of anatexis is not high,and the garnet plagioclase leucoleptite in the leucoleptite group has no obvious Eu enrichment,and the rare earth distribution pattern has the same trend as the metamorphic diorite.Based on the above observations,the magmatic issue relate to quartz diorite(1893 ± 15 Ma)is a product of anatexis issue,which the origin rock is leucoleptite.And the mechanism of this anatexis issue is related to the crustal thickening caused by the Early Proterozoic orogenic events.According to the extend of metamorphism of the sample,I think that the feldspar-plagioclase leucoleptite and the garnet plagioclase garnet plagioclase leucoleptite represent the change of the anatexis degree of the study area from low to high,Therefore,it is inferred that the orogenic belt associated with this anatexis issue is similar to the Andean-type accretionary orogenic belt,and the original sedimentary strata are deformed by the compressive stress after the arc,forming the fold deformation zone and causing the crustal thickening,So that the shallow depth of the role of the anatexis effect,characterized by feldspar-plagioclase leucoleptite and melt veins symbiotic characteristics,deeper is garnet plagioclase and,quartz diorite.through the comparison of the orogenic event around the Tarim in the same period,I think that this orogeny event is related to the convergence of the Columbia supercontinent around 1.9Ga,which shows that the study area,The event is the response of the Columbia supercontinent collection. |
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