Magmatic evolution and source of a Proterozoic rapakivi granite complex in the North China Craton: New evidence from zircon U−Pb ages, mineral compositions, and geochemistry

• Published in: Journal of Asian earth sciences 2018-11, Vol.167, p.165-180
• Main Authors: Wang, Xiaoxia, Wang, Tao, Castro, Antonio, Ke, Changhui, Yang, Yang, Hu, Nenggao
• Format: Article
• Language: English
• Subjects: Geochemistry; Mineral composition; North China Craton; Origin; Rapakivi granite
• ISSN: 1367-9120
• DOI: 10.1016/j.jseaes.2017.10.019

[Display omitted] •The Shachang rapakivi granite complex was formed during 1700–1682 Ma.•Temperature and pressure decrease but fO2 increase during crystallization.•Source of the complex is similar to lower continental crust of the NCC. Typical Proterozoic rapakivi granite of the Northern Hemisphere occur in Precambrian shield areas, and are commonly associated with anorthosites, mangerites, and charnockites, thus belonging to the AMCG (anorthosite–mangerite–charnockite–granite) suite. A similar suite is represented in the North China Craton (NCC) by the Shachang rapakivi granite and Damiao anorthosite complexes. The Shachang complex consists of amphibole–biotite rapakivi granite, porphyritic biotite granite, coarse-grained biotite granite, medium- to fine-grained biotite granite, and two-mica granite (listed from the earliest to the latest phases). New zircon U–Pb dating shows that the complex was formed over the period 1700–1682 Ma. The mafic minerals of the complex are calcic amphibole (ferroedenite–ferrohastingsite) and biotite (annite–siderophyllite), and the compositions of the amphibole suggest that the matrix of the amphibole–biotite rapakivi granite crystallized at a pressure of ∼4 kbar. The temperatures of crystallization, obtained from the compositions of amphibole, biotite, and zircon, decreased from ∼780 °C for the amphibole–biotite rapakivi granite to ∼660 °C for the two-mica granite. Our study of the Shachang complex indicates an evolution from early potassium-rich magmas to late silicon-rich magmas. The early amphibole–biotite rapakivi granite crystallized under relatively high temperatures (760–780 °C) and low fO2, while the later rocks formed under lower temperatures (760–660 °C) and high fO2. The Shachang rapakivi granite and Damiao anorthosite complexes contain different mafic minerals and show diverse trace element ratios and disparate geochemical evolutionary trends, suggesting different sources. Zircon Lu–Hf and whole-rock Sm–Nd isotopic data for the Shachang complex are relatively homogeneous, with εHf(t) and εNd(t) values varying from −9.8 to −3.3 and −6.4 to −3.4, respectively. Corresponding two-stage Hf model ages and Nd depleted mantle model ages vary from 2650 to 2850 Ma and from 2480 to 2840 Ma, respectively. These model ages are similar to the ages of Neoarchean lower crustal metamorphic rocks in the NCC (2500–2800 Ma). In addition, the compositions of the amphiboles and biotites in the granite in the Shachang complex indicate