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。     

辽北地区早-中二叠世变质火山-碎屑岩年代学和地球化学特征:对华北板块北缘东段构造演化的启示SCIEI北大核心CSCD

新识别的“下二台”构造杂岩作为华北板块北缘东段分布的构造混杂岩带重要组成部分,其物质组成、形成时代和构造属性仍需进一步研究,这将为探讨华北板块北缘东段晚古生代构造演化提供重要依据。作者在“下二台”构造杂岩中识别出一套早-中二叠世变质火山-碎屑岩,其以变质碎屑岩为主,并夹变质火山岩,二者在野外产出上混杂在一起。变质火山岩原岩类型包括流纹岩、英安岩、安山岩、玄武安山岩,为一套钙碱性火山岩,属于准铝质-弱过铝质岩石。根据岩相学和地球化学特征,将其分为变质酸性火山岩和变质中-基性火山岩;二者均相对富集轻稀土元素,亏损重稀土元素,轻重稀土元素分馏明显,Eu负异常不明显,但变质酸性火山岩明显亏损P、Ti元素,结合高场强元素相关性特征,认为二者不是同一基性岩浆分异的产物。变质火山岩锆石LA-ICP-MS U-Pb同位素年龄为272~288Ma,代表其原岩结晶年龄,时代为早二叠世;变质酸性火山岩原始岩浆来源于地壳物质的部分熔融,变质中-基性火山岩原始岩浆来源于岩石圈地幔(俯冲带附近),并遭受了地壳物质的混染,二者均形成于活动大陆边缘火山弧环境。变质碎屑岩原岩恢复为泥砂质沉积岩和砂泥质沉积岩,相对亏损轻稀土元素,富集重稀土元素,轻重稀土元素分馏较明显,Eu异常不明显。两件碎屑岩样品锆石LA-ICP-MS U-Pb同位素年龄主要介于267~347Ma,推断其沉积下限为267Ma和269Ma,均为中二叠世;泥砂质沉积岩可能来源于再旋回的以长英质岩石为母岩的沉积岩,砂泥质沉积岩可能来源于再旋回的以长英质和镁铁质岩石为母岩的沉积岩,二者分别形成于活动大陆边缘大陆岛弧和大洋岛弧环境。下二台地区早-中二叠世变质火山-碎屑岩为“下二台”构造杂岩重要组成部分,它表明二叠纪时期华北板块北缘东段经历了三个构造演化阶段:早二叠世古亚洲洋加速俯冲,形成新的大陆弧阶段;中二叠世古亚洲洋持续俯冲,大陆弧和大洋弧碰撞阶段;晚二叠世陆-陆碰撞前阶段。     

长江经济带江苏段废弃露天矿山分布与生态修复遥感调查研究

江苏省长江沿岸废弃矿山修复治理是长江经济带生态修复的关键节点区域,如何快速、直观地获得区域内废弃矿山的分布和修复工程进展,成为长江经济带废弃矿山生态修复工程的重要工作之一。以江苏长江干流两岸10?km范围为研究区,以2017—2020?年4?期高分辨率遥感影像为数据源,采用ArcGIS平台人机交互解译和野外验证的方式,获取了研究区内露天废弃矿山分布情况、地质环境问题和生态修复情况等信息。结果表明:镇江市和南京市需修复面积较大,区内露天废弃矿山主要表现为矿山的采场和中转场地两类占地,涉及矿种以建筑石料用灰岩和建筑用砂矿为主;存在的主要矿山环境问题有地形地貌破坏、矿山地质灾害、矿区生态环境破坏和水土污染等;2018—2020 年研究区已修复面积和正在修复面积均呈上升趋势,截至2020 年10 月,研究区废弃矿山修复效果良好,修复面积占67.08%;主要生态修复措施有自然恢复、客土回填、土地平整、削坡、土地综合治理等。建议在进行修复治理工程时,最大限度地保护矿区原有地貌,充分利用土地资源。调查结果和建议可为同类型地区露天废弃矿山生态修复治理提供技术参考。     

Petrogenesis of Early Permian Intrusive Rocks from Southeastern Inner Mongolia, China: Constraints on the Tectonic Framework of the Southeastern Central Asian Orogenic Belt

The late Paleozoic tectonic framework of the southeastern Central Asian Orogenic Belt is key to restricting the accretion orogeny between the Siberia Craton and the North China Craton. To clarify the framework, petrogenesis of early Permian intrusive rocks from southeastern Inner Mongolia was studied. Zircon U-Pb dating for bojite and syenogranite from Ar-Horqin indicate that they were emplaced at 288–285 Ma. Geochemical data reveal that the bojite is highly magnesian and low-K to middle-K calc-alkaline, with E-MORB-type REE and IAB-like trace element patterns. The syenogranite is a middle-K calc-alkaline fractionated A-type granite and shows oceanic-arc-like trace element patterns, with depleted Sr-Nd-Hf isotopes, (87Sr/86Sr)I = 0.7032–0.7042, εNd(t) = +4.0 to +6.6 and zircon εHf(t) = +11.14 to +14.99. This suggests that the bojite was derived from lithospheric mantle metasomatized by subducted slab melt, while the syenogranite originated from very juvenile arc-related lower crust. Usng data from coeval magmatic rocks from Linxi?Ar-Horqin, the Ar-Horqin intra-oceanic arc was reconstructed, i.e., initial transition in 290–280 Ma and mature after 278 Ma. Combined with regional geological and geophysical materials in southeastern Inner Mongolia, an early Permian tectonic framework as ‘one narrow ocean basin of the PAO’, ‘two continental marginal arcs on its northern and southern’ and ‘one intra-oceanic arc in its southern’ is proposed.     

西藏北喜马拉雅成矿带锑金属成矿作用及找矿方向

北喜马拉雅成矿带是全球巨型成矿带——特提斯—喜马拉雅成矿域的重要组成部分,发育一系列锑、锑金、锑多金属、金、铅锌银、钨锡(铍)、汞、铯为主的矿床或矿(化)点,是全球地质学家关注的热点区域。北喜马拉雅成矿带锑成矿作用时间集中在24~16 Ma之间,与后碰撞造山成矿事件(N₁: 25~9 Ma)时间一致,锑来源于深部岩浆减压分熔形成的富含挥发分的次火山岩浆活动,形成喷流沉积-改造型、岩浆热液型、热泉型矿床系列。因此,矿区内的幔源基性-中性脉岩是锑成矿的重要控制因素,也是找矿的重要标志。Sb元素异常主要围绕羊卓雍错裂谷盆地边缘分布,部分与Au元素异常重合。Sb异常主要与低温热液矿床相关,可单独成矿,亦可与Au共生。当Sb异常与Pb-Zn-Ag异常组合在一起时,多为后期叠加改造成矿,并伴生Ga、Se、In等。锑或锑多金属矿体走向多为近SN向,形成串珠状的地球化学异常组合及矿化组合,主要受走滑正断系统及其次级构造控制,并且在矿带的东部,矿化由北向南具有Sb矿→Au-Sb矿→Au矿→Sb-Pb-Zn-Ag矿→W-Sn矿的规律性分布,揭示成矿中心应在扎西康矿床的深部或南部。锑金矿体走向多为近EW向,主要受拆离构造及其次级构造控制。北喜马拉雅被动大陆边缘中生代裂谷(陷)盆地周围盆山转换部位,特别是同沉积断裂带与新生代SN向堑式构造的交汇部位,是寻找锑、锑金、锑多金属矿床的最有利地区,已发现特提斯—喜马拉雅成矿域中规模第一的扎西康锑多金属矿床等一系列大-超大型矿床,显示巨大的找矿前景。综上所述,北喜马拉雅成矿带将会成为我国最重要的锑资源勘查开发后备基地之一。     

《秦岭造山带—鄂尔多斯盆地野外实践》课程之“造山带构造演化”野外教学设计

野外实习是地质学本科教学不可缺少的重要环节,也是课堂理论教学的补充和延伸。大学三年级的野外教学实习是在学生基本完成了专业课程学习的基础上进行的,着眼于创新思维的启发和科研方法的训练,帮助学生从理论学习向科学研究顺利过渡,是培养地质学专业学生成才的关键课程。文章重点以西北大学地质学系《秦岭造山带—鄂尔多斯盆地野外实践》课程之“造山带构造演化”为例,以板块构造理论为指导,通过考察研究典型路线剖面上保存的古洋壳残片（蛇绿岩）、俯冲—碰撞过程的岩浆、变质、沉积记录,培养学生重建造山带构造演化过程的思路和方法。     

鲜水河断裂带富硼地热水中稀土元素分布特征及其对硼来源的指示意义

高温地热系统地热水中普遍富含高浓度的硼,其来源的研究一直是地热地质学者关注的热点问题。尽管众多的学者对地热水中硼形成机理开展了广泛的研究,但富硼地热水中稀土元素的分布特征及其迁移规律能否指示热水中硼的来源尚不清楚。本研究以鲜水河断裂带富硼地热水为研究对象,通过野外调查取样、室内测试分析、水文地球化学模拟和综合研究等技术手段和方法,探究断裂带地热水中硼和稀土元素的分布特征和迁移规律。研究结果显示：鲜水河断裂带地热水中硼含量90%超过我国饮用水标准规定值0.5 mg/L(地热水中硼含量最大值为10.50 mg/L);地热水中稀土元素含量为0.08～3.49μg/L,且主要以LnCO₃⁺和Ln(CO₃)₂^-的络合物形态存在。地热水稀土元素PAAS归一化模式表现为重稀土元素相对于轻稀土元素富集((Nd/Yb)SN均值为0.41),且具有较显著的Eu(均值为0.34)和Ce(均值为0.07)正异常特征。地热水中硼和稀土元素的迁移均受到赋热含水层长英质和碳酸盐岩类矿物溶解过程的影响,且地热...     

Lithospheric dripping in a soft collision zone: Insights from late Paleozoic magmatism suites of the eastern Central Asian Orogenic Belt

The closure of Paleo-Asian Ocean is considered to have occurred along the Solonker Suture in the southernmost segment of the Central Asian Orogenic Belt (CAOB), the largest Phanerozoic accretionary orogen on the globe. The suture branches to the east to form the northern Hegenshan–Heihe Suture and the southern Solonker–Changchun Suture. The Hegenshan–Heihe Suture is an ideal natural laboratory for studying the post-collisional geodynamic processes operating in a soft collision zone driven by divergent double-sided subduction. Here we report results from an integrated study of the petrology, geochronology, geochemistry, and Sr–Nd–Hf isotopic compositions of the Early Carboniferous–Early Permian magmatic suite in the Hailar Basin of the Xing’an–Erguna Block. The Early Carboniferous igneous rocks are represented by 356–349 Ma andesitic tuffs, exhibiting typical subduction-related features, such as enrichment in large-ion lithophile elements and depletion in high-field-strength elements. These features, together with the relatively depleted Sr–Nd–Hf isotopic compositions, constant Nb/Y values, but highly variable Rb/Y and Ba values indicate that these rocks were generated by partial melting of a depleted mantle wedge metasomatized by slab-derived fluids. The Late Carboniferous–Early Permian magmatic suite (317–295 Ma) is characterized by high Sr contents (313–1080 ppm) and low Y contents (5–13 ppm), and these can be subdivided into calc-alkaline adakitic rocks and high-K calc-alkaline adakitic rocks. The calc-alkaline adakitic rocks have higher values of Sr/Y, (Sm/Yb)_{source normalized}, and Mg#, and lower values of Y, Yb_{source normalized}, and K₂O/Na₂O than the high-K calc-alkaline adakitic rocks, which suggests that the former was generated by partial melting of foundered lower continental crust and the latter by partial melting of normal lower continental crust. Based on our new data, in conjunction with those in previous studies, we conclude that the tectonic evolution of the Hegenshan–Heihe Suture involved Early Carboniferous double-sided subduction of the Nenjiang Ocean, latest Early Carboniferous soft collision between the Xing’an–Erguna and Songliao blocks, and Late Carboniferous–Early Permian post-collisional extension. We also propose a new geodynamic scenario in which removal of the lithospheric root might have occurred in a soft collision zone during the post-collision period via repeated and localized lithospheric dripping, which results from combined effects of hydration weakening of the lithosphere caused by pre-collision subduction and asthenospheric stirring triggered by slab break-off.     

阿拉善地块北大山地区两类辉长岩的锆石U-Pb定年、Hf同位素及地球化学特征——对中亚造山带构造演化的启示

作为中亚造山带的重要组成,阿拉善地块北缘已成为研究古亚洲洋构造演化历史的关键地区。本次工作对阿拉善地块北大山地区两类辉长岩进行LA-ICP-MS锆石U-Pb测年,获得成岩年龄分别为293±2Ma和267±2Ma,为早、中二叠世。早二叠世辉长岩为堆晶岩,呈亚碱性,拉斑玄武质,高Mg#值(64)、Eu显著正异常、极低的REE、富集大离子亲石元素(Ba、K、Sr),亏损高场强元素(Th、Nb、Ta、Hf、Zr),锆石的εHf(t)平均值为0.91,以上特征显示其岩浆源区为受俯冲板片混染或交代的岩石圈地幔,形成于俯冲相关的挤压环境;中二叠世辉长岩呈碱性、富集大离子亲石元素(Ba、K)和稀土元素,但Nb、Ta等高场强元素亏损不明显,锆石的εHf(t)平均值为3.5,显示其岩浆源区为受陆壳混染的亏损地幔,形成于大陆板内拉张环境。综合本文及前人研究成果,认为阿拉善地块北缘存在一条西起龙首山,东到狼山的晚古生代(328~262 Ma)超基性—基性岩浆带,其形成与古亚洲洋的俯冲—闭合—造山后伸展过程相关。在晚石炭世—早二叠世晚期,阿拉善地块北缘为大洋俯冲环境,到早二叠世晚期—中二叠世进入大陆板内拉张环境,限定了古亚洲洋在阿拉善地块北缘的最终闭合时代为早二叠世晚期—中二叠世。     

Petrogenesis and tectonic implications of early Palaeozoic igneous rocks of the western South Qilian Belt,central China

Early Palaeozoic granitoids in the South Qilian Belt, central China, record details of the tectonic evolution and crustal growth of the Qilian orogenic belt. Five representative granitoids from the western South Qilian Belt were sampled for zircon LA-ICPMS U–Pb dating, Lu–Hf isotopes, and whole-rock geochemical analyses. Zircon U–Pb dating of two porphyritic granodiorites and a porphyritic monzogranite yielded ages of 442.7 ± 3.5, 441.8 ± 4.3, and 435.4 ± 3.5 Ma, respectively. These granitoids exhibit a geochemical affinity to I-type granite, are metaluminous with a low aluminium saturation index (A/CNK = 0.75–1.15), have moderate Al₂O₃ and low MgO contents, high La/Yb and low Sr/Y ratios, and are depleted in Nb, Ta, P, and Ti, which suggests a subduction zone magmatic arc affinity, with mixing between a primary mantle-derived magma with lesser continental crustal material. The syenogranite and monzogranite from the South Qilian Belt, which yield U–Pb zircon ages of 440.4 ± 9.0 and 442.3 ± 1.2 Ma, respectively, have pronounced S-type geochemical affinities, are peraluminous with A/CNK values of 1.07–1.16, have relatively high SiO₂, Al₂O₃, K₂O, and Rb contents, low Y and Yb, low Sr/Y and La/Yb ratios, positive Th, U, and light Rare Earth Element (REE) anomalies, and depletions in Nb, Ta, Sr, and Ti. Their geochemical signature suggests derivation from partial melting of continental crust in a syn-collisional setting. The Hf isotopic data of zircons from the granitoids show a significant input of Paleoproterozoic crust in the crustal formation of the western South Qilian Belt in Palaeozoic. Compare the ε_Hf(t) value of S-type granite with that of I-type granite, the former may have a comparatively homogeneous source. Together with regional evidence, it is proposed that a collisional event occurred between the South Qilian Belt and the Central Qilian Belt at ca. 442–435 Ma.