The late Mesozoic–Cenozoic tectonic evolution of the South China Sea: A petrologic perspective

This paper presents a review of available petrological, geochonological and geochemical data for late Mesozoic to Recent igneous rocks in the South China Sea (SCS) and adjacent regions and a discussion of their petrogeneses and tectonic implications. The integration of these data with available geophysical and other geologic information led to the following tectono-magmatic model for the evolution of the SCS region. The geochemical characteristics of late Mesozoic granitic rocks in the Pearl River Mouth Basin (PRMB), micro-blocks in the SCS, the offshore continental shelf and Dalat zone in southern Vietnam, and the Schwaner Mountains in West Kalimantan, Borneo indicate that these are mainly I-type granites plus a small amount of S-type granites in the PRMB. These granitoids were formed in a continental arc tectonic setting, consistent with the ideas proposed by Holloway (1982) and Taylor and Hayes, 1980, Taylor and Hayes, 1983, that there existed an Andean-type volcanic arc during later Mesozoic era in the SCS region. The geochonological and geochemical characteristics of the volcanics indicate an early period of bimodal volcanism (60–43 Ma or 32 Ma) at the northern margin of the SCS, followed by a period of relatively passive style volcanism during Cenozoic seafloor spreading (37 or 30–16 Ma) within the SCS, and post-spreading volcanism (tholeiitic series at 17–8 Ma, followed by alkali series from 8 Ma to present) in the entire SCS region. The geodynamic setting of the earlier volcanics was an extensional regime, which resulted from the collision between India and Eurasian plates since the earliest Cenozoic, and that of the post-spreading volcanics may be related to mantle plume magmatism in Hainan Island. In addition, the nascent Hainan plume may have played a significant role in the extension along the northern margin and seafloor spreading in the SCS.     

Discussion on the dextral movement and its effect in continental China and adjacent areas since Cenozoic

Continental China has moved dextral Eastward since Cenozoic time, driven by the collision of the Indian with the Eurasian plate. Evidence for this comes from landscape evolution, the distribution of earthquake epicenters, Cenozoic sedimentary and volcanic rocks, and the measurement of GPS velocity vectors, the distribution of crustal stress, paleomagnetic data, and deep mantle structure, among others. This movement commenced around 40 Ma, coupled with thickened lithosphere and widespread stress release along strike-slip faults that bound the continental Chinese block. Because of continued Northward subduction of the Indian plate, manifestation of the dextral movement has intensified since 25 Ma. Far-reaching effects include extensive strike-slip movement on the Tan-Lu fault in Eastern China, formation of the Dabie ultrahigh pressure metamorphic terrane, extensive thrust faults in East China, delamination and thickening of the lithosphere of South China, a possible tectonic doubling of the Middle-Lower Yangtze Valley metallogenic belt, and the formation of the Japan, Huanghai (East China), and South China Sea.     

造山带中、新生代隆升作用构造年代学研究新进展

造山带中,新生代降 作用构造年代学研究在内容上强调隆升的细致过程和机制的研究,在方法上有４点值得重视：利用财核素测定年龄;利用ＭＤＤ模式定量研究山体隆升过程;利用磷灰石裂变径迹定年方法研究山脉的隆升与剥露;复地貌有关参数判断抬升机制。对大别造山带中,新生代隆升作用的构造年代学进行剖析后,得到一些规律性认识;隆升构造复杂多亲,可划分４类６型隆升构造;隆升作用在时间上显示缓慢和强烈或相间的节律性;空间     

长江源区新生代火山岩的系列及成因

长江源区的新生代火山岩系包括高钾钙碱性系列和钾玄岩系列.高钾钙碱性火山岩形成于始新世, 钾玄岩系列火山岩形成于中、上新世.总体而言, 该区火山岩富碱高钾, 富集大离子亲石元素, 稀土元素含量高且轻稀土相对富集.相对而言, 高钾钙碱性火山岩富集SiO₂、Al₂O₃, 无负Eu异常, 属于壳源岩浆系列, 其原始岩浆由加厚陆壳的榴辉岩质下地壳经部分熔融产生.钾玄岩系列火山岩富集K₂ O、TiO₂、P₂ O₅、MgO、FeO, ∑REE、HFSE、I_Sr值均较高, 弱负Eu异常, 属于幔源岩浆系列, 其原始岩浆由EMⅡ型富集地幔的部分熔融生成.2个系列的火山岩均是大陆碰撞造山后期岩浆作用的产物.始新世以来, 随着该区由碰撞、挤压作用发展到出现走滑, 应力环境由挤压转变为张性, 导致依次喷发高钾钙碱性火山岩和钾玄岩系列火山岩.      

新生代6次陨击事件研究及存在问题

陨击事件对古生物灭绝、古气候、古地质环境演化有重要影响。结合我们在陨击事件方面的新研究成果,探讨了新生代6次主要陨击事件的研究动态及存在问题。近几年来,一些新的陨击证据被进一步发现,有的微玻璃陨石场的分布范围进一步扩大,有的相关源陨击坑的研究取得了新的进展,当然,还有一些难解之谜需要进一步探讨。     

Geochemical Evolution and Environmental Changes of Qinghai—Xizang Plateau Since Late Cenozoic

Long-and short-term climatic curves were preliminarily established based on the comprehensive analysis of geochemical information since the Late Cenozoic in the Qinghai Xizang(Qinghai-Tibet)Plateau.The curves show that the climate in the plateau was alternatively dry-warm and cold-wet during the period of 30-3.4 Ma when the plateau was not uplifted to an enough altitude and the monsoon was not completely formed either,In the period of 3.4-0.73 Ma.the climate fluctuated between dry-cold and wet-warm when the plateau was rapidly uplifted and the Asian monsoon was consequently formed.Since 0.73 Ma.the climate became even drier when the plateau continuously rose.In the Holocene period.the climate alternatively changed with a complex model of being cool-dry,warm-wet and cold-wet.     

Mesozoic–Cenozoic stress field magnitude in Sichuan Basin,China and its adjacent areas and the implication on shale gas reservoir: Determination by acoustic emission in rocks

The Sichuan Basin is one of the vital basins in China, boasting abundant hydrocarbon reservoirs. To clarify the intensity of the tectonic stress field of different tectonic episodes since the Mesozoic and to identify the regional dynamic background of different tectonic movements in the Sichuan Basin and its adjacent areas, the characteristics of the acoustic emission in rocks in different strata of these areas were researched in this paper. Meanwhile, the tectonic stress magnitude in these areas since the Mesozoic was restored. The laws state that the tectonic stress varied with depth was revealed, followed by the discussion of the influence of structural stress intensity on structural patterns in different tectonic episodes. These were conducted based on the paleostress measurement by acoustic emission method and the inversion principle of the stress fields in ancient periods and the present, as well as previous research achievements. The results of this paper demonstrate that the third episode of Yanshanian Movement (Yanshanian III) had the maximum activity intensity and tremendously influenced the structural pattern in the study area. The maximum horizontal principal stress of Yanshanian III varied with depth as follows: 0.0168 x + 37.001 (MPa), R² = 0.8891. The regional structural fractures were mainly formed in Yanshanian III in Xujiahe Formation, west Sichuan Basin, of which the maximum paleoprincipal stress ranging from 85.1 MPa to 120.1 MPa. In addition, the law stating the present maximum horizontal principal stress varies with depth was determined to be 0.0159 x+10.221 (MPa), R²=0.7868 in Wuling Mountain area. Meanwhile, it was determined to be 0.0221 x+9.4733 (MPa), R²=0.9121 in the western part of Xuefeng Mountain area and 0.0174 x+10.247 (MPa), R²=0.8064 in the whole study area. These research results will not only provide data for the simulation of stress field, the evaluation of deformation degree, and the prediction of structural fractures, but also offer absolute geological scientific bases for the elevation of favorable shale gas preservation.     

Cenozoic high-K alkaline magmatism and associated Cu–Mo–Au mineralization in the Jinping–Fan Si Pan region,southeastern Ailao Shan–Red River shear zone,southwestern China–northwestern Vietnam

The Jinping–Fan Si Pan (JFP) Cenozoic magmatic and Cu–Mo–Au metallogenic belt in the southeastern part of the Ailao Shan shear zone host the Tongchang, Chang′an, Habo, and Chinh Sang Cu–Mo–Au deposits. These deposits form an integrated epithermal-porphyry regional mineralization system associated with 40–32 Ma high-K alkaline magmatism. The magmatic rocks in the belt have relatively low TiO₂ (<0.73 wt%), P₂O₅ (<0.29 wt%), and FeO^* (<4.99 wt%), and high Na₂O (2.86–4.75 wt%) and K₂O (4.01–7.98 wt%). They also have high contents of incompatible trace elements, and are enriched in LILE (Rb, Ba, K, Sr) and LREE. They have marked Nb, Ta, Ti and P depletion in primitive mantle-normalized spidergrams, and plot close to the EMII mantle field in the Sr–Nd isotopic diagram. These characteristics are similar to those of the Eocene high-K alkaline rocks along the northern Ailao Shan belt, eastern Tibet plateau. The sulfur and lead isotope analyses of sulfide minerals from both the ores and related magmatic rocks confirm the involvement of a magmatic ore fluid. The Cenozoic alkaline intrusions and Cu–Mo–Au mineralization in the JFP were formed prior to the initiation of left-lateral shearing along the Ailao Shan shear zone. The magmas appear to have been derived from enriched mantle, possibly with mixing of materials from the buried Tethyan oceanic lithosphere, and/or crust.     

基于程函方程与三维速度模型的中国东北地区地幔过渡带接收函数研究

本文利用中国东北地区NECESSArray记录到的45505条接收函数,结合该区域最新三维速度模型,采用快速行进法求解程函方程,计算了P-S转换波相对走时,并通过共转换点叠加成像方法获得了该地区下方地幔间断面起伏情况.结果显示,在长白山—五大连池连线一带东西约300 km,南北约900 km的狭长形区域内,660-km间断面下陷幅度达20~40 km.其结构可细分为南北两部分,南部更为狭窄且与日本海沟走向一致,对应于从日本海沟俯冲的太平洋板块在地幔过渡带的滞留区;北部对应于从千岛海沟俯冲的太平洋板块在地幔过渡带的滞留区.同时,在长白山西部,存在与长白山—五大连池下陷区形状类似的南北向狭长形抬升区,660-km间断面抬升幅度约为10 km,显示俯冲太平洋板块只延伸至松辽盆地东侧;而在盆地西侧,660-km间断面的下陷区可能与该地区岩石圈拆沉有关.同时,410-km间断面在松辽盆地—渤海一带,以及长白山火山西南和东北方向存在明显的下陷区;另外,在阿巴嘎及阿尔山也有小范围的下陷区.所有这些下陷区,均与地表新生代火山活动区/拉伸区有很好的对应关系,表明这些地表构造与深部热物质上涌有关.

     

Cenozoic Exhumation and Thrusting in the Northern Qilian Shan, Northeastern Margin of the Tibetan Plateau: Constraints from Sedimentological and Apatite Fission-Track Data

Abstract: The Qilian Shan lies along the northeastern edge of the Tibetan Plateau. To constrain its deformation history, we conducted integrated research on Mesozoic–Cenozoic stratigraphic sections in the Jiuxi Basin immediately north of the mountain range. Paleocurrent measurements, sandstone compositional data, and facies analysis of Cenozoic stratigraphic sections suggest that the Jiuxi Basin received sediments from the Altyn Tagh Range in the northwest, initially in the Oligocene (~33 Ma), depositing the Huoshaogou Formation in the northern part of the basin. Later, the source area of the Jiuxi Basin changed to the Qilian Shan in the south during Late Oligocene (~27 Ma), which led to the deposition of the Baiyanghe Formation. We suggest that uplift of the northern Qilian Shan induced by thrusting began no later than the Late Oligocene. Fission-track analysis of apatite from the Qilian Shan yields further information about the deformation history of the northern Qilain Shan and the Jiuxi Basin. It shows that a period of rapid cooling, interpreted as exhumation, initiated in the Oligocene. We suggest that this exhumation marked the initial uplift of the Qilian Shan resulting from the India–Asia collision.