西藏山南地区花岗质岩石成因及其对地壳结构变化的记录
doi: 10.3799/dqkx.2018.385
Petrogenesis and Geochemistry of Meso-Cenozoic Granitic Rocks and Implication of Crustal Structure Changes in Shannan Area, Southern Tibet
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摘要: 西藏拉萨地块南部发育大规模东西带状展布的花岗质岩石,记录了新特提斯洋壳俯冲晚期及随后印度-欧亚大陆碰撞、后碰撞过程的重要信息,受到了学者的广泛关注.对拉萨地块南部山南地区采集的6件花岗质岩石样品进行了LA-ICP-MS锆石U-Pb年代学、Hf同位素及全岩主微量元素和Sr-Nd同位素地球化学分析,获得了~90 Ma、65 Ma及23 Ma三阶段的锆石年龄,显示区域内发育了三期岩浆活动事件.三个时代的岩石样品均为亚碱性系列,具类似埃达克质岩特征,富集高场强元素并亏损大离子亲石元素,稀土元素分布图呈右倾型,具有弧岩浆的地球化学特征.本文所有样品的锆石εHf(t)均为正值(+5.6~+14.6),暗示它们可能来源于新生下地壳物质的部分熔融.结合前人已有数据,采用花岗质岩石的La/Yb比值定量还原了山南地区100 Ma以来的地壳厚度演化历史.从晚中生代开始,区域内地壳厚度由厚减薄,到新生代早期达到最薄,此后逐渐增厚.这与中新生代以来新特提斯洋俯冲至印度-欧亚大陆碰撞-后碰撞过程引起地壳结构变化较好地契合.
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关键词:
- 南拉萨地块 /
- 地壳厚度 /
- 定量计算 /
- La/Yb比值 /
- 中酸性岩浆 /
- 岩石学
Abstract: In the southern part of the Lhasa block in southern Tibet, large-scale zonal distribution of granitic rocks is developed, where the important information on the late subduction of the Neo-Tethys oceanic crust and subsequent collisions and post-collision processes in the Indian-Eurasia continent is recorded. In this paper, LA-ICP-MS zircon U-Pb geochronology, Hf isotope and total trace elements and Sr-Nd isotope geochemical analysis of six granitic rock samples collected in the southern Shannan area of the Lhasa block were obtained. The three-stage zircon ages of~90 Ma, 65 Ma and 23 Ma show that three phases of magmatic activity occurred in the area. The rock samples of the three eras are all subalkalic series, with similar adakite characteristics, enriched with high field strength elements and depleted with large ion lithophile elements. The distribution of rare earth elements is right-dip, geochemical with the feature of arc magma. The zircon εHf(t) of all samples in this paper are positive (+5.6-+14.6), suggesting that they may be derived from the partial melting of the new lower crust. Based on the previous data, the La/Yb ratio of granitic rocks is used to quantitatively show the evolution of crustal thickness in the Shannan area for 100 Ma. From the late Mesozoic, the thickness of the crust in the area was thinned from thick to thin in the Early Cenozoic, and gradually thickened thereafter. This is in line with the changes in the crustal structure caused by the subduction of the Neo-Tethys and the Indian-Eurasia collision-postcollision process since Mesozoic to Cenozoic.-
Key words:
- South Lhasa block /
- crustal thickness /
- quantitative calculation /
- La/Yb ratio /
- intermediate-acid magma /
- petrology
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图 1 青藏高原南部岩浆-构造分布简图及山南地区结巴乡地质图和样品情况
修改自 Chung et al.(2009); Jiang et al.(2014);MBT.主边界逆冲断层;MCT.主中央逆冲断层;STDS:藏南拆离断层系;Kf.钾长石;Hb.角闪石;Q.石英
Fig. 1. Sketch map of southern Tibetan Plateau showing major blocks and temporal spatial distribution of magmatic rocks and geological map and photos of granitic rocks of Jieba Village in Shannan area
图 2 山南地区花岗质岩石锆石U-Pb年龄谐和图
Fig. 2. Zircon U-Pb concordia diagrams of the granitic rocks in Shannan area
图 3 山南地区花岗质岩石锆石年龄与εHf(t)图解
Fig. 3. Plot of εHf(t) versus age for the granitic rocks in Shannan area
图 4 山南地区花岗质岩石TAS图解
Fig. 4. Plot of total alkali versus SiO2 of the granitic rocks in Shannan area
图 5 山南地区花岗质岩石(La/Yb)N-(Yb)N图解
Fig. 5. Plot of (La/Yb)N versus (Yb)N of the granitic rocks in Shannan area
图 6 山南地区花岗质岩石全岩原始地幔标准化微量元素蛛网图和球粒陨石均一化稀土分配图
Fig. 6. Primitive mantle-normalized trace element patterns and chondrite-normalized rare earth element (REE) patterns of the granitic rocks in Shannan area
图 7 山南地区花岗质岩石Sr-Nd同位素组成图解
数据底图据 Jiang et al.(2014)
Fig. 7. Plot of εHf(t) vs. (87Sr/86Sr)i of the granitic rocks in Shannan area
图 8 山南地区晚白垩世-中新世地壳厚度演化
Fig. 8. Crustal thickness evolution of Shannan area from Late Cretaceous to Miocene
表 1 山南地区花岗质岩石岩石Sr-Nd同位素分析结果
Table 1. Sr-Nd isotope analysis results of the granitic rocks in Shannan area
样品编号 87Rb/86Sr 87Sr/86Sr 2σ 87Sr/86Sri 147Sm/144Nd 143Nd/144Nd 1σ εHf(t) fSm/Nd tDM(Ma) tDM2(Ma) 13JBX-01 0.428 5 0.705 49 5 0.705 35 0.092 86 0.512 55 7 -1.1 -0.53 753 945 13JBX-02 0.263 8 0.704 38 5 0.704 03 0.099 98 0.512 77 8 4.8 -0.49 517 598 13JBX-03 2.431 3 0.706 13 5 0.703 88 0.102 98 0.512 75 9 3.7 -0.48 557 635 13JBX-04 1.558 1 0.705 06 5 0.703 03 0.092 52 0.512 76 6 4.8 -0.53 487 592 13JBX-05 0.816 4 0.704 90 6 0.703 86 0.095 62 0.512 76 8 4.7 -0.51 503 600 13JBX-06 0.638 1 0.705 18 6 0.704 39 0.101 09 0.512 74 10 4.1 -0.49 559 642 PHP网站源码荷坳百度竞价爱联阿里店铺运营沙井设计公司网站深圳网站优化按天计费大运百度标王大浪网站优化按天计费永湖关键词按天扣费光明SEO按天收费观澜网站推广系统沙井百度竞价福田建网站塘坑网站推广深圳百搜词包大浪百度seo民治高端网站设计福永网站建设设计坪山百度竞价包年推广坂田网站优化按天扣费龙岗企业网站制作光明品牌网站设计宝安关键词排名包年推广观澜网站改版罗湖高端网站设计双龙外贸网站制作平湖网站建设设计爱联百搜词包南澳seo优化罗湖网站优化推广坪山如何制作网站光明SEO按天扣费歼20紧急升空逼退外机英媒称团队夜以继日筹划王妃复出草木蔓发 春山在望成都发生巨响 当地回应60岁老人炒菠菜未焯水致肾病恶化男子涉嫌走私被判11年却一天牢没坐劳斯莱斯右转逼停直行车网传落水者说“没让你救”系谣言广东通报13岁男孩性侵女童不予立案贵州小伙回应在美国卖三蹦子火了淀粉肠小王子日销售额涨超10倍有个姐真把千机伞做出来了近3万元金手镯仅含足金十克呼北高速交通事故已致14人死亡杨洋拄拐现身医院国产伟哥去年销售近13亿男子给前妻转账 现任妻子起诉要回新基金只募集到26元还是员工自购男孩疑遭霸凌 家长讨说法被踢出群充个话费竟沦为间接洗钱工具新的一天从800个哈欠开始单亲妈妈陷入热恋 14岁儿子报警#春分立蛋大挑战#中国投资客涌入日本东京买房两大学生合买彩票中奖一人不认账新加坡主帅:唯一目标击败中国队月嫂回应掌掴婴儿是在赶虫子19岁小伙救下5人后溺亡 多方发声清明节放假3天调休1天张家界的山上“长”满了韩国人?开封王婆为何火了主播靠辱骂母亲走红被批捕封号代拍被何赛飞拿着魔杖追着打阿根廷将发行1万与2万面值的纸币库克现身上海为江西彩礼“减负”的“试婚人”因自嘲式简历走红的教授更新简介殡仪馆花卉高于市场价3倍还重复用网友称在豆瓣酱里吃出老鼠头315晚会后胖东来又人满为患了网友建议重庆地铁不准乘客携带菜筐特朗普谈“凯特王妃P图照”罗斯否认插足凯特王妃婚姻青海通报栏杆断裂小学生跌落住进ICU恒大被罚41.75亿到底怎么缴湖南一县政协主席疑涉刑案被控制茶百道就改标签日期致歉王树国3次鞠躬告别西交大师生张立群任西安交通大学校长杨倩无缘巴黎奥运
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