辽东早元古造山带隆滑构造初析

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。     

Convective destabilization of a thickened continental lithosphere

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.     

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

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。     

Geochemistry and Petrogenesis of the Tongshankou and Yinzu Adakitic Intrusive Rocks and the Associated Porphyry Copper-Molybdenum Mineralization in Southeast Hubei, East China

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.     

一种新的分层冻胀量观测方法及其在季节冻土区的应用

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.     

吉林至珲春地区晚二叠世-早三叠世花岗岩成因机制

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。     

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

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。     

东秦岭神林花岗岩的锆石U-Pb定年、地球化学特征及构造背景

神林花岗岩能够为反演东秦岭燕山期区域构造演化提供新的制约。它的主体岩性为斑状黑云母二长花岗岩,其锆石LA-ICP-MS U-Pb同位素定年结果为130.6±0.7 Ma。神林花岗岩样品具有高硅富碱和贫镁低钙的特征,属于高钾钙碱性系列,以准铝质—弱过铝质为主。它们富集大离子亲石元素（如Rb、Th和K）和亏损高场强元素（如Nb、Ta和Ti）,具有轻稀土富集、重稀土亏损的特征,其(La/Yb)N范围为17.6~22.2,δEu值为0.59~0.72。在LaN—(La/Yb)N图解中,神林花岗岩样品显示正相关关系,表明是源区组成和部分熔融作用控制其成分变异。神林花岗岩样品显示了高Sr、低Y和Yb的特征,Sr/Y值为24.3~37.9,属于高锶低钇中酸性岩（adakite,有人音译为埃达克岩）。神林花岗岩形成于加厚大陆下地壳的部分熔融,其源区深度大于50km,部分熔融源区残余相包括石榴子石、金红石和角闪石,无或者少量的斜长石。神林花岗岩锆石具有轻稀土亏损、重稀土富集、Ce正异常的特征,锆石的形成温度介于624~701 ℃之间,重稀土元素分配系数与年龄的变化特征表明神林花岗岩经历了深部岩浆/流体的注入与混合,这与暗色微粒包体所揭示的神林花岗岩深部成岩过程相吻合。混合活化后的岩浆/流体体系沿区域深大断裂上侵,在其次级断裂带内的断裂交汇处就位成岩。神林花岗岩形成于东秦岭陆（板）内造山阶段,是约131 Ma区域岩石圈拆沉作用的岩浆响应。     

华北克拉通南缘早白垩世天目山A型花岗岩的锆石稀土元素和岩石地球化学特征

天目山正长花岗岩位于华北克拉通南缘、北秦岭构造带及桐柏—大别造山带构造拼合地区,其岩石成因模型可为秦岭—大别造山带燕山期深部构造演化提供新的限定。它的n(206Pb)/n(238U)加权平均年龄为129. 2±1. 7 Ma,形成于早白垩世。天目山花岗岩锆石稀土元素具有轻稀土亏损、重稀土富集、Ce和Sm正异常及明显Pr、Nd和Eu负异常（δEu值介于0. 01 ~ 0. 19）,锆石的形成温度介于603 ~ 788 ℃之间,天目山锆石/熔体体系中稀土元素分配系数波动特征表明其形成中存在深部岩浆/流体混合作用。天目山花岗岩样品具有富硅、碱和贫钙、镁的特征,在SiO2 —K2O图解中落入高钾钙碱性系列。在微量元素蛛网图中,它们显示了明显的Rb、Th及Zr、Hf的异常峰和Sr、P、Ti的异常谷。它们的稀土总量介于106??10-6~ 139??10-6之间,(La/Yb)N值范围是5. 94 ~ 9. 22,其稀土配分模式具轻稀土富集、中稀土亏损和重稀土略微富集的“V”型（海鸥型）特征,Eu负异常明显（δEu值介于0. 06 ~ 0. 16）。它们的10000Ga/Al值介于3. 38 ~ 4. 15,Nb和Ta的含量分别为63. 5??10-6~ 131??10-6和3. 20??10-6~ 7. 55??10-6（Nb/Ta值介于17. 3 ~ 22. 9）,天目山花岗岩属于A型花岗岩中富Nb的A1亚类。天目山花岗岩部分熔融源区位于角闪岩相,源区残余相主要为角闪石和斜长石且无石榴子石残余。天目山花岗岩形成于板内构造环境,它是早白垩世~130 Ma桐柏山三合店—鸡公山区域岩石圈拆沉作用的岩浆响应,幔源富Nb岩浆/流体因此得以快速释放,上侵途中混合活化壳源岩浆/流体库之后就位固结成岩。     

Petrology, geochronology and tectonic implications of Mesozoic high Ba–Sr granites in the Haemi area, Hongseong Belt, South Korea

Collision between the North and South China continental blocks began in the Korean peninsula during the Permian (290–260 Ma). The Haemi area in the Hongseong collision belt (proposed as the eastern extension in South Korea of the Dabie–Sulu collision zone of China) within the Gyeonggi Massif comprises post-collisional high Ba–Sr granite with intermediate enclaves that intruded into the Precambrian rocks. The intermediate enclaves have a shoshonitic affinity whereas the granite is a high-K calc-alkaline variety. The chondrite-normalized rare earth element (REE) pattern with relative enrichment of LREE over HREE and absence of a significant negative Eu anomaly typifies both enclaves and granite. Geochemical similarities of enclaves and granite are attributed to the involvement of enriched mantle sources in their genesis. However, dominant crustal components were involved in the formation of high Ba–Sr granites. A granite crystallization age of 233 ± 2 Ma was obtained from SHRIMP U–Pb zircon dating. This age is slightly younger than the Triassic collision event in the Hongseong Belt. Geochemical data, U–Pb zircon age, and regional tectonics indicate that the Haemi high Ba–Sr granite formed in a post-collisional tectonic environment. A Mesozoic post-collisional lithospheric delamination model can account for the genesis of high Ba–Sr granite in the Haemi area.