Mantle Driven Early Eocene Magmatic Flare-up of the Gangdese Arc, Tibet: A Case Study on the Nymo Intrusive Complex

Magmatic periodicity is recognized in continental arcs worldwide, but the mechanism responsible for punctuated arc magmatism is controversial. Continental arcs in the Trans-Himalayan orogenic system display episodic magmatism and the most voluminous flare-up in this system was in early Eocene during the transition from subduction to collision. The close association of the flare-up with collision is intriguing. Our study employs zircon Lu-Hf and bulk rock Sr-Nd isotopes, along with mineral geochemistry, to track the melt sources of the Nymo intrusive complex and the role of mantle magma during the early Eocene flare-up of the Gangdese arc, Tibet. The Nymo intrusive complex is composed of gabbronorite, diorite, quartz diorite, and granodiorite which define an arc-related calc-alkaline suite. Zircon U-Pb ages reveal that the complex was emplaced between ~50–47 Ma. Zircon Hf isotopes yield εHf(t) values of 8.2–13.1, while whole-rock Sr and Nd isotopes yield εNd(t) values of 2.7–6.5 indicative of magmatism dominated by melting of a juvenile mantle source with only minor crustal assimilation(~15%–25%) as indicated by assimilation and fractional crystallization modeling. Together with published data, the early Eocene magmatic flare-up was likely triggered by slab breakoff of subducted oceanic lithosphere at depths shallower than the overriding plate. The early Eocene magmatic flare-up may have contributed to crustal thickening of the Gangdese arc. This study provides important insights into the magmatic flare-up and its significant role in the generation of large batholiths during the transition from subduction to collision.

Spatiotemporal mapping of(ultra‐)mafic magmatic mine areas:Implications of economic and political realities in China

The spatiotemporal extension/expansion of mine areas is affected by multiple factors.So far,very little has been done to examine the interaction between mine areas and political or economic realities.The(ultra‐)mafic magmatic mines in China played a specific role in supporting national development and providing an ideal research subject for monitoring their interrelationship.In this study,remote sensing and mining‐related GIS data were used to identify and analyze 1233(ultra‐)mafic magmatic mine area polygons in China,which covered approximately 322.96 km2 of land and included a V–Ti–Fe mine,a copper–nickel mine,a chromite mine,an asbestos mine,and a diamond mine.It was found that(1)the areal expansion of mines is significantly related to the mine types,perimeter,topography,and population density.(2)The mine area variation also reflects market and policy realities.The temporal expansion of the mine area from 2010 to 2020 followed an S‐shaped pattern(with the turning point occurring in 2014),closely related to iron overcapacity and tightened mining policies.(3)The complexity(D)of the mine area may reflect mine design and excavation practices.To be specific,lower D indicates early‐stage or artisanal/small‐scale mining,whereas higher D represents large‐scale mining.This study demonstrates that the detailed mapping of mine land can serve as an indicator to implement miningrelated market and policy changes.The(ultra‐)mafic mines area data set can be accessed at https://zenodo.org/record/7636616#.Y-p0uXaZOa0.

SHRIMP Zircon U-Pb Dating of the Tongshi Magmatic Complex in Western Shandong and Its Geological Implications

The SHRIMP U-Pb zircon dating result of the Tongshi magmatic complex in western Shandong is presented in this paper. The Tongshi magmatic complex comprises fine-grained porphyritic diorite and syenitic porphyry. Eighteen analyses for fine-grained porphyritic diorite gave two concordia ages, in which ten analyses constitute the young age group, giving ^206Pb/^238U ages ranging from 167.9 Ma to 183 Ma with a weighted mean age of 175.7±3.8 Ma, and the other eight yielded ^207Pb/^206Pb ages of 2502 Ma to 2554 Ma with a weighted mean 2518±11 Ma. Two analyses for syenitic porphyry gave ages of 2485 Ma and 2512 Ma, respectively. The age of 175.7±3.8 Ma indicates that the crystallization of the Tongshi magmatic complex occurred in the Middle Jurassic, whereas that of 2518±11 Ma is interpreted as the age of inherited magmatic zircons in the Neoarchean Wutai period.

A ca. 2.2Ga Acidic Magmatic Event at the Northern Margin of the Yangtze Craton: Evidence from U-Pb Dating and Hf Isotope Analysis of Zircons from the Kongling Complex

Objective The Yangtze craton collisional orogeny at ca. extensional events at ca. 1 experienced Paleoproterozoic 1.95-2.0 Ga and post-orogenic 85 Ga related to amalgamation of the Columbia （Nuna） supercontinent （Zhao and Cawood, 2012）. A ca. 2.15 Ga suprasubduction zone ophiolitic melange was recongized in the Archean- Paleoproterozoic Kongling Complex of the northern Yangtze craton （Han et al., 2017）. However, the tectonic evolution in early Paleoproterozoic from 2.4 Ga to 2.2 Ga remains unclear. We report here the presence of a suite of Paleoproterozoic （2.2 Ga） granites in the Huangling dome, northern Yangtze craton, which may provide important insights into crustal growth processes in the craton prior to the assembly of Columbia.

2.2Ga Subduction-Related Mafic Magmatic Rocks in the Kongling Complex:Evidence for the Assembly of the Columbia Supercontinent

Objective Petrogenesis of the Paleoproterozoic mafic dikes and their tectonic implications are of great significance to the tectonic evolution of the Yangtze craton as well as the paleoposition of the Yangtze craton relative to the Columbia supercontinent.Till now,

Geochemistry of an Alaskan-type mafic-ultramafic complex in Eastern Desert, Egypt:New insights and constraints on the Neoproterozoic island arc magmatism

Mikbi intrusion(MI) is a part of the Neoproterozoic Nubian Shield located along the NE-SW trending major fracture zones prevailing southern Eastern Desert of Egypt. In this study, we present for the first time detailed mineralogical and bulk-rock geochemical data to infer some constraints on the parental magma genesis and to understand the tectonic processes contributed to MI formation. Lithologically, it is composed of fresh peridotite, clinopyroxenite, hornblendite, anorthosite, gabbronorite, pyroxene amphibole gabbro, amphibole gabbro and diorite. All rocks have low Th/La ratios(mostly <0.2) and lack positive Zr and Th anomalies excluding significant crustal contamination. They show very low concentrations of Nb, Ta, Zr and Hf together with sub-chondritic ratios of Nb/Ta(2-15) and Zr/Hf(19-35),suggesting that their mantle source was depleted by earlier melting extraction event. The oxygen fugacity(logfO_2) estimated from diorite biotite is around the nickel-nickel oxide buffer(NNO) indicating crystallization from a relatively oxidized magma. Amphiboles in the studied mafic-ultramafic rocks indicate relative oxygen fugacity(i.e. ΔNNO; nickel-nickel oxide) of 0.28-3 and were in equilibrium mostly with 3.77-8.24 wt.% H_2 O_(melt)(i.e. water content in the melt), consistent with the typical values of subduction-related magmas. Moreover, pressure estimates(0.53-6.79 kbar) indicate polybaric crystallization and suggest that the magma chamber(s) was located at relatively shallow crustal levels. The enrichment in LILE(e.g., Cs, Ba, K and Sr) and the depletion in HFSE(e.g., Th and Nb) relative to primitive mantle are consistent with island arc signature. The olivine, pyroxene and amphibole compositions also reflect arc affinity. These inferences suggest that their primary magma was derived from partial melting of a mantle source that formerly metasomatized in a subduction zone setting. Clinopyroxene and bulkrock data are consistent with orogenic tholeiitic affinity. Consequently, the mineral and bulk-rock chemistry strongly indicate crystallization from hydrous tholeiitic magma. Moreover, their trace element patterns are subparallel indicating that the various rock types possibly result from differentiation of the same primary magma. These petrological, mineralogical and geochemical characteristics show that the MI is a typical Alaskan-type complex.

Eocene magmatism(Maden Complex) in the Southeast Anatolian Orogenic Belt: Magma genesis and tectonic implications

The origin and geodynamic setting of the Maden Complex, which is situated in the Bitlis-Zagros Suture Zone in the Southeast Anatolian Orogenic Belt, is still controversial due to lack of systematic geological and geochemical data. Here we present new whole rock major-trace-rare earth element and Sre Nd isotope data from the Middle Eocene volcanic rocks exposed in Maden Complex and discuss their origin in the light of new and old data. The volcanic lithologies are represented mainly by basalt and andesite, and minor dacite that vary from low-K tholeiitic, calc-alkaline, high-K calc-alkaline, and shoshonitic in composition. They exhibit enrichments in large ion lithophile and light rare earth elements, with depletions in high field strength elements. Basaltic rocks have uniform Sr and Nd isotope ratios with high εNd(t) values varying from t5.5 to t6.7, in contrast to, andesitic rocks are characterized by low εNd(t) values ranging from à1.6 to à10. These geochemical and isotopic characteristics indicate that two end-members, a subduction-related mantle source and a continental crust, were involved in the magma genesis. Considering all geological and geochemical data, we suggest that the Eocene Maden magmatism occurred as a post-collisional product by asthenospheric upwelling owing to convective removal of the lithosphere during an extensional collapse of the Southeast Anatolian ranges.

U-Pb SHRIMP-II Baddeleyite and Zircon Dating of the Early Proterozoic Monchegorsk Layered Mafite-Ultramafite Complex(Kola Peninsula): Evidence of Synchronous Magmatism

The Early Paleoproterozoic Monchegorsk Complex is exposed over an area of 550 km;and comprises two layered mafite–ultramafite intrusions:the Monchepluton of ultramafic and mafic rocks and the predominantly gabbroid

Petrogenesis of the Borjuri diorite pluton in the Mikir Massif of Northeast India:implications for post-collisional intermediate magmatism during the Pan-African orogeny

The Assam-Meghalaya Gneissic Complex(AMGC)of northeast India contains numerous Pan-African granitic bodies that have been attributed to post-collisional rift-related magmatism.The present study is concerned with the first appraisal of intermediate magmatism(diorite,monzonite,and monzodiorite)found in the Borjuri Pluton of Mikir Massif,which is the eastern extension of AMGC.The diorites are strongly metaluminous and exhibit enriched LREE([La/Yb]N=1.63–7.37)with respect to HREE([Gd/Yb]N=1.95–2.27).The studied rocks do not show any mineralogical or textural indication of metamorphism.Tectonic discrimination diagrams indicate that these rocks originated in a within-plate tectonic setting.The lower Mg#(33.49–38.69),low Cr(below detection limit),and Ni(27–41 ppm)contents along with elemental ratios such as Rb/Sr(0.32–0.95),La/Nb(0.49–4.21),and Nb/Ce(0.11–0.64)suggest a crustal source for the diorites.Discrimination diagrams coupled with elemental ratios suggest that these rocks originated due to partial melting of mafic components in the crust with possible contribution from mantle materials.The P–T conditions of diorite emplacement(7.4 kbar,688℃)were calculated using the amphibole-plagioclase geothermobarometer.Geochemical and geochronological data of the Pan-African felsic plutons reported from the AMGC indicate that these rocks were emplaced in a post-collisional extensional regime.The Borjuri Pluton is in close proximity with the Kathalguri Pluton,which has been reported as a product of PanAfrican magmatism.In view of the numerous extensional Pan-African felsic magmatism reported from the AMGC and based on the close vicinity of the Borjuri diorites with the Kathalguri granites,we speculate that the Borjuri diorites are products of the Pan-African post-collisional magmatism.

An Early Paleozoic Ultramafic Complex in the North Wulan Metamorphic Complex,North Qaidam:Contraints on the Nature of the Alaskan-type Continental Arc Root

Orogenic peridotite is an important component of orogenic belts and retains crucial information on mantle magmatic activity,slab subduction,and melt or fluid metasomatism.To determine the source of the mantle-derived parental magma of the peridotite and to investigate the metasomatism that it experienced,we undertook an integrated study of the petrography,whole-rock major-and trace-element compositions,in situ zircon U-Pb geochronology,and mineral majorand trace-element compositions of an early Paleozoic ultramafic complex in the North Wulan area of North Qaidam.The Halihatu ultramafic-mafic complex is composed of dunite,pyroxene peridotite,and gabbro,which are characteristic of Alaskan-type complexes.The dunite yields a weighted mean^(206)Pb/^(238)U age of 479±5 Ma(MSWD=0.7),which reflects the age of the metasomatism rather than the crystallization age of the ultramafic magma.The peridotites have high Mg^(#)(89.8-91.8)and Cr contents(2419-5190 ppm),low Al_(2)O_(3)(0.20-1.68 wt%)and Ni(289-1012 ppm)contents,and high olivine Fo contents(87-91),suggesting a large degree(~15%-22%)of partial melting of lithospheric ultramafic rocks followed by variable degrees of fractional crystallization of olivine and pyroxene.This is consistent with estimates of 15%-22.3%partial melting calculated using the Cr#of spinel crystals and with the low Yb(0.04-0.33 ppm)and Y(0.72-1.29 ppm)contents of clinopyroxene crystals.Whole-rock trace-element patterns show enrichment in large ion lithophile elements and depletion in high field strength elements,along with high Al_(2)O_(3)(2.10-6.47 wt%)and low TiO_(2)(0.01-0.21 wt%)contents of clinopyroxene crystals,suggesting an arc magma cumulate trend.These features,along with the high olivine Fo contents(87-91 ppm),imply that the Halihatu peridotite is an Alaskan-type crustal cumulates derived from Mgrich hydrous basaltic melts.The high estimated f O_(2)(FMQ+1.97 to FMQ+3.81)further supports the idea that they formed in an arc setting.The Ni/Co and Ni/Mn ratios and cumulate textures of the olivine,quenched boundaries between mafic and felsic melts,and the occurrence of tremolite and phlogopite reflect interactions between the Halihatu peridotite and injected silicate and carbonatitic melts in the lower crust.Therefore,we propose a new cumulate-infiltration model for the petrogenesis of Alaskan-type ultramafic complexes,which improves our understanding of the nature of Alaskan-type continental arc root.

老挝班康姆铜金矿床“岩浆核杂岩”隆起-拆离带构造控矿特征

老挝班康姆铜金矿床位于东南亚思茅—彭世洛地块南缘构造活跃带,是与中生代岩浆岩有关的大型铜金矿床。该区具有巨大的资源潜力,但地质研究程度相对较低,其成矿模式和演化规律等理论问题尚未完全解决。本文通过对成矿岩体分布特征、断裂构造变形特征和拆离带构造成矿特征的研究,揭示矿床岩浆核杂岩隆起特征与拆离带构造特征,认为班康姆矿床受控于“岩浆核杂岩”及其边界的隆起-拆离带构造,为岩浆核杂岩隆起-拆离带构造热液铜金矿床。班康姆矿床“岩浆核杂岩”构造由“岩浆杂岩体核、拆离带构造和火山-沉积岩”三个部分组成,岩浆杂岩体核主要由花岗闪长岩组成。花岗闪长岩与安山岩和灰岩接触带下盘发育有似片麻理构造,片理产状以核部花岗闪长岩为中心,呈现外倾的特征,推断为岩浆岩上侵过程中受到区域挤压剪切应力的作用形成。磁法和激电测量结果,反映班康姆矿床矿化蚀变带和岩浆核杂岩的分布关系,结合地质实测的岩体分布信息,推测深部存在隐伏岩体。拆离带构造发育于下盘花岗闪长岩体与上盘火山-沉积岩之间,是铜金矿化的集中地段,且拆离带构造中矿化蚀变岩的形成年龄(244~251 Ma),晚于杂岩体侵位年龄(264±10 Ma)。通过对拆离带构造及两侧小型构造观测与分析,可知拆离带构造剖面上呈上陡下缓的“铲”式形态学特征,具有明显的早期韧性变形、晚期脆性变形的特点,其上盘的主运动方向为NWW向。本文提出班康姆铜金矿床的东南部同样具有“岩浆核杂岩”隆起-拆离带构造成矿模式的特征,为有利的找矿靶区。

东昆仑古生代镁铁质岩浆镍钴成矿条件——希望沟地区超镁铁质岩C-He-Ne-Ar同位素制约

东昆仑造山带广泛发育古生代以来的镁铁质岩浆作用,不同的镁铁质岩浆在镍钴关键金属成矿潜力方面存在显著差异,希望沟地区出露的玄武岩及406.9Ma和270.7~264.9Ma两期镁铁-超镁铁质岩的Ni-Co成矿规模不同,是对比认识镍钴富集成矿条件差异的理想地区。本文测定了超镁铁质岩单矿物中流体挥发份的稀有气体和碳同位素组成,橄榄石、辉石和斜长石释出CO _(2)和CH4的δ^(13)C值变化范围大,δ^(13)CCO _(2)和δ^(13)C_(CH4)位于有机质热裂解成因及地壳值的范围内,δ^(13)C_(CH4)值具有I型有机质来源特征,CH4同系物的碳同位素组成随碳数呈正序及局部反序的分布特征,3He/4He与40Ar/36Ar指示大气饱和流体与大陆地壳端元,3He/4He与δ^(13)CCO _(2)揭示Ⅰ型沉积有机质与蚀变洋壳。3He/4He与4He含量负相关表明放射性成因4He~*的大量积聚,扣除掉4He~*后含镍钴成矿的406.9Ma岩体的3He/4He值达1.8Ra,揭示岩浆来源于岩石圈地幔。大陆地壳和沉积有机质可能来自围岩的沉积有机质热裂解组分,Ⅰ型沉积有机质、蚀变洋壳及大气饱和流体揭示岩浆地幔源区的俯冲洋壳板片携带再循环地壳组分。希望沟镁铁-超镁铁质杂岩体的地壳混染比例(32%)高于夏日哈木矿床,不是制约硫化物饱和熔离镍钴成矿的条件,270.7~264.9Ma岩体低的Ni-Co含量及成矿规模可能与深部岩浆房硫化物的熔离有关。

Application of General Shear Theory to the Study of Formation Mechanism of the Metamorphic Core Complex:A Case Study of Xiaoqinling in Central China

: The kinematic vorticity number and strain of the mylonitic zone related to the detachment fault increase from ESE to WNW along the moving direction of the upper plate of the Xiaoqinling metamorphic core complex (XMCC) and the geometry of quartz c-axis fabrics changes progressively from crossed girdles to single girdles in the same direction. Therefore, pure shear is dominant in the ESE part of the XMCC while simple shear becomes increasingly important towards WNW. However, the shear type does not change with the strain across the shear zone, thus the variation of shear type is of significance in indicating the formation mechanism. The granitic plutons within the XMCC came from the deep source and their emplacement was an active and forceful upwelling prior to the detachment faulting. The PTt path demonstrates that magmatism is an important cause for the formation of the XMCC. The formation mechanism of the XMCC is supposed to be active plutonism and passive detachment. Crustal thickening and magmatic doming caused necking extension with pure shear, and magmatic heating and doming resulted in detachment extension with simple shear and formed the XMCC.

Element mapping the Merensky Reef of the Bushveld Complex

The Merensky Reef hosts one of the largest PGE resources globally.It has been exploited for nearly 100 years,yet its origin remains unresolved.In the present study,we characterised eight samples of the reef at four localities in the western Bushveld Complex using micro-X-ray fluorescence and field emission scanning electron microscopy.Our results indicate that the Merensky Reef formed through a range of diverse processes.Textures exhibited by chromite grains at the base of the reef are consistent with supercooling and in situ growth.The local thickening of the Merensky chromitite layers within troughs in the floor rocks is most readily explained by granular flow.Annealing and deformation textures in pyroxenes of the Merensky pegmatoid bear testament to recrystallisation and deformation.The footwall rocks to the reef contain disseminations of PGE rich sulphides as well as olivine grains with peritectic reaction rims along their upper margins suggesting reactive downward flow of silicate and sulphide melts.Olivine-hosted melt inclusions containing Cl-rich apatite,sodic plagioclase,and phlogopite suggest the presence of highly evolved,volatile-rich melts.Pervasive reverse zonation of cumulus plagioclase in the footwall of the reef indicates dissolution or partial melting of plagioclase,possibly triggered by flux of heat,acidic fluids,or hydrous melt.Together,these data suggest that the reef formed through a combination of magmatic,hydrodynamic and hydromagmatic processes.

陆内岩浆核杂岩隆起-拆离构造--胶东地区研究实例

在胶东地区金矿矿田构造研究的基础上,把岩浆核杂岩和拆离构造联系起来,提出陆内岩浆核杂岩隆起-拆离构造的新模式,并认为中生代该区不发育变质核杂岩构造。经过10多年的构造变形蚀变岩相填图、岩浆岩结构构造填图和古地磁研究、运动学测量,结合地球物理资料分析发现,胶东地区典型的玲珑岩浆核杂岩隆起-拆离构造显示出长垣状、拱曲形态的穹窿,表现为:①穹窿核部由多期和多构造性质的花岗质杂岩组成;②花岗杂岩体被断层圈闭,这些中低角度铲状形态的拆离带剪切断裂,其宽大的破碎岩带显示了韧-脆性变形叠加,发生岩浆期后热液交代蚀变矿化作用;③拆离断层上盘岩石围绕岩浆核分布,由基底变质岩和中生代沉积岩组成,呈滑脱凹陷状态。岩浆核杂岩隆起-拆离构造是符合东亚陆内构造岩浆活化背景的一个新模式。通过岩浆核杂岩隆起-拆离构造研究,提出岩浆隆起和拉分盆地属于同一构造系统,挤压构造岩浆隆起和引张拆离凹陷带是应力场转化过程的产物,而拆离铲式断裂和脆-韧性叠加的构造岩带是成矿预测的目标,并把区域成岩成矿规律作为直接观测和勘查的标志,在区域地质成矿规律研究、地质调查、成矿预测等方面具有广泛推广价值和示范引导意义。

Rhyacian-Orosirian tectonic history of the Juiz de Fora Complex:Evidence for an Archean crustal reservoir within an island-arc system

The southern São Francisco Paleocontinent(SFP)comprises Archean nuclei and Paleoproterozoic complexes encompassing magmatic arcs juxtaposed during a Rhyacian to Orosirian orogenic event.The Juiz de Fora Complex(JFC)represents an imbricated thrust system that comprises orthogranulites with a wide compositional range formed in an intra-oceanic setting during the Siderian to the Orosirian and later accreted to the southeastern margin of the SFP.Here we report new petrological,geochemical,whole-rock Nd and Sr data,as well as zircon U–Pb ages from felsic and mafic orthogranulites from the JFC.The new data is combined with a regional compilation that enables an evaluation of the interaction between magmatism and orogenetic episodes in the context of the consolidation of São Francisco Paleocontinent during the Rhyacian–Orosirian.Pre collisional Island Arc tholeiites(IAT),Tonalites-Tron dhjemites-Granodiorites(TTGs)and sanukitoid magmatism occurred from 2200 Ma to 2085 Ma.This was followed by post-collisional magmatism,which is represented by hybrid granitoids coeval with the emplacement of E-MORB basic rocks.Crustal signatures for the Rhyacian to Orosirian evolution are highlighted by the dominance of negativeεNd(t)associated with Meso-to Neoarchean Nd TDMmodel ages as well as inherited zircon grains from the hybrid granitoids.The JFC is extensively highlighted in the literature as a primitive intra-oceanic arc,but here we propose the reworking or recycling of ancient crustal segments within the mature arc stage of the JFC,suggesting a Mesoarchean crustal source involved in the JFC evolution.

长江中下游九瑞矿集区彭山岩浆核杂岩隆起-拆离带成矿构造特征

九瑞矿集区属于长江中下游成矿带的组成部分。彭山多金属矿田位于九瑞矿集区的南部,蕴藏着丰富的矿产资源,但其构造样式还存在争议。通过地质特征、地球物理特征等综合分析,提出彭山矿田受控于岩浆核杂岩构造,岩浆核杂岩隆起-拆离带构造的核心由燕山中期隐伏的隆起即椭圆状花岗岩类侵入岩体构成,并在燕山晚期定型。外围沉积岩呈穹窿状、带状围绕彭山岩浆核杂岩展布。周围的断裂带倾向背离该岩浆核杂岩,呈铲状分布,反映出拆离构造的特征。彭山矿田以花岗杂岩体为中心,向四周出现高温矿种向低温矿种变化的砷矿(毒砂)-锡矿-铅锌矿-萤石矿-重晶石矿等“晕圈型”的矿带类型,亦均是沿着多层次滑脱拆离断层矿物富集的结果,矿化作用在岩浆核杂岩的内外接触带产生,最终在构造应力的松弛阶段形成矽卡岩型、斑岩型、热液脉状等锡-铅锌多金属矿床。

江西相山矿田铀成矿的特征、演化及启示

寻找富大硬岩型铀矿一直以来面临挑战。据深大断裂-临界水耦合成矿机制等新认识,重新梳理相山矿田火山杂岩铀成矿的主要特征,结合其他富大热液矿床的研究,探索富大热液矿床的共同规律。富大热液矿床多具有以下特征:首先,常有深大断裂与岩浆杂岩隆起组合的“一刀加一饼”的外形,深大断裂这“一刀”具多期次活动特点,因降压、升温、聚水,改变了周边区域的物理化学环境,驱动成岩成矿相关的物质运移、相变等,从而控制着与成矿密切相关的赋矿岩浆杂岩的形成、热液蚀变和铀成矿期次。其次,有3个主要构造层及与其相对应的三阶段式演化。再次,有2个主成矿期,早期高温成矿期(在相山铀矿田是115±0.5 Ma)与岩浆杂岩形成相关,而晚期低温成矿期(在相山铀矿田是98±8 Ma)与控盆断裂活动、盆地脱水相关,2期成矿叠加是富大矿体形成的必要条件。上述富大热液矿床的特征主要体现为具有“一刀加一饼”外形的、由深大断裂与岩浆杂岩隆起组成的构造岩性组合,其形成机制实质上仍是深大断裂多期活动成岩成矿。这些认识可能给中国富大热液铀矿成矿和找矿研究带来一些启示。

中国东部中生代晚期岩浆核杂岩隆起-拆离带构造成矿特征与金-多金属矿田勘查

中国东部中生代晚期发育伸展构造,诱发强烈的岩浆活动,出现大规模成矿事件。本文将伸展构造核部出露中生代晚期岩浆杂岩、边部出露拆离断层作为主要标志,将多期岩浆侵入形成的变质核杂岩和伸展穹窿均归入中生代晚期岩浆核杂岩隆起-拆离带构造范畴。前者主要形成深源金-多金属矿床,后者主要形成浅源有色金属矿床。前者主要产于古老变质岩区,后者主要产于古生代沉积-火山岩区。岩浆上侵的诱因,主要与晚中生代太平洋板块的俯冲-折返机制有关。结合地球物理资料,探讨了岩浆核杂岩的深部控制因素。基于“岩浆核杂岩隆起-拆离带”岩浆期后热液成矿模式,总结了岩浆热液型贵金属、有色金属矿床的分布规律、成矿条件和找矿标志,提出了中尺度“矿田找矿”的新方向,在辽南、皖北地区预测了有利的隐伏远景区。

岩浆核杂岩和变质核杂岩特征对比及控矿实例--南秦岭牛山-凤凰山变质核杂岩和牛山北岩浆核杂岩构造群落及控矿模式

以南秦岭牛山-凤凰山变质核杂岩和牛山北岩浆核杂岩为例,通过核杂岩的构造群落、变质程度、岩浆侵位与变形时代、构造层次与演化、控矿特征与控矿构造-蚀变岩相填图及测年研究,对比2类核杂岩的特征及其控矿作用。结果表明,2类核杂岩有相似的结构样式,但构造群落和演化差别较大。牛山-凤凰山变质核杂岩核部为新元古代武当岩群和耀岭河岩组中深变质岩,其中可见新元古代石英闪长岩和加里东期辉石岩-辉绿岩株,说明是在新元古代或加里东期形成的。核杂岩与外围震旦系-泥盆系浅变质岩间由剥离断层及韧性剪切带分割。志留系梅子垭岩组为浅变质强变形的岩片组合,发育多层次韧性剪切、固态流变、滑脱-逆冲-走滑变形3期新生面理及其置换。而牛山北岩浆核杂岩核部和外围是浅变质岩,在核部和外围填图、测试时发现新元古代、早古生代、三叠纪、侏罗纪4期侵入岩,与岩浆核杂岩相关的有三叠纪-早侏罗世二长花岗岩株和晚侏罗世花岗岩脉2期侵入岩。研究发现,与岩浆核杂岩伴随的岩浆侵位、韧性剪切变形与热变质增温-变斑晶加大-自然金沿S 2面理分布-金矿化热液蚀变等的时代均集中在晚三叠世-侏罗纪,指示了时代较新的陆内造山期岩浆核杂岩的脆-韧性剪切变形-立交桥式岩浆-热力垂向增生-热液蚀变成矿时空关联特点及深部找矿方向。