| 拉萨地块措勤-隆格尔地区铁矿床成岩时代、岩石成因及构造环境指示 |
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| 引用本文： | 于玉帅,周云,鲍波,高原,杨竹森.拉萨地块措勤-隆格尔地区铁矿床成岩时代、岩石成因及构造环境指示[J].地球科学,2019,44(6):1888-1904. |
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| 作者姓名： | 于玉帅 周云 鲍波 高原 杨竹森 |
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| 作者单位： | 1.东华理工大学核资源与环境国家重点实验室, 江西南昌 330013 |
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| 基金项目： | 国家自然科学基金项目41503040国家重点研发计划2016YFC0600306 |
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| 摘 要： | 为深入了解中北部拉萨地块构造背景, 利用LA-ICP-MS技术对洛布勒铁矿床成矿花岗闪长岩锆石进行了U-Th-Pb同位素测定, 分析了隆格尔、洛布勒铁矿床侵入岩岩石地球化学和Sr-Nd-Pb同位素组成.获得洛布勒花岗闪长岩锆石U-Pb年龄为111.3±1.6 Ma(MSWD=0.61, n=9).隆格尔和洛布勒铁矿床侵入岩高硅(66.63%~69.02%和64.33%~64.82%)、富碱(全碱为5.91%~6.40%和5.81%~6.05%)、低A/CNK(0.91~0.97和0.94~0.95)、SiO2与P2O5含量负相关；稀土元素总量较低(∑ REE为123.11×10-6~148.83×10-6和96.17×10-6~101.92×10-6), 球粒陨石标准化配分模式图右倾, 弱Eu负异常(0.70~0.82和0.79~0.81), 富集大离子亲石元素Rb、Th、U、K、Pb等, 亏损Ba和高场强元素Nb、Ta、Sr、Ti等.隆格尔花岗岩全岩和斜长石(206Pb/204Pb)t为18.474和18.626, (207Pb/204Pb)t为15.657和15.722, (208Pb/204Pb)t为38.592和39.145, (87Sr/86Sr)i为0.704 757 6和0.707 047 3, (143Nd/144Nd)i为0.512 281和0.512 339, εNd(t)为-4.13和-2.99, tDM2为1.15 Ga和1.24 Ga；洛布勒花岗闪长岩(206Pb/204Pb)t比值为18.281, (207Pb/204Pb)t比值为15.616, (208Pb/204Pb)t比值为38.369, (87Sr/86Sr)i为0.706 551 4；(143Nd/144Nd)i为0.512 309, εNd(t)为-3.62, tDM2为1.20 Ga.结果表明, 措勤-隆格尔铁矿床成矿侵入岩为中钾-高钾钙碱性岩Ⅰ型花岗岩, 为早白垩世晚期岛弧岩浆活动产物, 岩浆源于地壳物质部分熔融, 岩浆演化过程经历了壳幔岩浆混合和围岩混染.结合前人研究成果, 通过对比白垩纪中北部拉萨地块和南部羌塘地块成矿事件的差异, 提出中北部拉萨地块113±3 Ma岩浆活动和Fe(-Cu)成矿事件与向南俯冲的班公湖-怒江洋壳发生断离有关.
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| 关 键 词： | 成岩时代 岩石成因 Sr-Nd-Pb同位素 铁矿 措勤 隆格尔 拉萨地块 岩石学 |
| 收稿时间： | 2018-11-07 |
Geochronology,Petrogenesis and Its Tectonic Setting Significance of Intrusive Rocks from Coqen to Longgeer Iron Deposit,Lhasa Subterrane,Tibet, China |
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| Abstract: | In order to gain an in-depth understanding of the tectonic setting of the north and central of Lhasa block, bulk-rock elemental and Sr-Nd-Pb isotopic data for the ore-forming granodiorites of Luobule and Longgeer iron deposit are analyzed and LAICP -MS zircon U -Pb dating result (111.3±1.6 Ma; MSWD=0.61, n=9) for the granodiorite of Luobule deposit.The Luobule and Longgeer ore-forming granodiorites are characterized with high silica (SiO2 contents are 66.63%-69.02% and 64.33%-64.82%, respectively), high alkali (alkali oxides contents are 5.91%-6.40% and 5.81%-6.05%, respectively), but low A/CNK ratios (0.91-0.97 and 0.94-0.95).These intrusive rocks are enriched in LILEs (e.g., Rb、Th、U、K、Pb) while depleted in Ba and HFSEs (e.g., Nb、Ta、Sr、Ti).There have right oblique in chondrite-normalized REE patterns and similar primitive mantle normalized trace element spectrum.In addition, the intrusive granodiorites of Luobule and Longgeer have low ∑ REE (123.11×10-6-148.83×10-6 and 96.17×10-6-101.92×10-6, respectively) and negative Eu anomaly (0.70-0.82 and 0.79-0.81, respectively).The (206Pb/204Pb)t, (207Pb/204Pb)t, (208Pb/204Pb)t, (87Sr/86Sr)i and (143Nd/144Nd)i ratios of whole rock and plagioclase from Longgeer deposit are 18.474 and 18.626, 15.657 and 15.722, 38.592 and 39.145, 0.512 281 and 0.512 339, 0.704 757 6 and 0.707 047 3, respectively.The calculated εNd(t) and tDM2 of the whole rock and plagioclase from Longgeer deposit are -4.13 and -2.99, 1.15 Ga and 1.24 Ga, respectively.In contrast, the (206Pb/204Pb)t, (207Pb/204Pb)t, (208Pb/204Pb)t, (87Sr/86Sr)i, (143Nd/144Nd)i and εNd(t) values of whole rock from Luobule are 18.281, 15.616, 38.369, 0.512 309, 0.706 551 4, -3.62 and 1.20 Ga, respectively.The results above reveal that the ore-forming granodiorites were the product of arc magmatism in late stage of early Cretaceous and were medium -high -K calc-alkaline I-type granite.The primitive magma of the ore-forming plutons were mainly generated by partial melting of crustal materials with the mixing of crust-derived silicic melts and mantle-derived mafic melts and the assimilation of the corresponding wall rocks.Combined with the previous study, by force of contrast the metallogenic event of north and central Lhasa subterrane and southern Qiangtang subterrane, it is propose that there existed extensive magmatism (113±3 Ma) and Fe(-Cu) ore-forming events in north and central Lhasa subterrane are closely related to the break-off of Bangong CoNujiang subducted oceanic crust. |
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