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首页> 外文期刊>Journal of Asian earth sciences >Evolution Of The Solonker Suture Zone: Constraints From Zircon U-pb Ages, Hf Isotopic Ratios And Whole-rock Nd-sr Isotope Compositions Of Subduction- And Collision-related Magmas And Forearc Sediments
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Evolution Of The Solonker Suture Zone: Constraints From Zircon U-pb Ages, Hf Isotopic Ratios And Whole-rock Nd-sr Isotope Compositions Of Subduction- And Collision-related Magmas And Forearc Sediments

机译：Solonker缝合带的演化：锆石U-pb年龄，H同位素比率以及俯冲和与碰撞有关的岩浆和前臂沉积物的全岩Nd-sr同位素组成的约束

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摘要

The Solonker zone in northern Inner Mongolia (China) is considered as the suture between the North China Craton and the South Mongolian microcontinent. Two magmatic belts are recognized along the suture zone: a subduction-related magmatic belt (represented by the Baolidao arc rocks), and a younger, collision-related granite belt (represented by the Halatu granites). We use zircon U-Pb ages, zircon in-situ Hf isotopic analyses and whole-rock Nd-Sr isotopic data of the two magmatic belts and related fore-arc sediments (the Xilinhot metamorphic complex) to constrain timing of the suturing and to discuss the petrogenesis of the magmatic rocks. A gabbroic diorite (BLD-1) of the Baolidao arc was dated at 310 ± 5 Ma (by SHRIMP). This sample shows an ε_(Nd)(t) value of +2.5 and I_(sr) of 0.7052. Hf isotopic analyses on 25 zircons from the same sample show ε_(Hf)(t) = +5.4 to +11.5. Another diorite sample (XH-2) of the same arc from south of Xilinhot displays even more "depleted" isotopic compositions, with ε_(Nd)(t) = +5.6 and I_(Sr) = 0.7037. The main population of zircons from this sample have highly variable and depleted Hf isotopic compositions (ε_(Hf)(t) = 0-18.3). The large variation in Hf isotopic composition of zircons (with largely the same crystallization age) from a single pluton is explained by a mixing process between depleted mantle-derived magma and continental crust in an active continental arc setting. The Halatu granite (HLT-2) was dated at 234 ± 7 Ma (by SHRIMP). Zircons from the granite also show a large variation of ε_(Hf)(t) values (+9.1 to -26), despite most samples having whole-rock ε_(Hf)(t) > +2. The large variation in ε_(Hf)(t) values suggests that the granite formed probably by partial melting of two source regions - a dominant juvenile crust and a subordinate old continental crust. Most zircons from the Xilinhot metamorphic complex show ages comparable with those of the Baolidao arc rocks, suggesting that the protolith of the metamorphic complex was probably deposited during or after arc magmatism. Some zircons, however, show Precambrian ages that fall into two groups: one with ages of 780-900 Ma, resembling those from the South Mongolian microcontinent, and the other with ages of 1524-2900 Ma, similar to those of the North China Craton. Thus, the protolith of the metamorphic complex probably formed in a forearc basin during convergence of the two continents, and metamorphosed subsequently during collision in the late Paleozoic. Our zircon age data thus constrain timing of collision between the South Mongolian microcontinent and the North China Craton to have been between 296 and 234 Ma.
机译：内蒙古北部（中国）的Solonker带被认为是华北克拉通和蒙古南部微大陆之间的缝合线。沿缝合带识别出两条岩浆带：与俯冲有关的岩浆带（以宝利道弧岩为代表）和较年轻的与碰撞有关的花岗岩带（由哈拉图花岗岩为代表）。我们使用锆石的U-Pb年龄，锆石的原位Hf同位素分析以及两个岩浆带和相关的前弧沉积物（锡林浩特变质复合体）的全岩Nd-Sr同位素数据来限制缝合的时间，并讨论岩浆岩的成岩作用。宝利道弧的辉长岩闪长岩（BLD-1）的年代为310±5 Ma（由SHRIMP提供）。该样本显示ε_（Nd）（t）值为+ 2.5，I_（sr）为0.7052。对来自同一样品的25个锆石进行的Hf同位素分析显示ε_（Hf）（t）= +5.4至+11.5。来自锡林浩特以南的同一弧线的另一个闪长岩样品（XH-2）显示出更多的“耗尽”同位素组成，ε_（Nd）（t）= +5.6和I_（Sr）= 0.7037。该样品中的主要锆石种群具有高度可变的Hf同位素组成（ε_（Hf）（t）= 0-18.3）。单个活动岩体中锆石的Hf同位素组成（具有大致相同的结晶年龄）存在很大差异，这是由于活跃的大陆弧环境中地幔源岩浆和大陆壳之间的混合过程所致。 Halatu花岗岩（HLT-2）的年代为234±7 Ma（由SHRIMP提供）。尽管大多数样品的全岩石ε_（Hf）（t）> +2，但花岗岩中的锆石也显示出ε_（Hf）（t）值的较大变化（+9.1至-26）。 ε_（Hf）（t）值的较大变化表明，该花岗岩可能是由两个源区的部分熔融形成的-一个主要的幼年壳和一个从属的旧大陆壳。锡林浩特变质带中的大多数锆石显示出与宝里岛弧岩相当的年龄，表明该变质体的原石可能是在弧岩浆作用期间或之后沉积的。但是，一些锆石的前寒武纪年龄分为两组：一组年龄为780-900 Ma，类似于来自南蒙古微大陆的年龄；另一组年龄为1524-2900 Ma，类似于华北克拉通的年龄。 。因此，变质复合体的原石很可能在两大陆汇聚期间形成于前臂盆地，随后在古生代晚期发生碰撞时变质。因此，我们的锆石年龄数据将南蒙古微大陆与华北克拉通之间的碰撞时间限制在296至234 Ma之间。

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