North Qinling Paleozoic granite associations and their variation in space and time: Implications for orogenic processes in the orogens of central China |
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| Authors: | Tao Wang XiaoXia Wang Wei Tian ChengLi Zhang WuPing Li Shan Li |
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| Institution: | WANG Tao1,WANG XiaoXia2,TIAN Wei3,ZHANG ChengLi4,LI WuPing5 & LI Shan1 1 Institute of Geology,Chinese Academy of Geological Science,Beijing 100037,China,2 Institute of Mineral , Resource,3 Department of Geology,Peking University,Beijing 100871,4 Key Laboratory of Continental Dynamics of Northwest University,Department of Geology,Northwest University,Xi'an 710069,5 School of Civil Engineering,Guangzhou University,... |
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| Abstract: | Integrated zircon U-Pb dating and whole rock geochemical analyses have been carried out for two typical S- and I-type granitoids
in the north Qinling. Zircon dating by SIMS of the Piaochi S-type granitoids yields an emplacement age of 495±6 Ma. The granitoids
show whole-rock ɛ
Nd(t)=−8.2–−.8.8, zircon ɛ
Hf
(t)=−6–−39. The Huichizi I-type granitoids have emplacement ages of 421±27 Ma and 434±7 Ma established by LA-ICP-MS and SIMS
methods, respectively. Their whole-rock ɛ
Nd(t)=−0.9–0.9 and zircon ɛ
Hf(t)=−11–8.4. Combined with statistical analyses of 28 zircon ages of granitoid plutons collected from the literature, Paleozoic
magmatism in the north Qinling can be divided into three stages. The first-stage magmatism (∼505−470 Ma) mainly occurred in
the east part of the north Qinling and has features of an I-type arc, associated with which are S-type granitoids such as
Piaochi pluton. The early granitoids (∼505−490 Ma) have close spatio-temporal relations to ultra-high-pressure (UHP) rocks,
and thus are interpreted as an oceanic subduction system along a continental margin. The second-stage magmatism (∼450−422
Ma) occured through the whole north Qinling, and is characterized by I-type granitoids represented by the Huichizi pluton.
The magma is interpreted as partial melting of lower crust mixed by mantle-derived magma in a collisional setting with the
uplift of terranes. The third-stage magmatism (∼415−400 Ma) is dominated by I-type granitoids and only took place in the middle
part of the north Qinling, and is regarded as a late-stage collision. The spatial and temporal variations of the Qinling Paleozoic
magmatism reveal protracted subduction/collision. The subduction was initiated from the east part of the north Qinling, earlier
than that in the Qilian-northern Qaidam, Kunlun, and northern Dabie regions. This demonstrates variations in time of subduction,
accretion and collision of separate blocks or terranes in the orogenic systems in central China. |
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| Keywords: | zircon geochronology granite association Nd Hf isotopes Qinling orogen |
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