Zircon U–Pb ages and tectonic implications of 'Early Paleozoic' granitoids at Yanbian, Jilin Province, northeast China

Abstract   The Yanbian area is located in the eastern part of the Central Asian Orogenic Belt (CAOB) of China and is characterized by widespread Phanerozoic granitic intrusions. It was previously thought that the Yanbian granitoids were mainly emplaced in the Early Paleozoic (so-called 'Caledonian' granitoids), extending east–west along the northern margin of the North China craton. However, few of them have been precisely dated; therefore, five typical 'Caledonian' granitic intrusions (the Huangniling, Dakai, Mengshan, Gaoling and Bailiping batholiths) were selected for U–Pb zircon isotopic study. New-age data show that emplacement of these granitoids extended from the Late Paleozoic to Late Mesozoic (285–116 Ma). This indicates that no 'Caledonian' granitic belt exists along the northern margin of the North China craton. The granitoids can be subdivided into four episodes based on our new data: Early Permian (285 ± 9 Ma), Early Triassic (249–245 Ma), Jurassic (192–168 Ma) and Cretaceous (119–116 Ma). The 285 ± 9 Ma tonalite was most likely related to subduction of the Paleo-Asian Oceanic Plate beneath the North China craton, followed by Triassic (249–245 Ma) syn-collisional monzogranites, representing the collision of the CAOB orogenic collage with the North China craton and final closure of the Paleo-Asian Ocean. The Jurassic granitoids resulted from subduction of the Paleo-Pacific plate and subsequent collision of the Jiamusi–Khanka Massif with the existing continent, assembled in the Triassic. The Early Cretaceous granitoids formed in an extensional setting along the eastern Asian continental margin.     

The Liaonan metamorphic core complex, Southeastern Liaoning Province, North China: A likely contributor to Cretaceous rotation of Eastern Liaoning, Korea and contiguous areas

The Mesozoic Liaonan metamorphic core complex (mcc) of the southeastern Liaoning province, North China, is an asymmetric Cordilleran-style complex with a west-rooting master detachment fault, the Jinzhou fault. A thick sequence of lower plate, fault-related mylonitic and gneissic rocks derived from Archean and Early Cretaceous crystalline protoliths has been transported ESE-ward from mid-crustal depths. U–Pb ages of lower plate syntectonic plutons (ca. 130–120 Ma), ⁴⁰Ar–³⁹Ar cooling ages in the mylonitic and gneissic sequence (ca. 120–110 Ma), and a Cretaceous supradetachment basin attest to the Early Cretaceous age of this extensional complex. The recent discovery of the coeval and similarly west-rooting Waziyu mcc in western Liaoning [Darby, B.J., Davis, G.A., Zhang, X., Wu, F., Wilde, S., Yang, J., 2004. The newly discovered Waziyu metamorphic core complex, Yiwulushan, western Liaoning Province, North China. Earth Science Frontiers 11, 145–155] indicates that the Gulf of Liaoning, which lies between the two complexes, was the center of a region of major crustal extension.Clockwise crustal rotation of a large region including eastern Liaoning province and the Korean Peninsula with respect to a non-rotated North China block has been conclusively documented by paleomagnetic studies over the past decade. The timing of this rotation and the reasons for it are controversial. Lin et al. [Lin, W., Chen, Y., Faure, M., Wang, Q., 2003. Tectonic implication of new Late Cretaceous paleomagnetic constraints from Eastern Liaoning Peninsula, NE China. Journal of Geophysical Research 108 (B-6) (EPM 5-1 to 5-17)] proposed that a clockwise rotation of 22.5° ± 10.2° was largely post-Early Cretaceous in age, and was the consequence of extension within a crustal domain that tapers southwards towards the Bohai Sea (of which the Gulf of Liaoning is the northernmost part). Paleomagnetic studies of Early Cretaceous strata (ca 134–120 Ma) in the Yixian–Fuxin supradetachment basin of the Waziyu mcc indicate the non-rotation of North China and the basin [Zhu, R.X., Shao, J.A., Pan, Y.X., Shi, R.P., Shi, G.H., Li, D.M., 2002. Paleomagnetic data from Early Cretaceous volcanic rocks of West Liaoning: evidence for intracontinental rotation. Chinese Science Bulletin 47, 1832–1837]. Such upper-plate non-rotation supports our conclusion that the lower plates of the Waziyu and Liaonan metamorphic core complexes were displaced ESE-ward in an absolute sense away from the stable North China block, thus contributing to the rotation of Korea and contiguous areas. Rotation is inferred to have affected only the upper crust above mid-crustal levels into which we believe the Jinzhou and Waziyu detachment fault zones flattened. If this is the case, the regional Tan Lu fault that lies between the two core complexes was truncated at mid-crustal depth, since in areas to the south it forms the boundary between the North and South China lithospheric blocks. It is noteworthy that the two extensional complexes lie not far north of the Bohai Bay, the area proposed by Lin et al. [Lin, W., Chen, Y., Faure, M., Wang, Q., 2003. Tectonic implication of new Late Cretaceous paleomagnetic constraints from Eastern Liaoning Peninsula, NE China. Journal of Geophysical Research 108 (B-6) (EPM 5-1 to 5-17)] as the site of the pole of rotation for Korea's clockwise displacement.Lin et al. [Lin, W., Chen, Y., Faure, M., Wang, Q., 2003. Tectonic implication of new Late Cretaceous paleomagnetic constraints from Eastern Liaoning Peninsula, NE China. Journal of Geophysical Research 108 (B-6) (EPM 5-1 to 5-17)] were unaware of the Liaonan and Waziyu mcc's and argued that most of the regional block rotation was post-Early Cretaceous and, in part, early Cenozoic. However, the ca. 130–120 Ma ages of the two Liaoning mcc's and a Songliao basin mcc (Xujiaweizi), the latter discovered only by recent drilling through its younger stratigraphic cover, support our and some Korean coworkers' conclusions that most of the clockwise rotation was Early Cretaceous.     

苏鲁超高压变质带南部浅变质岩的全岩Rb-Sr同位素年龄

提供了苏鲁超高压变质带南部震旦纪浅变质千枚岩的全岩Rb Sr同位素年龄测试数据 ,获得了 2 2 1± 14Ma的等时线年龄。对测试结果的分析认为 :该年龄为浅变质岩的变质年龄。区域调查对比表明 ,低绿片岩相变质作用在造山带组成岩石中普遍存在 ,并叠加于超高压变质岩石 ,因而上述年龄代表在印支期存在普遍的退变质作用年龄。浅变质岩中印支期同位素年龄的获得 ,对正确认识超高压变质带的演化具有重要意义。     

三度剩余重力异常源全方位成像的理论和方法

根据三度体引力位V（p）和引力场（总引力场F（p）及其垂向分量△g（p））的球谐分析理论,在球坐标系内,就起伏观测面上的三度体剩余重力异常△g（p）,提出了一种异常源全方位成像的理论和方法.其特点是：直接利用起伏观测面上的异常数据；把垂直引力场△g（p）的全方位延拓及其向总引力场F（p）和引力位V（p）的转换,和△g（p）异常源质量、质心、形态、边界位置反演等诸多问题的解决有机地结合起来,给出了多方位的场源图像,能够为最优化反演方法提供初始模型选择的依据.     

1980．0年东亚地区地磁场的勒让德多项式模型

根据中国、原苏联等地区的地磁复测点和地磁台资料，利用勒让德多项式方法，计算出１９８０．０年东亚地区的地磁场模型，绘制出总强度（Ｆ）、磁偏角（Ｄ）和磁倾角（Ｉ）地磁图．地磁场模型的均方偏差分别为：总强度１４４．６ｎＴ，磁偏角１９．１′，磁倾角８．５′．将勒让德多项式模型与ＤＧＲＦ１９８０进行了比较，并绘制出总强度的差值分布图．本文计算出来的地磁场勒让德多项式模型能较好地表示东亚地区地磁场的分布．     

辽北太古宙变质岩中的振荡型矿物环带及意义

对辽北太古宙层状变质岩系中石榴石、黑云母的成分分析发现,其中存在明显的振荡型矿物环带。对其形成机理的研究表明,这是矿物在结晶过程中由于偏离理想状态而形成的一种非平衡态自组织现象,即耗散结构。矿物内部成分的振荡性并不是由于外界条件的周期变化所造成的,而是体系内部固有属性的反映。这种认识对研究变质作用的动力学过程具有重要的借鉴意义,文中还就这种振荡性矿物环带在变质作用研究中的意义作了进一步的阐述。     

Analysis of the rising and sinking movement of the crust in Qinghai－Xizang Plateau，China

ＡｎａｌｙｓｉｓｏｆｔｈｅｒｉｓｉｎｇａｎｄｓｉｎｋｉｎｇｍｏｖｅｍｅｎｔｏｆｔｈｅｃｒｕｓｔｉｎＱｉｎｇｈａｉ－ＸｉｚａｎｇＰｌａｔｅａｕ，ＣｈｉｎａＺｉ－ＬｉｎｇＬＵ（吕梓龄），ＺｈｅｎｇＺＨＵＡＮＧ（庄真），Ｚｈｕ－ＷｕＦＵ（傅竹武），Ｊｉａ－...     

中国满洲里－绥芬河地学断面域古生代构造单元及其地质演化

额尔古纳－兴安地体（ＥＴ）、松嫩－张广才岭地体（ＳＴ）、佳木斯地体（ＳＴ）是断面域古生代具有独立发展演化历史的地质构造单元，ＥＴ与西伯利亚地台具有亲缘性，ＳＴ－ＪＴ与华北和西伯利亚地台均无亲缘关系；ＳＴ与ＪＴ、ＥＴ与ＳＴ－ＪＴ分别沿牡丹江和嫩江断裂拼贴，最终形成统一亚洲大陆的一部分。     

铜厂沟金矿床的地球化学特征及成矿远景

通过对青海铜厂沟金矿床地质特征、矿化蚀变带地球化学特征研究,提出该矿床为构造蚀变岩型矿床。从已查明南、北矿带的矿化特征分析,指出西部具有存在较大规模矿化体的前景,应进一步加强该地区的勘探及研究力度,以期获得找矿突破。     

Computation and analysis of the geomagnetic field model in China and its adjacent area for 2003

Based on the geomagnetic data at 135 stations and 35 observatories in China in 2003, the Taylor polynomial model and the spherical cap harmonic model in China and its adjacent area for 2003 were established. In the model calculation, the truncation order of the model and the influences of the boundary restriction on the model calculation were carefully analyzed. The results show that the geomagnetic data used are precise and reliable, and the selection of the truncation order is reasonable. The Taylor polynomial model and the spherical cap harmonic model in China and its adjacent area established in this paper are consistent very well.