THE DISCUSSION FOR THE NEW ACTIVITY OF THE TIANQUAN SEGMENT OF LONGMENSHAN FAULT ZONE AND ITS RELATIONSHIP TO THE 1327 TIANQUAN EARTHQUAKE,SICHUAN

The 2008 Wenchuan earthquake occurred along the Longmen Shan fault zone, only five years later, another M7 Lushan earthquake struck the southern segment where its seismic risk has been highly focused by multiple geoscientists since this event. Through geological investigations and paleoseismic trenching, we suggest that the segment along the Shuangshi-Dachuan Fault at south of the seismogenic structure of the Lushan earthquake is active during Holocene. Along the fault, some discontinuous fault trough valleys developed and the fault dislocated the late Quaternary strata as the trench exposed. Based on analysis of historical records of earthquakes, we suggest that the epicenter of the 1327 Tianquan earthquake should be located near Tianquan and associated with the Shuangshi-Dachuan Fault. Furthermore, we compared the ranges of felt earthquakes(the 2013 M7 Lushan earthquake and the 1970 M_S6.2 Dayi earthquake)and suggest that the magnitude of the 1327 Tianquan earthquake is more possible between 6½ and 7. The southern segment of the Longmen Shan fault zone behaves as a thrust fault system consisting of several sub-paralleled faults and its deep structure shows multiple layers of decollement, which might disperse strain accumulation effectively and make the thrust system propagate forward into the foreland basin, creating a new decollement on a gypsum-salt bed. The soft bed is thick and does not facilitate to constrain fault deformation and accumulate strain, which produces a weak surface tectonic expression and seismic activity along the southern segment, this is quite different from that of the middle and northern segments of the Longmen Shan fault zone.     

龙门山构造带晚新生代剥蚀作用与均衡隆升的地表过程研究

基于SRTM DEM数据,以青藏高原东缘龙门山地区为研究区域,本文通过条带状剖面分析、古地形面(残余面)恢复以及弹性挠曲模拟等研究手段,计算了青藏高原东缘龙门山地区晚新生代地壳均衡隆升与地表剥蚀之间的定量关系,探讨了龙门山地区表面剥蚀作用与均衡隆升作用之间的地表响应过程,从而为研究青藏高原东缘龙门山地区晚新生代以来的剥蚀—成山作用的隆升机制提供定量依据。研究表明:(1)晚新生代以来龙门山的地表剥蚀量为(0.74～1.14)×105km3;(2)大量的地表剥蚀作用驱动了青藏高原东缘龙门山的地壳均衡反弹,使龙门山隆升了近2 km;(3)龙门山地区地表剥蚀量和均衡隆升量具有空间匹配性,岷山断块及龙门山中、南段的均衡隆升量高于青藏高原东缘其它区域,反映了晚新生代以来龙门山地区在不同分段内差异化的构造地貌形态及与剥蚀—隆升相关的地表过程。(4)龙门山的隆升是多期、多种隆升机制叠加的产物,其隆升过程具有历史性和复合性。均衡隆升和剥蚀作用在相似的时间尺度上和空间尺度上控制着龙门山地貌的形成,约束了青藏高原东缘龙门山的隆升机制。     

生物酶改良膨胀土的修正殷宗泽模型

以描述生物酶改良膨胀土的应力?应变关系为研究目的,提出基于生物酶掺量的修正殷宗泽模型。开展了一系列三轴排水剪切试验。对不同生物酶掺量下改良膨胀土的弹性形变演化规律进行了分析,同时研究了生物酶掺量与剪切压缩、剪切膨胀相关的屈服面形状的演化规律,以及与破坏线方程的演化规律。在此基础上分析了生物酶掺量对殷宗泽模型的参数影响规律。引入生物酶掺量作为修正殷宗泽模型的修正因子,最终对殷宗泽模型进行了修正。研究结果表明：生物酶能有效地提高改良膨胀土的力学性能,修正殷宗泽模型能够很好地描述生物酶改良膨胀土的土体本构关系。对比修正殷宗泽模型的理论计算值与试验值,两者具有很高的吻合度,且修正殷宗泽模型的参数确定方法与殷宗泽模型参数确定方法相同。     

Zircon and molybdenite geochronology and geochemistry of the Kalmakyr porphyry Cu–Au deposit,Almalyk district,Uzbekistan: Implications for mineralization processes

Copper, gold and molybdenum mineralization of the Kalmakyr porphyry deposit in Uzbek Tien Shan occurs as stockworks, veinlets and disseminations in the phyllic and K-silicate alteration zones developed predominantly in a middle to late Carboniferous intrusive complex composed of monzonite and granodiorite porphyry. Zircon U–Pb dating yielded an age of 327.2 ± 5.6 Ma for the ore-hosting monzonite and an age of 313.6 ± 2.8 Ma for the ore-bearing granodiorite porphyry. Re–Os dating of seven molybdenite samples from stockwork and veinlet ores yielded model ages from 313.2 to 306.3 Ma, with two well-constrained isochron ages of 307.6 ± 2.5 Ma (five stockwork ores) and 309.1 ± 2.2 Ma (five stockwork ores and two veinlet ores), respectively. These results indicate that Cu–Au mineralization post-dated the emplacement of the monzonite, started right after the emplacement of the granodiorite porphyry, and lasted for ca. 7 Ma afterward. The geochronological and geochemical data suggest that the Kalmakyr deposit was formed in a late Carboniferous mature magmatic arc setting, probably related to the latest subduction process of the Turkestan Ocean beneath the Middle Tien Shan. The ε_Hf(t) values of zircon grains from the monzonite vary from +11 to +1.7, with an average of +5.1, and those of zircon grains from the granodiorite porphyry range from +5.7 to −1.8, with an average of +2.4. These data indicate that the magma of both monzonite and granodiorite porphyry was derived from partial melting of a thickened lower crust with input of mantle components and variable crustal contamination, and that there was more mantle contribution to the formation of the monzonite than the granodiorite porphyry. The high rhenium concentrations of molybdenite (98–899 ppm) also indicate major mantle contribution of rhenium and by inference ore metals. The relatively high Eu_N/Eu_N¹ values (average 0.68), Ce⁴⁺/Ce³ values (average 890) and Ce/Nd values (average 36.8) for zircon grains from the granodiorite porphyry than those from the monzonite (average Eu_N/Eu_N¹ = 0.33, average Ce⁴⁺/Ce³ = 624, average Ce/Nd = 3.9) suggest that the magma for the syn-mineralization granodiorite porphyry has higher oxygen fugacity than that for the pre-mineralization monzonite. Based on these data, it is proposed that while the monzonite was emplaced, the oxygen fugacity and volatile contents in the magma were relatively low, and ore metals might disperse in the intrusive rock, whereas when the granodiorite porphyry was emplaced, the oxygen fugacity and volatile contents in the magma were increased, favoring copper and gold enrichment in the magmatic fluids. The Kalmakyr deposit formed from a long-lived magmatic-hydrothermal system connected with fertile magmatic sources in relation to the subduction of the Turkestan Ocean beneath the Middle Tien Shan.     

龙门山造山带的早期活动及其对造山作用的启示

2008年汶川地震后,在映秀-北川同震地表破裂带南段虹口乡八角庙地区发现有假玄武玻璃出露于~240m宽的断裂带内,代表了断裂带以往地震和断裂活动的直接产物。这套假玄武玻璃的高温熔融成因得到了元素地球化学和熔融结构的证实。玻璃基质、蚀变矿物和碎屑斑晶的化学分析显示假玄武玻璃继承了碎裂岩/超碎裂岩围岩的主要化学成分,除石英外,主要由长石和云母两种端员组分选择性熔融形成,并呈现出了化学组分分布的不均一性。假玄武玻璃的锆石U-Pb和玻璃基质~(40)Ar/~(39)Ar定年结果证实映秀-北川断裂的古地震发生于229~216Ma的中-晚三叠世,并具有11~14km的震源深度,表明映秀-北川断裂的早期活动始于印支期的造山运动。伴随着印支造山运动的发生,龙门山断裂带形成了其初始构造框架,并对之后的构造演化产生了深远的影响。     

中部地壳剪切带花岗质岩石变形及其对于构造-岩浆关系的约束:以滇西点苍山为例

哀牢山-红河剪切带剪切时间的厘定至今存在较多的争议,争议的本质更确切地说是对于剪切带内及其附近剪切作用与岩浆作用认识的差异。点苍山杂岩是位于哀牢山-红河剪切带北端的一个杂岩体,由西部的深变质岩、东部的叠加退变质带和不同时代的花岗质岩石组成。为了正确厘定剪切前、剪切期(包括剪切前期和剪切后期)、剪切后花岗质岩脉,剪切作用过程中构造变形与岩浆作用之间的关系,同时对哀牢山-红河剪切带剪切时间进行新的约束,本文围绕点苍山杂岩开展详细的宏观构造解析、显微构造观察和组构分析,以查明岩体(脉)岩浆流动构造和晶质塑性变形构造,同时对同剪切岩脉开展锆石U-Pb学分析。结果显示,剪切不同阶段就位的花岗质岩石具有不同的宏观构造、显微构造与组构特征。现今所见岩石变形构造、显微构造和组构特点一方面取决于递进剪切变形作用过程中的时间早晚,另一方面还与它们在递进剪切变形作用过程中的构造位置有密切联系。获得两组同剪切年龄为28.54±0.15Ma和27.31±0.23Ma,其中前者为剪切早期阶段同就位的花岗岩脉,后者为剪切稍晚阶段同就位的花岗岩。研究揭示出就位较晚的岩脉(即后者)因其位于递进剪切变形的高应变带而具有较为复杂的变形构造、显微构造和组构型式,就位较早的岩脉(前者)因在递进剪切变形作用过程中位于低应变带而具有简单的变形构造、显微构造和组构型式,并仍然保留有岩浆结晶组构特点。哀牢山-红河剪切带在28.54~27.31Ma间持续发生着从早期阶段较高温(~700℃),向中期阶段中高温(550~600℃)和晚期阶段低温(低于400℃)环境的递进剪切变形作用。     

鄂尔多斯盆地东南部山2段物源与曲流河三角洲沉积体系

鄂尔多斯盆地东南部山2段是该盆地重要的天然气富集层位。通过重矿物分布、岩屑组分、砂岩岩屑类型及阴极发光特征分析山2段沉积物源体系,经研究认为盆地东南部山2段沉积同时受南、北部物源供源。山2段为曲流河三角洲前缘沉积亚相,碎屑颗粒分选中等偏好、磨圆较好、颗粒之间接触紧密,沉积构造主要为板、槽状交错层理、平行层理及浪成交错层理。本区山2段沉积物以跳跃组分和悬浮组分为主,水下分流河道微相粒度概率曲线呈现三段式和四段式;河口坝微相分选较好、粒度概率曲线形态为两段式和三段式。研究区北部、南部及中部志丹、甘泉等地区砂体发育较厚,剖面上河道砂体呈不对称式相互叠置,水动力条件中等-较强。通过物源体系重建、沉积特征分析与薄片特征鉴定,建立了鄂尔多斯盆地东南部山2段双物源曲流河三角洲沉积模式。该研究明确了盆地东南部山2段物源方向,明晰了山2段沉积特征,创建了典型曲流河三角洲沉积模式,为进一步勘探开发提供了理论支持。     

Jurassic-Cretaceous Basin-range Pattern in the Southwestern Tian Shan Foreland Basin: Evidence from Detrital U-Pb Zircon GeochronologyEI北大核心CSCD

The Mesozoic basin-range pattern in the Tian Shan area is actively debated, especially on the southern flank of the Tian Shan. This important and contrasting hypothesis involves an intracontinental foreland basin, and a passive subsiding basin characterized by a wide source area, a weak basin-range differentiation, as well as a positive physiographic feature. This study focuses on the critical stage of basin-range relationship and reports detrital zircon U-Pb ages from the sandstones of Middle Jurassic Yangye Formation and Lower Cretaceous Group collected from the Kangsu section, aiming to constrain the Mesozoic provenance of the southwestern Tian Shan foreland basin. The U-Pb isotopic ages of zircons from these two units of clastic rocks were obtained by using in situ LA-ICP-MS. The U-Pb ages of detrital zircons from the Middle Jurassic series range from 369 Ma to 2687 Ma and can be divided into three main groups: (1) 369-404 Ma (accounting for 4%), (2) 418-501 Ma (accounting for 19%), (3) 544-2687 Ma (accounting for 77%), and the zircon ages from the Lower Cretaceous series range from 243 Ma to 2820 Ma and can be divided into three groups: (1) 253-414 Ma (accounting for 35%), (2) 423-489 Ma (accounting for 27%), (3) 668-2820 Ma (accounting for 37%). All age groups are prominent in the Middle Jurassic sample, suggesting a large-scale drainage system and wide source area characterized by established connection between the basin and main sources. The distribution of U-Pb ages of detrital zircons from the Lower Cretaceous sample has more groups and reflects a shrink age in coeval source area. The southern flank of southwestern Tian Shan and the Kuqa rejuvenated foreland basin have difference sediment provenance during the Middle Jurassic, whereas in the Early Cretaceous they have similar sedimentary provenance. The southwestern Tian Shan foreland basin, as well as the other areas of the south margin of the Tian Shan underwent a minor tectonic inversion and adjustment throughout the Early Cretaceous, which led to an intension in basin-range differentiation and corresponding uplift-exhumation, and a deconstruction of the link between sedimentary piedmont and older basements distributed in interior of the mountain. © 2017, Science Press. All right reserved.     

Textual research of 1219 A.D. Guyuan earthquake in Ningxia Hui Autonomous Region,China and discussion on its causative structure

On the basis of textual research on the historical earthquake data and the field investigation of 1219 A.D.Guyuan earthquake,we suggest that there is only one strong earthquake occurred in Guyuan area in 1219 A.D.,instead of two or three strong earthquakes.We further suggest that the earthquake parameters recorded in the present earth-quake catalogs are not definite and should be modified.The occurrence time of this earthquake should be about 11 am,August 7,1219 A.D.and the heavily-damaged area of this earthquake,the VIII intensity area,should be lo-cated among the regions of Guyuan,Pingliang and Longde county cities.The epicenter area should be near Gu-yuan city.The magnitude of this earthquake is about 7 and it has intensity about larger than or equal to IX within the epicenter area.The major axis direction of the heavily-damaged area strikes in north-northwest that is ap-proximately consistent with the strike of the Liupan Shan thrust fault zone.The new tectonic activity of the Liupan Shan thrust fault zone resulted in the M7 Guyuan earthquake in 1219 A.D.     

Crustal Uplift in the Longmen Shan Mountains Revealed by Isostatic Gravity Anomalies along the Eastern Margin of the Tibetan Plateau

This study examines the relationship between high positive isostatic gravity anomalies (IGA), steep topography and lower crustal extrusion at the eastern margin of the Tibetan Plateau. IGA data has revealed uplift and extrusion of lower crustal flow in the Longmen Shan Mountains (the LMS). Firstly, The high positive IGA zone corresponds to the LMS orogenic belt. It is shown that abrupt changes in IGA correspond to zones of abrupt change of topography, crustal thickness and rock density along the LMS. Secondly, on the basis of the Airy isostasy theory, simulations and inversions of the positive IGA were conducted using three-dimensional bodies. The results indicated that the LMS lacks a mountain root, and that the top surface of the lower crust has been elevated by 11 km, leading to positive IGA, tectonic load and density load. Thirdly, according to Watts’s flexural isostasy model, elastic deflection occurs, suggesting that the limited (i.e. narrow) tectonic and density load driven by lower crustal flow in the LMS have led to asymmetric flexural subsidence in the foreland basin and lifting of the forebulge. Finally, based on the correspondence between zones of extremely high positive IGA and the presence of the Precambrian Pengguan-Baoxing complexes in the LMS, the first appearance of erosion gravels from the complexes in the Dayi Conglomerate layer of the Chengdu Basin suggest that positive IGA and lower crustal flow in the LMS took place at 3.6 Ma or slightly earlier.