Lithospheric thinning and ignition of a Cordilleran magmatic flare-up: Geochemical and O-Hf isotopic constraints from Cretaceous plutons in southern Korea     

《地学前缘(英文版)》2023,14(1):101492

Northeast Asian continental margins contain the products of magma emplacement driven by prolonged subduction of the (paleo-)Pacific plate. As observed in many Cordilleran arcs, magmatic evolution in this area was punctuated by high-volume pulses amid background periods. The present study investigates the early evolution of the Cretaceous magmatic flare-up using new and published geochronological, geochemical, and O-Hf isotope data from plutonic rocks in the southern Korean Peninsula. After a long (～50 m.y.) magmatic hiatus and the development of the Honam Shear Zone through flat-slab subduction, the Cretaceous flare-up began with the intrusion of monzonites, granodiorites, and granites in the inboard Gyeonggi Massif and the intervening Okcheon Belt. Compared to Jurassic granitoids formed during the former flare-up, Albian (～111 Ma) monzonites found in the Eopyeong area of the Okcheon Belt have distinctly higher zircon ε_Hf(t) (?7.5 ± 1.3) and δ¹⁸O (7.78‰ ± 0.25‰) values and lower whole-rock La/Yb and Sr/Y ratios. The voluminous coeval granodiorite and granite plutons in the Gyeonggi Massif are further reduced in Sr/Y and to a lesser extent, in La/Yb, and have higher zircon ε_Hf(t) values (?13 to ?19) than the Precambrian basement (ca. ?30). These chemical and isotopic features indicate that Early Cretaceous lithospheric thinning, most likely resulting from delamination of tectonically and magmatically overthickened lithospheric keel that was metasomatized during prior subduction episodes, and consequent asthenospheric upwelling played vital roles in igniting the magmatic flare-up. The O-Hf isotopic ranges of synmagmatic zircons from the Albian plutons and their Paleoproterozoic and Jurassic inheritance attest to the involvement of lithospheric mantle and crustal basement in magma generation during this decratonization event. Arc magmatism then migrated trenchward and culminated in the Late Cretaceous, yielding widespread granitoid rocks emplaced at shallow crustal levels. The early Late Cretaceous (94–85 Ma) granites now prevalent in Seoraksan-Woraksan-Sokrisan National Parks are highly silicic and display flat chondrite-normalized rare earth element patterns with deep Eu anomalies. Synmagmatic zircons in these granites mimic their host rock’s chemistry. Delamination-related rejuvenation of crustal protoliths is indicated by zircon ε_Hf(t) values of granites (?6 to ?20) that are consistently higher than the Precambrian basement value. Concomitant core-to-rim variation in zircon O-Hf isotopic compositions reflects a typical sequence of crustal assimilation and fresh input into the magma chamber.  相似文献   

规模经济、对外贸易与区域双核结构模式探讨——以山东半岛济南—青岛双核结构为例     

盛科荣  孙威 《地理科学进展》2012,31(12):1636-1644

区域双核结构模式是一种重要的经济地理现象。基于新经济地理学的研究视角和分析框架,论文构建模型,分析了规模经济和对外贸易推动区域双核结构模式的生成过程和经济机理。模型研究表明,规模经济和对外贸易是塑造区域双核结构模式的基本力量:规模经济的增强放大了本地市场效应,导致了区域核心城市的出现;对外贸易影响着沿海地区的经济地理优势,决定着港口区位核心城市和内陆地区核心城市的并存。山东半岛济南—青岛双核结构模式生成过程的实证研究也表明,双核结构模式是制造业活动完成由以手工业为主导向现代化大生产为主导转变、区域发展环境完成由相对封闭向相对开放转变之后才产生的经济地理现象。  相似文献   

中南半岛与南海热力差异对南海季风爆发的影响   总被引：5，自引：1，他引：4  

刘宣飞  李青  何金海  王平 《气象学报》2009,67(1):100-107

利用1958-1998年NCEP/NCAR再分析资料和1975-1998年OLR资料,分析了中南半岛与南海热力差异的季节和年际变化特征,以及这种热力差异对南海季风爆发的影响.结果表明,中南半岛与南海热力差异存在明显的季节变化,从第3候歼始,感热加热的作用使中南半岛地表温度高于南海并一直持续到第25候,之后,中南半岛与南海热力差异发生逆转,这种逆转是由于第22-23候出现在中南半岛的对流及降水造成中南半岛地表温度降低所致.进一步研究指出,中南半岛与南海热力差异的上述季节变化特征还表现出最著的年际差异,这种年际差异对南海季风的爆发有着重要影响.首先,上述热力差异的逆转是南海季风爆发的一个必要条件:1958-1998年,逆转时间均早于(或等于)南海季风爆发时间;其次,中南半岛地表温度高于南海的持续时间与南海季风爆发日期之间呈显著正相关,即中南半岛地表温度高于南海的时间越早、转为低于南海的时间越迟,则南海季风爆发越迟.  相似文献   

辽东半岛一次大暴雨的中尺度模拟及物理结构分析   总被引：3，自引：3，他引：0       下载免费PDF全文

李燕  邹耀仁  胡筱敏  叶成志 《高原气象》2009,28(4):915-923

2005年7月25日辽东半岛南部及海峡地区发生了大暴雨天气。利用中尺度模式MM5的双向二重嵌套网格对其进行模拟, 表明该模式对这次暴雨过程有较好的模拟能力。模拟的地面气压场及流场基本与客观分析场一致。模拟结果较好地再现了辽东半岛大暴雨的大尺度和中尺度天气系统的发展和演变, 揭示了造成此次暴雨的中尺度系统结构为高空强辐散, 低空强辐合及对应的强上升运动和气旋性涡柱是造成此次暴雨的动力机制, 低空西南气流对这次暴雨的产生和发展起着重要的作用。  相似文献   

Zircon U-Pb age,geochemical and Nd isotopic data of Middle Jurassic high-Mg dioritic dike in Liaodong Peninsula,NE China     

LI Zhuang  ;PEI Fuping  ;MENG En 《世界地质(英文版)》2014,17(3):143-154

Zircon LA-ICP-MS U-Pb age, geochemical and Nd isotopic data are presented for a newly recognized high-Mg dioritic dike from Haicheng, Liaodong Peninsula, NE China, to constrain its petrogenesis. The zircons from the high-Mg diorite exhibit striped absorption and oscillatory growth zoning in the cathodoluminescence （CL） images, and have high Th/U ratios （0. 05-0.9）, indicating a magma origin. Zircon LA-ICP-MS U-Pb dating indicates that 206pb/238U ages of 12 spots of zircons are between 167 Ma and 178 Ma, yielding a weighted mean 206pb/238U age of 172 ＋ 2 Ma （MSWD =4. 1 ）, which represents the forming age of the high-Mg dioritic dike, i. e. Middle Jurassic. Geochemically, the samples have SiO2 =55.4-60. 6 wt. % , Na20 =2. 2-2.76 wt. % , K20 = 1.32-2. 02 wt. % and （Na2O ＋ K2O） =3.82--4. 47 wt. %, belonging to sub-alkaline series and displaying a calc-alkaline evolutionary trend. They are characterized by high MgO （4. 75-6.85 wt. % ）, Mg# （55-61）, Cr（130-262 ppm）, Ni（63-130 ppm）, Sr（568-857 ppm）, and Ba（484-1 130 ppm） contents, with geochemical features analogous to those of high-Mg adakites. They show variable end （t） values （ - 1.3 to - 3.9） , with a weighted value of - 2. 7, which plot intermediately between the field of the ancient continental crust and the depleted mantle source, indicating that both the lower crust and mantle source are necessary for the generation of the parent magma of the Haicheng high-Mg diorites. The Haicheng high-Mg dioritic dike in the Liaodong Peninsula and the Jurassic magmatism in the eastern North China Craton formed under a continental crustal thickening setting that may be related to subduction of the Paleo-Pacific oceanic plate.  相似文献   

胶东辽上特大型金矿床地质特征          下载免费PDF全文

纪攀  丁正江  李国华  宋明春  钱烨 《山东国土资源》2016,32(6)

辽上金矿床位于胶东新发现的胶莱盆地东北缘成矿区之内,为胶东东部首例特大型金矿。矿区金成矿以充填作用为特征,载金矿物主要为自形—半自形结构黄铁矿和白云石,以网脉状、细脉状、微细脉状黄铁矿白云石细脉形式出现于岩石碎裂隙中,或以黄铁矿白云石大脉状充填于断裂构造中。矿石包括含金黄铁矿白云石脉型和含黄铁矿白云石脉蚀变岩型2大类。通过对比认为,该矿床为一新类型,即黄铁矿白云石脉型金矿床。这一新类型特大型金矿的发现,预示着胶莱盆地边缘地区具有较好的找矿前景,尤其在金牛山地区应有可能在短期内取得更大的找矿突破。  相似文献   

A Mineralogical Study of Diatomite in Leizhou Peninsula   总被引：5，自引：0，他引：5  

王辅亚  张惠芬等 《中国地球化学学报》1995,14(2):140-151

In this paper diatomite samples taken from the Leizhou Peninsula have been studied by chemical analysis, DTA, TG, XRD, IR ,SEM and X-ray Energy Spectroscopy.The study shows that the diatomaceous genera and species and their organic contents are variable with buried depth ,from Melosira to Stephanodiscus and then to Cyclotella. Various impurities in the samples, such as quartz, kaolinite and montmorillonite indicate different sedimentary environments. When heated, the diatom would change in shape due to the phase transformation in which amorphous silica crystallized from disordered opal to ordered cristobalite. The temperatures of phase transformation are different for various diatoms due to the presence of different impurities and constituents of diatomaceous genera and species.  相似文献   

胶东西北部北截岩体岩石成因:锆石U-Pb年龄、岩石地球化学与Sr-Nd-Pb同位素制约   总被引：1，自引：0，他引：1  

宋英昕  于学峰  李大鹏  耿科  尉鹏飞  左晓敏  王秀凤 《岩石学报》2020,36(5):1477-1500

胶东半岛西北部是我国最重要的金矿集区,95%以上的金资源储量赋存于晚侏罗世玲珑型和早白垩世郭家岭型花岗岩中。然而,对郭家岭型花岗岩形成的大地构造背景及其与金成矿的关系,尤其是岩石成因仍存有争议。本文通过对归属于郭家岭型花岗岩的北截岩体开展详细的岩相学、岩石地球化学、锆石U-Pb年代学和Sr-Nd-Pb地球化学研究,识别出细粒花岗闪长岩、含斑细粒花岗闪长岩、斑状中粒花岗闪长岩、斑状粗粒花岗闪长岩和花岗伟晶岩脉5种侵入岩类型,它们具有相似的地球化学特征和同位素组成,呈连续演化关系,为同一期岩浆活动的产物。电子探针分析显示,样品中的黑云母具有富FeO~T、MgO、高Al_2O3低TiO_2的特点,为岩浆成因的富铁黑云母,Mg和Al元素的负相关性表明结晶过程中二者可能发生了置换。岩石地球化学研究表明,花岗闪长岩具有高的全碱(K_2O+Na_20=6.92%～9.31%)、Ba(518×10~(-6)～3330×10~(-6))、Sr(305×10~(-6)～1371×10~(-6)),低的Al_2O_3(14.41%～15.82%)、MgO(0.19%～0.77%)、Rb(39.3×10~(-6)～105×10~(-6))、Y(1.2×10~(-6)～6.05×10~(-6))、Yb(0.08×10~(-6)～0.40×10~(-6))含量特征,轻稀土(LREE)富集、重稀土(HREE)相对亏损(LREE/HREE=13.13-21.40),轻、重稀土元素分馏明显[(La/Yb) N=18.39～45.76],Rb、Sr、Ba、Pb等大离子亲石元素(LILE)富集,Nd、Ta、Zr、Hf等高场强元素(HFSE)明显亏损,具有高Ba-Sr花岗岩的地球化学特征。锆石LA-ICP-MS定年结果表明,斑状粗粒花岗闪长岩形成于131.53±0.86Ma,花岗伟晶岩脉形成于127.4±1.3Ma,说明其形成于早白垩世早期,伟晶岩脉应该是本次岩浆活动后期的产物。Sr-Nd同位素分析表明,初始~(87)Sr/~(86)Sr(I_(Sr))和ε_(Nd)(t)分别为0.710658-0.711568和-18.53～-11.17,二阶段亏损地幔模式年龄(t_(DM2))为2107-2425Ma,与胶东群变质岩年龄一致,指示了其原始岩浆有部分熔融的胶东群参与;Pb同位素分析表明,初始~(206)Pb/~(204)Pb和初始~(208)Pb/~(204)Pb分别为17.047～17.945和37.744～38.389,说明有大量的下地壳物质参与成岩。上述数据分析表明,北截岩体是基底岩石胶东群变质岩部分熔融形成的下地壳酸性岩浆与幔源基性岩浆混合作用的结果,太平洋板块向欧亚板块俯冲构造背景下的软流圈物质上涌和下地壳的部分熔融可能是形成这套花岗岩的机制,是板块俯冲产生的欧亚板块边缘火山弧的组成部分;在区域金成矿方面,其为金成矿提供了有利的赋存空间,而应该不是成矿流体来源或热动力条件。  相似文献   

Regional significance of kilometric-scale north-east vergent recumbent folds associated with east to south-east directed shear on the southern border of the Central Iberian Zone (Hornachos-Oliva region,Variscan belt,Iberian Peninsula)     

A. Azor  F. González Lodeiro  D. Martínez Poyatos  J. F. Simancas 《International Journal of Earth Sciences》1994,83(2):377-387

On the southern border of the Central Iberian Zone there are two sectors with different styles of deformation. To the south-west, in the Hornachos sector, large-scale recumbent folds associated with ductile shearing can be seen. This shearing is characterized by a direction of movement parallel to the fold axes and can be correlated for 150 km along strike. The K-values of the strain ellipsoid range from 0.8 to 2.0. Stretching in the X direction, parallel to the recumbent fold axes, is more than 100%. To the north-east, in the Oliva sector, first-phase folds are upright and the strain intensity is lower than in the Hornachos sector. Metamorphic, geometric and kinematic considerations lead us to conclude that the shearing in the Hornachos sector is better explained as conjugate to a main shear zone along which the southern border of the Central Iberian Zone is moved onto the Ossa-Morena Zone. This main thrust is at present obliterated by a left-lateral extensional shear zone that affects a high pressure exotic unit located between the Central Iberian and the Ossa-Morena Zones. This high pressure unit constitutes a suture of the Variscan belt in the Iberian Peninsula.  相似文献   

Meteorological factors associated with floods in the north-eastern part of the Iberian Peninsula     

M. C. Llasat  M. Puigcerver 《Natural Hazards》1994,9(1-2):81-93

The main meteorological features of catastrophic rainfall events in Catalonia are described. Data come from several sources listed in the text. Surface and upper air synoptic and some subsynoptic conditions under which these events occur are described. Two kinds of events are identified, depending on the amount of forced lift required to release potential instability: Type A events, which take place on the coastal area when the forcing due to littoral and prelittoral hills is enough, and type B events require a large forced lift and occur near the Pyrenees. Local topographical and mesoscale meteorological conditions turn out to have a relevant role in connection with such events.  相似文献