Adakitic火成岩对大陆地壳增厚过程的指示:以青藏北部火山岩为例   总被引：38，自引：0，他引：38  

许继峰  王强 《地学前缘》2003,10(4):401-406

Adakitic火成岩可以通过几种不同的岩浆作用方式产生,其中下地壳镁铁质岩石的直接部分熔融和拆沉下地壳的部分熔融可能是两种重要的adakitic火成岩形成方式。在一个大陆厚地壳背景,adakitic火成岩的产生指示了它们的岩浆源区位于大于40 km的下地壳之中,因此,暗示该大陆地壳的最小厚度超过40 km。青藏高原腹地的羌塘地区分布有40 Ma左右的“低镁”和“高镁”adakitic安山岩-英安岩-流纹岩,它们应分别是青藏高原厚大陆地壳下部镁铁质岩石直接部分熔融和拆沉的下地壳脱水熔融的产物。这套adakitic火山岩的厘定指示出在40 Ma左右时,青藏羌塘地区或更大范围的大陆地壳已经加厚到超过40 km,其地表在当时或稍后可能已经开始了隆升。  相似文献   

辽东早元古造山带隆滑构造初析     

李三忠  杨振升  刘永江 《吉林大学学报(地球科学版)》1996,(3)

辽东早元古代裂谷带内的隆滑构造是在吕梁造山前期伸展体制下的第一幕变形期间形成的。本区隆滑构造的内核隆起部位大致与中南岩基空间分布一致，由同构造侵位的二长花岗岩（辽吉花岗岩）组成，在裂谷带西区和东区，辽吉花岗岩皆顺基底与盖层之间的接合面呈席状侵位。由于辽吉花岗岩局部隆起，引起外壳内多层滑脱型韧性剪切带（简称韧变带）及流褶层的形成，在递进变形过程中流褶层会发生尖灭。因变形分解作用，在形成韧变带及流褶层的同时，也形成一些巨型透镜体，它们为弱变形域或未变形域，其内原生构造保存完整。对流褶层内流动褶皱的倒向及拉伸线理的统计，结果进一步表明中南岩基为辽河群内隆滑构造的隆起部位。现今东区和西区的穹形构造是初始席状侵位的叠加性构造，即在吕梁运动期间收缩体制下，辽吉花岗岩仍呈塑性并向背斜部位聚集，呈底辟式重就位；第三幕构造形迹横跨叠加于第二幕构造形迹之上，从而最终使辽吉花岗岩有规律地分布于穹形构造核部。  相似文献   

Convective destabilization of a thickened continental lithosphere   总被引：2，自引：0，他引：2  

C. Morency  M.-P. Doin 《Earth and Planetary Science Letters》2002,202(2):303-320

Removal or delamination of the lithospheric mantle in a late stage of mountain building is a process often invoked to explain syn orogenic extension, high temperature metamorphism, magmatism and uplift. One mechanism that could explain the lithospheric root detachment is the development of convective instabilities within the peridotitic lithosphere due to its high density. This mechanism is studied by two-dimensional convective numerical simulations in the simple case of a strongly temperature dependent viscous rheology appropriate for upper mantle rocks. We neglect here the weakening effect of a brittle rheology and of a crustal layer, and therefore we did not model tectonic deformations. Depending on the upper mantle viscosity and activation energy, a 300 km thick root can be inferred to be either indefinitely stable or to thicken with time or to thin with time. When the lithosphere is initially thicker than its equilibrium thickness, the convective flow at the base and on the sides of the lithospheric root is strong enough to cancel downwards heat conduction and to progressively remove the root. This flow is due to the finite density perturbations induced by the topography of the isotherms on the base and at the sides of the root. We derive two general parameterizations of the convective removal duration as a function of the equilibrium thickness, the thickening factor, the root width, and the rheological temperature scale. Using these relationships, and assuming that the lithospheric equilibrium thickness is about 100 km, the removal duration of a 250 km thick root ranges from 55 to 750 Myr depending on the root width. It is too small to explain the long term stability of cratonic lithospheric root, but too long to explain any sudden change in the stress and strain states in mountain belts development.  相似文献   

豫西焦沟正长岩锆石U-Pb定年、地球化学特征及其地质意义     

梁涛  卢仁  卢欣祥  温静静 《地质通报》2020,(5):681-691

豫西纸房—黄庄地区是东秦岭造山带印支期碱性侵入岩规模最大的出露区,对其中的焦沟岩体进行了LA-ICP-MS锆石U-Pb定年和元素地球化学分析,探讨其源区特征及深部动力学背景。焦沟岩体定年样品JG1701为霓辉正长岩,出现了约2.6 Ga、约2.5 Ga、约2.4 Ga、约2.3 Ga、约2.1 Ga、约1.9 Ga和约243 Ma 7个年龄组,形成了锆石年龄谱,最晚一组6颗锆石测点的206Pb/238U年龄为243.2±4.8 Ma,表明其形成于中三叠世。焦沟岩体的Na2 O+K2 O含量为11.50%~14.01%,碱度率(AR)和K2O/Na2O值分别为3.92~9.17和3.78~10.25,属于碱性-过碱性系列,且具有超钾质岩石的特征。焦沟岩体的稀土元素总量介于176×10^-6~315×10^-6之间,(La/Yb)N范围为9.51~20.43,稀土元素配分模式具有右倾、轻稀土元素富集、重稀土元素亏损和无明显负Eu异常的特征。焦沟岩体强烈富集大离子亲石元素、亏损高场强元素,在微量元素蛛网图中显示了一致的Th、Nb、Ta、P、Ti异常谷,以及Ba、K、Zr、Hf异常峰。它的部分熔融源区位于石榴子石-尖晶石过渡带,埋深介于60~80 km之间,残余矿物包括金云母、富钛矿物(如金红石和钛铁矿)、石榴子石和尖晶石。焦沟岩体是幔源富钾岩浆/流体与壳源岩浆/流体库混合活化之后形成的,深部控制过程为岩石圈拆沉作用。  相似文献   

胶辽地块古元古代构造—热演化与深部过程   总被引：22，自引：0，他引：22       下载免费PDF全文

李三忠郝德峰  韩宗珠赵国春 孙敏 《地质学报》2003,77(3):328-340

近年来的研究表明，华北克拉通由东部地块和西部地块于1．85Ga沿中部带碰撞形成，且碰撞前东部地块的西缘为活动陆缘，研究程度高。相比之下，东部地块的东缘大面积分布的古元古代胶辽吉造山带研究薄弱。根据新近多学科研究成果，综合揭示出胶辽吉造山带古元古代的构造—热演化和深都地质作用过程如下：早期底侵可能与深都地幔柱相关，发生于2．53～2．36Ga之间，导致2．47～2．33Ga岩墙事件、胶辽吉裂谷带的形成和双峰式火山活动。该幕底侵不仅导致地壳上都沉积格架的不同，也导致地壳内初始热结构的分异，从而决定不同空间上变质作用类型和PTt轨迹的差异。晚期底侵导致地壳下部于2．17Ga左右产生A型辽吉花岗岩、2．2Ga与2．0Ga的伟晶岩事件和顺层伸展变形。其主要的造山运动发生在1．911～1．883Ga之间，裂谷封闭、收缩变形，在该造山带南部出现高压变质。之后，1．875～1．66Ga之间，出现小断块的拆沉、环斑花岗岩、钾长花岗岩和正长岩的非造山岩浆事件、伟晶岩脉和基性岩墙群事件和榆树砬子群沉积。东都地块南缘大别—苏鲁一带1．7～1．6Ga期间应是一个重要的古元古代强烈活动陆缘带。中元古代1．6Ga以后大别—苏鲁一带经历了一系列再造事件而与东都地块主体形成显著差异。总之，胶辽吉造山带的底侵样式、碰撞过程、拆沉方式都直接制约着浅部地壳的构造—热演化特征。  相似文献   

地球内部主要层圈相互作用研究的若干进展     

张瑞生  路凤香  郑建平  储玲林 《世界地质》2003,22(3):237-245,251

20世纪90年代以来，人们正在探索建立一个统一的全球动力学体系及各圈层相互作用的热、物质运动机制。通过对地核、核幔边界、过渡带、岩石圈—软流圈地幔、地幔柱理论、壳幔边界和地壳内热、物质的交换和圈层流变运动方式等进行分析，讨论了地球各圈层之间存在的热与物质的交换机制以及底侵作用、拆沉作用和岩浆部分熔融作用等壳幔相互作用过程。认为壳幔作用过程表现为一种阶段式、递进式动力学和物理化学演化过程。壳幔相互作用不仅是大陆动力学演化的主要机制，而且与深部地幔的交代及上地壳变形、造山带、盆地形成和演化之间存在耦合过程。基于壳幔热和物质相互作用的研究可以对上地幔及更深层次的地质作用过程进行限定。  相似文献   

Geochemistry and Petrogenesis of the Tongshankou and Yinzu Adakitic Intrusive Rocks and the Associated Porphyry Copper-Molybdenum Mineralization in Southeast Hubei, East China   总被引：11，自引：0，他引：11  

Qiang Wang    Zhen-Hua Zhao    Zhi-Wei Bao    Ji-Feng Xu    Wei Liu  Chao-Feng Li  Zheng-Hua Bai  Xiao-Lin Xiong 《Resource Geology》2004,54(2):137-152

Abstract. The late Jurassic Tongshankou and Yinzu plutons in southeast Hubei have been investigated for their contrasting metal mineralization features. The former is closely associated with porphyry Cu‐Mo mineralization, while the latter is barren of metal mineralization, althouth both are located very close to each other. The Tongshankou granodiorite porphyries and the Yinzu granodiorites are geochemically similar to adakites, e.g., high Al₂O₃ and Sr contents and La/Yb and Sr/Y ratios, enriched in Na₂O, depleted in Y and Yb, very weak Eu anomalies and positive Sr anomalies. However, different geochemi‐cal characteristics exist between the two plutons: the Tongshankou adakitic rocks (1) are relatively enriched in SiO₂, K₂O, MgO, Cr, Ni, and Sr and depleted in Y and Yb; (2) have higher degree REE differentiation; (3) have positive Eu anomalies in contrast with very weak negative or unclear Eu anomalies in the Yinzu rocks; and (4) isotopically have relatively higher eP_Nd(t) values (‐5.19 to ‐5.38) and lower initial ⁸⁷Sr/⁸⁶Sr ratios (0.7060 to 0.7062), while the Yinzu adakitic rocks have relatively lower eP_Nd(t) values (‐7.22 to ‐8.67) and higher initial ⁸⁷Sr/⁸⁶Sr ratios (0.7065 to 0.7074). The trace element and isotopic data demonstrate that the Tongshankou adakitic rocks were most probably originated from partial melting of delaminated lower crust with garnet being the main residual mineral whereas little or no plagioclase in the source. On the contrary, the Yinzu adakitic rocks were likely derived from partial melting of thickened lower crust, with residual garnet and a small quantity of plagioclase and hornblende in the source. Interactions between the adakitic magmas and mantle peridotites possibly took place during the ascent of the Tongshankou adakitic magmas through the mantle, considering that MgO, Cr, and Ni contents and eP_Nd(t) values of the adakitic magmas were possibly elevated and initial ⁸⁷Sr/⁸⁶Sr ratios were possibly lowered due to the contamination of mantle peridotites. In addition, the Fe₂O₃ of the adakitic magmas was likely released into the mantle and the oxygen fugacities (?_o2) of the latter were obviously possibly raised, which made metallic sulfide in the mantle oxidized and the chalcophile elements such as Cu were incorporated into the adakitic magmas. The ascent of the adakitic magmas enriched in Cu and Mo will lead to the formation of porphyry Cu‐Mo deposit. Nevertheless, the Yinzu adakitic magmas were possibly lack of metallogenetic materials due to not interacting with mantle peridotite, and thus unfavorable to metal mineralization.  相似文献   

一种新的分层冻胀量观测方法及其在季节冻土区的应用     

陈继  张喜发  王英梅 《冰川冻土》2004,26(Z1):319-324

Observation of delamination frost-heave is of significance in the study of foundation frost damage. The three main methods of observing delamination frost-heave, which are mono-frost-heave-ruler method, multi-frost-heave-ruler method and magnetic-loop method, are briefly introduced in this paper at first. Their respective advantages and disadvantages are analyzed. And then, according to the mechanism of frost-heave and the law of water migration and ice-forming in the freezing soil, a new approximate indirect method of observing the delamination frost-heave, which is antitheses, is brought forward by comparing surface frost-heave and frost-depth. On the basis of observation result in Chengyu Expressway and Daqing, its applicability is analyzed from three aspects under different groundwater level and soil property in seasonal frozen area. The result shows that this method is applicable for these two areas.  相似文献   

吉林至珲春地区晚二叠世-早三叠世花岗岩成因机制   总被引：5，自引：0，他引：5  

齐成栋  纪春华  韩江  郭安臣  邸新  孙元喜 《吉林地质》2005,24(2):10-15

吉林——蛟河——敦化——珲春地区的晚二叠世——早三叠世花岗闪长质岩石中暗色微粒闪长质包体广泛发育，其形成与基性岩浆同酸性岩浆混合作用有关。该岩浆岩带形成于晚古生代末期陆——陆碰撞造山的动力背景下，碰撞过程中俯冲岩石圈的拆沉导致幔源岩浆的底侵作用是其形成重要机制。  相似文献   

豫西崤山白石崖岩株的深部过程——锆石年龄谱和稀土元素证据     

梁涛  卢仁 《地质论评》2023,69(3):2023030003-2023030003

崤山北部早白垩世侵入岩的简单年龄结果中包含了复杂地质信息,六个岩株的侵位年龄集中于~130 Ma和~145 Ma两期,复杂的单颗粒锆石年龄谱为反演区域构造背景提供了新途径。白石崖岩株锆石的U- Pb年龄和微量元素特征不仅对探讨其岩石成因和深部过程具有重要作用,而且为建立崤山北部燕山期侵入岩的精细的年代学框架和整合的成因模型提供新限定。白石崖岩株定年样品BSY03为斑状黑云母二长花岗岩,三次LA- ICP- MS锆石U- Pb测试中分析了77个测点,其中73个有效测点的年龄值分成~132 Ma（15个）、~145 Ma（49个）和~158 Ma（9个）三个年龄组,形成了锆石年龄谱,最晚一组加权平均年龄132. 1±1. 0 Ma为白石崖岩株的形成时代。3组年龄锆石均显示了轻稀土亏损和重稀土富集的特征,整体为Ce正异常及Pr、Nd负异常,~145 Ma和~158 Ma两组锆石的稀土总量分别为694×10-6 ~ 2213×10-6（平均值1309×10-6）和950×10-6~ 1849×10-6（平均值1360×10-6）,~132Ma组锆石的稀土总量变化范围介于429×10-6 ~ 2210×10-6,平均值为1495×10-6。3组锆石总体的形成温度为539 ~ 748 ℃;~158 Ma组锆石的温度较高,为601 ~ 748℃（平均值662℃）; ~145 Ma组和~132 Ma组锆石的温度分别介于539 ~ 717℃（平均值629℃）和553 ~ 701℃（平均值633℃）。锆石测点的Er、Yb、Lu和Y含量随年龄由早及晚的整体变化趋势均为升高,~132 Ma和~145 Ma组锆石的Ce4+/Ce3+值分别介于13. 2 ~ 121（平均值69. 7）和27. 6 ~ 107（平均值70. 3）,~158 Ma组锆石的Ce4+/Ce3+值介于3. 53 ~ 81. 4,其由早及晚的整体趋势均为先升高后降低。白石崖岩株的形成受控于崤山北部岩石圈拆沉作用,深部岩浆/流体因此得以释放,促成上部处于未完全固结晶粥状态的岩浆/流体库发生混合再活化作用,重获上侵能力的岩浆/流体卷携多期锆石（如~158 Ma和~145 Ma的锆石）在浅部构造有利部位固结成岩,并晶出~132 Ma锆石。  相似文献