論文中英文摘要

1、附件2論文中英文摘要作者姓名：張少兵論文題目：揚(yáng)子陸核古老地殼及其深熔產(chǎn)物花崗巖的地球化學(xué)研究作者簡(jiǎn)介：張少兵，男，1980年10月生，2004年9月師從中國(guó)科學(xué)技術(shù)大學(xué)鄭永飛教授攻讀博士學(xué)位，2008年7月獲地球化學(xué)博士學(xué)位。中 文 摘 要研究前寒武紀(jì)大陸地殼的形成和演化規(guī)律，是理解大陸動(dòng)力學(xué)、發(fā)展板塊構(gòu)造理論的重要方向之一。湖北省宜昌市三峽地區(qū)不僅出露有揚(yáng)子克拉通最古老的基底，而且有大量的新元古代巖漿巖產(chǎn)出，是研究大陸地殼的生長(zhǎng)和演化、花崗巖的成因與源區(qū)物質(zhì)控制、新元古代巖漿活動(dòng)與Rodinia超大陸裂解等科學(xué)問題最理想的天然實(shí)驗(yàn)室。本文利用多種地球化學(xué)分析手段，包括主量元素和微量元素分析

2、、鋯石U-Pb定年、Rb-Sr和Sm-Nd同位素分析、礦物氧同位素分析以及最新發(fā)展起來的鋯石Lu-Hf同位素分析，研究了崆嶺雜巖中的片麻巖、混合巖、花崗巖、變沉積巖和角閃巖，對(duì)黃陵花崗巖基中的四個(gè)巖套進(jìn)行了系統(tǒng)的對(duì)比研究，特別是仔細(xì)解剖了曉峰鎂鐵質(zhì)長(zhǎng)英質(zhì)巖墻以及相關(guān)的淺成花崗巖，并對(duì)蓮沱砂巖中的一百多粒碎屑鋯石進(jìn)行了U-Pb定年和Lu-Hf同位素分析。結(jié)果不僅對(duì)三峽地區(qū)這些巖石的成因提供了可靠的地球化學(xué)制約，而且有助于了解揚(yáng)子克拉通基底的演化和華南陸塊新元古代構(gòu)造，從而為了解大陸的生長(zhǎng)、分異和演化以及花崗巖，尤其是TTG質(zhì)花崗巖的成因機(jī)制提供了新的思路。崆嶺雜巖由基底巖石加表殼巖石組成，另外有

3、一些基性巖侵入其中。基底巖石中以TTG質(zhì)巖石為主，少量為花崗質(zhì)巖石。表殼巖石主要為變沉積巖，其主微量元素變化范圍大，受物源組成的控制。對(duì)基底巖石中的混合巖、片麻巖和花崗巖共七個(gè)樣品進(jìn)行鋯石U-Pb定年，得到三組不同的年齡。第一組年齡為巖漿活動(dòng)時(shí)間，除一個(gè)花崗巖年齡為2.85Ga外，其余六個(gè)的年齡都在2.903.00Ga。第二組年齡是在混合巖和片麻巖中的繼承鋯石核上獲得的，為3.123.35Ga。另外，在一個(gè)混合巖的鋯石增生邊上，得到了約1.98Ga的第三組年齡，代表了混合巖化的時(shí)間。對(duì)表殼巖中的兩個(gè)變沉積巖進(jìn)行鋯石U-Pb定年，得到兩個(gè)變質(zhì)年齡分別為1.95Ga和1.98Ga。對(duì)一個(gè)角閃巖的鋯

4、石U-Pb定年也得到相似的1.94Ga的年齡。這些年齡與混合巖化時(shí)間接近，說明崆嶺雜巖記錄了一期古元古代(1.97±0.03Ga)的構(gòu)造熱事件，引起了揚(yáng)子陸核的增生乃至克拉通化，可能與同時(shí)期的全球構(gòu)造活動(dòng)有關(guān)?；讕r石氧同位素組成與典型太古代TTG巖石相似，鋯石18O值大多都小于6，而變沉積巖氧同位素組成則顯著偏高，與其原巖為沉積來源一致。對(duì)混合巖、片麻巖和花崗巖中三組不同年齡的鋯石，都進(jìn)行了鋯石Lu-Hf同位素分析。2.9Ga的鋯石顆粒的Hf同位素組成基本相似，Hf(t)值為2.1到5.2，對(duì)應(yīng)Hf模式年齡主要分布在3.43.5Ga之間。對(duì)來自不同樣品的13個(gè)繼承核進(jìn)行了鋯石Hf同

5、位素分析，其Hf同位素比值相對(duì)2.9Ga的鋯石略低，所得Hf(t)值加權(quán)平均為1.6，對(duì)應(yīng)Hf模式年齡為3.55Ga。這些數(shù)據(jù)說明揚(yáng)子陸核的地殼生長(zhǎng)至少從3.5Ga就已經(jīng)開始。只對(duì)混合巖中的一個(gè)古元古代鋯石增生邊進(jìn)行了Hf同位素分析，其Hf(t)值為21.7。兩個(gè)變沉積巖的鋯石Hf同位素組成非常相似，Hf(t)值分布范圍為13.3到1.0，加權(quán)平均值分別為6.4和6.5。角閃巖鋯石Hf同位素比值變化范圍大。崆嶺雜巖中混合巖、片麻巖和花崗巖的Rb-Sr和Sm-Nd同位素組成比較相似，計(jì)算到2.9Ga的Nd(t)值都在0左右，為1.9+2.6。變沉積巖的Nd同位素組成變化范圍較大，與源區(qū)物質(zhì)的組成

6、不同有關(guān)。角閃巖和輝長(zhǎng)巖計(jì)算到1.97Ga的Nd(t)值分別為4.3和+4.4。對(duì)崆嶺雜巖的研究表明，揚(yáng)子陸核地殼生長(zhǎng)至少從3.5Ga就已經(jīng)開始，經(jīng)過太古代的生長(zhǎng)之后在古元古代受到了再造。黃陵巖基可以劃分為四個(gè)巖套，分別是黃陵廟奧長(zhǎng)花崗巖花崗閃長(zhǎng)巖巖套，三斗坪石英閃長(zhǎng)巖英云閃長(zhǎng)巖巖套，大老嶺二長(zhǎng)閃長(zhǎng)巖二長(zhǎng)花崗巖巖套以及由淺成花崗巖和鎂鐵質(zhì)長(zhǎng)英質(zhì)巖墻組成的曉峰巖套。除曉峰巖套之外，其余三個(gè)巖套中的絕大多數(shù)花崗巖都以富Na、富Sr，Y和HREE含量低，虧損Nb、Ta為特征，具有典型的TTG特征。但各巖套的主微量元素之間存在系統(tǒng)的差異，黃陵廟巖套相對(duì)三斗坪和大老嶺巖套Sr/Y比和La/Yb比較高，而

7、Nb/La比則較低。曉峰巖套中的兩個(gè)花崗巖的鋯石U-Pb年齡分別為797±5Ma和799±2Ma，測(cè)得一個(gè)長(zhǎng)英質(zhì)巖墻年齡為806±12Ma，一個(gè)鎂鐵質(zhì)巖墻年齡為806±4Ma，顯然曉峰巖套中的巖墻和花崗巖都形成于800Ma左右。對(duì)黃陵廟巖套中的6個(gè)花崗巖進(jìn)行鋯石U-Pb定年，得到的年齡從821Ma到800Ma，加權(quán)平均值為815±7Ma，繼承核給出了古元古代到太古代的源巖年齡。三斗坪巖套的兩個(gè)英云閃長(zhǎng)巖給出了相似的兩組年齡，分別為803±11Ma和919±15Ma， 810±15Ma和911±14Ma，前

8、者為三斗坪巖套的結(jié)晶年齡，后者可能反映了格林威爾期造山運(yùn)動(dòng)的影響。大老嶺巖套的一個(gè)英云閃長(zhǎng)巖鋯石U-Pb定年結(jié)果為817±22Ma。因此，黃陵巖基各巖套都是在800820Ma期間形成的。單礦物氧同位素分析表明，黃陵花崗巖基絕大多數(shù)樣品具有與典型的I型花崗巖相似的氧同位素組成，巖墻侵入花崗巖時(shí)，只發(fā)生了有限的小規(guī)模的高溫水巖反應(yīng)。黃陵巖基四個(gè)巖套的Sr同位素組成總體上比較相似，Sr同位素初始比值為0.7050.708。各巖套Nd同位素比值變化范圍較大，曉峰巖套Nd(t)值為6.4到10.4，黃陵廟巖套Nd(t)值為9.3到21.3，三斗坪巖套Nd(t)值為2.1到9.2，一個(gè)大老嶺英云

9、閃長(zhǎng)巖的Nd(t)值為4.4。鋯石Hf同位素分析顯示，曉峰巖套Hf(t)值8.312.9，三斗坪巖套Hf(t)值為10.513.1，一個(gè)大老嶺英云閃長(zhǎng)巖Hf(t)值為6.1。黃陵廟巖套中新元古代鋯石和古老的繼承鋯石具有截然不同的Hf同位素組成，新元古代鋯石的Hf(t)值為10.324.1，繼承核的Hf同位素比值雖然受到新元古代巖漿活動(dòng)的擾動(dòng)，仍然顯著偏低，最低的繼承核Hf(t)值與崆嶺雜巖中的太古代巖石相似。這些結(jié)果說明，黃陵巖基是由古老地殼在800820Ma期間遭受深熔作用形成的，這些古老地殼包括下覆于崆嶺TTG之下的太古代巖石和古元古代角閃巖，太古代巖石熔融深度較深，殘留相中含石榴石，而古

10、元古代巖石熔融深度相對(duì)較淺，殘留相主要為角閃石。黃陵巖基的源區(qū)物質(zhì)為太古代和古元古代地殼，說明它不可能是與地幔柱或者洋殼俯沖有關(guān)的巖漿活動(dòng)的產(chǎn)物，而更有可能與板塊裂谷假說所陳述的古造山帶構(gòu)造垮塌有關(guān)。這對(duì)TTG巖石的成因、I型花崗巖的形成以及陸殼成分的演化都有著重要的意義。蓮沱組砂巖不整合覆蓋于黃陵巖基之上，沉積時(shí)代約為750Ma。對(duì)來自其中的106粒碎屑鋯石進(jìn)行了U-Pb定年，并選取其中的39粒鋯石進(jìn)行了Lu-Hf同位素分析。根據(jù)U-Pb年齡，這些鋯石可以分為四組，分別為>3.0Ga，約2.95Ga，約1.95Ga以及820-750Ma。其中3.8Ga的鋯石代表了揚(yáng)子最古老的地殼殘片，

11、其Hf(t)值為0.8，模式年齡為4.0Ga。約3.3Ga的鋯石具有+4.2的Hf(t)值，暗示了新生地殼的生長(zhǎng)。所有鋯石都具有太古代的Hf模式年齡，主要峰期在3.23.6Ga，可能代表了重要的地殼生長(zhǎng)時(shí)間。約2.95Ga，約1.95Ga和820-750Ma的鋯石都具有負(fù)的Hf(t)值和太古代模式年齡，反映了太古代物質(zhì)在不同期次的幕式再造。最年輕的鋯石U-Pb年齡約750Ma，與蓮沱組沉積時(shí)代一致，反映了裂谷盆地中表殼物質(zhì)的迅速再循環(huán)，可能與Rodinia超大陸的裂解有關(guān)。關(guān)鍵詞： 揚(yáng)子克拉通 崆嶺雜巖 黃陵巖基 曉峰巖墻 深熔作用 同位素年代學(xué) 地球化學(xué)Geochemistry of the

12、 Yangtze Continental Nucleusand Its Anatectic GranitoidsZhang Shao-BingABSTRACTInvestigation of the growth and evolution of Precambrian crust is a key to understanding of continental dynamics and developing of the plate tectonic theory. The Kongling Complex, which is the oldest basement of the Yangt

13、ze craton, and the Neoproterozoic Huangling Batholith are located in the Yangtze Gorge at Yichang in Hubei Province. In this thesis, a detailed study of major and trace element analyses, zircon U-Pb dating, Rb-Sr and Sm-Nd isotope analyses, mineral Oxygen isotope analyses and newly-developed zircon

14、Lu-Hf isotope analyses was carried out for different rocks from the Kongling Complex, the Huangling Batholith and the Liantuo Formation. The results not only place geochemical constraints on the genesis of these rocks, but also provide insight into the basement evolution of the Yangtze craton and th

15、e geodynamics of Neoproterozoic continental reworking in the South China Block. Our study is of great implications for the continental crust growth, differentiation and evolution, and petrogenetic mechanism of granites (especially TTG rocks).The Kongling Complex consists of basement rocks, supracrus

16、tal rocks and some mafic rocks occurring as lenses, boudins or layers. The basement rocks are mainly TTG rocks with minor granites. The chemical compositions of metasedimentary rocks varied significantly and are controlled by the source materials. Three groups of ages are obtained from zircon U-Pb d

17、ating on seven basement rocks, including migmatites, gneisses and granites. The first group represents the time of magmatic activity at 2.90-3.00 Ga except one granite with an age of 2.85 Ga. The second group is obtained on the inherited cores of some migmatites and gneisses, ranging from 3.12 Ga to

18、 3.35 Ga. The third group at about 1.98 Ga represent the time of migmatization, which is obtained on the zircon overgrowth of a migmatite. Zircon U-Pb dating is carried out for two metasedimentary rocks of the Kongling Complex, yielding two metamorphic ages of 1.95 Ga and 1.98 Ga. A similar age of 1

19、.94 Ga is obtained by zircon U-Pb dating on an amphibolite. These ages are close to the time of migmatization, indicating an episode of tectonothermal event at 1.97±0.03 Ga, consistent with contemporaneous global events. It is this event that causes accretion of the Yangtze continental nucleus

20、even cratonization. The O isotope compositions of basement rocks are similar to typical Archean TTG rocks, with most zircon 18O values lower than 6. The O isotopic ratios for the metasedimentary rocks are obviously higher, consistent with its sedimentary sources. Zircon Lu-Hf isotopes are measured f

21、or the three groups of zircons from migmatites, gneisses and granites. The 2.9 Ga grains from different rocks have similar Hf isotope compositions, with Hf(t) values of 2.1 to 5.2 and Hf model ages of 3.4-3.5 Ga. The Hf isotopic ratios obtained on 13 inherited cores are lower than the 2.9 Ga grains.

22、 The weighted mean of their Hf(t) values is 1.6 and corresponding Hf model age is 3.55 Ga. The Hf isotopic data suggests that the growth of Yangtze continental crust had begun as early as 3.5 Ga. Hf isotopic analysis was carried out for one Paleoproterozoic zircon overgrowth rim, yielding an Hf(t) v

23、alue of 21.7. Zircons from the two metasedimentary rocks have similar Hf isotope compositions, Hf(t) values ranging from 13.3 to 1.0 and weighted mean values being 6.4 and 6.5, respectively. The amphibolite has a wide range of Hf isotopic ratios, reflecting the effect of metamorphism. The migmatites

24、, gneisses and granites of the Kongling Complex have similar Rb-Sr and Sm-Nd isotope compositions. The Nd(t) values calculated to 2.9 Ga are all around zero, from 1.9 to +2.6. The Nd isotopic ratios of the metasedimentary rocks varied greatly and are controlled by the source materials. The amphiboli

25、te and gabbro have Nd(t) values (t = 1.97 Ga) of 4.3 and +4.4, respectively. The study on the Kongling Complex suggests that the initial growth of Yangtze continental crust started no later than 3.5 Ga and suffered reworking in the Paleoproterozoic after the growth in the Archean.The Huangling Batho

26、lith is subdivided into four rock suites, namely the Huanglingmiao trondhjemite-granodiorite suite, the Sandouping quartz diorite-tonalite suite, the Dalaoling monzodiorite-monzogranite suite, and the Xiaofeng composite suite including mafic-felsic dykes and associated epigranite. Except for the Xia

27、ofeng Suite, most rocks from the other three suites are characterized by high Na and Sr, low Y and HREE, depletion of Nb and Ta, similar to typical TTG rocks. However, different rock suites show systematical differences in chemical compositions. The Huanglingmiao suite has higher Sr/Y and La/Yb rati

28、os, but lower Nb/La ratios than the Sandouping and Dalaoling suite. Two granites of the Xiaofeng suite have zircon U-Pb age of 797±5 Ma and 799±2 Ma, respectively. Two dykes, felsic and mafic in composition, have ages of 806±12 Ma and 806±4 Ma, respectively. Thus all rocks in the

29、 Xiaofeng Suite formed simultaneously at about 800 Ma. Zircon U-Pb dating on six granites from the Huanglingmiao suite, yielding ages from 821 Ma to 800 Ma, with a weighted mean of 815±7 Ma, and Paleoproterozoic to Archean ages on the inherited cores which constrains the ages of source rocks. T

30、wo Sandouping tonalites both gave two groups of ages, 803±11 Ma and 919±15 Ma, 810±15 Ma and 911±14 Ma. The younger age represents the crystallization age of the Sandouping Suite, whereas the older age reflects the possible influence of Grenvillian orogen. A Dalaoling tonalite sh

31、ow a zircon U-Pb age of 817±22 Ma. Therefore, four rock suites of the Huangling Batholith are formed in the period of 800-820 Ma. Mineral O isotope analyses show that most rocks from the Huangling Batholith have O isotope compositions similar to typical I-type granite and only small-scaled high

32、-temperature water-rock interactions happened during the intrusion of dykes into the granitoids. Four suites of the Huangling Batholith generally have similar Sr isotope compositions with initial Sr isotopic ratios of 0.705-0.708. Nd(t) values for each rock suite are, 6.4 to 10.4 for the Xiaofeng su

33、ite, 9.3 to 21.3 for the Huangling suite, 2.1 to 9.2 for the Sandouping suite, and 4.4 for a Dalaoling tonalite. Zircon Lu-Hf isotope analyses gave Hf(t) values of 8.3 to 12.9 for the Xiaofeng suite, 10.5 to 13.1 for the Sandouping suite, and 6.1 for the Dalaoling tonalite. The Neoproterozoic co-mag

34、matic zircons and ancient inherited cores have contrasting Hf isotopic compositions, with Hf(t) values of 10.3 to 24.1 for co-magmatic zircons and significantly lower Hf isotopic ratios for the inherited cores in spite of the alteration by Neoproterozoic magmatism. The lowest Hf(t) values are simila

35、r to Archean rocks of the Kongling Complex. These suggest that the Huangling Batholith is the anatexis product of ancient crust at 800-820 Ma. The ancient crust includes the Archean rocks underlying Kongling TTGs and Paleoproterozoic amphibolites. The Archean rocks were melted at great depth with ga

36、rnet in the residual and the melting depth of Paleoproterozoic rocks was relatively shallower with amphibole as a major residual phase. The source materials of the Huangling Batholith are Archean and Paleoproterozoic crusts, suggesting that it was not the product of either mantle plume or oceanic crust subduction, but related to ancient orogen tectonic collapse as stated in the plate-rift hypothesis. This has significant implications for TTG petrogenesis, I-type granite origin and continental crust evolution.The Liantuo Formation with deposition time