TY - JOUR
T1 - Neoproterozoic active continental margin of the Cathaysia block
T2 - evidence from geochronology, geochemistry, and Nd-Hf isotopes of igneous complexes
AU - Xia, Yan
AU - Xu, Xisheng
AU - Zhao, Guochun
AU - Liu, Lei
PY - 2015/10/1
Y1 - 2015/10/1
N2 - Previous studies have suggested that northwest Cathaysia was a passive continental margin during Neoproterozoic time, given the absence of Neoproterozoic magmatism. However, this view has been challenged by recent discoveries of mafic and felsic magmatic rocks with geochemical affinities to continental arc or back-arc volcanic rocks from the 1.0-0.9Ga Wuyi-Yunkai belt, indicating the development of an early Neoproterozoic continental margin arc and back-arc system in the Cathaysia block. In this paper we present new age data for the Miaohou and Shanhou arc complexes, demonstrating that the active continental margin of the Cathaysia block lasted until ca. 830Ma. The Miaohou complex is composed of gabbro, diorite, and granite, the Shanhou complex of diorite and granite, and both complexes are bound by the Jiangshao Fault. Twelve samples from the Miaohou and Shanhou complexes give zircon U-Pb ages of ca. 830Ma, indicating that the magmatism of the Miaohou and Shanhou complexes were coeval. The Miaohou gabbro has high zircon e{open}Hf(t) (+2.8 to +9.6) and whole-rock e{open}Nd(t) (+3.9) values together with the geochemical features of volcanic arc basalts, while the Miaohou and Shanhou diorites and granites show large variations and high values of zircon e{open}Hf(t) and e{open}Nd(t) [e{open}Nd(t) (+1.1 to +5.5) and e{open}Hf(t) (-6.1 to +12.3) for the diorites, and e{open}Nd(t) (+0.3 to +3.1) and e{open}Hf(t) (-3.8 to +11.3) for the granites] together with a similar geochemistry to continental arc felsic rocks (e.g., Cordilleran batholiths). The geochemical and isotopic data suggest that the southeastwards subduction of an oceanic plate under the Cathaysia block caused the dehydration of sediments in the subducted slab, leading to the metasomatism of the mantle wedge by subduction-related fluids, partial melting of the mantle wedge, followed by varying degrees of assimilation and fractional crystallization (AFC) as the magmas ascended. These processes provide a reasonable explanation for the Neoproterozoic arc magmatism on the northwestern margin of the Cathaysia block, represented by the Miaohou and Shanhou complexes.
AB - Previous studies have suggested that northwest Cathaysia was a passive continental margin during Neoproterozoic time, given the absence of Neoproterozoic magmatism. However, this view has been challenged by recent discoveries of mafic and felsic magmatic rocks with geochemical affinities to continental arc or back-arc volcanic rocks from the 1.0-0.9Ga Wuyi-Yunkai belt, indicating the development of an early Neoproterozoic continental margin arc and back-arc system in the Cathaysia block. In this paper we present new age data for the Miaohou and Shanhou arc complexes, demonstrating that the active continental margin of the Cathaysia block lasted until ca. 830Ma. The Miaohou complex is composed of gabbro, diorite, and granite, the Shanhou complex of diorite and granite, and both complexes are bound by the Jiangshao Fault. Twelve samples from the Miaohou and Shanhou complexes give zircon U-Pb ages of ca. 830Ma, indicating that the magmatism of the Miaohou and Shanhou complexes were coeval. The Miaohou gabbro has high zircon e{open}Hf(t) (+2.8 to +9.6) and whole-rock e{open}Nd(t) (+3.9) values together with the geochemical features of volcanic arc basalts, while the Miaohou and Shanhou diorites and granites show large variations and high values of zircon e{open}Hf(t) and e{open}Nd(t) [e{open}Nd(t) (+1.1 to +5.5) and e{open}Hf(t) (-6.1 to +12.3) for the diorites, and e{open}Nd(t) (+0.3 to +3.1) and e{open}Hf(t) (-3.8 to +11.3) for the granites] together with a similar geochemistry to continental arc felsic rocks (e.g., Cordilleran batholiths). The geochemical and isotopic data suggest that the southeastwards subduction of an oceanic plate under the Cathaysia block caused the dehydration of sediments in the subducted slab, leading to the metasomatism of the mantle wedge by subduction-related fluids, partial melting of the mantle wedge, followed by varying degrees of assimilation and fractional crystallization (AFC) as the magmas ascended. These processes provide a reasonable explanation for the Neoproterozoic arc magmatism on the northwestern margin of the Cathaysia block, represented by the Miaohou and Shanhou complexes.
KW - Assimilation fractional crystallization (AFC) process
KW - Cathaysia block
KW - Nd isotopes
KW - Neoproterozoic active continental margin
KW - Zircon U-Pb-Hf isotopes
UR - http://www.scopus.com/inward/record.url?scp=84940775692&partnerID=8YFLogxK
U2 - 10.1016/j.precamres.2015.08.006
DO - 10.1016/j.precamres.2015.08.006
M3 - Article
AN - SCOPUS:84940775692
SN - 0301-9268
VL - 269
SP - 195
EP - 216
JO - Precambrian Research
JF - Precambrian Research
ER -