摘要
自中生代以来，华北克拉通岩石圈地幔发生了显著地减薄和再富集，岩石学和地球化学观察表明地幔交代作用对于岩石圈地幔的再富集过程具有重要影响，但是地幔交代作用的机制包括熔流体的性质和来源仍然未完全厘清。为更好的理解地幔捕虏体和熔流体之间的反应过程，本论文对位于华北克拉通东部郯庐断裂带中段山东北岩地区的地幔捕虏体和寄主玄武岩进行了详细的野外调研、岩相学观察、全岩主微量元素组成、单矿物主量元素、全岩和单斜辉石Hf、Nd、Sr同位素组成、全岩Mg同位素组成研究。并在此基础上讨论了地幔交代作用与Hf-Nd 耦合关系的相互作用。
基于矿物组成北岩地幔捕虏体分为二辉橄榄岩、富单斜辉石二辉橄榄岩、异剥橄榄岩和橄榄单斜辉石岩四种类型。其中二辉橄榄岩的主量元素组成与深海橄榄岩相似，代表新增生的年轻岩石圈地幔的残余，且其亏损程度小于10%。含水矿物金云母、角闪石、长石以及碳酸盐矿物方解石、铁白云石和反应结构的出现表明其后期遭受了显性地幔交代作用改造。相比于二辉橄榄岩，富单斜辉石二辉橄榄岩全岩具有更低的Mg#值(85.0~89.6)、橄榄石具有较低的Fo值(86.5~89.4)、轻稀土富集、较高的稀土总量(∑REE =9.19~26.3 ppm)和较为富集的Sr-Nd-Hf同位素组成，而且富单斜辉石二辉橄榄岩BY13-08(δ26Mg=-0.03±0.07‰)和BY13-16(δ26Mg=-0.12±0.09‰)的Mg同位素组成显著重于二辉橄榄岩和正常地幔值(δ26Mg=-0.25±0.07‰)。结合北岩富单斜辉石二辉橄榄岩的高Sr/Hf比值、富集Sr、亏损Zr的微量元素特征，推断这些富单斜辉石二辉橄榄岩可能是二辉橄榄岩和流体反应的结果，而且这一反应流体继
承了俯冲太平洋板片的重Mg同位素特征。
与富单斜辉石二辉橄榄岩相似，相比于二辉橄榄岩，北岩异剥橄榄岩全岩Mg#值(81.2~87.3)较低，橄榄石Fo值(81.1~86.2)偏低、轻稀土富集、较高的稀土总量(∑REE =9.04~16.1 ppm)和较低的Nd-Hf同位素组成。异剥橄榄岩Mg同位素组成(δ26Mg=-0.12‰~-0.43‰)变化范围较大，样品BY13-29和BY13-33的Mg 同位素组成较正常地幔值偏高，而样品BY13-03、BY13-30、BY13-31和BY13-32偏低，这与富单斜辉石二辉橄榄岩存在很大差异。岩相学观察发现北岩异剥橄榄岩记录了斜方辉石与低硅玄武质熔体反应生成单斜辉石、橄榄石和高硅熔体的反应过程。而寄主玄武岩与中国东部新生代玄武岩一样具有显著轻的Mg同位素组成，且Sr-Nd-Hf同位素组成富集，所以北岩异剥橄榄岩可能是由与寄主玄武岩组分相似的具有轻Mg同位素组成的玄武质熔体与二辉橄榄岩或富单斜辉石二辉橄榄岩反应形成，其重Mg同位素组成来源于对富单斜辉石二辉橄榄岩重Mg 同位素组成的继承。
北岩二辉橄榄岩(全岩：ΔεHf=-2.57~7.08，单斜辉石：ΔεHf=-0.72~6.69)和富单斜辉石二辉橄榄岩(全岩：ΔεHf=-1.91~2.66，单斜辉石：ΔεHf=0.47) Hf-Nd同位素组成均匀分布在地幔演化线两侧，说明具有重Mg同位素组成的流体交代并未导致北岩地幔捕虏体的Hf-Nd同位素发生解耦。而异剥橄榄岩(全岩：ΔεHf=-3.51~-0.90，单斜辉石：ΔεHf=-5.39~-2.22)和橄榄单斜辉石岩(全岩：ΔεHf=-2.91~-2.19，单斜辉石：ΔεHf=-4.27~-2.81)全岩和单斜辉石的Hf-Nd同位素组成均出现弱负解耦现象，这可能与具有较低Hf同位素组成的熔体交代有关。关键词：岩石圈地幔，地幔捕虏体，Mg同位素，Hf同位素，熔/
流体-岩石反应微笑不语
ABSTRACT
The North China Craton has been reactivated since the Mesozoic with significant thinning and refertilization of the subcontinental lithospheric mantle. Petrological and geochemical obrvations both indicate that mantle metasomatism play an important role in the refertilization of lithospheric mantle. However, the mechanism of metasomatism including the nature and source of metasomatic melt/fluid is still difficult to be thoroughly revealed. To better understand the interaction between xenolith and melt/fluid, I prent an integrated field, petrographical, whole rock major and trace elements concentrations, minerals major element concentrations, whole rock and clinopyroxene Hf, Nd, Sr and whole rock Mg isotope investigation for the mantle xenoliths and the host alkaline basalts in Beiyan within the Tancheng-Lujiang (Tan-Lu) wrench fault zone, eastern North China Craton. The relationship between mantle metasomatism and coupling Hf-Nd isotopes has also been discusd bad on the obtained data.
Bad on the mineral component, Beiyan xenoliths were subdivided into four types: lherzolite, cpx-rich lherzolite, wehrlite and olivine clinopyroxenite. The lherzolites containing similar major elements
to abyssal peridotites reprent the fragment of newly accreted oceanic-like lithospheric mantle which experienced subquent less than 10% melt extraction. The occurrence of hydrous minerals such as phlogopite, amphibole, feldspar and carbonates such as calcite, ankerite and reacted texture indicate the existence of remarkable mantle metasomatism. Compared with the lherzolites, the cpx-rich lherzolites show lower Mg# values (85.0~89.6), lower olivine Fo values (86.5~89.4), LREE-enriched patterns, higher ∑REE (9.19~26.3 ppm), more fertile Sr-Nd-Hf isotopic compositions. Particularly, the Mg isotopic compositions of cpx-rich lherzolites BY13-08 (δ26Mg=-0.03±0.07‰) and BY13-16 (δ26Mg=-0.12±0.09‰) are heavier than lherzolites and mantle normal value (δ26Mg=-0.25±0.07‰). Combining to the high Sr/Hf ratio, enrichment of Sr, depletion of Zr, the cpx-rich lherzolites may be the result of interaction between lherzolite and fluid inheriting the heavy Mg isotopic compositions of subducted Pacific slab.
Similarly, the wehrlites also show lower Mg# values (81.2~87.3) of whole rock, lower Fo value (81.1~86.2) of olivine, LREE-enriched patterns, higher ∑REE (9.04~16.1 ppm) and lower Nd-Hf isotopic values than lherzolites. But the most distinct difference between cpx-rich lherzolite and wehrlite is that the latter show variable Mg isotopic compoisiton (δ26Mg = -0.12‰ to -0.43‰). Part of wehrlites BY13-29 and BY13-33 contain higher Mg isotopic compositions, while sample BY13-03, B
Y13-30, BY13-31 and BY13-32 have lower Mg isotopic compositions than normal mantle value. The petrographical obrvations indicated that wehrlites record the reaction between orthopyroxene and low-SiO2 basalt to form cond clinopyroxene, olivine and high-SiO2 melt. Coincidentally, we obrved that the host basalt also contain fertile Sr-Nd-Hf isotopes and light Mg isotope values. Hence, the wehrlites with variable Mg isotopic compositions are formed by lherzolites or cpx-rich lherzolites and basalts which have similar low Mg isotopic compositions to
host magma. And part of wehrlites inherite the heavy Mg isotopic compositions from cpx-rich lherzolites
The Hf-Nd isotopic compositions of Beiyan lherzolites (whole rock: ΔεHf=-2.57~7.08, clinopyroxene: ΔεHf=-0.72~6.69) and cpx-rich lherzolites (whole rock: ΔεHf=-1.91~2.66, clinopyroxene: ΔεHf=0.47) locates near the mantle array, which indicate fluid containing heavy Mg isotopic compositions does not induce the Hf-Nd isotopic compositions of Beiyan mantle xenoliths to decouple. While Beiyan wehrlites (whole rock: ΔεHf=-3.51~-0.90, clinopyroxene: ΔεHf=-5.39~-2.22) and olivine clinopyroxenites (whole rock: ΔεHf=-2.91~-2.19, clinopyroxene: ΔεHf=-4.27~-2.81) show weakly negative Hf-Nd decoupling, which may be the results of reaction between basaltic melts containing low Hf isotopes and peridotites. Keywords: Lithospheric mantle; Mantle xenoliths; Magnesium isotop
es; Hafnium isotopes； Melt/fluid-rock interaction
荷花样子目录
第一章绪论 (1)
1.1 研究背景及现状 (1)
1.2 选题依据及意义 (2)
1.3 研究内容及方法 (6)
第二章区域地质概况 (8)
2.1 华北克拉通 (8)
太阳丘
2.2 北岩地区新生代玄武岩 (9)
第三章北岩地区地幔包体及寄主岩岩石学特征 (11)北京旅游必去十大景点
3.1 岩石分类 (11)
3.2 不同岩石类型特征描述 (14)
3.2.1 橄榄岩类 (14)
3.2.2 辉石岩类 (16)
3.2.3 玄武岩类 (16)
3.3 交代结构和交代矿物 (17)
第四章分析方法 (20)
4.1 主量元素分析方法 (20)
4.2 矿物主量元素分析方法 (20)
4.3 微量元素分析方法 (20)
4.4 Sr-Nd同位素分析方法 (21)
4.5 Hf同位素分析方法 (22)
沔阳县4.6 Mg同位素分析方法 (22)
第五章地幔捕虏体及围岩的地球化学特征 (24)
5.1 全岩主量元素组成 (24)
5.2 矿物主量元素组成 (24)
5.2.1 橄榄石 (24)
5.2.2 斜方辉石 (25)
5.2.3 单斜辉石 (27)
5.2.4 尖晶石 (28)
5.3 全岩微量元素组成 (28)
5.4 Sr-Nd同位素组成 (30)
5.4.1 全岩Sr-Nd同位素组成 (30)
鹅蛋的作用
5.4.2 单斜辉石Sr-Nd同位素组成 (31)虎宝宝取名
5.4.3 全岩和单斜辉石Sr-Nd同位素之间的比较 (31)
5.5 Hf同位素组成 (32)
5.5.1 全岩Hf同位素组成 (32)
5.5.2 单斜辉石Hf同位素组成 (33)
5.5.3 全岩和单斜辉石Hf同位素之间的比较 (34)
5.6 Mg同位素组成 (35)
5.7 地幔捕虏体平衡温压估算 (36)
第六章交代介质的性质和来源 (56)
6.1 岩石圈地幔性质 (56)
6.2 交代介质的性质 (57)
求助信怎么写
6.3 交代介质的来源 (61)
第七章地幔捕虏体Hf-Nd同位素研究 (65)
7.1 Hf-Nd同位素在地幔地球化学中的研究进展 (65)
7.2 北岩地幔捕虏体及寄主岩的Hf-Nd关系 (67)
第八章结论 (71)
致谢 (72)
参考文献 (74)
附录作者简介 (84)
