秦嶺造山帶中段花崗巖的時空格架、源區(qū)物質(zhì)及其對地殼深部物質(zhì)組成的示蹤
發(fā)布時間：2018-08-22 18:19
【摘要】：秦嶺造山帶的深部物質(zhì)組成是人們一直關(guān)注的問題�；◢徺|(zhì)巖石作為大陸地殼的重要組成部分,記載了陸殼的形成、殼幔相互作用以及巖石圈演化的各種信息,通過花崗巖的同位素地球化學(xué)示蹤研究,能夠有效揭示大陸巖石圈物質(zhì)組成、區(qū)別陸塊地球化學(xué)差異性和相關(guān)性、以及反演地球深部的演化過程。秦嶺造山帶中段位于東西秦嶺的交接轉(zhuǎn)換地帶,是了解秦嶺造山帶組成結(jié)構(gòu)和發(fā)育歷史的關(guān)鍵地帶。古元古代至中生代花崗巖在該地區(qū)廣泛發(fā)育,為開展該區(qū)域的花崗巖同位素填圖及深部物質(zhì)示蹤研究提供了可能。在系統(tǒng)收集研究區(qū)花崗質(zhì)巖石的鋯石U-Pb年齡、Nd-Hf同位素組成等資料的基礎(chǔ)上,本次研究針對研究薄弱的巖體開展了詳細(xì)的野外調(diào)查和室內(nèi)分析,建立了秦嶺造山帶中段花崗巖的年代學(xué)格架,系統(tǒng)分析了花崗巖的Nd-Hf同位素組成特征,探討了秦嶺中段深部物質(zhì)組成結(jié)構(gòu),對比秦嶺中段與東秦嶺中生代花崗巖的源區(qū)和深部物質(zhì)組成特征的異同,取得了如下主要成果和認(rèn)識。(1)系統(tǒng)收集的95件和本次實測的19件鋯石U-Pb年齡數(shù)據(jù)顯示,秦嶺造山帶中段花崗巖漿演化大致經(jīng)歷了古元古代(1806～1741Ma)、新元古代(962～704Ma)、早古生代(470～424Ma)、晚古生代(417～373Ma)和中生代(248～187Ma)五期。(2)古元古代花崗巖零星出露于北秦嶺構(gòu)造帶中,以片麻狀黑云母二長花崗巖為主,為強(qiáng)變形的Ⅰ型花崗巖。新元古代花崗巖主要分布在揚子地塊北緣,在其他構(gòu)造單元中零星展布,該期花崗巖自早至晚具有由強(qiáng)變形的S型花崗巖向無變形的Ⅰ型或I-A過渡型花崗巖變化的趨勢。早古生代花崗巖主要分布在華北地塊南緣和北秦嶺構(gòu)造帶,巖石類型以黑云母二長花崗巖和石英閃長巖為主,多為Ⅰ型花崗巖,少量見I-A過渡型。晚古生代花崗巖在華北地塊南緣和北秦嶺零星出露,以二長花崗巖為主,見少量的花崗閃長巖和正長花崗巖,多為Ⅰ型花崗巖。中生代花崗巖在研究區(qū)的4個構(gòu)造單元內(nèi)均有出露,其中,222～206Ma是該期花崗巖的主體,巖石類型多樣,以Ⅰ型為主,伴有少量的I-A過渡型。(3)分布于北秦嶺的古元古代花崗巖具有負(fù)的εNd(t)值(-15.8～-14.5)和εHf(t)值(-10.1～-8.2)以及古老的Nd-Hf模式年齡,分別為3.19～2.96Ga、3.05～2.93Ga,表明其主要來源于中太古代地殼物質(zhì)的部分熔融,揭示北秦嶺存在太古宙的深部物質(zhì)信息。(4)新元古代花崗巖的Nd-Hf同位素組成顯示,自北秦嶺→南秦嶺→揚子地塊北緣,花崗巖的εNd(t)值逐漸增大,TDM逐漸變年輕,源區(qū)物質(zhì)組成中年輕組分的參與逐漸增多,反映其深部物質(zhì)組成也具有逐漸變年輕的趨勢。另外,揚子地塊北緣花崗巖的εHf(t)值變化較大,反映該區(qū)域的基底組成比較復(fù)雜,除了中元古代新生的地殼組分外,還有少量太古宙-古元古代的古老物質(zhì)。(5)古生代花崗巖多具有負(fù)的εNd(t)值和正的εHf(t)值,其源區(qū)主要為中元古代新生地殼物質(zhì)的部分熔融。華北地塊南緣花崗巖的TDM和TDMC一般比北秦嶺年輕,且華北地塊南緣個別花崗巖具有εHf(t)高的Nd-Hf解耦,而北秦嶺個別巖體具有εH(t)低的Nd-Hf解耦現(xiàn)象,指示花崗巖的源區(qū)組成自華北地塊南緣→北秦嶺,古老地殼組分的參與逐漸增多,華北地塊南緣具有比北秦嶺更年輕的深部物質(zhì)組成。(6)中生代花崗巖貫穿全區(qū),Nd-Hf同位素特征表明這些花崗巖的源區(qū)均以古老殼源物質(zhì)為主,并有少量的年輕組分參與。但北秦嶺和南秦嶺中生代花崗巖的源區(qū)組成比華北地塊南緣和揚子地塊北緣復(fù)雜,其中包含了更多的古老地殼物質(zhì)。花崗巖的Nd-Hf同位素組成示蹤顯示,北秦嶺和南秦嶺具有較古老且復(fù)雜的深部物質(zhì)組成,而華北地塊南緣和揚子地塊北緣的深部物質(zhì)組成相對較年輕。(7)秦嶺造山帶中段的地殼增生主要發(fā)生在中元古代,北秦嶺、南秦嶺和揚子地塊北緣中還可見少量太古宙和古元古代的地殼再造,而華北地塊南緣缺少古老的(古元古代以前)的地殼改造事件,反映出研究區(qū)華北地塊南緣可能具有與北秦嶺、南秦嶺、揚子地塊北緣不同的地殼演化歷史和構(gòu)造屬性。(8)對比研究顯示,秦嶺中段地區(qū)華北地塊南緣的深部物質(zhì)組成與祁連地區(qū)更為相似,而與東秦嶺地區(qū)的不同,這為進(jìn)一步認(rèn)識秦嶺造山帶不同區(qū)段的演化提供了新的依據(jù)。
[Abstract]:As an important part of the continental crust, granitic rocks record various information about the formation of continental crust, the interaction between crust and mantle, and the evolution of the lithosphere. Isotope geochemical tracing of granites can effectively reveal the composition of the continental lithosphere. The middle part of the Qinling orogenic belt is located in the transitional zone between the eastern and Western Qinling Mountains. It is a key area to understand the composition and development history of the Qinling orogenic belt. Based on the systematic collection of zircon U-Pb ages and Nd-Hf isotopic compositions of the granitic rocks in the study area, detailed field investigation and laboratory analysis have been carried out for the weakly studied rocks, and the age of the granites in the middle Qinling orogenic belt has been established. The Nd-Hf isotope composition characteristics of the granites are systematically analyzed, and the deep material composition and structure of the middle Qinling Mountains are discussed. The similarities and differences between the source areas and the deep material composition characteristics of the Mesozoic granites in the middle Qinling Mountains and those in the eastern Qinling Mountains are compared. The main achievements and understandings are as follows. (1) 95 pieces of zircon U-Pb collected systematically and 19 pieces of zircon U-Pb measured in this study. Age data show that the middle Qinling orogenic belt has undergone five stages of granitic magma evolution: Paleoproterozoic (1806-1741 Ma), Neoproterozoic (962-704 Ma), Early Paleozoic (470-424 Ma), Late Paleozoic (417-373 Ma) and Mesozoic (248-187 Ma). (2) The Paleoproterozoic granites are sporadically exposed in the North Qinling tectonic belt, and secondly gneissic biotite. The Neoproterozoic granites are mainly distributed in the northern margin of the Yangtze massif and sporadically distributed in other tectonic units. From early to late, the Neoproterozoic granites have a tendency to change from strongly deformed S-type granites to non-deformed I-A type granites. The Early Paleozoic granites are mainly distributed in the northern margin of the Yangtze massif. In the southern margin of the North China massif and the North Qinling tectonic belt, the rock types are mainly biotite monzonite and quartz diorite, mostly type I granite and a few type I-A transitional granite. Late Paleozoic granite is sporadically exposed in the southern margin of the North China massif and the North Qinling Mountains, mainly monzonite, a small amount of granodiorite and syenite, mostly type I granite. The Mesozoic granites are all exposed in the four tectonic units in the study area, of which 222-206Ma is the main body of the granites, and the types of rocks are various, mainly of type I, with a small number of I-A transitional types. (3) The Paleoproterozoic granites in the North Qinling Mountains have negative values of epsilon Nd (t) (-15.8-14.5) and epsilon Hf (t) (-10.1-8.2) as well as negative values of epsilon Hf (t) (-10.1-8.2). The ages of the old Nd-Hf model are 3.19-2.96 Ga and 3.05-2.93 Ga, respectively, indicating that they are mainly derived from partial melting of the Middle Archean crustal materials, revealing the existence of deep Archean materials in the North Qinling Mountains. (4) The Nd-Hf isotopic compositions of the Neoproterozoic granites show that the granites are from the northern Qinling to the southern Qinling to the northern margin of the Yangtze Block, and that the granites are of epsilon Nd (t) The values of epsilon Hf (t) of the granites in the northern margin of the Yangtze massif vary greatly, reflecting the complexity of the basement composition in this area, except for the Mesoproterozoic Cenozoic crustal components. (5) Most of the Paleozoic granites have negative epsilon Nd (t) values and positive epsilon Hf (t) values, and their source areas are mainly partial melting of Mesoproterozoic Cenozoic crustal materials. The TDM and TDMC of granites in the southern margin of the North China Block are generally younger than those in the North Qinling Mountains, and some granites in the southern margin of the North China Block have higher epsilon Hf (t). The Nd-Hf decoupling and the Nd-Hf decoupling phenomena of low epsilon H(t) in some rocks in the North Qinling indicate that the source area of the granite is from the southern margin of the North China Block to the North Qinling. The participation of the ancient crustal components is gradually increasing, and the southern margin of the North China Block has a younger and deeper material composition than the North Qinling. (6) Mesozoic granite runs through the whole area, Nd-Hf isotope characteristics. The source areas of these granites are dominated by ancient crustal materials with a small amount of young components. However, the source areas of the Mesozoic granites in the North Qinling and South Qinling Mountains are more complex than those in the southern margin of the North China Block and the northern margin of the Yangtze Block, and contain more ancient crustal materials. There are more ancient and complicated deep material compositions in the Ling and South Qinling Mountains, while the deep material compositions in the southern margin of the North China Block and the northern margin of the Yangtze Block are relatively younger. (7) Crustal accretion in the middle of the Qinling orogenic belt mainly occurred in the Mesoproterozoic, North Qinling, South Qinling and the northern margin of the Yangtze Block. The lack of ancient crustal reformation events (before Paleoproterozoic) in the southern margin of the North China Block reflects that the southern margin of the North China Block in the study area may have different crustal evolution history and tectonic attributes from the northern Qinling, southern Qinling and northern margin of the Yangtze Block. (8) The comparative study shows that the deep material composition and the southern margin of the North China Block in the middle Qinling Mountains are different from those in the northern Qinling, southern Qinling The Qilian area is more similar to the eastern Qinling area, which provides a new basis for further understanding the evolution of different sections of the Qinling orogenic belt.
【學(xué)位授予單位】：中國地質(zhì)科學(xué)院
【學(xué)位級別】：博士
【學(xué)位授予年份】：2017
【分類號】：P588.121
[Abstract]:As an important part of the continental crust, granitic rocks record various information about the formation of continental crust, the interaction between crust and mantle, and the evolution of the lithosphere. Isotope geochemical tracing of granites can effectively reveal the composition of the continental lithosphere. The middle part of the Qinling orogenic belt is located in the transitional zone between the eastern and Western Qinling Mountains. It is a key area to understand the composition and development history of the Qinling orogenic belt. Based on the systematic collection of zircon U-Pb ages and Nd-Hf isotopic compositions of the granitic rocks in the study area, detailed field investigation and laboratory analysis have been carried out for the weakly studied rocks, and the age of the granites in the middle Qinling orogenic belt has been established. The Nd-Hf isotope composition characteristics of the granites are systematically analyzed, and the deep material composition and structure of the middle Qinling Mountains are discussed. The similarities and differences between the source areas and the deep material composition characteristics of the Mesozoic granites in the middle Qinling Mountains and those in the eastern Qinling Mountains are compared. The main achievements and understandings are as follows. (1) 95 pieces of zircon U-Pb collected systematically and 19 pieces of zircon U-Pb measured in this study. Age data show that the middle Qinling orogenic belt has undergone five stages of granitic magma evolution: Paleoproterozoic (1806-1741 Ma), Neoproterozoic (962-704 Ma), Early Paleozoic (470-424 Ma), Late Paleozoic (417-373 Ma) and Mesozoic (248-187 Ma). (2) The Paleoproterozoic granites are sporadically exposed in the North Qinling tectonic belt, and secondly gneissic biotite. The Neoproterozoic granites are mainly distributed in the northern margin of the Yangtze massif and sporadically distributed in other tectonic units. From early to late, the Neoproterozoic granites have a tendency to change from strongly deformed S-type granites to non-deformed I-A type granites. The Early Paleozoic granites are mainly distributed in the northern margin of the Yangtze massif. In the southern margin of the North China massif and the North Qinling tectonic belt, the rock types are mainly biotite monzonite and quartz diorite, mostly type I granite and a few type I-A transitional granite. Late Paleozoic granite is sporadically exposed in the southern margin of the North China massif and the North Qinling Mountains, mainly monzonite, a small amount of granodiorite and syenite, mostly type I granite. The Mesozoic granites are all exposed in the four tectonic units in the study area, of which 222-206Ma is the main body of the granites, and the types of rocks are various, mainly of type I, with a small number of I-A transitional types. (3) The Paleoproterozoic granites in the North Qinling Mountains have negative values of epsilon Nd (t) (-15.8-14.5) and epsilon Hf (t) (-10.1-8.2) as well as negative values of epsilon Hf (t) (-10.1-8.2). The ages of the old Nd-Hf model are 3.19-2.96 Ga and 3.05-2.93 Ga, respectively, indicating that they are mainly derived from partial melting of the Middle Archean crustal materials, revealing the existence of deep Archean materials in the North Qinling Mountains. (4) The Nd-Hf isotopic compositions of the Neoproterozoic granites show that the granites are from the northern Qinling to the southern Qinling to the northern margin of the Yangtze Block, and that the granites are of epsilon Nd (t) The values of epsilon Hf (t) of the granites in the northern margin of the Yangtze massif vary greatly, reflecting the complexity of the basement composition in this area, except for the Mesoproterozoic Cenozoic crustal components. (5) Most of the Paleozoic granites have negative epsilon Nd (t) values and positive epsilon Hf (t) values, and their source areas are mainly partial melting of Mesoproterozoic Cenozoic crustal materials. The TDM and TDMC of granites in the southern margin of the North China Block are generally younger than those in the North Qinling Mountains, and some granites in the southern margin of the North China Block have higher epsilon Hf (t). The Nd-Hf decoupling and the Nd-Hf decoupling phenomena of low epsilon H(t) in some rocks in the North Qinling indicate that the source area of the granite is from the southern margin of the North China Block to the North Qinling. The participation of the ancient crustal components is gradually increasing, and the southern margin of the North China Block has a younger and deeper material composition than the North Qinling. (6) Mesozoic granite runs through the whole area, Nd-Hf isotope characteristics. The source areas of these granites are dominated by ancient crustal materials with a small amount of young components. However, the source areas of the Mesozoic granites in the North Qinling and South Qinling Mountains are more complex than those in the southern margin of the North China Block and the northern margin of the Yangtze Block, and contain more ancient crustal materials. There are more ancient and complicated deep material compositions in the Ling and South Qinling Mountains, while the deep material compositions in the southern margin of the North China Block and the northern margin of the Yangtze Block are relatively younger. (7) Crustal accretion in the middle of the Qinling orogenic belt mainly occurred in the Mesoproterozoic, North Qinling, South Qinling and the northern margin of the Yangtze Block. The lack of ancient crustal reformation events (before Paleoproterozoic) in the southern margin of the North China Block reflects that the southern margin of the North China Block in the study area may have different crustal evolution history and tectonic attributes from the northern Qinling, southern Qinling and northern margin of the Yangtze Block. (8) The comparative study shows that the deep material composition and the southern margin of the North China Block in the middle Qinling Mountains are different from those in the northern Qinling, southern Qinling The Qilian area is more similar to the eastern Qinling area, which provides a new basis for further understanding the evolution of different sections of the Qinling orogenic belt.
【學(xué)位授予單位】：中國地質(zhì)科學(xué)院
【學(xué)位級別】：博士
【學(xué)位授予年份】：2017
【分類號】：P588.121
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