长江中下游水阳江流域BZK0402孔多重地层划分及其冰后期海平面变化的沉积响应

【研究目的】开展水阳江流域标准孔BZK0402孔多重地层划分,探讨长江支流水阳江流域冰后期海平面变化的沉积响应以及古丹阳湖的成因和形成时代。【研究方法】以岩石地层为基础,在磁性地层和年代地层的双重约束下,对BZK0402孔进行多重地层划分。对比分析BZK0402孔和长江河谷、长江三角洲等邻区钻孔。【研究结果】BZK0402孔第四纪地层可划分为中—下更新统大桥镇组、全新统芜湖组。钻孔所属的长江三角洲西缘河湖环境沉积物对末次盛冰期以来海平面升降和气候变化存在沉积响应:末次盛冰期,长江中下游河流比降大,区内河流侵蚀作用强烈,沉积物以砂砾石层为主;全新世早期,区内受冰后期海侵影响,沉积物粒度逐渐变细,沉积环境由河漫滩相向湖相过渡。植被覆盖类型以针叶林为主,林下蕨类植物生长茂盛。平原地区发育湖泊沼泽;全新世中期,海侵逐渐至最大,区内发育湖相淤泥质黏土。森林面貌以针叶-落叶阔叶混交林为主;全新世晚期至今,区内沉积物有扰动现象。【结论】长江支流水阳江河谷中不仅是全新世沉积,还发育更新世沉积。水阳江流域内古丹阳湖形成于全新世早期,其形成与全新世海侵在时间上存在一致性。

Molybdenite Re-Os,titanite and garnet U-Pb dating of the Magushan skarn Cu-Mo deposit,Xuancheng district,Middle-Lower Yangtze River Metallogenic Belt

The Magushan skarn Cu-Mo deposit is a representative example of the skarn mineralization occurring within the Xuancheng ore district of the Middle-Lower Yangtze River Metallogenic Belt of eastern China.The precise age of an ore deposit is important for understanding the timing of mineralization relative to other geological events in a region and to fully place the formation of a mineral deposit within the geological context of other processes that occur within the study area.Here,we present new molybdenite Re-Os and titanite and andradite garnet U-Pb ages for the Magushan deposit and use these data to outline possible approaches for identifying genetic relationships in geologically complex areas.The spatial and paragenetic relationships between the intrusions,alteration,and mineralization within the study area indicates that the formation of the Magushan deposit is genetically associated with the porphyritic granodiorite.However,this is not always the case,as some areas contain complexly zoned plutons with multiple phases of intrusion or mineralization may be distal from or may not have any clear spatial relationship to a pluton.This means that it may not be possible to determine whether the mineralization formed as a result of single or multiple magmatic/hydrothermal events.As such,the approaches presented in this study provide an approach that allows the identification of any geochronological relationships between mineralization and intrusive events in areas more complex than the study area.Previously published zircon U-Pb data for the mineralization-related porphyritic granodiorite in this area yielded an age of 134.2±1.2 Ma(MSWD=1.4)whereas the Re-Os dating of molybdenite from the study area yielded an isochron age of 137.7±2.5 Ma(MSWD=0.43).The timing of the mineralizing event in the study area was further examined by the dating of magmatic accessory titanite and skarn-related andradite garnet,yielding U-Pb ages of 136.3±2.5 Ma(MSWD=3.2)and 135.9±2.7 Ma(MSWD=2.5),respectively.The dating of magmatic and hydrothermal activity within the Magushan area yields ages around 136 Ma,strongly suggesting that the mineralization in this area formed as a result of the emplacement of the intrusion.The dates presented in this study also provide the first indication of the timing of mineralization within the Xuancheng district.providing evidence of a close genetic relationship between the formation of the mineralization within the Xuancheng district and the Early Cretaceous magmatism that occurred in this area.This in turn suggests that other Early Cretaceous intrusive rocks within this region are likely to be associated with mineralization and should be considered highly prospective for future mineral exploration.This study also indicates that the dating of garnet and titanite can also provide reliable geochronological data and evidence of the timing of mineralization and magmatism,respectively,in areas lacking other dateable minerals(e.g.,molybdenite)or where the relationship between mineralization and magmatism is unclear,for example in areas with multiple stages of magmatism,with complexly zoned plutons,and with distal skarn mineralization.

Large Igneous Provinces, Their Giant Mafic Dyke Swarms, and Links to Metallogeny

Giant mafic dyke swarms are a key component of the feeder system of Large Igneous Provinces（LIPs）,large volume（>0.1 Mkm;;frequently above>1 M km;）,mainly mafic（-ultramafic）magmatic events of intraplate affinity.

Combined garnet,scheelite and apatite U-Pb dating of mineralizing events in the Qiaomaishan Cu-W skarn deposit,eastern China

Determining the precise timing of mineralization and mineralizing events is crucial to understanding regional mineralizing and other geological events and processes.However,there are a number of mineralogical and analytical limitations to the approaches developed for the absolute dating of mineralizing systems,such as molybdenite Re-Os and zircon and garnet U-Pb,among others.This means that the precise and accurate dating of mineralizing systems that may not contain minerals suitable for dating using existing approaches requires the development of new(and ideally in situ)approaches to absolute dating.This study outlines a new in situ analytical approach that has the potential to rapidly and accurately evaluate the timing of ore formation.Our study employs a novel application of in situ scheelite U-Pb dating analysis using laser ablation-inductively coupled plasma-mass spectrometry(LA-ICP-MS)and samples from the Qiaomaishan deposit,a representative example of skarn mineralization within the Xuancheng ore district of eastern China.Our approach to scheelite dating of the deposit is verified by cross-comparison to dating of cogenetic garnet and apatite,proving the effectiveness of this approach.Our new approach to dating of scheelite-bearing geological systems is rapid,cheap,requires little sample preparation,and is undertaken in situ,allowing crucial geological and mineralogical context to be retained during analysis.The approaches outlined here not only allow the determination of the absolute timing of formation of the Qiaomaishan deposit through the U-Pb dating of scheelite[138.6±3.2 Ma,N=39,mean square weighted deviation(MSWD)=1.17],garnet(138.4±1.0 Ma,N=40,MSWD=1.3),and apatite(139.6+3.3 Ma,N=35,MSWD=0.72),but also further supports the theoretical genetic links between this mineralization and the emplacement of a proximal porphyritic granodiorite intrusion(zircon U-Pb age:139.5±1.2 Ma,N=23,MSWD=0.3).Moreover,our research indicates that the higher the concentrations of U within scheelite,the more suitable that scheelite is for U-Pb dating,with the main factor controlling the U content of scheelite seemingly being variations in oxygen fugacity conditions.This novel approach provides a potentially powerful tool,not just for the dating of skarn systems but also with potential applications in orogenic and intrusion-related gold,porphyry W-Mo,and greisen mineralizing systems as well as other scheelite-bearing geological bodies or geological systems.