Detrital zircon U-Pb ages of the late Mesoproterozoic–Neoproterozoic Qiaotou formation in the Liao-Ji area of the North China Craton: implications for Rodinia reconstruction

The Qiaotou Formation comprises the late Mesoproterozoic to early Neoproterozoic strata in southern Jilin and Liaoning Provinces at the eastern margin of the North China Craton (NCC). The depositional age of the formation is 1.1–0.9 Ga, as constrained from the ages of the youngest detrital zircons and later mafic intrusions. U-Pb age dating of detrital zircons yielded age peaks at 1.16, 1.58, and 1.74 Ga, and a minor peak of 2.47 Ga. The late Neoarchaean to Palaeoproterozoic detrital zircons were derived from the ca. 2.5 Ga Longgang and Liaonan blocks, ca.1.9 Ga magmatic/metamorphic rocks and late Palaeoproterozoic extensional-related magmatic rocks in NCC. The abundance of Mesoproterozoic zircon grains is less easy to explain. The possible source may represent (i) possibly concealed/vanished Grenvillian magmatic rocks in NCC, or (ii) derivation from the Qinling Microcontinent or (iii) Fennoscandian shield, or (iv) São Francisco–Congo Craton.

桥头组（Qiaotou Formation）分布于华北克拉通（North China Craton, NCC）东缘的吉南与辽南地区，属于中元古代晚期至新元古代早期地层。该组的沉积时代被限定为1.1~0.9 Ga，这一年代约束基于最年轻碎屑锆石（detrital zircons）的年龄以及后期镁铁质侵入岩（mafic intrusions）的年代数据。对碎屑锆石开展U-Pb定年（U-Pb age dating）分析显示，其年龄峰值分别为1.16 Ga、1.58 Ga与1.74 Ga，另有一处次要年龄峰值2.47 Ga。晚新太古代至古元古代的碎屑锆石物源来自约2.5 Ga的龙岗地块（Longgang blocks）与辽南地块（Liaonan blocks）、华北克拉通内约1.9 Ga的岩浆/变质岩，以及古元古代晚期与伸展作用相关的岩浆岩。中元古代锆石颗粒的丰度则难以通过现有认知得到合理解释，其可能的物源包括以下四类：（1）华北克拉通内可能被埋藏或消失的格林威尔造山期岩浆岩（Grenvillian magmatic rocks）；（2）秦岭微大陆（Qinling Microcontinent）；（3）芬诺斯坎迪亚地盾（Fennoscandian shield）；（4）圣弗朗西斯科-刚果克拉通（São Francisco–Congo Craton）。