海南岛蓬莱地区超镁铁岩包体及其寄主玄武岩的研究

蓬莱地区寄主玄武岩为晚第三纪火山喷发的产物,主要岩石为碧玄岩,碱性橄榄玄武岩和橄榄玄武岩,其中含有超镁铁岩包体。寄主玄武岩属碱性系列,是地幔橄榄岩低度部分熔融的产物。超镁铁岩包体具有局部熔融的迹象和弱亏损型地幔岩的特征,推测为上地幔橄榄岩低度部分熔融后的难熔残余。     

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.     

Block‐and‐ash flow deposit of the Narcondam Volcano: Product of dacite–andesite dome collapse in the Burma–Java subduction complex

Narcondam Island in the Andaman Sea represents a dacite–andesite dome volcano in the volcanic chain of the Burma–Java subduction complex. The pyroclasts of andesitic composition are restricted to the periphery of the dome predominantly in the form of block‐and‐ash deposits and minor base surge deposits. Besides pyroclastic deposits, andesitic lava occurs dominantly at the basal part of the dome whereas dacitic lava occupies the central part of the dome. The pyroclasts are represented by non‐vesiculated to poorly vesiculated blocks of andesite, lapilli, and ash. The hot debris derived from dome collapse was deposited initially as massive to reversely‐graded beds with the grain support at the lower part and matrix support at the upper part. This sequence is overlain by repetitive beds of lapilli breccia to tuff breccia. These deposits are recognized as a basal avalanche rather than lahar deposit. This basal avalanche was punctuated by an ash‐cloud surge deposit representing a sequence of thinly bedded units of normal graded unit to parallel laminated beds.     

On tectonic movement in the South China Sea during the Cenozoic

The tectonic movement taking place at the end of Cretaceous and the beginning of Cenozoic had opened the Cenozoic phase of polycyclic tectonic movements, then the whole crust of the South China Sea had been mainly subjected to the regional stress field of tectonic tension, which was characterized by rifting depression. Seven times of regional tectonic movement and sedimentation had been assembled into a geological development history of polycyclic oscillation. Especially, the tectonic movements were strongly intensified at the end of Cretacious and the beginning of Paleagene, between Late Eocene and MidOligocene, during Mid and Late Miocene. These three times of tectonic movement had built the most important regional tectonic interfaces in the South China Sea. Crust movements of the South China Sea were the result and epitome of interaction of the Eurasia, Pacific and IndoAustralia plates, that is, they were introduced by polycyclic changes of directions, rates and strengths of lithospheric movements and asthenospheric flows across the Pacific and IndoAustralia plates.     

Seismic analyses of Cenozoic contourite drift development in the Northern Norwegian Sea

Four drift accumulations have been identified on the continental margin of northern Norway; the Lofoten Drift, the Vesterålen Drift, the Nyk Drift and the Sklinnadjupet Drift. Based on seismic character these drifts were found to belong to two main groups; (1) mounded, elongated, upslope accretion drifts (Lofoten Drift, Vesterålen Drift and Nyk Drift), and (2) infilling drifts (Sklinnadjupet Drift). The drifts are located on the continental slope. Mainly surface and intermediate water circulation, contrary to many North Atlantic and Antarctic drifts that are related to bottom water circulation, and sediment availability have controlled their growth. Sediments were derived both from winnowing of the shelf and upper slope and from ice sheets when present on the shelf. The main source area was the Vøring margin. This explains the high maximum average sedimentation rate of the nearby Nyk (1.2 m/ka) and Sklinnadjupet (0.5 m/ka) Drifts compared with the distal Lofoten (0.036 m/ka) and Vesterålen (0.060 m/ka) Drifts. The high sedimentation rate of the Nyk Drift, deposited during the period between the late Saalian and the late Weichselian is of the same order of magnitude as previously reported for glacigenic slope sediments deposited during glacial maximum periods only. The Sklinnadjupet Drift is infilling a paleo-slide scar. The development of the infilling drift was possible due to the available accommodation space, a slide scar acting as a sediment trap. Based on the formation of diapirs originating from the Sklinnadjupet Drift sediments we infer these sediments to have a muddy composition with relatively high water content and low density, more easily liquefied and mobilised compared with the glacigenic diamictons.     

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.

     

库车坳陷克拉苏河新生代沉积岩磁组构特征与古流向分析

塔里木盆地库车坳陷克拉苏河沿岸发育良好的新生界地层.我们对克拉苏河沿岸新生界剖面分A、B两段进行系统采样,获得定向岩芯样品1700余块. 岩石磁学研究表明,新生代沉积岩中磁性矿物以赤铁矿为主,含有少量磁铁矿;磁组构测试结果显示,两段剖面磁面理均较磁线理发育,最小磁化率主轴近于直立,显示原生沉积组构. A剖面磁化率主轴к1的偏角指示古流向. 库姆格列木群沉积时的古水流方向为NEE-SWW向,至苏维依组沉积时,流向变为NNE-SSW向. 河流古流向在苏维依组形成时发生急剧变化,说明南天山此时可能发生了明显的隆升,且以北西部隆升为主;B剖面为吉迪克组、康村组和库车组粗粒碎屑岩,磁组构显示к1-к2构成的磁面理与层理面小角度相交,к3呈叠瓦状分布,可以用来指示古水流方向.从吉迪克组至库车组下段,古流向均为NNW-SSE,但逐渐偏东,暗示天山在此期间处于缓慢的隆升期或东西部处于同步隆升,且西部隆升速度快于东部.     

柴达木盆地东部新生代盆地结构与演化

本文对柴达木盆地东部新生代盆地结构和构造演化进行了研究.地震剖面揭示柴达木盆地东部新生界分别向南、北盆地边缘变薄和尖灭,盆地北部被欧龙布鲁克山和埃姆尼克山隆起强烈改造.通过对新生代地层厚度横向变化以及地层剖面分析,确定欧北断裂自中新世晚期开始向北逆冲,导致欧龙布鲁克山发生隆升和德令哈凹陷的形成.埃北断裂从上新世开始活动,与欧北断裂同时向北逆冲,导致德令哈凹陷进一步沉降,形成厚度达2600 m的狮子沟组.埃南断裂在第四纪开始大规模向南逆冲,不仅造成其北侧的欧龙布鲁克山和埃姆尼克山隆起强烈抬升和向南推覆,而且导致南侧霍布逊凹陷的形成,成为柴达木盆地第四纪沉积中心.早期提出的前陆盆地和背驮式盆地模型显然不能解释柴达木盆地东部新生代构造格架和演化历史.本次研究认为柴达木盆地东部的形成是强烈的水平挤压作用导致地壳发生大规模褶皱的结果,即柴达木盆地东部新生代是一个大规模向斜.该向斜盆地模型很好地解释了新生代地层向盆地边缘减薄以及沉积中心主要位于盆地中部等现象.了解柴达木盆地东部构造发展对了解青藏高原侧向扩展具有重要意义.     

Palynostratigraphy of the Erkovtsy field of brown coal (the Zeya-Bureya sedimentary basin)

The Erkovtsy brown coal field in the northwestern Zeya-Bureya sedimentary basin (129°–130° E, 46°–47° N) is structurally confined to southern flank of the Mesozoic-Cenozoic Belogor’e depression. The verified stratigraphic scheme of the coalfield sedimentary sequence is substantiated by palynological data on core samples from 18 boreholes sampled in the course of detailed prospecting and by paleobotanical analysis of sections in the Yuzhnyi sector of the coalfield (data of 1998 by M.A. Akhmetiev and S.P. Manchester). Sections of the Erkovtsy, Arkhara-Boguchan, and Raichikha brown-coal mines are correlated. Stratigraphic subdivisions distinguished in the studied sedimentary succession are the middle and upper Tsagayan subformations (the latter incorporating the Kivda Beds), Raichikha, Mukhino, Buzuli, and Sazanka formations.