博格达山晚石炭纪造山活动的变形地质记录

主要由钙碱性火山岩、火山碎屑岩组成的博格达古岛弧是天山缝合造山带的重要组成部分 ,是一个发育较成熟的山链 ,其演化经历了晚古生代的韧性剪切收缩 ;中生代伸展调整及新生代再造山过程。晚古生代的造山活动在博格达山有很好的地质记录 ,并以显著的韧性剪切变形带的形成和发育同造山的褶皱构造为特点。剪切变形带内同构造的石英脉中的锆石U PbSHRIMP测年结果与山链中花岗岩、辉长岩年龄颇为一致 (311～ 316Ma) ,这个年龄反映在结束洋盆散聚、碰撞焊接的晚华力西期造山过程中 ,博格达古岛弧内存在一次虽不甚强烈 ,但又较为明显的构造岩浆事件 ,其成因可能与引起石炭纪大规模裂陆式喷发的深部断裂构造重新活动有关。

印支期秦岭造山活动对鄂尔多斯盆地延长组沉积特征的影响

通过对鄂尔多斯盆地上三叠统延长组沉积时区域古构造活动规律、沉积地质背景研究以及延长组沉积特征和沉积相序演化规律分析 ,重点探讨了延长组沉积特征及沉积环境变化与印支期秦岭造山活动之间的关系 ,分析了印支期秦岭造山活动对盆地边界性质、盆地内延长组沉积物源、碎屑搬运和沉积机理的影响 ,以及沉积体系类型及沉积相带展布规律的控制作用。

晚三叠世火山活动对鄂尔多斯盆地长7优质烃源岩发育的影响

岩芯和露头剖面观察结果表明,鄂尔多斯盆地长7优质烃源层中广泛分布薄层和纹层状凝灰岩,薄层凝灰岩的SiO2含量介于49.37%～72.45%之间,以中、酸性为主。岩石薄片的镜下观察结果表明,常见晶屑凝灰岩、玻屑凝灰岩和双屑凝灰岩,并可见到呈有序结构(成分和粒度)的凝灰岩纹层,同期喷发、大气降落沉积特征明显。根据其岩石类型、主元素和微量元素组成、锆石U-Pb年龄等的对比,以及凝灰岩的平面分布特征判断,盆地内长7优质烃源层中的凝灰岩可能主要来自秦岭地区的同期火山喷发活动。扬子与华北陆块碰撞、秦岭造山的区域构造活动的活跃是引起长7最大湖泛的主要动力因素,为优质烃源岩发育提供了基本的地质条件,同期频繁的火山喷发活动与湖底热液活动等共同促进了优质烃源岩的大规模发育。

秦岭造山带斜向俯冲—碰撞与南秦岭金—铅锌矿床成矿作用的响应

南秦岭金-多金属矿床聚集区是秦岭成矿带乃至我国中央造山成矿带的重要组成部分,该卡林型-类卡林型金矿床、热水沉积改造铅锌矿床和沉积改造汞锑矿床及聚集区的形成与成矿演化,成矿地质背景,容矿与含矿建造,矿床类型、规模及时空分布规律,均与现代板块构造活动机制有密切的耦合关系。具体分析了造山带俯冲碰撞活动过程中,成矿构造地质背景、成矿盆地环境、沉积建造、成矿作用与矿床分布规律对造山作用的积极响应。

褶皱造山带油气

近年来,在地壳稳定区的边缘带及活动造山带发现了大量油气资源,使人们对传统的稳定地台区油气富集的观念有所更新。重视造山带的油气,已成为油气勘探的新的趋势。造山期前的快速沉降和造山期后的不均衡活动是造山带油气富集和保存的主要条件。另外,造山带油气聚集的深度随造山带的年代变晚而加深,其生油门限深度也表现出同样的规律。

中国阿尔泰山流域侵蚀速率及其控制因素

流域侵蚀速率的时空变化对于理解活动造山带的地貌演化具有重要意义。以阿尔泰山8个山地流域为研究对象,利用1964—2011年的水文数据,采用河流输沙量法估算了年代际山地流域侵蚀速率。首先确定悬移质、推移质和溶解质对河流输沙量的贡献,然后计算各流域的年代际侵蚀速率,并结合已有研究结果,探讨了阿尔泰山流域侵蚀速率的时空特征及其控制因素。结果表明:阿尔泰山8个山地流域的平均侵蚀速率为0.03 mm·a^(-1),其中乌伦古河山地流域侵蚀速率最小(0.01 mm·a^(-1)),额尔齐斯河支流克兰河山地流域侵蚀速率最大(0.05 mm·a^(-1))。进一步对侵蚀速率与气候、地形、岩性、构造和植被等因素进行相关分析,发现流域侵蚀速率与地形因子(流域面积、地形起伏度)和气候因子(径流深度、平均温度)的相关性较强,表明这些因素可能对阿尔泰山山地流域侵蚀起主要影响。与阿尔泰山百万年尺度的剥蚀速率(0.07~0.3 mm·a^(-1))相比,研究时段内的流域侵蚀速率偏低,这表明中亚地区晚新生代持续的干旱气候可能制约了阿尔泰山地表侵蚀。

鲁西前寒武纪基性岩墙群

鲁西地区发育大规模的中元古代基性岩墙群,侵位于早前寒武纪结晶基底内,未变形未变质,以北北西向和近南北向为主,是鲁西前寒武纪最引人注目的一种伸展构造标志。鲁西基性岩墙群属于板内大陆裂谷拉斑玄武岩系列,与板内大陆裂谷活动密切相关,代表一种非造山岩浆活动。该岩墙群富集大离子亲石元素(L IL E) ,略亏损高场强元素(HFSE) ,比较富集Cr、Ni,明显亏损Th。稀土元素配分模式为轻稀土略富集的右倾曲线。鲁西基性岩墙群的微量元素和稀土元素特征反映源区为略富集的地幔。从时空分布特征、构造特征、岩石化学相关性、岩浆源区和古构造应力场分析,鲁西基性岩墙群与燕辽—中条拗拉槽系有一定的成生联系。

Spatial Distribution Characteristic of the b-value in Dabie-Sulu and Its Adjacent Areas

The Tanlu （Tancheng-Lujiang） fault is one of the major structures in eastern China, which cuts across different blocks and controls the tectonic activity. Using the seismic data from the China Earthquake Networks Center, we investigate the spatial variations of the b-value in the Dabie-Sulu （Jiangsu-Shandong） organic belt by calculating the b-value of each grid （1~ xl~） from 1970 to 2010. The study shows that： the b-value is smaller in the Tanlu fault and its adjacent area, which might suggest that the major earthquake recurrence period is relatively long due to the lower frequency of small earthquake activity. In both sides of Tanlu fault, the b-value is higher at the edge of Sulu block and the eastern part of Dabie orogenic belt. The b values are higher in North China central orogenic belt, and small earthquake activity which occurred along the central orogenic belt is frequent. Additionally, combined with geological and geophysical study, we find that the b-value has a certain correspondence relationship with the lithologic distribution, which informs us that seismic activity features are closely related to the inhomogeneous media in the crust.

Late Quaternary Activity and Paleoearthquakes along the Nanyukou Segment of the Northern Piedmont Fault of Wutai Mountain

The northern piedmont fault of Wutai Mountain is located at the north of the Shanxi Graben system, which is the dominating fault of the south boundary of the Fanshi-Daixian depression. This paper discusses the fault activity and paleoearthquakes around the Nanyukou segment of the northern piedmont fault of Wutai Mountain during the late Quaternary through field investigation along the fault, measuring geomorphic deformation and excavating trenches at some important sites. From Nanyukou to the southwest of Shanhui, we find obviously dislocated alluvial fans, with strong neotectonic movement at these sites. Since nearly 20ka, the vertical average slip rate is 1.55mm/a to 2.0mm/a. However,since nearly 6ka,it has reached as high as 2.3mm/a, which is twice that on other segments. 2 trenches were excavated around Nanyukou with 6 events discovered. The referenced ages of the events are before 7600a, 6700a - 7600a, 5321a - 5575a, 4400a - 5400a,420Oa-4400a and after 1600a B.P. with approximate recurrence interval 1400a. The latest event is likely to be the earthquake occurring at 512 A. D. ,so it is necessary to do further work to verify this in the future.

Research on the Seismotectonic Zones and Seismicity State in the Southern Xinjiang Region

Based on the studies of earthquake activity, tectonic movement, crustal shortening rate, fault activity, local stress field and historical characteristics of strong earthquake activities in Xinjiang, we divide the south part of Xinjiang into 4 seismotectonic zones, namely, the eastern segment of south Tianshan seismic belt, the Kalpin block, the Kashi-Wuqia junction zone, and the west Kunlun Mountains seismic belt. Using earthquake catalogues from Xinjiang since 1900, and on the basis of integrity analysis of earthquake records in different magnitude ranges, the seismicity state of different seismotectonic zones is analyzed quantificationaUy by calculating the mean value of annual strain energy release, annual rate of earthquakes with different lower limits of magnitude, b-value, and the parameter m of accelerating strain release model. The characteristic indexes of seismicity state for each of the seismic tectonic zones are then determined, which provide a quantitative basis for earthquake tendency analysis and judgment.

Fluvial terraces and their implications for Weihe River valley evolution in the Sanyangchuan Basin

Fluvial terraces are important geomorphic markers for modern valley development.When coupled with numeric ages,terraces can provide abundant information about tectonic,climatic,paleohydrological and the paleoenvironmental changes.On the basis of the paleomagnetic,electron spin resonance(ESR) and optically stimulated luminescence(OSL) dating,in addition to an investigation of local loess-paleosol sequences,we confirmed that 13 fluvial terraces were formed,and then preserved,along the course of the Upper Weihe River in the Sanyangchuan Basin over the past 1.2 Ma.Analyses of the characteristics and genesis of these terraces indicate that they resulted from the response of this particular river system to climate change over an orbital scale.These changes can further be placed within the context of local and regional tectonic uplift,and represent an alternation between lateral migration and vertical incision,dependent upon the predominance of climatic and tectonic controls during different periods.Most of the terraces are strikingly similar in that they have several meters of paleosols which have developed directly on top of fluvial deposits located on the terrace treads,suggesting that the abandonment of terraces due to river incision occurred during the transitions from glacial to interglacial climates.The temporal and spatial differences in the distribution patterns of terraces located on either side of the river valley indicate that a tectonic inversion occurred in Sanyangchuan Basin at-0.62 Ma,and that this was characterized by a transition from overall uplift to depression induced by fault activity.Synthesized studies of the Basin's terraces indicate that formation of the modern valley of the Upper Weihe River may have begun in the late Early Pleistocene between1.4-1.2 Ma.

Mercury concentration in natural gas and its distribution in the Tarim Basin

Here I collected natural gas samples from 41 industrial gas wells in the Tarim Basin,and studied the mercury distribution in the area.My data show that there is certain regularity in the distribution of mercury in the Tarim Basin.Generally,the mercury concentration is high at the edge of the basin and low in the central basin.The highest mercury concentration occurs in the Southwest Depression,ranging from 15428.5 to 296763.0ng/m3 with an average of 156095.7ng/m3,followed by the Kuqa Depression ranging from 15.0 to 56964.3ng/m3 with an average of 11793.7ng/m3,and the Hade oil and gas field in the North Depression has the lowest mercury concentration ranging from 17.7 to 3339.5ng/m3 with an average of 1678.6ng/m3.The mercury concentrations in the natural gases of different structural units are various,with the highest mercury concentration in the zone of strong structural activity of Southwest Depression.It is profitable of Hg accumulation in the self sourced and self accumulated gas reservoirs or volcanic existence;in contrast,the low Hg concentration exists in the secondary gas reservoir.The mercury concentration in the natural gas generated under continental depositional environment is higher than that in marine gas.Therefore,the mercury concentration in the natural gases is constrained by gas genesis,depositional environment of source rocks,tectonic activity,and volcanic activity,and the tectonic activity is the main factor for the mercury concentration in the natural gas,followed by volcanic activity and depositional environments.

Magmatism during continental collision, subduction, exhumation and mountain collapse in collisional orogenic belts and continental net growth: A perspective

Continental orogens on Earth can be classified into accretionary orogen and collisional orogen.Magmatism in orogens occurs in every periods of an orogenic cycle,from oceanic subduction,continental collision to orogenic collapse.Continental collision requires the existence of prior oceanic subduction zone.It is generally assumed that the prerequisite of continental deep subduction is oceanic subduction and its drag force to the connecting passive-margin continental lithosphere during continental collision.Continental subduction and collision lead to the thickening and uplift of crust,but the formation time of the related magmatism in orogens depends on the heating mechanism of lithosphere.The accretionary orogens,on the other hand,have no strong continental collision,deep subduction,no large scale of crustal thrusting,thickening and uplift,and no UHP eclogite-facies metamorphic rocks related to continental deep subduction.Even though arc crust could be significantly thickened during oceanic subduction,it is still doubtful that syn-or post-collisional magmatism would be generated.In collisional orogens,due to continental deep subduction and significant crustal thickening,the UHP metamorphosed oceanic and continental crusts will experience decompression melting during exhumation,generating syn-collisional magmatism.During the orogen unrooting and collapse,post-collisional magmatism develops in response to lithosphere extension and upwelling of asthenospheric mantle,marking the end of an orogenic cycle.Therefore,magmatism in orogens can occur during the continental deep subduction,exhumation and uplift after detachment of subducted oceanic crust from continental crust,and extensional collapse.The time span from continental collision to collapse and erosion of orogens(the end of orogenic cycle)is 50–85 Myr.Collisional orogens are the key sites for understanding continental deep subduction,exhumation,uplift and orogenic collapse.Magmatism in collisional orogens plays important roles in continental reworking and net growth.

Granitoid magmatism in the Qinling orogen, central China and its bearing on orogenic evolution

The Qinling orogen is a typical composite orogen for understanding multi-stages of magmatism and orogenic processes. Many studies have been carried out on the magmatic rocks in the Qinling orogen but their petrogenesis is still controversial. This pa- per presents a review of all granitoid rocks based on previous and new studies of geochronology and geochemistry. Four dis- tinct periods of granitoid magmatism, Neoproterozoic （979-711 Ma）, Paleozoic （507-400 Ma）, Early Mesozoic （250-185 Ma） and Late Mesozoic （160-100 Ma）, have been recognized from the Qinling orogen according to zircon U-Pb ages, intrusion as- sociations and deformation, as well as regional geology. The Neoproterozoic granitic rocks consist of three stages at 979-911, 894-815 and 759-711 Ma, respectively, corresponding to strongly deformed S-type, weakly deformed I-type and A-type gran- itoids. They can be interpreted as magmatic occurrences in syn-collisional, post-collisional and extensional settings, respec- tively, in response to old continental terranes of the Neoproterozoic tectonomagmatic events in the old continents of China, such as South China and Tarim cratons. Although this continental terrane would be involved in the Phanerozoic Qinling orog- eny, the Neoproterozoic magmatic rocks are not the products of the Qinling orogenic processes. The Paleozoic magmatic rocks can be classified into three stages at 507-470, 460-422 and 415-400 Ma, respectively. The first-stage magmatism is temporal- ly associated with ultra-high pressure metamorphism in the North Qinling terrane. These magmatic rocks are interpreted as magmatic occurrences in subductional, syn-collisional and post-collisional settings, respectively. The Early Mesozoic mag- matic rocks occur in two stages at 252-185 and 225-200 Ma, respectively. The first-stage granitoids are mainly represented by I-type quartz diorites and granodiorites, and the second stage by granodiorites and monzogranites with the 1- to A-type charac- teristics and some with rapakivi textures. Their emplacement ages and geochemical parameters such as A/CNK, K2O/Na2O ra- tios and εNd（t） values do not show any polarity change in perpendicular to subduction/collision zone. Therefore, all these Early Mesozoic granitoids are unlikely the product of continental subduction as some researchers suggested. Instead, they are plausi- bly related to the subduction of the Mianlue Ocean and the subsequent collision between the South China Craton and the South Qinling terrane. The Late Mesozoic granitoids were emplaced mainly at two stages of 160-130 and 120-100 Ma, and charac- terized by the evolution from I- to I-A- and A-type granitoids. These characteristics are consistent with the granitoid magmatic evolution from contractional to extensional settings during the Jurassic/Cretaceous in eastern China. Accordingly, the Late Mesozoic granitoid rocks in the Qinling orogen probably have a similar petrogenetic mechanism to those of the huge magmatic belt along the western Pacific margin, i.e., intra-continent magmatism related to a far-field effect of the subduction of Paleo-Pacific plate.