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Rock Deformation, Component Migration and 18 O/ 16 O Variations during Mylonitization in the Southern Tan‐Lu Fault Belt
Author(s) -
Xiaoyong YANG,
Deliang LIU,
Min FENG,
Qingni YU,
Kuiren WANG
Publication year - 2007
Publication title -
acta geologica sinica ‐ english edition
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.444
H-Index - 61
eISSN - 1755-6724
pISSN - 1000-9515
DOI - 10.1111/j.1755-6724.2007.tb00953.x
Subject(s) - mylonite , geology , shear zone , gneiss , protolith , quartz , metamorphic rock , mineralogy , zircon , shear (geology) , petrology , geochemistry , tectonics , seismology , paleontology
This paper discusses the relationship between the volume loss, fluid flow and component variations in the ductile shear zone of the southern Tan‐Lu fault belt. The results show that there is a large amount of fluids flowing through the shear zone during mylonitization, accompanied with the loss of volume of rocks and variations of elements and oxygen isotopes. The calculated temperature for mylonitization in different mylonites ranges from 446 to 484°C, corresponding to that of 475 to 500°C for the wall rocks. The condition of differential stress during mylonization has been obtained between 99 and 210 MPa, whereas the differential stress in the wall rock gneiss is 70–78 MPa. The mylonites are enriched by factors of 1.32‐1.87 in elements such as TiO 2 , P 2 O 5 , MnO, Y, Zr and V and depleted in SiO 2 , Na 2 O, K 2 O, Al 2 O 3 , Sr, Rb and light REEs compared to their protolith gneiss. The immobile element enrichments are attributed to enrichments in residual phases such as ilmentite, zircon, apatite and epidote in mylonites and are interpreted as due to volume losses from 15% to 60% in the ductile shear zone. The largest amount of SiO 2 loss is 35.76 g/100 g in the ductile shear zone, which shows the fluid infiltration. Modeling calculated results of the fluid/rock ratio for the ductile shear zone range from 196 to 1192 by assuming different degrees of fluid saturation. Oxygen isotope changes of quartz and feldspar and the calculated fluid are corresponding to the variations of differential flow stress in the ductile shear zone. With increasing differential flow stress, the mylonites show a slight decrease of δ 18 O in quartz, K‐feldspar and fluid.