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Zircon U–Pb ages and Hf isotope compositions of migmatites from the North Qinling terrane and their geological implications
Author(s) -
Liu Q.,
Wu Y.B.,
Wang H.,
Gao S.,
Qin Z.W.,
Liu X.C.,
Yang S.H.,
Gong H.J.
Publication year - 2014
Publication title -
journal of metamorphic geology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.639
H-Index - 114
eISSN - 1525-1314
pISSN - 0263-4929
DOI - 10.1111/jmg.12065
Subject(s) - zircon , protolith , geology , metamorphism , migmatite , geochemistry , terrane , anatexis , granulite , rodinia , supercontinent , metamorphic rock , partial melting , petrology , gneiss , craton , mantle (geology) , facies , paleontology , tectonics , structural basin
Migmatites are predominant in the North Qinling (NQ) orogen, but their formation ages are poorly constrained. This paper presents a combined study of cathodoluminescence imaging, U–Pb age, trace element and Hf isotopes of zircon in migmatites from the NQ unit. In the migmatites, most zircon grains occur as new, homogeneous crystals, while some are present as overgrowth rims around inherited cores. Morphological and trace element features suggest that the zircon crystals are metamorphic and formed during partial melting. The inherited cores have oscillatory zoning and yield U–Pb ages of c . 900 Ma, representing their protolith ages. The early Neoproterozoic protoliths probably formed in an active continental margin, being a response to the assembly of the supercontinent Rodinia. The migmatite zircon yields Hf model ages of 1911 ± 20 to 990 ± 22 Ma, indicating that the protoliths were derived from reworking of Palaeoproterozoic to Neoproterozoic crustal materials. The anatexis zircon yields formation ages ranging from 455 ± 5 to 420 ± 4 Ma, with a peak at c . 435 Ma. Combined with previous results, we suggest that the migmatization of the NQ terrane occurred at c . 455–400 Ma. The migmatization was c . 50 Ma later than the c . 490 Ma ultra‐high‐ P (UHP) metamorphism, indicating that they occurred in two independent tectonic events. By contrast, the migmatization was coeval with the granulite facies metamorphism and the granitic magmatism in the NQ unit, which collectively argue for their formation due to the northward subduction of the Shangdan Ocean. UHP rocks were distributed mainly along the northern margin and occasionally in the inner part of the NQ unit, indicating that they were exhumed along the northern edge and detached from the basement by the subsequent migmatization process.