Abstract
Abundant Early Cretaceous magmatism is conserved in the central and southern Great Xing’an Range (GXR) and has significant geodynamic implications for the study of the Late Mesozoic tectonic framework of northeast China. In this study, we provide new high-precision U–Pb zircon geochronology, whole-rock geochemistry, and zircon Hf isotopic data for representative intrusive rocks from the northern part of the Ulanhot area to illustrate the petrogenesis types and magma source of these rocks and evaluate the tectonic setting of the central-southern GXR. Laser ablation inductively coupled plasma–mass spectrometry (LA-ICP-MS) zircon U–Pb dating showed that magmatism in the Ulanhot area (monzonite porphyry: 128.07 ± 0.62 Ma, quartz monzonite porphyry: 127.47 ± 0.36, quartz porphyry: 124.85 ± 0.34, and granite porphyry: 124.15 ± 0.31 Ma) occurred during the Early Cretaceous. Geochemically, monzonite porphyry belongs to the metaluminous and alkaline series rocks and is characterized by high Al2O3 (average 17.74 wt.%) and TiO2 (average 0.88 wt.%) and low Ni (average 4.63 ppm), Cr (average 6.69 ppm), Mg# (average 31.11), Y (average 15.16 ppm), and Yb (average 1.62 ppm) content with enrichment in Ba, K, Pb, Sr, Zr, and Hf and depletion in Ti, Nb, and Ta. The granitic rocks (e.g., quartz monzonite porphyry, quartz porphyry, and granite porphyry) pertain to the category of high-K calc-alkaline rocks and are characterized by high SiO2 content (>66 wt.%) and low MgO (average 0.69 wt.%), Mg# (average 31.49 ppm), Ni (average 2.78 ppm), and Cr (average 8.10 ppm) content, showing an affinity to I-type granite accompanied by Nb, Ta, P, and Ti depletion and negative Eu anomalies (δEu = 0.57–0.96; average 0.82). The Hf isotopic data suggest that these rocks were the product of the partial melting of juvenile crustal rocks. Notably, fractionation crystallization plays a crucial role in the process of magma emplacement. Combining our study with published ones, we proposed that the Early Cretaceous intrusive rocks in the Ulanhot area were formed in an extensional tectonic background and compactly related to the subduction of the Paleo-Pacific Ocean plate.
Highlights
As a key component of NE China, the Great Xing’an Range (GXR) exhibits voluminous Early Cretaceous granitoids (Figure 1c) [2,36,37,38,39], indicating that tectonic-magmatic activity peaked during the Early Cretaceous [1,7,40,41,42,43,44]
There is still some debate regarding the petrogenesis and geodynamic background of these rocks, including the following explanations: (1) the upwelling magmas associated with the mantle plume [9,46]; (2) a post-collision gravitational collapse of the Mongol–Okhotsk Ocean plate [47,48,49,50,51,52]; (3) lithospheric delamination induced by the contribution of westward subduction of the Paleo-Pacific slab [53,54,55,56]; and (4) retreat of the Paleo-Pacific Ocean (PPO) plate and the successive upwelling of the varying degrees of asthenospheric mantle [35,57,58,59]
We provided new high-precision U-Pb zircon age testing, whole-rock geochemical measurements, and zircon Lu-Hf isotopic analysis for representative intrusive rocks from the northern part of the Ulanhot region, with the purpose of illustrating the formation time, petrogenesis types, and magmatic origin of these rocks, further discussing their geodynamic implications and evaluating the tectonic background of this place, restricting the evolution of tectonic magmatic history in the GXR during the Early Cretaceous
Summary
Northeast (NE) China, which is well-known for its extensive distribution of Late Mesozoic igneous rocks [1,2,3,4,5,6,7,8], is situated in the eastern segment of the Central Asian Orogenic Belt and bounded by the northern part of the North China Craton, the southern part of the Siberia Craton and the western Pacific rim (Figure 1a) [9,10,11,12,13,14,15,16,17,18,19,20]. During the Late Mesozoic, this region experienced multi-stage structural superposition and tectonic reformation of the Paleo-Pacific Ocean (PPO) and Mongol–Okhotsk Ocean tectonic domains, recording multiple tectonic-thermal events of different scales by widespread intrusive rocks [13,21,22,23,24,25,26,27] It has been a hot area for the interpretation of mantle-crust interactions and crustal evolution over the past two decades and an important metallogenic belt (Figure 1b) [28,29,30,31,32,33,34,35]. Either way, clarifying the petrogenesis, magma source of the intrusive rocks, and intensive crust-mantle interaction of the GXR are vital steps in explaining the tectonic evolution history of the PPO plate and the Mongol–Okhotsk Ocean plate and mastering the GXR tectonic frameworks during the Early Cretaceous
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