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91.
Donna L. Whitney Christian Teyssier Annia K. Fayon Michael A. Hamilton Matt Heizler 《Tectonophysics》2003,376(1-2):37-60
Mafic high-pressure granulite, eclogite and pyroxenite xenoliths have been collected from a Mesozoic volcaniclastic diatreme in Xinyang, near south margin of the Sino-Korean Craton (SKC). The high-pressure granulite xenoliths are mainly composed of fine-grained granoblasts of Grt+Cpx+Pl+Hbl±Kfs±Q±Ilm with relict porphyritic mineral assemblage of Grt+Cpx±Pl±Rt. P–T estimation indicates that the granoblastic assemblage crystallized at 765–890 °C and 1.25–1.59 GPa, corresponding to crustal depths of ca. 41–52 km with a geotherm of 75–80 mW/m2. Calculated seismic velocities (Vp) of high-pressure granulites range from 7.04 to 7.56 km/s and densities (D) from 3.05 to 3.30 g/cm3. These high-pressure granulite xenoliths have different petrographic and geochemical features from the Archean mafic granulites. Elevated geotherm and petrographic evidence imply that the lithosphere of this craton was thermally disturbed in the Mesozoic prior to eruption of the host diatreme. These samples have sub-alkaline basaltic compositions, equivalent to olivine– and quartz–tholeiite. REE patterns are flat to variably LREE-enriched (LaN/YbN=0.98–9.47) without Eu anomaly (Eu/Eu*=0.95–1.11). They possess 48–127 ppm Ni and 2–20 ppm Nb with Nb/U and La/Nb ratios of 13–54 and 0.93–4.75, respectively, suggesting that these high-pressure granulites may be products of mantle-derived magma underplated and contaminated at the base of the lower crust. This study also implies that up to 10 km Mesozoic lowermost crust was delaminated prior to eruption of the Cenozoic basalts on the craton. 相似文献
92.
Origin and tectonic significance of a Mesozoic multi-layer over-thrust system within the Yangtze Block (South China) 总被引:21,自引:0,他引:21
Dan-Ping Yan Mei-Fu Zhou Hong-Lin Song Xin-Wen Wang John Malpas 《Tectonophysics》2003,361(3-4):239-254
In the Yangtze Block (South China), a well-developed Mesozoic thrust system extends through the Xuefeng and Wuling mountains in the southeast to the Sichuan basin in the northwest. The system comprises both thin- and thick-skinned thrust units separated by a boundary detachment fault, the Dayin fault. To the northwest, the thin-skinned belt is characterized by either chevron anticlines and box synclines to the northwest or chevron synclines to the southeast. The former structural style displays narrow exposures for the cores of anticlines and wider exposures for the cores of synclines. Thrust detachments occur along Silurian (Fs) and Lower Cambrian (Fc) strata and are dominantly associated with the anticlines. To the southeast, this style of deformation passes gradually into one characterized by chevron synclines with associated principal detachment faults along Silurian (Fs), Cambrian (Fc) and Lower Sinian (Fz) strata. There are, however, numerous secondary back thrusts. Therefore, the thin-skinned belt is like the Valley and Ridge Province of the North American Applachian Mountains. The thick-skinned belt structurally overlies the thin-skinned belt and is characterized by a number of klippen including the Xuefeng and Wuling nappes. It is thus comparable to the Blue Ridge Province of Appalachia.The structural pattern of this thrust system in South China can be explained by a model involving detachment faulting along various stratigraphic layers at different stages of its evolution. The system was developed through a northwest stepwise progression of deformation with the earliest delamination along Lower Sinian strata (Fz). Analyses of balanced geological cross-sections yield about 18.1–21% (total 88 km) shortening for the thin-skinned unit and at least this amount of shortening for the thick-skinned unit. The compressional deformation from southeast to northwest during Late Jurassic to Cretaceous time occurred after the westward progressive collision of the Yangtze Block with the North China Block and suggests that the orogenic event was intracontinental in nature. 相似文献
93.
Structural vergence within the Western Subprovince of the Lachlan Fold Belt is towards the hinterland rather than the foreland, in contrast to many well-known orogenic belts. High angle-reverse faults and upright folds verge eastwards, away from the Australian craton, towards the inferred centre of orogenic and magmatic activity. We designed a series of analogue models to test the anomalous vergence in the western Lachlan Fold Belt, particularly the interaction of a stable Australian craton with Tasman Line geometry, interacting with weaker oceanic or transitional lithospheric material. We found consistently that vergence direction in the models was towards the hinterland, not the foreland, as in the western Lachlan Fold Belt, irrespective of the way the model was deformed. Strength gradients between the oceanic and cratonic lithosphere control the deformation patterns. An important result of the models is that they demonstrate that fold belts with different vergences can be generated without the requirement of subducting oceanic lithosphere. 相似文献
94.
This paper deals with the taxonomic revision of the Early Cretaceous large, many-chambered planispiral planktonic foraminifera, historically assigned to the genus Globigerinelloides or alternatively assigned in the 1990s to the genera Globigerinelloides Cushman and ten Dam, Biglobigerinella Lalicker, Blowiella Krechmar and Gorbachik and Alanlordella BouDagher-Fadel. In a previous paper we demonstrated that the morphological and microstructural features used in the literature for distinguishing Blowiella from Globigerinelloides have value only at species level, and the former genus was thus invalidated (being the junior synonym). Moreover, the Late Aptian specimens assigned to Biglobigerinella by some authors, based on the presence of twin last chamber(s), are also included in Globigerinelloides because individuals sharing the same features (number of chambers, growth rate, size of umbilicus, and a finely perforate wall) may or may not possess twin last chamber(s). Meanwhile, Moullade et al. questioned the taxonomic value of Alanlordella, erected by BouDagher-Fadel to accommodate planispiral taxa possessing a macroperforate wall. All the species analysed here possess a finely perforate wall and consequently cannot be assigned to this taxon.The large species of Globigerinelloides retained here, with six or more chambers in the outer whorl, are G. algerianus Cushman and ten Dam, G. aptiensis Longoria, G. barri (Bolli, Loeblich and Tappan) and G. ferreolensis (Moullade).In the sections studied, Globigerinelloides aptiensis was first found close to the Barremian/Aptian boundary, even though this species was recorded in Spain (Rio Argos) in the mid Upper Barremian; very rare, small, seven-chambered individuals here assigned to Globigerinelloides ferreolensis are recorded in the Lower Aptian (just below and within the Selli Level, OAE1a), while a few specimens belonging to Globigerinelloides barri occur in the Globigerinelloides ferreolensis Zone (Upper Aptian). Globigerinelloides aptiensis and G. ferreolensis range up to the Ticinella bejaouaensis Zone while Globigerinelloides barri disappears at the top of the Globigerinelloides algerianus Zone; finally, Globigerinelloides algerianus obviously spans the eponymous total range zone.From an evolutionary point of view, two lineages within the many-chambered Globigerinelloides have been recognized. In the first, already known in the literature, Globigerinelloides aptiensis gave rise to G. ferreolensis, which evolved into G. algerianus; the latter in turn gave rise to Pseudoplanomalina cheniourensis as the final evolutionary member. In the second lineage Globigerinelloides barri originated from G. blowi. 相似文献
95.
对下扬子与华南边界结合带东延问题的地球物理探讨 总被引:2,自引:1,他引:2
以江山-绍兴、铅山-宜春等断裂带作为华南与扬子块体之间的边界结合带,这种认识目前已基本为大家所接受.但是,这条边界结合带向东延伸入海之后的位置与去向一直是多年来研究的热点.本文基于黄、东海研究区的地球物理数据(空间重力数据、布格重力数据和地震层析成像结果),利用方向导数等处理方法,对研究区的地球物理数据进行处理,并对研究区的地球物理场进行了分析,划分出不同的区块.结合研究区的磁力与地质资料,利用各种成图、成像技术,形成一系列分析图件.在此基础上对华南与扬子块体之间的边界结合带进行了追踪.研究结果认为:该结合带的位置有可能比传统认识中自长江口至大黑山群岛的位置更向南一些,在杭州湾-长崎、对马海峡一线,并呈现向北略微凸出的弓形.边界结合带在深度上属于深大断裂带,一直可以追索到上地幔的顶部.与中朝与扬子块体之间的边界结合带相比较,本条结合带的踪迹不是十分清晰.表明加里东运动之后,该结合带的运动明显减弱. 相似文献
96.
WANG Tiefeng Northeast Investigation Design Research Institute China ZHANG Zhi Northeast Investigation Design Research Institute China YI Yue Northeast Investigation. Design Research Institute China 《国际泥沙研究》1997,(3)
I.INTRODUCTIONThePtlmped-storagepoll,erprojectofPushiriverisconsistedofupperreservoir,lobal-erreset'oir.watertransmissionSystemandpotvergeneratingsystem.ThelowerreservoirIviththecatchmentbasinareaof1141kmZisthewatersupplierl-c'hichislocatedonthedownstreamofthePushiriverinthesouthernpactofNortheastChina.Theupperreservoirisabout300-400metershigherthanthelowerresen!oirattheleftsideoftheriverwithcatchmentbasinareaof1.12km2.Thecharacteristicsoftheprojectandreservoirareshottviintablel-l.Ino… 相似文献
97.
将有限差分层析反演方法用于大别造山带人工地震测深剖面上部地壳初至波的走时层析成像,得到这一剖面上部地壳横向不均匀结构图像表明,在南大别地区的超高压变质带发现榴辉岩相岩石,其下方3km深度以内的基底仍具有大陆地壳构造中正常的结晶基底速度(6.00km/s左右);北大别地区在整个上地壳保持正常的速度,而在超高压带下方3km深度以下为6.20-630km/s的相对高速异常区,这一现象可能与超高压变质岩的含量增大有关.同时还表明,南大别和北大别之间至少在上地壳已有明显差异,它们之间的水吼一五河断裂可能是大别造山带内部的主要构造分界线. 相似文献
98.
The application of both thermoluminescence and infrared stimulated luminescence dating to the extensively studied “classical” Hungarian loess/paleosol sequences from Basaharc, Mende, and Paks provides a reliable chronological framework and climatostratigraphic reconstruction for the last interglacial/glacial cycle. Based on this combined luminescence dating study a new chronology is proposed for the “Young Loess” in Hungary. Luminescence dating suggests that the loess below the MF2 horizon formed during the penultimate glaciation. The MF1 horizon probably formed during an interstade within oxygen isotope stage 3. For the youngest loess, overlying MF1, a very high accumulation rate was determined. Large time gaps occur above MF2 and MF1, indicating that most of the record of the last glaciation is missing in the standard sections at Basaharc, Mende, and Paks. Either large discontinuities or a very low accumulation rate occurred in all three type sections during the soil-forming periods. High-resolution studies of climatic proxies using this combined luminescence dating approach provide a reliable chronological framework for loess and loess derivatives of the last glacial cycle in Hungary, although a precise and complete chronostratigraphic reconstruction cannot be achieved from the incomplete records found at these sites. 相似文献
99.
100.
临兴区块上古生界储集层为致密砂岩,裂缝发育特征及对致密气富集影响尚不清楚,一定程度上制约了甜点区预测。
根据岩心、露头、薄片及测井资料,分析了研究区裂缝发育特征,探讨了裂缝对致密砂岩气富集的影响。临兴区块上古生界主
要发育高角度缝,其次为中低角度缝及水平缝,微观上根据裂缝与矿物颗粒的相对位置关系,可识别出粒内缝、粒缘缝和穿粒
缝,其中粒缘缝最为发育。受塑性泥岩阻挡,裂缝垂向延伸较差,一般延伸1~2 m后消失于泥岩层中,受燕山期北西—南东向
地应力影响,裂缝走向多为北东—南西向,裂缝密度一般2~5条/m。裂缝可改善储集空间、提高油气充注效率,储层裂缝发育
区渗透率可增大1~2个数量级,含气饱和度高,此外,研究区裂缝是油气垂向运移的有效通道,影响着石盒子组及石千峰组致
密气的富集,在后期的勘探开发过程中应充分寻找裂缝发育区,并通过进一步压裂获得高产。 相似文献