Deep incision in an Aptian carbonate succession indicates major sea‐level fall in the Cretaceous     

Telm Bover‐Arnal  Ramon Salas  Joan Guimerà  Josep Anton Moreno‐Bedmar 《Sedimentology》2014,61(6):1558-1593

Long‐term relative sea‐level cycles (0·5 to 6 Myr) have yet to be fully understood for the Cretaceous. During the Aptian, in the northern Maestrat Basin (Eastern Iberian Peninsula), fault‐controlled subsidence created depositional space, but eustasy governed changes in depositional trends. Relative sea‐level history was reconstructed by sequence stratigraphic analysis. Two forced regressive stages of relative sea‐level were recognized within three depositional sequences. The first stage is late Early Aptian age (intra Dufrenoyia furcata Zone) and is characterized by foreshore to upper shoreface sedimentary wedges, which occur detached from a highstand carbonate platform, and were deposited above basin marls. The amplitude of relative sea‐level drop was in the order of tens of metres, with a duration of <1 Myr. The second stage of relative sea‐level fall occurred within the Late Aptian and is recorded by an incised valley that, when restored to its pre‐contractional attitude, was >2 km wide and cut ≥115 m down into the underlying Aptian succession. With the subsequent transgression, the incision was backfilled with peritidal to shallow subtidal deposits. The changes in depositional trends, lithofacies evolution and geometric relation of the stratigraphic units characterized are similar to those observed in coeval rocks within the Maestrat Basin, as well as in other correlative basins elsewhere. The pace and magnitude of the two relative sea‐level drops identified fall within the glacio‐eustatic domain. In the Maestrat Basin, terrestrial palynological studies provide evidence that the late Early and Late Aptian climate was cooler than the earliest part of the Early Aptian and the Albian Stage, which were characterized by warmer environmental conditions. The outcrops documented here are significant because they preserve the results of Aptian long‐term sea‐level trends that are often only recognizable on larger scales (i.e. seismic), such as for the Arabian Plate.  相似文献   

Petrogenesis of the Yangchang Mo‐bearing granite in the Xilamulun metallogenic belt,NE China: geochemistry,zircon U–Pb ages and Sr–Nd–Pb isotopes     

Qingdong Zeng  Jinhui Yang  Zuolun Zhang  Jianming Liu  Xiaoxia Duan 《Geological Journal》2014,49(1):1-14

The Yangchang granite‐hosted Mo deposit is typical of the Xilamulun metallogenic belt, which is one of the important Mo–Pb–Zn–Ag producers in China. A combination of major and trace element, Sr, Nd and Pb isotope, and zircon U–Pb age data are reported for the Yangchang batholith to constrain its petrogenesis and Mo mineralization. Zircon LA‐ICPMS U–Pb dating yields mean ages of 138 ± 2 and 132 ± 2 Ma for monzogranite and granite porphyry, respectively. The monzogranites and granite porphyries are calc‐alkaline with K₂O/Na₂O ratios of 0.75–0.92 and 1.75–4.42, respectively. They are all enriched in large‐ion lithophile elements (LILEs) and depleted in high‐field‐strength elements (HFSEs) with negative Nb and Ta anomalies in primitive‐mantle‐normalized trace element diagrams. The monzogranites have relatively high Sr (380–499 ppm) and Y (14–18 ppm) concentrations, and the granite porphyries have lower Sr (31–71 ppm) and Y (5–11 ppm) concentrations than those of monzogranites. The monzogranites and granite porphyries have relatively low initial Sr isotope ratios of 0.704573–0.705627 and 0.704281, respectively, and similar ²⁰⁶Pb/²⁰⁴Pb ratios of 18.75–18.98 and 18.48–18.71, respectively. In contrast, the ε_Nd(t) value (−3.7) of granite porphyry is lower than those of monzogranites (−1.5 to −2.7) with Nd model ages of about 1.0 Ga. These geochemical features suggest that the monzogranite and granite porphyries were derived from juvenile crustal rocks related to subduction of the Paleo‐Pacific plate under east China. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

从地壳上地幔构造看大陆岩石圈伸展与裂解     

杨文采 《地质论评》2014,60(5):945-961

本篇讨论大陆岩石圈拆沉、伸展与裂解作用过程。由于大陆岩石圈厚度大而且很不均匀,产生裂谷的机制比较复杂。大陆碰撞远程效应的触发,岩石圈拆沉,以及板块运动的不规则性和地球应力场方向转折,都可能产生岩石圈断裂和大陆裂谷。岩石圈拆沉为在重力作用下"去陆根"的作用过程,演化过程可分为大陆根拆离、地壳伸展和岩石圈地幔整体破裂三个阶段。大陆碰撞带、俯冲的大陆和大洋板块、克拉通区域岩石圈,都可能产生岩石圈拆沉。大陆岩石圈调查表明,拉张区可见地壳伸展、岩石圈拆离、软流圈上拱和热沉降;它们是大陆岩石圈伸展与裂解早期的主要表现。从初始拉张的盆岭省到成熟的张裂省,拆离后地壳伸展成复式地堑,下地壳幔源玄武岩浆侵位,断裂带贯通并切穿整个岩石圈,表明地壳伸展进入成熟阶段。中国东北松辽盆地和西欧北海盆地曾处于成熟的张裂省。岩石圈破裂为岩浆侵位提供了阻力很小的通道网。岩浆侵位作用伴随岩石圈破裂和热流体上涌,成熟的张裂省可发展成大陆裂谷。多数的大陆裂谷带并没有发展成威尔逊裂谷带和洋中脊,普通的大陆裂谷要演化为威尔逊裂谷带,必须有来自软流圈的长期和持续的热流和玄武质岩浆的供应。威尔逊裂谷带岩石圈地幔和软流圈为地震低速带,其根源可能与来自地幔底部的地幔热羽流有关。  相似文献   

苏鲁造山带古元古代超高温麻粒岩及其构造意义   总被引：1，自引：0，他引：1  

雷恒聪  向华  张泽明  祁敏  董昕  林彦蒿 《岩石学报》2014,30(8):2435-2445

本文报道了在苏鲁超高压变质带北端威海地区识别出的古元古代超高温泥质麻粒岩。泥质麻粒岩与大理岩、钙硅酸盐岩和片麻岩等变质表壳岩伴生。这些表壳岩以透镜体的形式产于经历了三叠纪超高压变质的新元古代正片麻岩中。泥质麻粒岩由石榴石、夕线石、斜长石、钾长石、反条纹长石、石英、黑云母、白云母和金红石组成。黑云母和白云母呈石榴石和夕线石的冠状体产出,为退变质矿物。相平衡模拟结果表明,麻粒岩峰期变质的温度和压力条件为~940℃和~1.2GPa。泥质麻粒岩中的锆石近等粒状或椭圆形,具有扇状或冷杉状分带,大多数具有平坦甚至亏损的重稀土配分模式,并有Eu负异常,为典型的麻粒岩相变质锆石。锆石的LA-ICP-MS U-Pb定年结果给出了1845±9Ma的207Pb/206Pb加权平均年龄,表明超高温麻粒岩形成于古元古代。结合现有的其他研究结果,我们推测扬子板块北缘经历了古元古代的增生造山作用。  相似文献   

基于逾渗模型的盐岩损伤与破坏研究     

孙中秋  谢凌志  刘建锋 《岩土力学》2014,299(2):441-448

逾渗是一种分形模型,利用声发射点定位盐岩内部破坏网格来建立逾渗模型,可以分析三轴压缩条件下盐岩逾渗特征以及损伤演变发展。研究发现,各试样逾渗模型团簇(cluster)数与最大团簇占有率关系曲线斜率在70%应力峰值后基本相等,利用最大团簇沿试样轴向的延伸来描述裂缝的扩展规律,并通过最大团簇在轴向的延伸终点得到了各试样逾渗的临界破坏比率,它对于研究渗透陡增点非常重要。提出利用逾渗关联长度(关联长度?代表处于同一团簇中的两个点的平均距离)确定试样损伤起始点,并通过计算逾渗模型破坏比率得到损伤变量,它和基于AE振铃计数以及AE能量计算得到的损伤变量结果相近。研究结果表明,逾渗可以形象地表述岩石内部破裂过程和损伤情况,为研究岩石破坏失效及裂缝衍生发展提供了新的思路。  相似文献   

空间集聚对在京日企就业规模的影响研究     

王茂军  马慧汶  邵静  曹田敏达 《地理研究》2022,41(7):1845-1863

FDI企业的空间集聚已经成为重要空间现象,但其对FDI企业规模的影响尚未引起学者的重视。既有研究发现的国家尺度集聚对制造业企业规模扩张的促进效应,是否适用于制造业和服务业共存的大都市区尺度?这也需要进行再商榷。论文基于企业内部生产技术条件、企业外部交易行为,搭建了大都市区范围内企业规模分异的解析框架,利用在京日企微观数据,分析了其空间集聚特征,讨论了其就业规模与分工的时空间变动特征,解析了集聚对在京日企的就业规模影响。研究发现：① 在京日企围绕集聚中心,呈现清晰的中心-外围分异特征。1995—2016年,集聚程度增强,集聚区重心外移,集聚空间规模扩大。2016年时形成了使馆区-CBD集聚区、BDA亦庄集聚区、首都机场集聚区、Z-Park中关村集聚区。② 在京日企的单环节化、服务化空间分异特征明显。单环节日企更临近分布重心,复合环节日企更趋外;服务型日企更趋中,生产型日企更趋外。集聚区内服务功能型日企更多,集聚区外生产功能型的日企更多。③ 新增日企,无论单环节还是复合环节日企,就业规模均显著减小。越是临近分布重心、越是位于集聚区内的日企,平均就业规模越小。④ 大都市区范围内,集聚更利于吸引中小日企扎堆布局,更利于抑制其规模扩张冲动;日企主营业务的技术经济特点会影响分工作用的显现,隶属行业、进驻时长和独合资模式等也有显著性影响。  相似文献   

Aseismic deep subduction of the Philippine Sea plate and slab window     

《Journal of Asian Earth Sciences》2013

We have made great efforts to collect and combine a large number of high-quality data from local earthquakes and teleseismic events recorded by the dense seismic networks in both South Korea and West Japan. This is the first time that a large number of Korean and Japanese seismic data sets are analyzed jointly. As a result, a high-resolution 3-D P-wave velocity model down to 700-km depth is determined, which clearly shows that the Philippine Sea (PHS) plate has subducted aseismically down to ∼460 km depth under the Japan Sea, Tsushima Strait and East China Sea. The aseismic PHS slab is visible in two areas: one is under the Japan Sea off western Honshu, and the other is under East China Sea off western Kyushu. However, the aseismic PHS slab is not visible between the two areas, where a slab window has formed. The slab window is located beneath the center of the present study region where many teleseismic rays crisscross. Detailed synthetic tests were conducted, which indicate that both the aseismic PHS slab and the slab window are robust features. Using the teleseismic data recorded by the Japanese stations alone, the aseismic PHS slab and the slab window were also revealed (Zhao et al., 2012), though the ray paths in the Japanese data set crisscross less well offshore. The slab window may be caused by the subducted Kyushu-Palau Ridge and Kinan Seamount Chain where the PHS slab may be segmented. Hot mantle upwelling is revealed in the big mantle wedge above the Pacific slab under the present study region, which may have facilitated the formation of the PHS slab window. These novel findings may shed new light on the subduction history of the PHS plate and the dynamic evolution of the Japan subduction zone.  相似文献   

Complex slab structure and arc magmatism beneath the Japanese Islands     

《Journal of Asian Earth Sciences》2013

A dense nationwide seismic network recently constructed in Japan has resulted in the production of a large amount of high-quality data that have enabled the high-resolution imaging of deep seismic structures in the Japanese subduction zone. Seismic tomography, precise locations of earthquakes, and focal mechanism research have allowed the identification of the complex structure of subducting slabs beneath Japan, revealing that the subducting Philippine Sea slab underneath southwestern Japan has an undulatory configuration down to a depth of 60–200 km, and is continuous from Kanto to Kyushu without disruption or splitting, even within areas north of the Izu Peninsula. Analysis of the geometry of the Pacific and Philippine Sea slabs identified a broad contact zone beneath the Kanto Plain that causes anomalously deep interplate and intraslab earthquake activity. Seismic tomographic inversions using both teleseismic and local events provide a clear image of the deep aseismic portion of the Philippine Sea slab beneath the Japan Sea north of Chugoku and Kyushu, and beneath the East China Sea west of Kyushu down to a depth of ∼450 km. Seismic tomography also allowed the identification of an inclined sheet-like seismic low-velocity zone in the mantle wedge beneath Tohoku. A recent seismic tomography work further revealed clear images of similar inclined low-velocity zones in the mantle wedge for almost all other areas of Japan. The presence of the inclined low-velocity zones in the mantle wedge across the entirety of Japan suggests that it is a common feature to all subduction zones. These low-velocity zones may correspond to the upwelling flow portion of subduction-induced convection systems. These upwelling flows reach the Moho directly beneath active volcanic areas, suggesting a link between volcanism and upwelling.  相似文献   

Contemporary crustal motion and deformation of South America plate     

Jin Shuanggen  Zhu Wenyao 《地球空间信息科学学报》2013,16(2):8-12

This paper presents the contemporary motion and active deformation of South America plate and relative motion of Nazca-South America plate using space geodetic data. The South America plate is moving at average 14.5 mm/a with an azimuth of 15.2° and shrinking in the west-east at 10.9 mm/a. The geodetic deformations of sites with respect to the South America plate are in quite good agreement with the estimated deformations from NNR-NUVEL1A, but the deformation of the western South America regions is very large.  相似文献   

Axisymmetric wave propagation in multilayered poroelastic grounds due to a transient acoustic point source     

《Soil Dynamics and Earthquake Engineering》2013

This paper deals with the study of axisymmetric wave propagation in various acoustic/porous stratified media coupling configurations. It presents the theoretical developments of a semi-analytical method, its validation for a limit test-case half-space ground, and an extension to a realistic multilayered seabed, when spherical waves are emitted from a transient point source in water.  相似文献