U–Pb ages and Hf isotopic composition of zircons and whole rock geochemistry of volcanic rocks from the Fangniugou area: Implications for early–middle Paleozoic tectonic evolution in Jilin Province, NE China

Abstract

The Changchun-Yanji suture in Jilin Province, NE China is generally interpreted to mark the closure position of the Paleo-Asian Ocean along the north margin of the North China Craton. However, the issue about the earlymiddle Paleozoic tectonic evolution in this region has long been debated. In order to provide evidence for resolving this issue, we carried out a geochemical and zircon U-Pb-Hf study on the Fangniugou and Taoshan volcanic rocks from the Fangniugou area of Jilin Province, in the Changchun-Yanji suture zone. Laser ablationinductively coupled plasma-mass spectrometry (LA-ICP-MS) zircon U-Pb dating indicates that the Fangniugou volcanic rocks are products of at least two volcanic events (~425 and 390 Ma) and that episodes of magmatism existed in Jilin Province during the early-middle Paleozoic period. These rocks, in conjunction with relevant data from the literature, indicate that early-middle Paleozoic magmatism occurred along the Changchun-Yanji suture. The volcanic rocks belong to medium-to high-K calc-alkaline series and display features of I-type granites of subduction-related igneous rocks. During the late Silurian-middle Devonian, the Y and Yb concentrations progressively decreased with time, accompanied by an increase in K 2 O concentrations and (La/Yb) N values, indicating a process of crustal thickening. This interpretation is supported by the presence of early Paleozoic arc igneous rocks and the formation of early Devonian molasse in central Jilin Province. Zircon grains separated from the rocks have high ε Hf (t) values and two-stage Hf model (T DM2 ) ages varying from +4.92-8.76 and 0.84-1.09 Ga, respectively. All these characteristics, in conjunction with trace element features, suggest that the late Silurian rocks were generated by partial melting of a depleted mafic lower crust in a subduction zone setting, whereas the middle Devonian rocks were derived from partial melting of a thickened lower crust the most probably related to a collisional event.

Geochemistry and Zircon U-Pb-Hf Isotopes of Metamorphic Rocks from the Kaiyuan and Hulan Tectonic Mélanges, NE China: Implications for the Tectonic Evolution of the Paleo-Asian and Mudanjiang Oceans

“…They play a key role in the interpretation of sutured ocean basins, including those that have experienced metamorphism and deformation during continental collision [4][5][6][7]. A case in point is the tectonic evolution of the NE China, which has traditionally been considered to be the eastern segment of the Central Asian Orogenic Belt (CAOB; Figure 1a) [8][9][10][11][12][13][14][15][16][17][18][19][20][21]. During its long tectonic evolutionary history, the NE China witnessed the amalgamation of several micro-continental blocks (Figure 1b) and the final closure of the Paleo-Asian Ocean (PAO) during the Paleozoic to Early Mesozoic, which was subsequently overprinted by post-Mesozoic Mongol-Okhotsk and circum-Pacific tectonic regimes [22][23][24][25][26].…”

The Late Triassic Molasse Deposits in Central Jilin Province, NE China: Constraints on the Paleo-Asian Ocean Closure

“…This region is adjacent to the Dunhua-Mishan Fault and the Songliao Basin to the east and west, respectively (Figure 1b). The CYS is composed mainly of Phanerozoic granitoids with a series of subduction-related tectonic mélanges, including the Kaiyuan, Xia ertai, Hulan, Seluohe, Qinglongcun, and Kaishantun tectonic mélanges [12,15,[21][22][23][25][26][27][28]31,35,47]. In addition, minor Paleozoic and Mesozoic sediments are also distributed in the "granite ocean" [39,[43][44][45][46][48][49][50].…”

“…This region is Dunhua-Mishan Fault and the Songliao Basin to the east and west, respe 1b). The CYS is composed mainly of Phanerozoic granitoids with a series related tectonic mélanges, including the Kaiyuan, Xia′ertai, Hulan, Seluohe and Kaishantun tectonic mélanges [12,15,[21][22][23][25][26][27][28]31,35,47]. In additio zoic and Mesozoic sediments are also distributed in the "granite ocean" [3 The study area is to the southeast of Jilin City, in central Jilin Prov According to the 1:200,000 geological map, this area mainly contains the Daheshen, the Upper Permian Fanjiatun and Yangjiagou, and the Triass dingzi formations [80] (Figure 2).…”

“…This view is supported by some Early Paleozoic mid-ocean ridge basalt (MORB)-like and arc-like magmatic rocks identified in the study area and adjacent regions, including the Zhangjiatun meta-diabase dyke (493 Ma), hornblende gabbro (486 Ma), quartz diorite (476 Ma), and tonalite (443 and 440 Ma) [117,118]; the Xiaosuihe serpentinite (494 Ma) and pyroxene andesite (467 Ma) [118]; the Toudaogou metamorphic intermediate-mafic and ultramafic rocks (474, 468, 466, and 465 Ma) [13]; and the Fangniugou rhyodacite (425 Ma) [12]. In addition, the Early Paleozoic zircons in the conglomerate have positive ε Hf (t) values (Figure 9a), similar to those in the above magmatic rocks but distinct from the Phanerozoic zircons from the NCC that generally have negative ε Hf (t) values [87].…”

“…Northeast (NE) China, also called the Xing an-Mongolian Orogenic Belt (XMOB), is located between the North China Craton (NCC) and Siberia Craton (SC) and is an important component of the Central Asian Orogenic Belt (CAOB; Figure 1a) [1][2][3][4][5][6][7][8]. It formed as a result of multiple subduction-and collision-related processes during the closure of the Paleo-Asian Ocean (PAO) and the amalgamation of micro-continental blocks with different origins and geological histories (Figure 1b) [4][5][6][7][8][9][10][11][12][13][14][15]. It is widely accepted that the Solonker-Xra Moron-Changchun-Yanji suture belt tectonically separates the NCC in the south from the micro-continental blocks in the north, and it marks the final closure of the Paleo-Asian Ocean [4][5][6][16][17][18][19][20].…”