Architecture and mineral deposit settings of the Altaid orogenic collage: a revised model

The Altaids are an orogenic collage of Neoproterozoic–Paleozoic rocks located in the center of Eurasia. This collage consists of only three oroclinally bent Neoproterozoic–Early Paleozoic magmatic arcs (Kipchak, Tuva–Mongol, and Mugodzhar–Rudny Altai), separated by sutures of their former backarc basins, which were stitched by new generations of overlapping magmatic arcs. In addition, the Altaids host accreted fragments of the Neoproterozoic to Early Paleozoic oceanic island chains and Neoproterozoic to Cenozoic plume-related magmatic rocks superimposed on the accreted fragments. All these assemblages host important, many world-class, Late Proterozoic to Early Mesozoic gold, copper–molybdenum, lead–zinc, nickel and other deposits of various types.In the Late Proterozoic, during breakup of the supercontinent Rodinia, the Kipchak and Tuva–Mongol magmatic arcs were rifted off Eastern Europe–Siberia and Laurentia to produce oceanic backarc basins. In the Late Ordovician, the Siberian craton began its clockwise rotation with respect to Eastern Europe and this coincides with the beginning of formation of the Mugodzhar–Rudny Altai arc behind the Kipchak arc. These earlier arcs produced mostly Cu–Pb–Zn VMS deposits, although some important intrusion-related orogenic Au deposits formed during arc–arc collision events in the Middle Cambrian and Late Ordovician.The clockwise rotation of Siberia continued through the Paleozoic until the Early Permian producing several episodes of oroclinal bending, strike–slip duplication and reorganization of the magmatic arcs to produce the overlapping Kazakh–Mongol and Zharma-Saur–Valerianov–Beltau-Kurama arcs that welded the extinct Kipchak and Tuva–Mongol arcs. This resulted in amalgamation of the western portion of the Altaid orogenic collage in the Late Paleozoic. Its eastern portion amalgamated only in the early Mesozoic and was overlapped by the Transbaikal magmatic arc, which developed in response to subduction of the oceanic crust of the Paleo-Pacific Ocean. Several world-class Cu–(Mo)-porphyry, Cu–Pb–Zn VMS and intrusion-related Au mineral camps, which formed in the Altaids at this stage, coincided with the episodes of plate reorganization and oroclinal bending of magmatic arcs. Major Pb–Zn and Cu sedimentary rock-hosted deposits of Kazakhstan and Central Asia formed in backarc rifts, which developed on the earlier amalgamated fragments. Major orogenic gold deposits are intrusion-related deposits, often occurring within black shale-bearing sutured backarc basins with oceanic crust.After amalgamation of the western Altaids, this part of the collage and adjacent cratons were affected by the Siberian superplume, which ascended at the Permian–Triassic transition. This plume-related magmatism produced various deposits, such as famous Ni–Cu–PGE deposits of Norilsk in the northwest of the Siberian craton.In the early Mesozoic, the eastern Altaids were oroclinally bent together with the overlapping Transbaikal magmatic arc in response to the northward migration and anti-clockwise rotation of the North China craton. The following collision of the eastern portion of the Altaid collage with the Siberian craton formed the Mongol–Okhotsk suture zone, which still links the accretionary wedges of central Mongolia and Circum-Pacific belts. In the late Mesozoic, a system of continent-scale conjugate northwest-trending and northeast-trending strike–slip faults developed in response to the southward propagation of the Siberian craton with subsequent post-mineral offset of some metallogenic belts for as much as 70–400 km, possibly in response to spreading in the Canadian basin. India–Asia collision rejuvenated some of these faults and generated a system of impact rifts.     

非洲磁异常对地磁场结构及其长期变化的控制作用

地球非偶极磁场在主磁场结构及其长期变化中起着重要作用.非偶极磁场主要表现为行星尺度磁异常,它们是南大西洋磁异常、非洲磁异常、欧亚大陆磁异常、澳洲磁异常和北美磁异常.在这5块磁异常中,非洲磁异常对磁赤道的形状和位置以及全球长期变化特征有极大的影响.非洲磁异常的重要性主要表现在3方面：第一,由于异常区位于赤道这一特殊的地理位置,所以它极大地影响磁赤道的形状和位置.相对于偶极场的地磁赤道而言,异常区所在的中北非洲和中大西洋地区的磁赤道向北移动,最大移动量可达约15°.第二,非洲磁异常的快速西漂对全球长期变化的分布起着决定性作用,它在该异常区西边的中美洲形成了全球最主要的长期变化区,在1900~2005年期间,最大年变率Zmax超过200 nT/a.第三,非洲负磁异常区与其南面的南大西洋正磁异常区相结合,〖HJ〗它们的变化使西半球地磁场强度大大减弱,也使全球磁场发生显著畸变.这两块磁异常与深部的反极性斑区有着成因联系.     

非偶极子磁场西向漂移的频散特征

根据第8代国际参考地磁场的资料,本文采用Briggs方法对1900～2000年期间m=1～10次谐波的磁位的全球平均西向漂移速度进行了计算和分析,得出了与Hide的理论预测完全不同的频散特征,即地磁场西向漂移呈现出负频散特征.本文还就Briggs方法得到的结果与采用Malin纬度剖面法的结果进行了比较和讨论,结果表明,正是由于非偶极子磁场的某些谐波分量及其漂移速度的全球分布存在着纬度依赖性,导致了两种方法计算出的个别谐波的漂移速度存在着较大的差异.     

Study on the current structure of the thermohaline front in the southeastern entrance of the Yellow Sea during winter

A thermohaline front is located at the southeastern entrance of the Yellow Sea in winter, and it is generated by the intrusion of warm saline water into the Yellow Sea caused by a strong northerly wind. Recently, a westward transversal current traveling away from the west coast of Korea toward the open sea area along the front was reported. The westward transversal current is dominant in the surface layer during the temperature inversion period. The formation and structure of this current are examined using a numerical vertical ocean-slice model. When two different water masses meet, a front is formed and adjusted geostrophically. In this frontal zone, a horizontal pressure gradient flow by the vertically inclined isopycnal occurs under the thermal wind process in a baroclinic effect, and the cold fresh coastal water moves westward along the front in the upper layer. The barotropic effect across the front and the bottom friction effect strengthen the westward component of the velocity. The velocity of the bottom layer decreases remarkably in the increase of the bottom drag coefficient. This means that the bottom friction with the strong background tidal current causes a reduction in the current in the bottom layer.     

内蒙古二连盆地早三叠世地层及孢粉组合的发现

二连盆地曾被认为是缺失三叠纪沉积的地区。通过阿拉坦合力凹陷坦参１井的孢粉化石分析,首次证实了在二连盆地存在早三叠世地层。坦参１井的下三叠统的视厚度１ ３３９ｍ （井深５５８～１ ８９７ｍ ）,以紫红色、棕红色的泥岩为主,夹灰绿色泥岩,向下岩性变粗,含砾泥岩、砂砾岩增加,与上覆侏罗系及下伏上二叠统皆呈不整合接触。井深７００～１ ８９６ｍ 产以Ｌｉｍ ａｔｕｌａｓｐｏｒｉｔｅｓ大量出现、Ｔａｅｎｉａｅｓｐｏｒｉｔｅｓ具一定含量、出现Ｌｕｎｄｂｌａｄｉｓｐｏｒａ、Ａｒａｔｒｉｓｐｏｒｉｔｅｓ和Ｌｕｅｃｋｉｓｐｏｒｉｔｅｓ为主要特征的早三叠世孢粉化石组合。这一发现对重新认识二连盆地的地质发育历史颇有意义     

内蒙古中部太古代麻粒岩递增变质成因

由早元古代造山运动早期自北西向南东推覆作用引起并使之得以保存的太古代变质作用强度逆转的剖面出露在内蒙古中部的固阳－武川地区。变质镁铁质岩石中矿物组合的变化在低级区为阳起石＋绿帘石＋绿泥石→普通角闪石＋钠长石→普通角闪石＋斜长石→石榴石（或透辉石）＋普通角闪石＋斜长石→无色角闪岩＋钠长石;在高级区为普通角闪石＋斜长石→紫苏辉石＋透辉石＋斜长石→石榴石＋透辉石（２）＋石英。这些变化已被用来恢复太古代时期从低绿片岩相到麻粒岩相的递增变质序列及尔后经历的近等压冷却的退变质作用过程。高级区变质表壳岩与低级区绿岩带的岩石组合、岩石化学、岩石地球化学和变质作用演化序列的对比研究结果表明,两者属于太古代同一火山－沉积单位。其变质程度的不同起因于在经受区域性递增变质作用时,两者处在地壳的不同位置     

西太平洋副热带高压西伸过程的合成特征及其可能机理

利用1970~2000年6月NCEP/NCAR逐日再分析资料,根据(20~30°N,115~125°E)区域内500 hPa的涡度变化选取了12次西太平洋副热带高压西伸过程,合成了西太平洋副热带高压西伸过程中对流层高层和低层的环流演变特征。结果表明,(20~30°N,115~125°E)区域内500 hPa负涡度的增加对应着西太平洋副热带高压的西伸过程。在副热带高压西伸过程中,对流层高层南亚高压的中心位置虽然稳定少动,但是由于日本东南部反气旋的西移,使得南亚高压东侧的脊明显地加强东伸,这可能对对流层中层副热带高压的西伸具有重要作用。在对流层低层,源于澳大利亚北侧的气流越过赤道向北传播,经由南海季风槽后到达我国江淮流域,从而影响副热带高压西侧的偏南气流。     

Early Mesozoic tectono-magmatic activity and mineralization in Northeast China: evidence from Re–Os to U–Pb studies of the Taipingchuan porphyry Cu–Mo deposit in the Derbugan metallogenic belt

The Taipingchuan Cu–Mo deposit is a recently discovered large porphyry deposit located in the north of the Derbugan metallogenic belt of northeastern China. The geochronological data of the deposit yielded a Late Triassic zircon U–Pb age of 202 ± 6 Ma from a granodiorite porphyry that hosts the Cu–Mo mineralization. Measured Re–Os isotopes of seven disseminated molybdenite samples yielded an isochron age of 200 ± 5 Ma with mean square of weighted deviates of 2.7, while those of seven veinlet molybdenite samples also produced an isochron age of 200.1 ± 2.5 Ma and mean square of weighted deviates of 3.3. These isochron ages show that a Cu–Mo mineralization event occurred at ca. 200 Ma. Based on regional tectonic evolution, we propose that the Late Triassic Cu–Mo mineralization of the host porphyry in the Derbugan metallogenic belt was mainly associated with the subduction of the Mongol–Okhotsk Ocean slab under the Ergun block, contrary to previous suggestion that it was related to the subduction of the Mesozoic Palaeo-Pacific plate.     

2012年12月20-23日巴州寒潮降雪天气的特征分析

利用常规观测资料、自动站、T639客观分析资料,结合天气学原理和天气动力学诊断分析方法,对2012年12月20-23日巴音郭楞蒙古自治州（以下简称巴州）的寒潮天气过程的成因和降雪天气特征进行分析,并给出巴州降雪天气概念模型。结果表明：这次寒潮降雪过程是北欧阻塞高压向东南衰退,导致脊前横槽转成竖槽东南移,高空冷空气南压至40°N附近,造成巴州强降温、强降雪等寒潮天气,降雪阶段关键影响系统是700 hPa上的冷暖切变和风场辐合,水汽主要源自中低层西北方的经向和低层东南方的纬向输送;后续的冷凝降雪和阴雪阶段天气局地特征明显,水汽源自850 hPa至近地层局地的垂直输送。     

东亚大陆磁异常的西向漂移

西向漂移是地磁场长期变化最重要的特点之一,而西漂最显著的部分是非偶极子场部分．本文以１９００-２０００年国际参考地磁场（ＩＧＲＦ）为依据,运用无线电科学中的"移动变形图案相关分析"方法对近百年来东亚大陆磁异常的漂移运动进行了分析,得到磁异常各分量漂移矢量随时间的变化．结果表明,最能代表地磁场西漂特征的Ｚ分量异常近百年来平均西漂速度为０.０７°／ａ,明显小于全球磁场西漂的平均速度０．２°／ａ．Ｚ分量还显示出０.０２°／ａ的缓慢北向漂移．详细分析还表明,东亚大陆磁异常的漂移分为３个阶段：１９００-１９３０年为较快的西漂,平均速度为０.１０°／ａ;１９３０-１９８０年为西北向漂移,平均西漂速度分量０．０７°／ａ,北漂速度分量为０．０４°／ａ;１９８０年后漂移几乎停止,并有转为东漂的迹象．