贺兰山构造带及邻区中-新生代构造事件:来自不整合面和裂变径迹的约束

贺兰山构造带及邻区的构造属性长期以来存在争议,确定该地区中新生代的构造事件及隆升过程是了解这一重要陆内变形带动力学机制的关键所在。本文采用不整合面分析法和低温热年代学方法,综合分析探讨了贺兰山构造带及邻区中新生代的构造事件及其构造演化过程。通过对该地区的野外地质调查,本次在中-新生代地层中由底到顶识别出6个不同类型的不整合面,它们分别是:(1) T_(2-3)/P平行不整合面;(2) J/AnJ角度不整合面-微角度不整合面;(3) K_1/AnK_1高角度不整合面;(4) E_3q/AnE_3;(5) N_1/AnN_1;(6) Q/An Q。在T_3d~3、J_2y和K_1变形前锋,可见与逆冲-褶皱造山带相关的同构造沉积生长地层,其在形态上表现为超覆、削截,在黄草滩等地局部与倒转背斜相伴生。这些不整合和生长地层是构造活动的直接证据。本次研究对采自该地区的12件样品分别进行了磷灰石、锆石裂变径迹测年及热史模拟分析。结果表明,裂变径迹年龄主要分布在4个区间,对应地质时代分别为中侏罗世-晚侏罗世(168～159Ma)、早白垩世末(139～91Ma)、晚白垩世末(79～66Ma)、始新世(59～50Ma),反映出该地区在这4个时期发生了明显的冷却抬升事件,且这4期构造事件与野外观察到的地质特征有很好的地质响应。同时,热史模拟表明该地区整体上经历了晚侏罗世、早白垩世、晚白垩世末-始新世3期快速隆升事件。综合研究表明,该地区主体逆冲褶皱的时间是从中侏罗世开始,早白垩世末构造运动最强烈,新生代又有所活动。     

长江中下游成矿带钨矿床

长江中下游成矿带是我国重要的铜-铁-金多金属成矿带,近年来在长江中下游成矿带内发现多处白钨矿床和矿化点,为该成矿带的成矿学研究提供了新的研究课题。相比成矿带铜铁金多金属矿床研究程度,钨矿床成矿作用研究明显薄弱,尚未进行系统的成矿作用和成矿规律总结。成矿带内发育的钨矿床主要为北亚带的东顾山矿床、主带(中亚带)的阮家湾矿床和南亚带的桂林郑矿床和高家塝矿床。本文对这四个钨矿床及几个含钨矿床的地质和地球化学特征、成岩成矿时代、成矿岩体地球化学特征等方面的研究资料和成果进行了总结,讨论和试图阐明长江中下游成矿带钨矿床的成矿作用。研究显示,长江中下游成矿带存在三期钨成矿作用,分别为146～143Ma、127Ma和97Ma,在成矿带的铜主成矿期前和铁成矿期均有钨成矿作业发生。钨矿床中白钨矿的Sr-Nd同位素组成分别落入董岭式基底或江南式基底范围,表明长江中下游成矿带的董岭式和江南式基底是形成原始含矿岩浆的物质基础。长江中下游成矿带的钨矿床成矿岩体为中酸性岩,ε_(Hf)(t)值很低,且Zr/Hf、K/Rb比值小,表明成钨岩浆岩为古老地壳物质重熔并经历了较充分的分异演化,对比成矿带中成铜、成铁岩体,源区性质可能是导致长江中下游成矿带金属成矿差异的根本原因。燕山期的陆内俯冲是造成长江中下游成矿带钨矿床成矿的主导机制。     

Final Closure Time of the Paleo‐Asian Ocean: Implication from the Provenance Transformation from the Yangjiagou Formation to Lujiatun Formation in the Jiutai Area,NE China

The Jiutai area is tectonically situated at the eastern segment of the Central Asian Orogenic Belt(CAOB) and is close to the North China Craton(NCC) to the south, serving as an ideal place to investigations of the closure of the PaleoAsian Ocean(PAO). Sandstone samples collected from the Yangjiagou Formation and the Lujiatun Formation in this area have been studied in detail in terms of petrology, geochronology and geochemistry. The maximum depositional time of the Yangjiagou and Lujiatun formations has been constrained to early Middle Triassic(ca. 245 Ma) and middle Late Triassic(ca. 219 Ma), respectively. The Yangjiagou Formation, with a major provenance of dissected island arcs, is dominantly composed of Phanerozoic sediments from Northeastern China(NE China) massifs. The Lujiatun Formation, with major sediments from active continental margins, has a relatively larger proportion of Precambrian sediments, in which the ～1.85 Ga and ～2.5 Ga sediments are typical of the crystalline basements of the NCC and NE China massifs, which were uplifted and eroded during the closure of the PAO. Besides, both formations show the enrichment in LREEs and the depletion in HREEs, the common Eu negative anomalies, and trace element contents similar to that of the upper continental crust. Based on the provenance analysis of these two formations, the final closure time of the PAO in this area is constrained as from the early Middle Triassic(ca. 245 Ma) to the middle Late Triassic(ca. 219 Ma).     

准噶尔盆地南缘前陆冲断带深层地质结构及对油气藏的控制作用:以霍尔果斯—玛纳斯—吐谷鲁褶皱冲断带为例

准噶尔盆地南缘前陆冲断带位于天山北麓,在晚新生代强烈的挤压作用下,地表发育数排背斜带。由于构造变形复杂、地震反射成像质量较差,对深层地质结构争议较大,另外前新生代盆地原型对晚新生代以来的褶皱冲断带构造格局的影响也尚未探讨。霍尔果斯—玛纳斯—吐谷鲁(简称霍-玛-吐)褶皱冲断带位于准噶尔盆地南缘前陆冲断带地表第二排背斜带,利用最新采集和处理的地震反射资料,并结合地表地质露头建立深层构造模型;利用平衡地质剖面复原和构造物理模拟实验的方法探索早侏罗世盆地原型结构对现今褶皱冲断带构造格局的影响;在此基础上分析霍-玛-吐褶皱冲断带深层天然气富集规律。霍-玛-吐褶皱冲断带垂向上发育古近系—第四系逆冲推覆构造、中上侏罗统—白垩系构造楔和下侏罗统半地堑断陷结构。控制早侏罗世半地堑系统的高角度正断层在晚期挤压构造变形体系中充当逆断坡,并控制上覆构造楔和浅层逆冲推覆构造的发育。早侏罗世半地堑系统具有分段性,并通过侧向断坡进行连接,侧向断坡上覆地层发育南北向走滑调节断层。油气勘探现状表明,霍-玛-吐褶皱冲断带内部南北向走滑调节断层具有高效沟通下侏罗统烃源岩的特点,是控制天然气的富集的重要因素。以上研究表明,中西部陆内前陆冲断带前新生代古构造对于晚新生代挤压冲断构造格局和深层天然气富集规律具有重要意义。     

羌塘盆地中央隆起带的抬升演化:构造-热年代学约束

本文综合磷灰石裂变径迹年龄(113~43 Ma)、锆石裂变径迹年龄(169~103 Ma)、锆石U-Pb年龄(215~206 Ma)、黑云母K-Ar年龄(186~178 Ma),通过磷灰石热史模拟,TASC图谱分析和矿物封闭温度年龄等手段,获得了中央隆起晚三叠世至今较为完整的冷却抬升历史。中央隆起主要经历了早侏罗世、晚侏罗世-早白垩世、晚白垩世-中新世早期和中新世晚期至今四期冷却事件,与南北羌塘板块后碰撞伸展、拉萨羌塘板块碰撞、新特提斯洋板片俯冲、印度欧亚板块碰撞以及中新世南北向走滑伸展存在动力学联系,造成11.4 km、2.85 km、4.3~5 km和0.85 km的抬升量。中央隆起在侏罗纪相对两侧盆地抬升,随着两侧盆地经历了侏罗纪的沉积增厚,与两侧盆地高差减小,在早白垩世早期可能位于海平面附近,随后快速抬升至2~2.5 km,统一接受晚白垩世红层沉积,并经历长期持续的逆冲推覆构造活动,进一步抬升至5 km,随后受到中新世古大湖夷平和南北向伸展作用影响,中央隆起相对盆地发生差异抬升。     

东昆仑古特提斯后碰撞阶段伸展作用:来自晚三叠世岩浆岩的证据

通过对东昆仑造山带晚三叠世岩浆岩的岩石类型、形成时代、岩石地球化学和同位素地球化学资料综合分析,对岩浆岩的岩石组合、分布特征和岩石成因进行研究,探讨东昆仑造山带晚三叠世构造演化的地球动力学背景。东昆仑造山带晚三叠世是古特提斯演化过程中重要的构造转换期,岩浆岩岩石类型多样,主要包括辉长岩、花岗闪长岩、二长花岗岩和正长花岗岩,并且广泛出露具埃达克质特征的岩浆岩和A型花岗岩。晚三叠世岩浆岩的出露规模与俯冲阶段相比,规模较小,一般以小岩体、岩株和岩脉侵入于早期岩体和地层中。东昆仑晚三叠世岩浆岩主体为准铝-弱过铝质高钾钙碱性-钾玄岩系列,轻重稀土元素具有一定分异,富集大离子亲石元素,亏损高场强元素,岩石类型不同时分异程度、富集和亏损程度有一定差异。大部分晚三叠世花岗质岩浆岩的同位素特征与晚二叠世-三叠纪镁铁质岩浆岩近似,部分具有更高的εNd(t)和εHf(t)值。镁铁质岩浆岩、普通花岗岩、埃达克质岩浆岩在东昆仑各个构造带皆有分布,A型花岗岩主要分布在祁漫塔格构造带(东昆北)的阿牙克库木湖-香日德断裂附近。东昆仑晚三叠世镁铁质岩浆岩具有弧岩浆岩特征,为俯冲流体交代的地幔楔部分熔融产物。普通花岗岩和埃达克质岩浆岩多为新生下地壳部分熔融产物,少量埃达克质岩浆岩由于与地幔的交代作用,具有幔源特征。A型花岗岩为残留下地壳部分熔融的产物。部分普通花岗岩、埃达克质岩浆岩和A型花岗岩由于岩浆混合作用,具幔源特征。构造环境研究表明,东昆仑在晚三叠世进入古特提斯演化的后碰撞阶段。巴颜喀拉地块同东昆仑地块的持续碰撞导致地壳加厚,密度增大,使岩石圈重力不稳定发生拆沉作用,引发岩石圈地幔减压熔融,产生大量的镁铁质岩浆岩;镁铁质岩浆底侵不同类型地壳熔融及拆沉地壳部分熔融而形成的岩浆交代地幔,以及岩浆混合和岩浆后期演化,形成了东昆仑造山带晚三叠世丰富多样的岩浆岩。     

Genesis of the Xiuwenghala Gold Deposit in the Beishan Orogen,Northwest China: Evidence from Geology,Fluid Inclusion,and H–O–S–Pb Isotopes

The Xiuwenghala gold deposit is located in the Beishan Orogen of the southern Central Asian Orogenic Belt. The vein/lenticular gold orebodies are controlled by Northeast‐trending faults and are hosted mainly in the brecciated/altered tuff and rhyolite porphyry of the Lower Carboniferous Baishan Formation. Metallic minerals include mainly pyrite and minor chalcopyrite, arsenopyrite, galena, and sphalerite, whilst nonmetallic minerals include quartz, chalcedony, sericite, chlorite, and calcite. Hydrothermal alterations consist of silicic, sericite, chlorite, and carbonate. Alteration/mineralization processes comprise three stages: pre‐ore silicic alteration (Stage I), syn‐ore quartz‐chalcedony‐polymetallic sulfide mineralization (Stage II), and post‐ore quartz‐calcite veining (Stage III). Fluid inclusions (FIs) in quartz and calcite are dominated by L‐type with minor V‐type and lack any daughter mineral‐bearing or CO₂‐rich/‐bearing inclusions. From Stages I to III, the FIs homogenized at 240–260°C, 220–250°C, and 150–190°C, with corresponding salinities of 2.9–10.9, 3.2–11.1, and 2.9–11.9 wt.% NaCl eqv., respectively. The mineralization depth at Xiuwenghala is estimated to be relatively shallow (<1 km). FI results indicate that the ore‐forming fluids belong to a low to medium‐temperature, low‐salinity, and low‐density NaCl‐H₂O system. The values decrease from Stage I to III (3.7‰, 1.7–2.4‰, and ?1.7 to 0.9‰, respectively), and a similar trend is found for their values (?104 to ?90‰, ?126 to ?86‰, and ?130 to ?106‰, respectively). This indicates that the fluid source gradually evolved from magmatic to meteoric. δ³⁴S values of the hydrothermal pyrites (?3.0 to 0.0‰; avg. ?1.1‰) resemble those of typical magmatic/mantle‐derived sulfides. Pyrite Pb isotopic compositions (²⁰⁶Pb/²⁰⁴Pb = 18.409–18.767, ²⁰⁷Pb/²⁰⁴Pb = 15.600–15.715, ²⁰⁸Pb^/204Pb = 38.173–38.654) are similar to those of the (sub)volcanic ore host, indicating that the origin of ore‐forming material was mainly the upper crustal (sub)volcanic rocks. Integrating evidence from geology, FIs, and H–O–S–Pb isotopes, we suggest that Xiuwenghala is best classified as a low‐sulfidation epithermal gold deposit.     

Geochronology and geochemistry of Permo-Triassic sandstones in eastern Jilin Province (NE China): Implications for final closure of the Paleo-Asian Ocean

In the eastern part of the Central Asian Orogenic Belt (CAOB) in northeastern (NE) China, scattered outcrops of molasse deposits mark the ending of an orogeny and are crucial for understanding the evolution of the Paleo-Asian Ocean (PAO). However, the timing of tectonic events and the relationships among these strata remain controversial. To better constrain these geologic events, a comprehensive study of the detrital zircon U-Pb geochronology and geochemistry of the sandstones of the Kaishantun (KST) Formation and Kedao (KD) Group in eastern Jilin Province, NE China, was conducted. The KST Formation is traditionally considered a molasse deposit. The sandstones display low CIA, PIA and high ICV values and low Th/U and Rb/Sr ratios, which suggest that the rocks were derived from an immature intermediate-felsic igneous source and experienced a simple sedimentary recycling history with relatively weak chemical weathering. LA-ICP-MS U-Pb dating of detrital zircons from two samples of the KST Formation yields ages of 748–252 Ma, suggesting that the KST Formation was deposited between 254.5 Ma and 252 Ma in Late Permian. The zircons were mainly derived from the continental northern part of the North China Craton (NCC). In contrast, the U-Pb dating of detrital zircons from five samples of the KD Group yields ages of 2611–230 Ma, suggesting that the KD samples were deposited in the Early to Middle Triassic (ca. 248–233 Ma). The detrital zircon ages for the KD samples can be divided into groups with peaks at 2.5 Ga, 1.8 Ga, 800–1000 Ma, 500 Ma and 440–360 Ma, which suggest that the samples were derived from bidirectional provenances in the Jiamusi-Khanka Block and the NCC. These new data, combined with previously published results, suggest that at least three orogenic events occurred in central-eastern Jilin Province during the Early Permian (270–262 Ma), Early Triassic (254–248 Ma) and Middle–Late Triassic (242–227 Ma). The final closure of the PAO occurred during 242–227 Ma in the Middle–Late Triassic along the Changchun-Yanji suture zone. The detrital zircon geochronological data clearly record plate convergence and the scissor-like closure of the PAO in the eastern CAOB.     

Tectonometamorphic evolution of the Atbashi high‐P units (Kyrgyz CAOB,Tien Shan): Implications for the closure of the Turkestan Ocean and continental subduction–exhumation of the South Kazakh continental margin

The South Tien Shan (STS) belt results from the last collision event in the western Central Asian Orogenic Belt (CAOB). Understanding its formation is of prime importance in the general framework of the CAOB. The Atbashi Range preserves high‐P (HP) rocks along the STS suture, but still, its global metamorphic evolution remains poorly constrained. Several HP units have been identified: (a) a HP tectonic mélange including boudins of mafic eclogites in a sedimentary matrix, (b) a large (>100 km long) high‐P metasedimentary unit (HPMU) and (c) a lower blueschist facies accretionary prism. Raman Spectroscopy on carbonaceous material combined with phengite and chlorite multiequilibria and isochemical phase diagram modelling indicates that the HPMU recorded homogeneous P–T conditions of 23–25 kbar and 560–570°C along the whole unit. ⁴⁰Ar/³⁹Ar dating on phengite from the HPMU ranges between 328 and 319 Ma at regional scale. These ages are interpreted as (re‐) crystallization ages of phengite during T_max conditions at a pressure range of 20–25 kbar. Thermobarometry on samples from the HP tectonic mélange provides similar metamorphic peak conditions. Thermobarometry on the blueschist to lower greenschist facies accretionary prism indicates that it underwent P–T conditions of 5–6 kbar and 290–340°C, highlighting a 17–20 kbar pressure gap between the HPMU‐tectonic mélange units and the accretionary prism. Comparison with available geochronological data suggests a very short time span between the prograde path (340 Ma), HP metamorphic peak (330 Ma), the T_max (328–319 Ma) and the final exhumation of the HPMU (303–295 Ma). Extrusion of the HPMU, accommodated by a basal thrust and an upper detachment, was driven by buoyant forces from 70–75 km up to 60 km depth, which directly followed continental subduction and detachment of the HPMU. At crustal depths, extrusion was controlled by collisional tectonics up to shallow levels. Lithological homogeneity of the HPMU and its continental‐derived character from the North Tien Shan suggest this unit corresponds to the hyper‐extended continental margin of the Kazakh continent, subducted southward below the north continental active margin of the Tarim craton. Integration of the available geological data allows us to propose a general geodynamic scenario for Tien Shan during the Carboniferous with a combination of (a) N‐dipping subduction below the Kazakh margin of Middle Tien Shan until 390–340 Ma and (b) S‐dipping subduction of remaining Turkestan marginal basins between 340 and 320 Ma.     

“一带一路”成员国居民健康状况的时空统计分析

健康是影响不同国家和地区发展的关键因素,全面了解“一带一路”成员国的居民健康状况,是探讨“一带一路”成员国之间健康医疗合作的重要基础。本文选择了4个代表性的健康状况指标（出生期望寿命、总生育率、过早非传染性疾病死亡率和结核病发病率）,利用Moran's I指数、Getis-Ord G指数对“一带一路”135个成员国的健康状况进行时空统计,分析了健康状况的空间相关性和空间分布模式,研究了健康状况的时空格局。研究发现：① 2000—2016年“一带一路”大部分成员国的各项健康状况指标均朝着改善和优化方向发展;健康状况指标均呈现显著的正空间自相关性;② 总体而言,在“一带一路”成员国中,欧洲国家的居民健康状况最好;南北美洲和大洋洲国家的居民健康状况良好;亚洲国家的居民健康状况总体良好,但东南亚部分国家的结核病发病率较高;非洲国家的居民健康状况虽有明显改善,但仍处于较低状态。因此,“一带一路”成员国应进一步加强健康医疗合作,共同推动健康丝绸之路的发展。