Late Cretaceous magmatic activity in the southern Lhasa terrane: insights from the Dazhuqu hornblende gabbro and the Xietongmen granite porphyry     

《International Geology Review》2012,54(13):1642-1665

ABSTRACT

The mechanisms triggering the emplacement of Cretaceous magmatic rocks related to Neo-Tethyan subduction in the southern Lhasa subterrane (SLT) remain controversial because geochronological, geochemical, and isotopic data from the Cretaceous magmatic rocks in the western portion of the SLT are lacking. This paper provides the first report indicating that the Dazhuqu hornblende gabbro and Xietongmen granite porphyry were generated in the Late Cretaceous (ca. 100 Ma and ca. 68 Ma, respectively) in the western portion of the SLT. The Dazhuqu hornblende gabbro is characterized by high MgO, Na₂O, Cr, Co, and Mg^# values, enrichment in light rare earth elements (LREEs) and large ion lithophile elements (LILEs), and depletion in high field strength elements with no Eu anomalies. The Xietongmen granite porphyry displays high SiO₂, low MgO, Mg^#, Cr, Co, and Ni, enrichment in LREEs and LILEs, flat heavy rare earth element (HREE) patterns and negative Eu anomalies. Zircons from the Dazhuqu hornblende gabbro and Xietongmen granite porphyry display high positive ε_Hf(t) ranges from 11.79 to 14.91 and from 9.05 to 12.38, respectively. The Dazhuqu hornblende gabbro was produced by the partial melting of 12–15% garnet peridotite in the depleted mantle that was metasomatized by fluids released from the dehydrating subducted Neo-Tethyan oceanic slab. This magma was then emplaced at an upper crustal depth of 5.3–7.0 km. The Xietongmen granite porphyry was generated by the partial melting of underplated basaltic crust during the subduction of the Neo-Tethyan oceanic crust and formed in the presence of pyroxene, plagioclase, and minor hornblende in its magmatic source. In combination with previously published data from Cretaceous magmatic rocks in the SLT, our data suggest that the petrogenesis of the Dazhuqu hornblende gabbro was related to flat or low-angle slab subduction of the Neo-Tethyan oceanic crust during 109–97 Ma and that the formation of the Xietongmen granite porphyry was related to lithospheric delamination in the western portion of the SLT after ca. 68 Ma.  相似文献   

Late orogenic rebound and oblique Alpine convergence: New constraints from subsidence analysis of the Austrian Molasse basin   总被引：1，自引：1，他引：0  

Johann Genser  Sierd A.P.L. Cloetingh  Franz Neubauer   《Global and Planetary Change》2007,58(1-4):214

Subsidence analysis of 16 wells in the Austrian Molasse basin documents major spatial and temporal changes in tectonic subsidence as well as a late-stage surface uplift. The timing of the main phase of tectonic subsidence shifted from early Oligocene in the western part of the peripheral foreland to the early Miocene in the eastern part. These temporal and spatial changes in tectonic subsidence reflect a change from oblique dextral to sinistral convergence between the Alpine nappe stack and its foreland. The main phase of sediment accumulation was delayed to the early Miocene and led to the infill of the basin and a major second, sediment-load driven phase of basement subsidence. Sediment accumulation rates in the basin reflect the build-up of topography in the Alpine mountain chain. Since approximately 6 Ma a pronounced regional uplift of the entire Molasse basin has taken place, marking the transition from lateral extrusion to orthogonal contraction within the Alpine system and deep-seated changes in geodynamic boundary conditions, possibly due to delamination of previously thickened lithosphere. Surface uplift is contemporaneous with similar processes in extra-Alpine Central Europe, where it is interpreted to reflect intra-plate stress changes.  相似文献   

托云盆地新生代幔源岩浆源区起止深度的限定   总被引：2，自引：0，他引：2  

梁涛  罗照华  李德东  黄凡  杨宗锋  陈必河 《岩石学报》2008,24(12):2820-2838

在详细介绍了地幔熔融柱模型原理(Langmuir et al., 1992)的基础上,基于平衡熔融和分离熔融模型分别计算获得了上地幔橄榄岩源区在不同初始压力条件下发生绝热减压部分熔融时熔体相中FeO-MgO和FeO-Na₂O成分的演化轨迹。依据深源岩石包体与托云玄武岩之间的寄主关系将本次研究的16件托云火山岩样品划分成Group-1(深源岩石包体寄主岩)和Group-2(非寄主岩)两群,将收集前人的40件样品依据是否测试获得FeO的质量百分含量划分成Group-3群(具有实测的FeO质量百分含量)和Group-4群(无实测FeO质量百分含量数据)。分别对以上四群样品运用地幔熔融柱模型进行反演获得上地幔部分熔融源区的起止深度范围：Group-1和Group-3样品具有相同的初始熔融深度113.2km (34.1kbar),但它们的部分熔融作用终止深度分别为110.1km (33.1kbar) 和88.4km (26.2kbar);Group-2样品数据所反演的岩浆起源的初始深度和终止深度分别为111.6km (33.6kbar)和84.3.1km(24.9kbar);Group-4样品反演所获得的岩浆源区的起止深度分别为121.7km(36.8kbar)和106.0km(31.8kbar)。依据实测FeO百分含量的样品群反演的结果,将托云火山岩部分熔融源区的深度限定在113.2 km至84.3km,即48.1Ma前托云盆地所处的岩石圈厚度为84.3km,对梁涛(2005)运用熔融柱模型反演的托云盆地岩石圈深度进行了修正。此外,由地幔熔融柱模型反演获得的托云火山岩部分熔融源区熔体的温度压力条件与基于玄武岩中高压巨晶所反演的岩浆演化温压轨迹具有十分吻合的继承演化关系。地球物理探测表明现今西南天山岩石圈的厚度为71km,区域岩石圈演化历程中深度上13.3km的差异足以证明岩石圈拆沉这一地球动力学过程的存在,为由宽SHRIMP年龄谱识别出的岩石圈拆沉作用提供了另一个有力的证据。  相似文献   

再论兴隆沟组火山岩成因   总被引：2，自引：0，他引：2  

邵济安  路凤香 《岩石学报》2008,24(6):1313-1322

本文通过对辽西北票地区兴隆沟组安山质火山岩的组分和岩相学研究,发现作为捕虏晶的斜方辉石存在反环带和韵律环带.根据具反环带结构的斜方辉石的微量元素丰度研究,提出兴隆沟组火山岩是岩浆混合作用的产物而非下地壳拆沉作用的产物.对比华北克拉通北缘不同时代,不同成因的单斜辉石,推测辉石有可能来源于早中生代下地壳的堆晶岩.  相似文献   

中国东部岩石圈减薄时间的制约及构造控制因素探讨   总被引：1，自引：0，他引：1  

袁平  王俊烈  齐成栋  卢兴波  张俊影 《吉林地质》2008,27(1)

华北地块中生代含幔源包体玄武岩同位素年龄、岩石化学、地球化学及Sr-Nd同位素研究成果表明:119 Ma~110 Ma之间华北地块岩石圈地幔性质由富集型岩石圈地幔转化为亏损的软流圈地幔,岩石圈地幔性质的显著变化,说明中国东部岩石圈减薄的主要时间发生在早白垩世晚期119~100 Ma之间。中生代古太平洋伊泽奈崎大洋板块(Izanagi Plate)向欧亚板块俯冲所导致的拆沉,应是岩石圈减薄的重要控制因素。  相似文献   

Petrogenesis of the Mesozoic intrusive rocks in the Tongling area,Anhui Province,China and their constraint on geodynamic process   总被引：39，自引：0，他引：39  

王强  许继峰  赵振华  熊小林  包志伟 《中国科学D辑(英文版)》2003,46(8):801-815

TheTonglingarea,whichiscalledtheChineseCopperCapital,isoneofthemostimportantnon-ferrousmetalproducersinChina(e.g.Cu,AuandAg,especiallyCu).ManyresearchershavenotedthatthemetaldepositsarecloselyrelatedtotheMesozoicintrusiverocksinthisarea.Therefore,theTongl…  相似文献   

A-type granite and adakitic magmatism association in Songpan–Garze fold belt, eastern Tibetan Plateau: Implication for lithospheric delamination     

Hong-Fei Zhang  Randall Parrish  Li Zhang  Wang-Chun Xu  Hong-Lin Yuan  Shan Gao  Quentin G. Crowley 《Lithos》2007,97(3-4):323-335

The Songpan–Garze fold belt covers a huge triangular area (> 200,000 km²), confined by the South China (Yangtze), North China and Tibetan Plateau continental blocks. In the Songpan–Garze fold belt, Triassic adakitic granitoids have been identified. However, whether there are Triassic A-type granites is unclear. Here, we report our first finding of an A-type granite (Nianbaoyeche), which occurs in the central part of the Songpan–Garze fold belt. The Nianbaoyeche granite ( 820 km²) is characterized by arfvedsonite in its mineral assemblage. Using both LA-ICPMS and TIMS U–Pb zircon dating methods, we obtain a magma crystallization age of 211 ± 1 Ma, which is slightly younger than Triassic adakitic granitoids (216–221 Ma) in the Songpan–Garze fold belt. The Nianbaoyeche granite is enriched in Si, K, Na, Rb, REE, HFSE (Nb, Ta, Zr, Hf), with elevated FeO^tot/(FeO^tot + MgO) and Ga/Al ratios, but is depleted in Al, Mg, Ca, Ba and Sr. The REE compositions show moderately fractionated patterns with (La/Yb)_N = 2.67–7.54 and Eu/Eu = 0.09–0.34. These geochemical characteristics indicate that the Nianbaoyeche granite has an A-type affinity. Geochemical data and U–Pb zircon age, combined with regional studies, show that the Nianbaoyeche granite formed in a post-collisional tectonic setting. Sr–Nd isotopic data for the granite exhibit I_Sr = 0.7090–0.7123 and ε_Nd(t) = − 2.72 to − 4.26 with T_DM = 1.15–1.51 Ga, suggesting that the magma has a dominantly crustal source, though a minor contribution from the mantle cannot be ruled out. Melting to produce an A-type granite may have resulted from Triassic lithospheric delamination after Triassic crustal thickening of the Songpan–Garze fold belt due to convergence between the Yangtze, North China and North Tibet continental blocks. The lithospheric delamination model also helps to explain the Triassic adakitic magma generation in the Songpan–Garze belt. We conclude that association of A-type granite and adakitic granitoids in post-collisional environment could be a useful indicator of lithospheric delamination.  相似文献   

关于华北克拉通燕山期岩石圈减薄的机制与过程的讨论:是拆沉,还是热侵蚀和化学交代?   总被引：37，自引：5，他引：37  

邓晋福  苏尚国  刘翠  赵国春  赵兴国  周肃  吴宗絮 《地学前缘》2006,13(2):105-119

关于华北克拉通燕山期岩石圈减薄作用,主要有两种模型:(1)岩石圈拆沉;(2)热侵蚀和/或化学交代。文中主要从岩浆活动与构造变形两个途径,通过(1)燕山带造山幕和结构要素组合以及造山过程的p-T-t轨迹;(2)收缩构造变形、火成岩构造组合和下地壳岩石捕虏体3个独立证据提出陆壳的构造加厚;(3)火成岩成因的壳幔相互作用模型和热模拟等,试图讨论华北地区克拉通有浮力的岩石圈如何转变为密度大的岩石圈,随之发生拆沉作用,而不是热侵蚀或化学交代机制使岩石圈地幔改造为EMI印记实现的减薄作用。大量对流的软流圈物质注入克拉通是诱发陆壳发生局部熔融所必需的条件。底侵玄武质岩浆的加热并弱化先前的冷和强的克拉通地壳,创造一个流变学条件,以使收缩构造变形和陆壳加厚成为可能。陆壳最下部和岩石圈地幔中形成的大量玄武质岩石,在构造加厚作用下,相转变为榴辉岩,致使原先有浮力的岩石圈转变为密度大的岩石圈,随之发生拆沉作用。  相似文献   

Melting experiments on hydrous low-K tholeiite: Implications for the genesis of tonalitic crust in the Izu–Bonin – Mariana arc     

KATSUJI  NAKAJIMA & MAKOTO  ARIMA 《Island Arc》1998,7(3):359-373

A series of water-deficient partial melting experiments on a low-K tholeiite were carried out under lower crustal P–T–H₂O conditions (900–1200 °C, 0.7–1.5 GPa, 2 and 5 wt% H₂O added) using a piston-cylinder apparatus. With increasing temperature at 1.0 GPa, supersolidus mineral assemblages vary from amphibolitic to pyroxenitic. Garnet crystallizes in the higher pressure runs (> 1.2 GPa). Melt compositions show low-K calc-alkalic trends, and are classified as metaluminous or peraluminous tonalite. These features are similar to the felsic rocks in the Izu–Bonin – Mariana (IBM) arc, for example Tanzawa plutonic rocks. The anatectic origin of Tanzawa tonalites is consistent with geochemical modeling, which demonstrates that the rare earth element (REE) characteristics of Tanzawa plutonic rocks (which represent the middle crust of the IBM arc) can be generated by partial melting of amphibolite in the lower crust (∼ 50% melting at 1050 °C and below 1.2 GPa). Estimated densities of pyroxenitic restites (∼ 3.9 g/cm³) after extraction of andesitic melts are higher than that of mantle peridotite beneath the island arc (3.3 g/cm³). The high density of the restite could cause delamination of the IBM arc lower crust. Rhyolitic magmas in the IBM arc (e.g. Niijima) could be formed by low degrees of partial melting of the amphibolitic crust at a temperature just above the solidus (10% melting at or below 900 °C).  相似文献   

下地壳拆沉作用及大陆地壳演化   总被引：13，自引：0，他引：13  

高山 Ducea  MN 《高校地质学报》1998,4(3):241-249

讨论了下地壳拆沉作用的地球化学示踪方法,并以近来对秦岭－大别造山带和美国西部内华达岩基地区的研究成果为例,说明了下地壳拆沉在两地区壳－幔演化方面可能起的重要作用。  相似文献