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Global Geology
 
2025 Vol.28 Issue.2
Published 2025-06-25

79 Detrital zircon U–Pb ages of sandstone from Jiufengshan Formation in Nenjiang area, Heilongjiang Province: Provenance and tectonic implications
JIA Xianghe, LIANG Chenyue and ZHENG Changqing
During Early Cretaceous, NNE-trending extensional basins filling with various volcanic sedimentary formations developed in the northeastern Da Hinggan Ling (Mts.), northeastern China. This study investigates the formation age and geological background of Jiufengshan Formation, providing insights into its tectonic setting and formation mechanisms. Detrital zircons from four sandstone samples of Jiufengshan Formation in Nenjiang area indicate a maximum depositional age of 116±1 Ma, corresponding to late Early Cretaceous. Petrographic analysis and zircon age peak comparisons suggest these sandstones originated from proximal deposits with nearby provenances of earlier and contemporaneous volcanic rocks. Further research on the sandstone framework and trace elements in detrital zircons indicates that the formation process of Jiufengshan Formation was likely related to the low-angle subduction of the Paleo Pacific plate.

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2025 Vol. 28 (2): 79-98 [Abstract] ( 27 ) [HTML 1KB] [ PDF 799KB] ( 71 )
99 Bitumen source in Tangjiashan lead-zinc deposit, southwestern Sichuan Basin
GUO Yuhan, GAO Jingxin and LIU Gang
The Tangjiashan lead-zinc deposit, located on the southwestern margin of the Sichuan Basin, is rich in bitumen, and the lead-zinc ore and bitumen coexist closely, indicating a close genetic relationship between lead-zinc mineralization and hydrocarbon reservoir formation. However, whether bitumen shares the same source as the current gas reservoirs within the basin or other destroyed gas reservoirs along the basin margins remains unknown. Here, we conducted an organic geochemical analysis of bitumen in this deposit and identified the sources of hydrocarbons by comparing biomarker compounds with those of potential source rocks. The authors found that the bitumen in the Tangjiashan lead-zinc deposit has good comparability with the hydrocarbon source rocks of the Cambrian Qiongzhusi Formation, suggesting that the primary sources of oil in this ancient hydrocarbon reservoir are muddy source rocks of the Qiongzhusi Formation. This research is important for enhancing the understanding of the genetic connection between lead-zinc mineralization and hydrocarbon formation, providing crucial insights for strategies to explore both metal ores and hydrocarbons and advancing the geological understanding of petroleum systems in the Sichuan Basin.?

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2025 Vol. 28 (2): 99-110 [Abstract] ( 19 ) [HTML 1KB] [ PDF 535KB] ( 80 )
111 Petrogenesis of Late Triassic harzburgite in Qingyuan area, northern Liaoning Province: Evidence from zircon U–Pb geochronology and geochemistry
WANG Shuo, YANG Debin*, YAN Xiangyu, WU Ke and LIU Jianning

This study presents LA–ICP–MS U–Pb dating and whole-rock geochemical analyses of the Late Triassic Gangshan harzburgite in the Qingyuan area, with the aim of elucidating its petrogenesis and further constraining the early Mesozoic tectonic evolution of the eastern segment of the northern margin of the North China Block (NCB). Zircons from the harzburgites exhibit typical oscillatory growth zoning or striped absorp tion in cathodoluminescence images. U–Pb analyses of zircons yield ages ranging from 2 525 Ma to 225 Ma, with two youngest ages (225±7 Ma) indicating that the harzburgites were formed during Late Triassic. Geochemical analyses of the Gangshan harzburgites show that the rocks have low concentrations of SiO2 (42.38%–42.85%) and Al2 O3 (3.31%–3.33%), along with high concentrations of MgO (41.32%–41.76%), Cr (4 856×10-6–5 191×10-6) and Ni (1 942×10-6–2 041×10-6). They also display low REE abundances (∑REE=4.38×10-6–4.69×10-6) and flat REE patterns with low (La/Yb)N ratios (1.24–1.56) and slightly po- sitive Eu anomalies (δEu=1.13–1.16). These features suggest that the Gangshan harzburgites are cumulates of basaltic magma derived from the depleted lithospheric mantle. Combined with previous studies, these Late Triassic mafic–ultramafic rocks, together with coeval granitoids in adjacent regions, constitute a typical bimodal association, suggesting that they formed in a post-orogenic extensional environment after the final closure of the Paleo-Asian Ocean.


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2025 Vol. 28 (2): 111-124 [Abstract] ( 16 ) [HTML 1KB] [ PDF 826KB] ( 75 )
125 Constraints on closure timing of Jilin–Heilongjiang Ocean by geochemical characteristics of blueschists and zircon U–Pb dating of Heilongjiang Complex
BAI Shurui, ZHAO Liangliang, CHEN Zhuo, ZHOU Jianbo, LI Chengqiang and LI Gongyu

There have always been academic debates regarding the timing and geodynamics of the superimposition and transformation between the Paleo-Pacific Ocean and the Paleo-Asian Ocean. To resolve the relevant issues over this debate, the authors selected the Jilin–Heilongjiang high-pressure metamorphic belt (Ji–Hei HP Belt) between the Jiamusi–Khanka Block and the Songliao Block in NE China as the study area. This area preserves important records of the superimposition and transformation between these two tectonic domains. This study aims to address this issue through geochemical and zircon U–Pb dating analyses of the Yilan blueschist of Heilongjiang Complex exposed in the Ji–Hei HP Belt. In the geochemical analysis, it has been discovered that the protoliths of the blueschist in the Yilan area consist of subalkaline basalt, which displays geochemical characteristics of Ocean Island Basalt that indicated an oceanic island setting. The LA–ICP–MS zircon U–Pb analysis yields ages of 248±4 Ma and 259±2 Ma from the magma zircons of the blueschists, indicating that the basalt protolith was formed in Late Permian to Early Triassic (259–248 Ma). Based on the results of this study and the regional data, it is proposed that the Jilin–Heilongjiang Ocean opened during Late Permian to Early Triassic (259–248 Ma). This period marks a crucial stage from the closure of the Paleo-Asian Ocean to the initiation of Paleo-Pacific oceanic subduction.


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2025 Vol. 28 (2): 125- [Abstract] ( 13 ) [HTML 1KB] [ PDF 714KB] ( 84 )
 

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