The result of tangential layered solid-state flow deformation in the middle and lower crust:The Yardoi dome in the eastern Himalayan orogenic belt
Tangential(near-horizontal)layered solid-state flow deformation in the middle and lower crust of the continent is one of the important forms of crustal material flow,and it is also an important formation mechanism of gneiss domes.The Yardoi Dome,located in the eastern end of the Tethyan Himalayan sequence,consists of a series of rocks of different ages and metamorphic grades that resulted from a series of intensely ductile shear deformations and multiple magmatic events.It is a natural laboratory for the study of tectonic deformation and magmatic history during the orogenic process.This study takes the Yardoi dome as the research object,and carries out detailed field tectonic analysis and microscopic observation,etc.,from which the following three characteristics are summarized:(1)The rocks at different crust levels within the Yardoi dome have experienced the same tectonic mechanism but with different deformation conditions:the deformation temperature gradually increases from 390℃ to 600℃ from the up to the lower units of the dome;the differential stress gradually decreases from 24.58MPa to 8.72MPa;the strain rate gradually accelerates from 1.27 × 10-13～1.28 × 10-13/s to 5.19 × 10-11～5.21 × 10-11/s,reflecting the strong stratified rheological characteristics of the active crustal zone.(2)Three stages of the dome deformation(D1,D2 and D3)are confined in conjunction with the previous studies.The D1 is a top-to-S shear,and the D2 is a top-to-N shear.The main deformation phase D2 is further divided into two phases,i.e.,the early phase and the main deformation phase D2.The D2 is further divided into two phases,among which the early phase is mainly the type of shear dominated by single shear,while the late phase is the type of shear dominated by pure shear.(3)With regard to the distribution characteristics of the foliations and lineations in the D2,it can be concluded that the plunge of the lineations of the deeper rocks is nearly horizontal,whereas that of the shallower rocks is nearly vertical.According to the above research,the rocks of all parts of the dome were subjected to shear deformation.And rocks of different structural levels exhibit geometric consistency and kinematic decoupling,reflecting the changes in the direction during the development of the dome.Combined with the variation law of the plunge of the lineations in various parts of the dome,we suggest that the Yardoi dome reflect stratified flow of the middle to lower crust,and the formation of the dome can be ascribed to dominant subhorizontal flow and subsidiary vertical flow in the middle to lower crust.
Yardoi gneiss domeSouth TibetFormation mechanism of gneiss domeLayered solid-state flow deformationMiddle and lower crustStrain rateKinematic vorticity
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万方数据
维普
