华北克拉通南缘小秦岭地区花岗质浅色脉体锆石U-Pb年龄、稀土元素特征及其地质意义     

王宏晖  陈虹  陈龙耀  白和  张欢欢 《地球学报》2022,43(5):633-644

小秦岭地区发育有大量古元古代晚期的花岗质浅色脉体, 这为理解同时期华北克拉通南缘的深熔作用和构造演化提供了重要的窗口。本文对小秦岭地区三条花岗质浅色脉体中的锆石开展了CL图像、LA-ICP-MS U-Pb年代学及稀土元素的研究。浅色脉体中的锆石具有深熔成因锆石的斑杂状、平面状或弱振荡环带的内部结构及较为自形的外部形态特征, 测得的锆石207Pb/206Pb年龄分别为(1867±13) Ma (MSWD=0.22, n=21)、(1849±17) Ma (MSWD=0.79)和(1828±15) Ma (MSWD=0.33, n=20), 代表了该区深熔作用发生的时间。与上述三组年龄相对应, 其锆石稀土元素配分曲线由具较弱负Eu异常(Eu/Eu*=0.12~0.81)的重稀土相对富集型, 转变为中等负Eu异常(Eu/Eu*=0.29~0.61)的近平坦重稀土型、再到显著负Eu异常(Eu/Eu*=0.15~0.54)的重稀土富集型, 结合锆石Ti温度计获取其结晶温度为574~708 °C, 表明地壳深熔作用的发生可能与高角闪岩相-麻粒岩相的退变质作用有关。结合前人的变质年代学数据可知, 小秦岭地区1.87~1.82 Ga的深熔作用应与~1.95 Ga时东、西部陆块碰撞造山所致增厚地壳的长期抬升和冷却过程有关。  相似文献   

青海昆仑河北地区岩浆活动、金矿成矿特征及找矿前景分析     

焦和  康继祖  黄国彪  贾建团  彭建  鲁海峰  雷延祥 《地质力学学报》2022,28(3):383-405

青海昆仑河北地区靠近昆中断裂带,经历早古生代、晚古生代—中生代多期岩浆活动,近年来自西至东陆续发现黑海北、拉陵灶火、苏海图、加祖它士西、向阳沟、加祖它士东、大灶火、黑刺沟等多个金矿床（点）,形成一条东西长度近150 km长的成矿带。文章在总结带内金矿成矿基本特征基础上,选取黑海北金矿和加祖它士东金矿的赋矿围岩开展锆石U-Pb定年,结果显示黑海北硅化二长花岗岩锆石206Pb/238U加权平均年龄为443±8 Ma,形成于原特提斯洋向柴达木地块俯冲碰撞后伸展环境;加祖它士东的花岗闪长岩脉含有较多的继承锆石,锆石206Pb/238U加权平均年龄为250±1 Ma,继承锆石206Pb/238U加权平均年龄为420±2 Ma,加祖它士东花岗闪长岩侵位于古特提斯洋向北俯冲背景下的大陆弧构造环境。综合分析认为昆仑河北地区金矿成矿作用与早中生代三叠纪岩浆活动关系更为密切,其矿床类型存在造山型金矿与岩浆热液型金矿两种不同认识。昆仑河北地区土壤化探异常、低阻高极化激电异常、主要断裂（穿矿区）的次级断裂形成的蚀变破碎带等可以作为区内主要的找矿标志,推测该成矿带具有较大的找矿前景。   相似文献   

锆石Ce 氧逸度计和早期地球的氧化还原状态     

肖路毅  杨晓志 《高校地质学报》2022,28(4):484-492

氧逸度可以用于定量描述一个体系的氧化还原状态,是地球科学非常重要的一个热力学指标。早期地球的氧逸度及其变化趋势的重建,对大气圈、水圈、生物圈乃至整个地球的起源和演化具有重要的科学意义,也是地球科学长期探索的重要目标。锆石提供了地球上已发现的最古老天然样品,几乎是目前研究早期(冥古宙)地球的唯一可靠对象。近年来的研究发现,锆石中Ce的含量对其母岩浆体系的氧逸度很敏感,并由此发展出了锆石的Ce氧逸度计。这一技术对认识早期地球的氧化还原状态十分关键。文章对锆石Ce氧逸度计进行了简单介绍,进而对早期地壳和地幔的氧化还原状态进行了综合评述。在此基础上,对早期地球几个重要圈层(大气圈、大陆地壳和上地幔)氧逸度的演化及相互间的耦合关系进行了讨论。  相似文献   

三江南段勐海布朗山地区浅变质岩系碎屑锆石U-Pb定年及其构造意义          下载免费PDF全文

孙载波  段向东  朱才  周坤  刘和松  赵江泰  浦涛  赵毅  赵枫 《沉积与特提斯地质》2022,42(4):613-625

布朗山位于西南三江南段勐海地区,大面积出露澜沧岩群。澜沧岩群主要由低级变质作用的砂泥质岩石和少量变中基性火山岩组成,其形成时代、物质来源以及地质意义等一系列问题一直存在很多争议。本文选取该地区澜沧岩群上部层位不含变火山岩地层的浅变质岩开展碎屑锆石阴极发光图像分析和LA-ICP-MS U-Pb年代学研究,明显的环带和较高的Th/U比值表明4件浅变质岩的大部分碎屑锆石是岩浆成因。年代学结果显示,该套地层浅变质岩中的锆石记录了与罗迪尼亚、冈瓦纳超大陆拼合及原、古特提斯洋俯冲有关的岩浆作用信息(1182~1104 Ma、593~560 Ma和378 ~328 Ma),其最年轻的碎屑锆石年龄(328 Ma),暗示该套地层形成不早于早石炭世,而非以往认为的新元古代。结合其岩石组合特征,推测该套晚古生代浅变质岩系可能为泥盆-石炭系南段组。在澜沧岩群的年龄频谱特征图中,年轻的550 Ma左右峰期年龄与特提斯喜马拉雅碎屑锆石年龄峰期相同,说明其物源主要为东冈瓦纳北缘的特提斯喜马拉雅构造带,与原特提斯洋和古特提斯洋相关。  相似文献   

黄河上游物质在新近纪未流入晋陕峡谷^*          下载免费PDF全文

林旭  李玲玲  刘海金  陈济鑫 《古地理学报》2022,24(3):568-582

河流的出现是其流域内构造活动和气候变化综合作用的结果。晋陕峡谷位于黄河上游和中游的衔接部位,对于研究上游黄河何时进入晋陕峡谷具有无可替代的地理位置优势。目前对于黄河何时进入晋陕峡谷一直存有较大争议,存在中新世、上新世和更新世几种主要观点。基于此,作者对晋陕峡谷北段新近纪地层开展碎屑锆石U-Pb年龄分析和沉积相观察。首次报道了磨扇沟、大烟墩、高家窨子3个剖面270颗碎屑锆石 U-Pb 年龄结果。通过和区域内潜在源区进行对比,以及古流向都是自东向西的现象,判定磨扇沟和大烟墩2个剖面的物质来自近源的吕梁山北段; 高家窨子剖面底部的砂岩流向为自南向北,其物源区来自鄂尔多斯地块北部中生代地层。结合这些地层已经报道的古地磁年龄,认为晋陕峡谷北段在6.2~3.7 Ma期间以近源堆积为主,是对青藏高原隆升远程效应和东亚夏季风增强的沉积响应,而和黄河上游物质不存在物源联系。  相似文献   

Precambrian Tectonic Affinity of the Southern Langshan Area, Northeastern Margin of the Alxa Block: Evidence from Zircon U-Pb Dating and Lu-Hf Isotopes     

NIU Pengfei  QU Junfeng  ZHANG Jin  ZHANG Beihang  ZHAO Heng 《《地质学报》英文版》2022,96(5):1516-1533

The Alxa Block is the westernmost part of the North China Craton (NCC), and is regarded as one of the basement components of the NCC. Its geological evolution is of great significance for the understanding of the NCC. However, the Precambrian basement of the Alxa Block is still poorly studied. In this study, we present new in situ LA-ICP-MS zircon U-Pb and Lu-Hf isotope data from the Diebusige Metamorphic Complex (DMC) which located in the eastern Alxa Block. Field and petrological studies show that the DMC consists mainly of metamorphic supracrustal rocks and minor metamorphic plutonic rocks and has experienced amphibolite-granulite facies metamorphism. Zircon U-Pb dating results suggested that the amphibolite sample yields a crystallization age of 2636 ± 14 Ma and metamorphic ages of 2517–2454 Ma and 1988–1952 Ma, proving the existence of exposed Archean rocks in the Langshan area and indicating that late Neoarchean to Paleoproterozoic metamorphic events existed in the Alxa Block. Two paragneiss samples show that the magmatic detrital zircons from the DMC yield 207Pb/206Pb ages ranging from 2.48 Ga to 2.10 Ga with two youngest peaks at 2.13 Ga and 2.16 Ga, respectively, and they were also overprinted by metamorphic events at 1.97–1.90 Ga and 1.89–1.79 Ga. Compilation of U-Pb ages of magmatic detrital and metamorphic zircons suggested that the main part of the DMC may have been formed at 2.1–2.0 Ga. Zircon Lu-Hf isotope data show that the source materials of the main part of the DMC were originated from the reworking of ancient Archean crust (3.45–2.78 Ga). The Hf isotope characteristics and the tectonothermal event records exhibit different evolution history with the Khondalite Belt and the Yinshan Block and the other basements of the Alxa Block, indicating that the Langshan was likely an independent terrain before the middle Paleoproterozoic and was subjected to the middle to late Paleoproterozoic tectonothermal events with the Khondalite Belt as a whole.  相似文献   

Petrogenesis and Tectonic Implications of A-type Granites in Zhaheba in the East Junggar Region of Xinjiang, China: Evidence from Geochronology, Geochemistry and Sr-Nd Isotopic Compositions     

TANG Hejun  MENG Guixiang  WU Zhenhan  WANG Zhaolin  DENG Zhen  YAN Jiayong  QI Guang  XUE Ronghui 《《地质学报》英文版》2022,96(3):938-953

The magma source, petrogenesis, tectonic setting and geochronology of the late Paleozoic A-type granites widely exposed in the Zhaheba area, East Junggar, have thus far not been well-constrained. A better understanding of these issues will help to reveal the magmatic processes and continental growth of Central Asia. The A-type granites in Zhaheba include the Ashutasi alkaline granites and the Yuyitasi syenogranites, which were emplaced at 321.5 ± 4.8 Ma and 321.7 ± 0.6 Ma, respectively. The major rock-forming minerals are orthoclase, perthite, arfvedsonite and quartz, which exhibit the following principal geochemical characteristics of A2-type granites. (1) Their REE distribution curves each exhibit a ‘V’-shaped pattern and a marked depletion in Eu. They are rich in large-ion lithophile elements Rb, Th and U as well as high-field-strength elements Nb, Ta, Zr and Hf, but significantly depleted in Ba, Sr, P and Ti. (2) Their (87Sr/86Sr)i values (0.7021–0.7041), εNd(t) values (4.57–5.16) and REE distribution patterns are in basic agreement with those of the Kalamaili A-type granite belt in East Junggar. The TDM2 values of the alkaline granites and syenogranites range from 661 to 709 Ma. The A-type granites may be the products of upwelling asthenosphere-triggered partial melting of immature lower crust. The alkaline granites were late-stage products of crystallization and differentiation. Compared to the syenogranites, the alkaline granites are significantly lower in K2O, Na2O, Al2O3, FeO, MgO and CaO, but significantly higher in incompatible elements (e.g., SiO2, Rb, and Sr). The magmatic crystallization temperatures of the syenogranites and alkaline granites are 874°C and 819°C, respectively. As their age gradually decreases (peak ages: 322 Ma and 307 Ma, respectively), there is a gradual decrease in the TDM2 of the A-type granites and a gradual increase in the εNd(t) value from the Ulungur belt to the Kalamaili belt in East Junggar. The study of A-type granites is therefore one of the keys to understanding the laws and mechanisms of crustal accretion during the Phanerozoic period, as well as also being of great significance for understanding the Paleozoic accretion.  相似文献   

Extensional Setting of Hainan Island in Mesoproterozoic: Evidence from Granitic Intrusions in the Baoban Group     

LIU Yuheng  MAO Jingwen  QIU Kunfeng  HU Jun  WANG Lei  XU Deming 《《地质学报》英文版》2022,96(4):1199-1212

The Mesoproterozoic Baoban Group is the oldest basement in Hainan Island and has played an important role in Columbia (Nuna) supercontinent reconstructions. The Mesoproterozoic granitic intrusions in the Baoban Group are the most widely-exposed Precambrian magmatic rocks and are the key to understanding the tectonic settings of Hainan Island and its relationship with the South China Block and the Columbia supercontinent. New LA-ICP-MS zircon U-Pb dating on three mylonitic granite samples from the Tuwaishan and Baoban areas yield ages ranging from 1447 Ma to 1437 Ma, representing the absolute timing of the emplacement of the granitic intrusions. Combined with previously published geochronological data for rocks from the Baoban Group and regional mafic intrusions, it is concluded that the Baoban Group formed at 1460–1430 Ma, coeval with the emplacement of the granitic and mafic intrusions. New in-situ zircon Lu-Hf isotope analyses for the three mylonitic granite samples yielded positive εHf(t) values, ranging from +0.49 to +8.27, with model ages (TCDM) ranging from 2181 Ma to 1687 Ma, suggesting that the granitic intrusions originated from a mixed source of Paleoproterozoic crust with juvenile crust. New zircon trace element data show characteristics of high Th/U values of 0.24–1.50, steep slopes from LREE to HREE and negative Pr, Eu anomalies with positive Ce, Sm anomalies, representing typical magmatic zircons formed in continental crust. Compared with available magmatic and detrital zircon ages from Precambrian rocks in the Cathaysia Block, Yangtze Block and western Laurentia, it is inferred that Hainan Island was separated from both the Cathaysia Block and the Yangtze Block, instead being connected with western Laurentia in the Columbia supercontinent. Considering the decreasing tendency of basin deposition time along the western margin of Laurentia, it is proposed that Hainan Island was located to the north or northwest of the Belt-Purcell Supergroup, along the western margin of Laurentia, during the breakup of the Columbia supercontinent.  相似文献   

Application of Optically Stimulated Luminescence Technique in Exploring a Concealed Sandstone-type Uranium Deposit     

KANG Huan  CHEN Yuelong  XUE Guoliang  ZHAO Junxiang  ZHANG N  ZHANG Yangyang 《《地质学报》英文版》2022,96(2):571-581

Identifying ore-induced geochemical anomalies at the surface that indicate concealed deposits in buried areas remains a significant challenge in geochemical exploration. In this study, in order to trace the source of the geochemical anomalies, systematic luminescence intensity analyses were conducted on quartz grains from the Quaternary regolith at the Hadatu sandstone-type uranium deposit in the Erenhot Basin. The optically stimulated luminescence (OSL) ages were much older than the depositional ages of the Quaternary regolith. Moreover, quartz OSL ages were closely related to both borehole grades and sampling depths. Thus, the abnormal mineral OSL ages from near-surface sediments were ultimately controlled by the sandstone-type uranium deposits. This is identical to the rapid changes of quartz OSL ages (0.063 ka/cm) and equivalent doses (0.19 Gy/cm) with depths in a given sampling site. The instantaneous soil radon concentration was positively correlated with the quartz OSL apparent age, indicating their ore-induced origin and, as a result, their effectiveness in the exploration of concealed uranium deposits. Other parameters, including mobile-state uranium and 210Po contents, were poorly correlated with quartz OSL ages and therefore should only be used with caution for geochemical exploration. This is the first time an attempt has been made to discriminate the ore-induced sources for different surface anomaly parameters, including instantaneous soil radon, mobile-state uranium and 210Po contents for concealed sandstone-type uranium deposits.  相似文献   

基于机器学习的锆石成因分类研究     

朱紫怡  周飞  王瑀  周统  侯照亮  邱昆峰 《地学前缘》2022,29(5):464-475

锆石是在自然界中多种温压条件下能够稳定保存,并记录原岩年龄信息的副矿物。锆石微量元素能完整记录地质演化过程信息。通过微量元素分析锆石成因的研究已久,通常利用Th-U图解和La_N-(Sm/La)_N图解等二元图解对锆石进行分类研究。然而,随着锆石研究的深入,以及二元图解无法呈现数据高维度信息的局限性,传统图解已经不能满足对锆石类型进行准确判别,且对已知类型的锆石出现判定偏差。因此,本文将地质大数据与机器学习相结合,训练出高维度锆石成因分类器。文中收集了3 498条不同成因类型的锆石微量元素数据,并通过测试和运用随机森林、支持向量机、人工神经网络和k近邻等4种机器学习算法,最终得出准确率为86.8%的线性支持向量机锆石成因分类器,用于锆石类型的判定与预测。这项工作为锆石分类研究提供了更高维度的判别手段,极大提高了微量元素分析成因结果的精度。将锆石微量元素数据与机器学习方法相结合,是大数据分析与机器学习技术在地球化学研究中的积极探索。  相似文献