本文關(guān)鍵詞：造山帶地殼的深熔作用：北大別混合巖地球化學(xué)研究　出處：《中國科學(xué)技術(shù)大學(xué)》2016年博士論文　論文類型：學(xué)位論文

  更多相關(guān)文章： 造山帶 地殼深熔 構(gòu)造演化 水致部分熔融 鋯石學(xué)

【摘要】：造山帶的演化和部分熔融關(guān)系密切。大別-蘇魯造山帶是典型的大陸碰撞型造山帶,在其演化的不同階段發(fā)生了深熔作用,是研究造山帶地殼深熔作用理想地區(qū)。本學(xué)位論文對(duì)作為深熔作用產(chǎn)物的北大別混合巖進(jìn)行了系統(tǒng)的巖石學(xué)和地球化學(xué)研究,對(duì)混合巖的形成機(jī)制、部分熔融性質(zhì)、深熔作用時(shí)限、熔體演化、礦物響應(yīng)等進(jìn)行了詳細(xì)討論,為造山帶地殼在折返和碰撞后階段的深熔作用提供了有力證據(jù),豐富了造山帶化學(xué)地球動(dòng)力學(xué)。對(duì)北大別混合巖進(jìn)行了巖石學(xué)、礦物學(xué)和地球化學(xué)研究,結(jié)果表明混合巖是由水致部分熔融形成。北大別混合巖以發(fā)育大顆粒嵌晶狀角閃石為特征,角閃石自形發(fā)育,且顆粒邊界晶面發(fā)育,指示其為轉(zhuǎn)熔礦物。角閃石中含有黑云母、石英和斜長石包裹體,角閃石-斜長石溫壓計(jì)結(jié)果說明混合巖形成的溫壓條件為：700-751℃和3.5-5.2kbar,該溫壓條件顯著低于黑云母脫水熔融的固相線,表明發(fā)生部分熔融的反應(yīng)為：黑云母+石英+斜長石+流體=轉(zhuǎn)熔角閃石+熔體�；旌蠋r中淡色體含量顯著高于基底片麻巖中含水礦物分解所能產(chǎn)生的熔體量,也指示了北大別混合巖是造山帶地殼水致部分熔融形成。含水的轉(zhuǎn)熔礦物(角閃石)、低于含水礦物固相線的溫壓條件和高的熔體含量是區(qū)分水致部分熔融和脫水部分熔融的標(biāo)志�；旌蠋r中淡色體具有明顯不同的地球化學(xué)和礦物學(xué)組成,指示熔體形成后經(jīng)歷了復(fù)雜的演化過程。淡色體具有英云閃長質(zhì)到花崗質(zhì)的組成,相較于中間體,具有高的Si02,Na2O,Sr,和Ba,低的CaO,FeO,MgO,Ti02和MnO2.部分淡色體表現(xiàn)為高La/YbN比值,低的HREE含量,無或弱Eu異常,是北大別花崗質(zhì)片麻巖部分熔融后,轉(zhuǎn)熔角閃石殘留源區(qū)形成的熔體：大多數(shù)部分熔融的初始熔體經(jīng)歷了巖漿演化過程,形成了具有高HREE和低La/YbN比值的淡色體,是這是富含HREE的轉(zhuǎn)熔礦物角閃石夾帶進(jìn)入熔體的結(jié)果,部分淡色體具有顯著Eu正異常和低REE含量的特征,表明在結(jié)晶分異過程中,發(fā)生了長石的堆晶。對(duì)北大別混合巖的年代學(xué)和同位素地球化學(xué)進(jìn)行了研究,混合巖具有顯著不同的氧同位素組成和原巖年齡,既有新元古代的遭受過高溫?zé)嵋何g變的低δ18O值的巖石,也有來自太古代晚期到古元古代早期的高δ18O值古老地殼經(jīng)歷了碰撞后的混合巖化作用。新元古代年齡和低的鋯石δ180值是華南板塊的獨(dú)有特征,表明北大別混合巖原巖來自于華南板塊。進(jìn)入片麻巖中引起水致部分熔融的流體可能來源于和具有不同的氧同位素組成的原巖具有相似組成的巖石在深部的脫水,因此流體的氧同位素組成繼承自源區(qū)的不均一性。北大別混合巖的Sr-Nd同位素總體和基底花崗質(zhì)正片麻巖類似,表明混合巖的形成機(jī)制為北大別片麻巖的原地部分熔融�；旌蠋r化的年代為早白堊世,和早期埃達(dá)克巖的年齡一致,是造山帶地殼在不同層位深熔作用的產(chǎn)物。部分熔融所需熱源來自于構(gòu)造體制由擠壓到伸展的轉(zhuǎn)換時(shí)升高的熱流值,說明大別造山帶開始伸展的時(shí)間不晚于150Ma。對(duì)北大別混合巖中多相生長的鋯石進(jìn)行了原位的鋯石U-Pb定年和微量元素分析,識(shí)別出原巖鋯石,變質(zhì)鋯石和兩階段的深熔鋯石,揭示了混合巖的復(fù)雜演化歷程。原巖鋯石具有高的Th/U比值(0.1)和中等的U含量,陡峭的稀土配分型式,中等到強(qiáng)烈的Eu負(fù)異常和顯著的Ce正異常,和典型的巖漿鋯石特征致,鋯石U-Pb定年給出新元古代的年齡,代表了混合巖原巖為來自新元古代的巖漿巖。變質(zhì)鋯石具有平坦的重稀土配分型式(Yb/Gd=1.7～7.2),低的HREE、Na+Ta、Y、Th、U含量,低的Th/U(0.1)比值,輕微的Eu負(fù)異常到正異常(0.85～1.44),指示變質(zhì)鋯石為榴輝巖相變質(zhì)鋯石,混合巖經(jīng)歷了三疊紀(jì)(211～230Ma)的超高壓榴輝巖相變質(zhì)。深熔鋯石的研究表明存在兩期的部分熔融,第一期深熔發(fā)生在晚三疊-早侏羅紀(jì)(188～206Ma),鋯石具有高的HREE、Na+Ta、Y、U含量,低的Th/U比值(0.01～0.12),極其陡峭的MREE-HREE配分型式(Yb/Gd=79～738)和顯著的Eu負(fù)異常,這些微量元素特征說明鋯石結(jié)晶于深熔熔體。鋯石Ti溫度為698～868℃,達(dá)到了實(shí)驗(yàn)得到的多硅白云母脫水熔融的溫度,表明超高壓含水礦物多硅白云母在熱折返階段發(fā)生脫水部分熔融；第二期深熔發(fā)生在碰撞后早白堊紀(jì)(116～141Ma),鋯石具有中等的U含量,變化的Th/U比值(0.03～1.04),陡峭的稀土配分型式(Yb/Gd=14～80)和顯著的Eu負(fù)異常(0.14～0.78),鋯石Ti含量溫度計(jì)計(jì)算給出的溫度為699～821℃,高于含水條件下花崗巖固相線和黑云母脫水熔融的固相線,表明造山帶地殼的經(jīng)歷了水致部分熔融和脫水部分熔融。早期深熔作用和深俯沖陸殼從地幔深度的熱折返階段相關(guān),晚期深熔和碰撞后造山帶從擠壓到伸展構(gòu)造轉(zhuǎn)換相關(guān)。
[Abstract]:The evolution of the orogenic belt is closely related to the partial melting of the orogenic belt. The Dabie Su Lu orogenic belt is a typical continental collision orogenic belt. Deep melting has occurred in different stages of its evolution, and it is an ideal area for studying the crustal deep penetration in orogenic belt. In this thesis as the anatexis product in North Dabie mixed rock of petrological and chemical research on the earth system, the mixed rock formation mechanism, partial melting properties, anatexis, time evolution of mineral melt response are discussed in detail, anatexis of the orogenic belt crust in the exhumation and after collision the stage provides strong evidence, enrich the geochemical dynamics of orogenic belt. The petrology, mineralogy and geochemistry of the North Dabie mixed rocks have been studied. The results show that the mixed rocks are formed by partial melting of water. North Dabie mixed rock by the development of large particles of poikilitic amphibole is characterized, amphibole euhedral growth, and grain boundary plane development, indicating its turn molten mineral. Contain biotite, quartz and plagioclase inclusions of hornblende, plagioclase hornblende thermobarometer showed mixed rock formation temperature and pressure conditions were: 700-751 C and 3.5-5.2kbar, the solidus temperature and pressure conditions was significantly lower than that of biotite dehydration melting, partial melting reactions of biotite + plagioclase + quartz + = peritectic fluid amphibole + melt. The content of the pale body in the mixed rocks is significantly higher than that in the gneiss, and also indicates that the Dabie mixed rocks are formed by partial melting of the crust in the orogenic belt. The water bearing melt minerals (hornblende), temperature and pressure conditions below the solidus of water bearing minerals and high melt content are the marks to distinguish partial melting of water from partial melting and dehydration. The light color bodies in the mixed rocks have distinct geochemical and mineralogical composition, indicating a complex evolution process after the formation of the melts. Light body with tonalitic to form granitic, compared to the intermediate, with high Si02, Na2O, Sr, and Ba, low CaO, FeO, MgO, Ti02 and MnO2. part of Leucosome showed high La/YbN ratio and low HREE content, no or weak Eu anomaly, is North Dabie granite quality of gneiss after partial melting, melting to hornblende residual melt source region is formed: most part of initial melting through the process of magmatic evolution, forming a pale body has high HREE and low La/YbN ratio, this is HREE rich peritectic amphibole mineral entrained into the melt, part of body with light a significant feature of positive Eu anomalies and low REE content, showed that the crystallization differentiation process, the feldspar cumulates. On the North Dabie mixed rock geochronology and isotope geochemistry of mixed rocks have different oxygen isotopic composition and protolith age, both Neoproterozoic high temperature hydrothermal alteration by low 18O values of rock, but also from the late Archean to Paleoproterozoic high Delta 18O early generation the value of migmatization of ancient crust experienced after the collision. The Neoproterozoic zircon age and low delta 180 value is the unique characteristics of the Southern China plate, show that the North Dabie protolith mixed from Southern China plate. The fluid causing partial melting of gneiss may originate from deep dehydration of rocks with similar composition of oxygen isotopic composition of Yuan Yan, so the oxygen isotopic composition of fluids inherits from the heterogeneity of source area. North Dabie mixed rock Sr-Nd isotopic overall and basement granitic orthogneiss indicate similar formation mechanism of mixed rock for the North Dabie gneiss in partial melting. In the early Cretaceous migmatization, and early adakites in the same age, is a product of crustal anatexis in different layers. The heat source needed for partial melting comes from the increase of heat flow value when the tectonic system is transformed from extrusion to extension, indicating that the Dabie orogenic belt began to extend at a later time than 150Ma. Zircon U-Pb dating and trace element analysis of zircons in multiphase growth in the North Dabie mixed rock indicate that zircons, metamorphic zircons and two stages of deep melting zircon are identified, revealing the complex evolution of the mixed rocks. The protolith zircon has high Th/U ratios (0.1) and medium U content of REE in steep sub type, moderate to strong negative Eu anomalies and positive anomaly in Ce, and the typical characteristics of magmatic zircon, zircon U-Pb dating are Neoproterozoic age, on behalf of the protolith is from magma mixing Neoproterozoic rocks. Metamorphic zircon has flat REE pattern (Yb/Gd=1.7 ~ 7.2), HREE, Na+Ta, Y, Th, low U content, low Th/U ratio (0.1), slight negative Eu anomaly to positive anomalies (0.85 ~ 1.44), indicating the metamorphic zircon as eclogite facies metamorphic zircon, mixed rock experience the Triassic period (211 ~ 230Ma) of the ultrahigh pressure eclogite facies metamorphism. Study on deep penetration of zircon indicate that there are two stages of partial melting, the first phase of deep penetration occurred in Late Triassic early Jurassic three (188 ~ 206Ma), HREE, Na+Ta, Y with zircon, high U content, low Th/U ratio (0.01 ~ 0.12), extremely steep MREE-HREE pattern (Yb/Gd=79 ~ 738) and significant negative Eu anomaly, the characteristics of these trace elements in zircon crystallization of anatectic melts. Zircon Ti temperature is 698 to 868 DEG C, reached the phengite dehydration melting experiments on the temperature, the Biao Mingchao high hydrous minerals phengite occurred dehydration partial melting in the heat phase second reentry stage; deep penetration in the impact after the early Cretaceous (116 ~ 141Ma), zircon has moderate U contents, Th/U the change of the ratio of (0.03 ~ 1.04), the steep REE types (Yb/Gd=14 ~ 80) and significant negative Eu anomalies (0.14 ~ 0.78), the content of Ti presented the zircon thermometer temperature is 699 ~ 821 degrees higher than the solidus solidus, granite and biotite dehydration melting of water under the condition that the crust orogenic belt has experienced partial melting and water
【學(xué)位授予單位】：中國科學(xué)技術(shù)大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2016
【分類號(hào)】：P584;P588.36

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