秦岭造山带中段花岗岩的时空格架、源区物质及其对地壳深部物质组成的示踪
发布时间：2018-08-22 18:19
【摘要】：秦岭造山带的深部物质组成是人们一直关注的问题。花岗质岩石作为大陆地壳的重要组成部分,记载了陆壳的形成、壳幔相互作用以及岩石圈演化的各种信息,通过花岗岩的同位素地球化学示踪研究,能够有效揭示大陆岩石圈物质组成、区别陆块地球化学差异性和相关性、以及反演地球深部的演化过程。秦岭造山带中段位于东西秦岭的交接转换地带,是了解秦岭造山带组成结构和发育历史的关键地带。古元古代至中生代花岗岩在该地区广泛发育,为开展该区域的花岗岩同位素填图及深部物质示踪研究提供了可能。在系统收集研究区花岗质岩石的锆石U-Pb年龄、Nd-Hf同位素组成等资料的基础上,本次研究针对研究薄弱的岩体开展了详细的野外调查和室内分析,建立了秦岭造山带中段花岗岩的年代学格架,系统分析了花岗岩的Nd-Hf同位素组成特征,探讨了秦岭中段深部物质组成结构,对比秦岭中段与东秦岭中生代花岗岩的源区和深部物质组成特征的异同,取得了如下主要成果和认识。(1)系统收集的95件和本次实测的19件锆石U-Pb年龄数据显示,秦岭造山带中段花岗岩浆演化大致经历了古元古代(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)古元古代花岗岩零星出露于北秦岭构造带中,以片麻状黑云母二长花岗岩为主,为强变形的Ⅰ型花岗岩。新元古代花岗岩主要分布在扬子地块北缘,在其他构造单元中零星展布,该期花岗岩自早至晚具有由强变形的S型花岗岩向无变形的Ⅰ型或I-A过渡型花岗岩变化的趋势。早古生代花岗岩主要分布在华北地块南缘和北秦岭构造带,岩石类型以黑云母二长花岗岩和石英闪长岩为主,多为Ⅰ型花岗岩,少量见I-A过渡型。晚古生代花岗岩在华北地块南缘和北秦岭零星出露,以二长花岗岩为主,见少量的花岗闪长岩和正长花岗岩,多为Ⅰ型花岗岩。中生代花岗岩在研究区的4个构造单元内均有出露,其中,222～206Ma是该期花岗岩的主体,岩石类型多样,以Ⅰ型为主,伴有少量的I-A过渡型。(3)分布于北秦岭的古元古代花岗岩具有负的εNd(t)值(-15.8～-14.5)和εHf(t)值(-10.1～-8.2)以及古老的Nd-Hf模式年龄,分别为3.19～2.96Ga、3.05～2.93Ga,表明其主要来源于中太古代地壳物质的部分熔融,揭示北秦岭存在太古宙的深部物质信息。(4)新元古代花岗岩的Nd-Hf同位素组成显示,自北秦岭→南秦岭→扬子地块北缘,花岗岩的εNd(t)值逐渐增大,TDM逐渐变年轻,源区物质组成中年轻组分的参与逐渐增多,反映其深部物质组成也具有逐渐变年轻的趋势。另外,扬子地块北缘花岗岩的εHf(t)值变化较大,反映该区域的基底组成比较复杂,除了中元古代新生的地壳组分外,还有少量太古宙-古元古代的古老物质。(5)古生代花岗岩多具有负的εNd(t)值和正的εHf(t)值,其源区主要为中元古代新生地壳物质的部分熔融。华北地块南缘花岗岩的TDM和TDMC一般比北秦岭年轻,且华北地块南缘个别花岗岩具有εHf(t)高的Nd-Hf解耦,而北秦岭个别岩体具有εH(t)低的Nd-Hf解耦现象,指示花岗岩的源区组成自华北地块南缘→北秦岭,古老地壳组分的参与逐渐增多,华北地块南缘具有比北秦岭更年轻的深部物质组成。(6)中生代花岗岩贯穿全区,Nd-Hf同位素特征表明这些花岗岩的源区均以古老壳源物质为主,并有少量的年轻组分参与。但北秦岭和南秦岭中生代花岗岩的源区组成比华北地块南缘和扬子地块北缘复杂,其中包含了更多的古老地壳物质。花岗岩的Nd-Hf同位素组成示踪显示,北秦岭和南秦岭具有较古老且复杂的深部物质组成,而华北地块南缘和扬子地块北缘的深部物质组成相对较年轻。(7)秦岭造山带中段的地壳增生主要发生在中元古代,北秦岭、南秦岭和扬子地块北缘中还可见少量太古宙和古元古代的地壳再造,而华北地块南缘缺少古老的(古元古代以前)的地壳改造事件,反映出研究区华北地块南缘可能具有与北秦岭、南秦岭、扬子地块北缘不同的地壳演化历史和构造属性。(8)对比研究显示,秦岭中段地区华北地块南缘的深部物质组成与祁连地区更为相似,而与东秦岭地区的不同,这为进一步认识秦岭造山带不同区段的演化提供了新的依据。
[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.
【学位授予单位】：中国地质科学院
【学位级别】：博士
【学位授予年份】：2017
【分类号】：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.
【学位授予单位】：中国地质科学院
【学位级别】：博士
【学位授予年份】：2017
【分类号】：P588.121
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