Zircon evolution from migmatite to crustally-derived granite: A case study of late Neoarchean migmatite in the Yishan area, western Shandong, North China Craton

• Published in: Gondwana research 2022-12, Vol.112, p.82-104
• Main Authors: Li, Yuan, Xie, Hangqiang, Dong, Chunyan, Wang, Shijin, Wan, Yusheng
• Format: Article
• Language: English
• Subjects: Anatexis; Diatexite; Magma evolution; Western Shandong; Zircon
• ISSN: 1342-937X; 1878-0571
• DOI: 10.1016/j.gr.2022.09.008

[Display omitted] •Late Neoarchean migmatites and crustally-derived K-rich granites are widespread in Yishan, western Shandong.•Progressive changes in the features of zircons from paleosome, through migmatite, to granite.•The oscillatory zoning of newly-grown zircons becomes more pronounced with migmatite evolution.•The widespread granites in western Shandong did not form through further evolution of the diatexites.•These granites formed by higher-temperature melting of the source region. Sequential changes in the texture, composition and U-Pb age of zircon from the late Neoarchean migmatites and related rocks in the Yishan area of western Shandong, eastern North China Craton, record the evolution of melt and magma from paleosome to crustally-derived granite. Zircon grains from the paleosome and metatexite have features of recrystallization, with narrow rims; those from leucosome have inherited cores and wide homogenous rims; those from diatexite preserve evidence of a complex evolution involving dissolution and growth, with the euhedral morphology of the rims, and the cross-cutting relationship between cores and rims, consistent with a magmatic origin. With the increase in melt content toward granite, the newly-grown zircon has clearer magmatic zoning and higher Th/U ratios. The low whole-rock Zr saturation temperatures (684–728 ℃) indicate that the diatexites, with abundant residual zircon, might be the product of low-temperature melting. The contemporaneous, crustally-derived granites, however, contain no or much less xenocrystic zircon and have high zircon saturation temperatures (740–868 ℃). Only at the higher temperature was sufficient partial melt produced to start the migration of magma out of the source region to form the granites. Anatectic (magmatic) zircons in diatexite commonly contain xenocrystic (residual) zircons, no matter how the magmatic system evolves further, the xenocrystic zircons in the anatectic (magmatic) zircons will still be retained. On the other hand, the crustlly-derived granites widely distributed in the area contain few residual zircons. Therefore, the crustally-derived granites widely distributed in western Shandong cannot form by further evolution of the diatexites, but require a higher degree of partial melting under higher temperature conditions. SHRIMP U-Pb zircon dating, combined with CL imaging, reveals that zircon crystals from the diatexites mostly are characterized by inherited cores with thick magmatic overgrowth