^(40)Ar/^(39)Ar Dating of Xuebaoding Granite in the Songpan-Garze Orogenic Belt,Southwest China,and its Geological Significance

Thus far, our understanding of the emplacement of Xuebaoding granite and the occurrence and evolution of the Songpan-Garze Orogenic Belt has been complicated by differing age spectra results. Therefore, in this study, the ^40Ar/^39Ar and sensitive high resolution ion micro-probe （SHRIMP） U-Pb dating methods were both used and the results compared, particularly with respect to dating data for Pankou and Pukouling granites from Xuebaoding, to establish ages that are close to the real emplacements. The results of SHRIMP U-Pb dating for zircon showed a high amount of U, but a very low value for Th/U. The high U amount, coupled with characteristics of inclusions in zircons, indicates that Xuebaoding granites are not suitable for U-Pb dating. Therefore, muscovite in the same granite samples was selected for ^40Ar/^39Ar dating. The ^40Ar/^39Ar age spectrum obtained on bulk muscovite from Pukouling granite in the Xuebaoding, gave a plateau age of 200.1±1.2 Ma and an inverse isochron age of 200.6±1.2 Ma. The 4^40Ar/^39Ar age spectrum obtained on bulk muscovite from Pankou granite in the Xuebaoding gave another plateau age of 193.4±1.1 Ma and an inverse isochron age of 193.7±1.1 Ma. The ^40Ar/^36Ar intercept of 277.0±23.4 （2σ） was very close to the air ratio, indicating that no apparent excess argon contamination was present. These age dating spectra indicate that both granites were emplaced at 200.6±1.3 Ma and 193.7±1.1 Ma, respectively. Through comparison of both dating methods and their results, we can conclude that it is feasible that the muscovite in the granite bearing high U could be used for ^40Ar/^39Ar dating without extra Ar. Based on this evidence, as well as the geological characteristics of the Xuebaoding W-Sn-Be deposit and petrology of granites, it can be concluded that the material origin of the Xuebaoding W-Sn-Be deposit might partially originate from the Xuebaoding granite group emplacement at about 200 Ma. Moreover, compared with other granites and deposits distributed in various positions in the Songpan-Garze Orogenic Belt, the Xuebaoding emplacement ages further show that the main rare metal deposits and granites in peripheral regions occurred earlier than those in the inner Songpan-Garze. Therefore, ^40Ar/^39Ar dating of Xuebaoding granite will lay a solid foundation for studying the occurrence and evolution of granite and rare earth element deposits in the Songpan-Garze Orogenic Belt.

Crustal structure beneath the Songpan——Garze orogenic belt

The Benzilan-Tangke deep seismic sounding profile in the western Sichuan region passes through the Song-pan-Garze orogenic belt with trend of NNE. Based on the travel times and the related amplitudes of phases in the record sections, the 2-D P-wave crustal structure was ascertained in this paper. The velocity structure has quite strong lateral variation along the profile. The crust is divided into 5 layers, where the first, second and third layer belong to the upper crust, the forth and fifth layer belong to the lower crust. The low velocity anomaly zone gener-ally exists in the central part of the upper crust on the profile, and it integrates into the overlying low velocity basement in the area to the north of Ma'erkang. The crustal structure in the section can be divided into 4 parts: in the south of Garze-Litang fault, between Garze-Litang fault and Xianshuihe fault, between Xianshuihe fault and Longriba fault and in the north of Longriba fault, which are basically coincided with the regional tectonics division. The crustal thickness decreases from southwest to northeast along the profile, that is, from 62 km in the region of the Jinshajiang River to 52 km in the region of the Yellow River. The Moho discontinuity does not obviously change across the Xianshuihe fault based on the PmP phase analysis. The crustal average velocity along the profile is lower, about 6.30 km/s. The Benzilan-Tangke profile reveals that the crust in the study area is orogenic. The Xianshuihe fault belt is located in the central part of the profile, and the velocity is positive anomaly on the upper crust, and negative anomaly on the lower crust and upper mantle. It is considered as a deep tectonic setting in favor of strong earthquake's accumulation and occurrence.

Geochemistry of Late Triassic pelitic rocks in the NE part of Songpan-Ganzi Basin,western China:Implications for source weathering,provenance and tectonic setting

Major, trace and rare earth element （REE） concentrations of Late Triassic sediments （fine- grained sandstones and mudstones） from Hongcan Well 1 in the NE part of the Songpan-Ganzi Basin, western China, are used to reveal weathering, provenance and tectonic setting of inferred source areas. The Chemical Index of Alteration （CIA） reflects a low to moderate degree of chemical weathering in a cool and somewhat dry climate, and an A-CN-K plot suggests an older upper continental crust prove- nance dominated by felsic to intermediate igneous rocks of average tonalite composition. Based on the various geochemical tectonic setting discrimination diagrams, the Late Triassic sediments are inferred to have been deposited in a back-arc basin situated between an active continental margin （the Kunlun- Qinling Fold Belt） and a continental island arc （the Yidun Island Arc）. The Triassic sediments in the study area underwent a rapid erosion and burial in a proximal slope-basin environment by the petrographic data,while the published flow directions of Triassic turbidites in the Aba-Zoige region was not supported Yidun volcanic arc source. Therefore, we suggest that the Kunlun-Qinling terrane is most likely to have supplied source materials to the northeast part of the Songpan-Ganzi Basin during the Late Triassic.

Land Remediation Projects in Poverty-stricken Counties in Tibetan Areas Promoting Poverty Alleviation——A Case Study of Songpan County,Sichuan Province

Songpan County is a poverty-stricken county in the four provinces of China,one of the concentrated areas in China. This paper analyzes the effectiveness of land consolidation in Songpan County to promote poverty alleviation and development through specific cases. The results show that land remediation has improved agricultural production conditions,promoted agricultural efficiency,increased farmers' income,improved rural living conditions,promoted the development of urban and rural integration,improved the ecological environment,solved the problem that restricts the survival and development of poverty-stricken areas,enhanced the ability of farmers to develop themselves,raised the level of civilization in rural areas,and promoted poverty alleviation and development. The poverty alleviation and development has provided certain financial support for land remediation. It has promoted land remediation,and pointed out key directions for land remediation. It has an indirect promotion effect on land remediation.

Correlation between the tilt anomaly on the vertical pendulum at the Songpan station and the 2021 MS7.4 Maduo earthquake in Qinghai province,China

Understanding the relationship between precursory deformation anomalies and strong earthquakes is vital for physical earthquake prediction. Six months before the 2021 MS7.4 Maduo earthquake in Qinghai province, China, the vertical pendulum at the Songpan station was observed to tilt southward with a high rate and large amplitude. Studies conducted before the 2021 MS7.4 Maduo earthquake inferred the tilt anomaly to be an earthquake precursor. However, after the earthquake, the relation between the earthquake and the anomaly became controversial, partly because the Songpan station is located at a great distance from the epicenter. In this study, based on the deformation anomaly characteristics, relationship between the seismogenic fault and the fault near the anomaly, and associated quantitative analyses, we concluded that this anomaly may be associated with the 2021 MS7.4 Maduo earthquake. The duration and amplitude of this anomaly matched with the magnitude and epicenter distance of the Maduo earthquake. We have also interpreted the reason why the anomaly occurred near a fault that is obliquely intersected with the seismogenic fault and why the anomaly is located far from the earthquake epicenter.

Crustal Structural and Tectonic Evolution and Oil Prospect Evaluation in the Songpan-Zoigê Block

Recent study of magnetotelluric （MT） inversion indicates that the basement of the Songpan- Zoige area could be a stable continental crust. There has developed quite thick and stable Paleozoic continental shelf margin-platform clastic and carbonate sediments during the Triassic. Preliminary field geologic investigation and hydrocarbon potential study show that good-quality source rocks, mainly argillaceous and carbonaceous shale, were deposited in the Cambrian and Silurian in this region, while diverse reservoirs of platform facies carbonate and clastic rocks were in the Carboniferous and Permian. The good vertical source-reservoir-seal configuration might indicate that there exists a certain potential for oil and gas exploration in this area.

Analysis of the Features of the Vernacular Plank Houses of the Qiang Ethnic Group in Southern Songpan County: A Case Study of Xiaoxinggou

The Qiang ethnic group in southern Songpan county lives in vernacular plank houses(VPHs) with an architectural tradition that dates to the period of the ancient Di people.VPHs are now mainly constructed in settlements of ethnic groups such as Baima Tibetans, Amdo Tibetans, and the Qiang people living in Wenxian county, Longnan city of Gansu province, and Maoxian, Lixian, Wenchuan, and Beichuan of Sichuan province respectively.Although VPHs of the Qiang people living in southern Songpan share many similarities with those of adjacent Tibetans in structure, construction, and spatial layout, they feature the Qiang people's unique architectural culture, and reflect a style transition from VPHs in the north to blockhouses in the south.The VPHs, as represented by those in Xiaoxinggou, play a significant role in the diversified architectural culture of this ethnic group.Their unique cultural value is worthy of further exploration and protection.

TECTONIC EVOLUTION OF THE YANGTZE PASSIVE MARGIN AND SONGPAN GARZ? FOLD BELT, CHINA

The Songpan Garzê Fold Belt records Triassic shortening of a relict Palaeo\|Tethyan basin during assembly and accretion of the Cimmerian continental chain to Laurasia’s southern margin. Enclosed by palaeo\|Laurasia and the Cimmerian fragments of Qiangtang (North Tibet) and Yangtze (South China), the Songpan Garzê Fold Belt was shortened by more than 50% during the Indosinian Orogeny c.200Ma. [BW(D(S,,)G2*7][BHDWG2*7,WK*2,WK5,WK15*2,WK17*2,WK*2W] 2000,7(增刊) 地 学 前 缘 [FK(K+6mm。17*2] 4\ Major Topic:Geology of the Inner Tibetan Plateau [BW(S(S,,)G2*7][BHDWG2*7,WK*2,WK17*2,WK15*2,WK5,WK*2W] [FK(K+6mm。17*2] 4\ Major Topic:Geology of the Inner Tibetan Plateau 地 学 前 缘 2000,7(增刊)South\|directed Indosinian compression decolléd onlapping basin sediments from the Yangtze Block’s passive margin—reactivating the margin’s tiered geometry and partitioning strain into margin\|normal and margin\|parallel structures on a large scale. Margin\|normal transport of the allochthonous sedimentary pile was accommodated by southeast\|directed nappe propagation in the Longmen Mountains Thrust—Nappe Belt, whilst conjugate, margin\|parallel (southwest\|directed) transport was accommodated by a flat\|lying detachment at the base of the sedimentary pile.The later is characteristic of deformation of the greater Songpan Garzê Fold Belt.

Multi-level Cooperation and Complementary Advantage Poverty Alleviation Model in Poverty-Stricken Counties of Tibetan Areas:A Case Study of Songpan County in Sichuan Province

Songpan County is a poverty-stricken county in Tibetan areas of Sichuan Province,it belongs to a concentrated poverty-stricken area in China.Through summarizing the specific conditions of multi-level cooperation and complementary advantage poverty alleviation model in Songpan County,this paper analyzed the effect of this model.Through the analysis on the cooperative poverty alleviation model(eastern-western cooperation,provincial targeted assistance,county-wide"four-leading and four-assistance"inner-party assistance,social force"10000 enterprises helping 10000 villages",and"visiting every household and keeping every person busy"),it summarized the implementation and actual results of each level.In addition,it summarized the problems encountered in the implementation process of multi-level cooperation and complementary advantage poverty alleviation model and came up with recommendations.With the aid of this successful multi-level cooperation and complementary advantage poverty alleviation model,Songpan County has achieved a decisive victory in the fight against poverty.At the end of April 2019,the poverty rate in the whole region fell to 0.45%,and it successfully took off the poverty hat.This paper analyzed and refined the specific practice,main achievements,successful experience,implications and reference significance of multi-level cooperation and complementary advantage poverty alleviation model,to provide necessary references for innovation of poverty alleviation model in poverty-stricken Tibetan areas,or even other similar provinces and regions.

Geological Characteristics of Oil and Gas Reservoirs in the Songpan-Aba Area,SW China

The Songpan-Aba area, similar to those basins on the Yangtze block, following the rifting and separation of the Yangtze block, gradually developed into a passive marginal basin on a passive continent margin in Early Paleozoic, and later, with the Qinling-Qilian oceanic crust subduction and ocean closure, the Caledonides were formed and the foreland basin was superimposed upon. Being influenced by the Paleo-Tethyan extension, intra-continental rifting-margin basins were formed in Late Paleozoic. Following the formation of peripheral orogenic belt, the Upper Triassic again superimposed the foreland basin. The Mesozoic and Cenozoic overprinted the faulted basin, forming the Qinghai-Tibet Plateau domes. Hydrocarbon source rock in the Early Paleozoic passive basin, the Upper Paleozoic platform carbonates and the Triassic mudstones comprise the main source-reservoircap combination. Each layer of this area is at the advanced stage of diagenetic evolution, being entered the middle and late diagenetic stages, and anadiagenetic stage. Besides the highly matured Triassic and Permian in Zoige and Hongyuan, almost all the area is at the early stage of over maturatation, generating much methane. This area has the potential for oil and gas.

The Songpan-Garze Massif: Its Relation to the QinlingFold Belt and Yangtze Platform and Developmental History

Whether there existed the Songpan-Garze massif is a controversial problem. This paper expounds and proves that the old basement of the massif is represented by the pre-Sinian granitic rock series. This massif and the South Qinling fold belt might both be a part of the old Yangtze platform. Rifting generated by the Caledonian orogeny in the terminal Early Palaeozoic caused the massif to be disintegrated from the northwestern part of the Yangtze platform. This disintegration, however, was not thorough, and the rift troughs were later gradually closed and filled up. The Emei taphrogeny that was initiated in the Early Permian Maokou' an Stage involved a second disintegration of this massif from the Yangtze platform. The rift line largely goes along the Muli-Pingwu line. This rifting belongs to synchronous extensional rifting at peripheries of the Yangtze platform and in its interior, showing that the posterior, lateral and interior extension resulting from rapid northward shift of the Yangtze platform led to isolation of this massif together with South Qinling from their adjacent areas. During the Ladinian Stage, the Songpan-Garze massif and southern Qinling sank strongly en masse. This subsidence continued till the end of the Late Triassic when the late Indosinian movement caused the sea trough to be closed and Songpan-Garze1 and southern Qinling to be folded and uplifted and become mountains.

Earthquake fault framework and seismotectonics of the Songpan-Garze region since 1900

Based on 4 781 observed faults （〉2 km length） from a 1：200 000 scale digital geologic map and 5 220 recorded seismic events since the year 1900, 993 earthquake faults are identified within the triangular Songpan-Garze study region. The study area is delineated by the nearly EW-trending East Kunlun fault zone to the north, the NW-trending Xianshuihe fault to the south and the NE-trending Longmenshan thrust belt to the east. Seismicity changes along these earthquake faults, spanning four 10-year intervals since 1970, show that following a strong earthquake swarm, which occurred in the Huya area in the mid-1970s, seismic activity increased from north to south, and migrated eastward along each major strike-slip fault zone. GPS observation data before 2008 indicate a displacement rate across the Xianshuihe fault zone to the south of -6.5- 8.6 mm/a, whereas across the East Kunlun fault zone to the north it was -1.8- 2.2 mm/a. The May 12, 2008 Ms8.0 Wenchuan earthquake, which occurred in the southeast corner of the study region, was the result of stable, high-speed left-lateral displacement along the Xianshuihe fault zone, and a sharp eastward bend of the fault trend in response to the presence of crystalline rocks in the Kangding area. Therefore, the 110-year established seismotectonic framework of the Songpan-Garze region can be defined by a network of various earthquake faults and the structural relations of the local earthquake activities.

Songpan:Water Source for Sichuan

The Mingjiang River originates on the southern slope of Gonggangling Peak of MingshanMountain, at the meeting place of Songpan and Jiuzaigou counties. It bisects Songpan, with a total length of 735 km, including 341 km within Aba Prefecture. The river has helped cultivate many generations in the province of Sichuan.The source of Mingjiang River features majestic peaks, lush grazing grass, deep forests, grotesque rocks, rare animals and a pleasant climate.In the summer and autumn, this part of the world turns into a shining lady whose hair and tender complexion merge with the blue skies and beckoning world of ancient pine trees and firs decorated by blossoming flowers.When winter comes, the shining lady dons a white robe as snow and ice take over.The area where the Mingjiang originates has the most sensitive ecosystem in Sichuan. To its north

基墨里造山与松潘-甘孜锂矿链成因的探讨

晚三叠世—早侏罗世,基墨里大陆和泛华夏陆块与欧亚大陆的碰撞,形成了4000 km长的基墨里造山带。位于三大陆之间、现今青藏高原北部的松潘-甘孜地体的造山属性的确定,对于探索松潘-甘孜锂矿链的成因有重要意义。松潘-甘孜地体西部和北部的早侏罗世陆相火山岩、底砾岩和煤系地层(~201 Ma)不整合在晚三叠世褶皱地层及花岗岩体之上,为晚三叠世—早侏罗世的基墨里造山时限提供了直接证据。松潘-甘孜地体中的甲基卡、可尔因、扎乌龙和白龙山-大红柳滩等稀有金属矿集区具有共同特征:赋存在由核部高分异S型花岗岩和幔部中晚三叠世浊积岩组成的片麻岩穹隆构造中、经历了巴罗-巴肯变质作用、含锂伟晶岩脉侵位在花岗岩体上部的伸展空间。通过对松潘-甘孜地体区域地质调查和对矿集区的变质、变形、岩浆和成矿作用及同位素年代学研究,提出该地体经历晚三叠世—早中侏罗世的基墨里造山过程:(1) 230~220 Ma:地壳缩短和加厚阶段,以盖层大规模强烈褶皱、逆冲带,盖层与基底之间向南的滑脱变形为特征,伴随深熔和巴罗式变质作用;(2) 220~190 Ma:地壳减压折返阶段,大量花岗岩侵位在中晚三叠世浊积岩中、形成片麻岩穹隆并伴随巴肯式变质作用。由于花岗质岩浆的高度分异及岩浆不混溶作用,导致侵位在片麻岩穹隆顶部伸展空间的伟晶岩稀有金属富集成矿。此外,伟晶岩型锂矿科学钻探(JSD)揭示了甲基卡矿集区多层次穹状花岗岩席控制含锂伟晶岩脉的成矿机制,推测大规模中下地壳基底深熔驱动岩浆上升,岩浆体沿上地壳中的构造面推叠形成岩席。

新疆大红柳滩伟晶岩型锂矿深部结构与区域成矿模型解释

为揭示花岗岩-伟晶岩型锂等稀有金属矿成矿系统的深部结构,对西昆仑造山带大红柳滩伟晶岩型锂矿集区开展了大地电磁测深法(MT)探测。通过MT三维反演电阻率模型,探测到两个0~20 km深度范围的高阻体,反映了出露于地表的大红柳滩复式花岗岩基和半隐伏的大红柳滩东花岗岩基;20~80 km深度范围内发现的大范围高导异常,则反映了深达上地幔的地壳重熔形成的大规模长英质岩浆储库。可见,成矿母岩大红柳滩花岗岩基是有根的,而且是规模巨大深达上地幔的岩浆储库,它们为超大型大红柳滩伟晶岩型锂矿的形成提供了物源和热源。与松潘-甘孜甲基卡超大型伟晶岩型锂矿集区对比,尽管川西甲基卡地区地表出露的花岗岩有限,但MT三维反演电阻率模型显示,其也存在深达上地幔的大范围高导异常,同样反映了大规模长英质岩浆储库的存在,只是剥蚀深度浅,上侵的花岗岩未被剥蚀出来而已。从而,深剥蚀的大红柳滩地区表现为大面积花岗岩出露的“热隆”特征,而浅剥蚀的甲基卡地区则表现为花岗岩围岩“片麻岩穹隆”热变质构造特征。西昆仑-松潘-甘孜伟晶岩型锂等稀有金属巨型成矿带两端的晚三叠世超大型矿床是大规模地壳重熔长英质岩浆作用中心的产物,由于锂等稀有金属的喜水性,H2O的饱和度是造就伟晶岩型锂超常富集的关键,并在长英质岩浆储库、上侵花岗岩和伟晶岩不同分异演化阶段,锂的“预富集”为大规模伟晶岩型锂矿成矿奠定了重要基础。

四川扎乌龙伟晶岩型稀有金属矿床的成矿机制及找矿标志

扎乌龙稀有金属矿床位于松潘-甘孜造山带,属于伟晶岩型锂辉石矿床,同时伴生铍和铌钽矿化。本文总结了扎乌龙矿床地球化学和矿物学特征,初步梳理了矿床成矿模式,并指出含矿性评价与找矿标志。扎乌龙伟晶岩脉在空间上围绕白云母花岗岩分布,具有类似的稀土元素和微量元素配分模式,但其稀土元素含量明显低于白云母花岗岩,表明伟晶岩脉为白云母花岗熔体分异演化的产物。扎乌龙白云母花岗岩岩石地球化学组分呈现高Rb/Sr和Rb/Ba、低CaO/Na_(2)O壳源特征,具有接近地壳的Sr-Nd-Hf同位素组成,表明其来源于松潘-甘孜大规模造山运动导致的西康群变泥质岩的深部重熔。矿物学和流体包裹体特征显示,扎乌龙伟晶岩脉的形成可划分为岩浆阶段和热液阶段。岩浆阶段主要结晶稀有金属矿物,如锂辉石、绿柱石和铌钽铁矿族矿物;热液阶段主要为原生矿物与流体发生再平衡,如原生锂辉石发生蚀变形成云母等矿物,原生绿柱石边部和内部缝隙产出相对富Cs_(2)O或Na_(2)O的次生绿柱石。锂矿物主要沉淀于相对封闭、高压(350MPa)的伟晶岩岩浆阶段。氢、氧同位素组成表明成矿流体主要来源于岩浆水,晚期流体来源于伟晶岩熔体的自身分异演化。扎乌龙锂辉石伟晶岩熔体分异程度属于中等,远低于高分异的新疆可可托海三号伟晶岩脉,而高于低分异的南爱尔兰Leinster伟晶岩脉。地质背景条件、围岩标志、断裂构造条件、矿物标型、物化探异常标志、遥感图像可作为扎乌龙重要找矿标志。

川西扎乌龙地区卡吉亚二云母花岗岩、稀有金属伟晶岩的地球化学、年代学特征及二者的成矿关系

锂-铍等稀有金属是中国乃至世界上重要的战略性关键金属矿产,美国、澳大利亚和日本等国早已将其列为禁止出口矿产名录,其战略地位非同一般。中国锂-铍矿产资源丰富,成矿背景优越,但地表第四纪覆盖严重,且分布不均。近年甜水海-松潘-甘孜造山带花岗伟晶岩型锂矿资源逐步被勘探发现,引起国内外学者广泛关注。川西石渠县扎乌龙锂矿作为该造山带中部重要的花岗伟晶岩型锂矿点,厘清该矿床锂资源聚集主控因素及其稀有金属富集规律将为甜水海-松潘-甘孜造山带下一步战略找矿行动提供指导和重要决策依据。本文对扎乌龙地区锂辉石钠长石伟晶岩脉、白云母钠长伟晶岩脉、电气石钠长石伟晶岩脉、卡吉亚二云母花岗岩体以及岩体边部的含电气石细晶岩、十字石黑云母片岩等进行系统采样分析,利用LA-ICP-MS独居石U-Th-Pb同位素定年技术,确定扎乌龙卡吉亚二云母花岗岩形成于晚三叠世213~211 Ma,含电气石细晶岩约形成于210 Ma,白云母钠长石伟晶岩约形成于210~200 Ma,富锂伟晶岩可能在205 Ma集中产出。结合前人年代学资料,综合分析认为扎乌龙矿区由二云母花岗岩、电气石细晶岩到白云母钠长石伟晶岩和锂辉石钠长石伟晶岩形成时代逐步年轻。210 Ma以后,岩浆演化逐步进入岩浆-热液阶段,在约10 Ma时间内发生了持续、多期次的岩浆侵位活动。此外,结合花岗岩向伟晶岩逐步降低的REE、K/Rb、Nb/Ta和Zr/Hf等微量特征值,以及高演化伟晶岩独居石矿物Nd、Eu负异常现象,表明花岗质岩浆的结晶分异作用在扎乌龙伟晶岩稀有金属富集过程中发挥着重要作用。

川西九龙白台花岗岩地球化学特征、锆石U-Pb年龄和Hf同位素组成及其稀有金属成矿意义

为揭示川西九龙白台花岗岩成因及其与稀有金属成矿的关系,笔者等对白台花岗岩开展了岩相学、岩石地球化学、LA-ICP-MS锆石U-Pb年代学、锆石微量元素地球化学、Hf同位素地球化学测试。结果显示,白台黑云母二长花岗岩具高SiO_(2)(69.01%~70.55%)、高K_(2)O(3.86%~4.99%)、高碱(K_(2)O+Na_(2)O=7.41%~8.18%),低CaO(1.49%~2.2%)、低MgO(0.44%~0.57%)等特征,里特曼指数σ=2.03~2.43,A/CNK=1.07~1.14,为弱过铝质的高钾钙碱性系列岩石;微量元素特征显示相对富集Rb、K等大离子亲石元素,相对亏损Nb、P、Hf等高场强元素;球粒陨石标准化的稀土元素配分模式为明显的轻稀土富集和重稀土亏损的右倾型。白台黑云母二长花岗岩锆石U-Pb年龄为(213~212)Ma,ε_(Hf)(t)值为-7.4~-1.1,Hf同位素二阶模式年龄T_(DM2)为(1.6~1.2)Ga。研究结果表明,白台花岗岩形成于后碰撞伸展背景,是在松潘—甘孜地块遭受挤压碰撞后,增厚的岩石圈地幔拆沉,软流圈地幔物质上涌后发生减压熔融形成的晚三叠世I型花岗岩。同时,笔者等认为白台伟晶岩型铍矿床与白台花岗岩密切相关,是该花岗岩体残余岩浆热液分异的产物。

四川阿坝可尔因锂矿田成矿规律与成矿预测

青藏高原东北缘的松潘-甘孜造山带是我国最重要的锂矿成矿带,其中部地区的可尔因锂铍稀有金属矿田是最重要的伟晶岩型锂矿资源基地之一。本文在已开展的地质矿产调查及勘查工作的基础上,系统总结了矿田内典型矿床地质特征、矿床地球化学特征、成岩成矿时代,完善了可尔因锂矿田成矿模型,并进一步指出了区域找矿方向,对提升区域伟晶岩型锂矿成矿规律及指导深部找矿意义重大。矿田内矿床类型均为花岗伟晶岩型稀有金属矿床,矿石矿物主要为锂辉石。花岗岩-伟晶岩与西康群变沉积岩具有近一致的Sr-Nd-Hf同位素组成,指示成岩成矿物质来源于西康群。自花岗岩至伟晶岩,原生矿物和全岩δ^(7)Li值均升高,指示伟晶岩形成于花岗岩浆分异;自钠长石伟晶岩至钠长石锂辉石伟晶岩,原生矿物δ^(7)Li值升高,而全岩δ^(7)Li值降低,指示伟晶岩浆演化过程中的分离结晶和出熔流体富集。可尔因复式岩体与伟晶岩具有相重叠的同位素年龄,为同期造山作用的产物,形成于印支造山晚期构造体制由挤压转为伸展的造山阶段。基于以上特征,对前人提出的可尔因矿田成岩成矿模式进行了完善,认为富锂的源区、适宜的构造背景、充分且强烈的岩浆结晶分异协同富水流体的富集共同促进了可尔因锂矿田的形成。此外,总结了可尔因锂矿田的找矿标志,并预测了找矿方向。