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1.
The Shihu gold deposit is situated in the central shear zone of the Meso-Cenozoic Fuping metamorphic core complex in the middle-northern part of the Taihang Mountains. This kind of gold deposits named after ‘Shihu type’ widely occurs in this region. Gold-bearing quartz veins are their most important industrial orebodies. Detailed laser 40Ar/39Ar geochronology of the mineralized quartz veins in the study area reveals details of its tectono-magmatic history. The 40Ar/39Ar ages for the quartz are between 134.4 Ma and 155.9 Ma with a mean age of 141±4 Ma on the isochron line and 139±7 Ma on the inverse isochron line, respectively, which is interpreted to be the best estimate of the crystalline age of the quartz veins. The gold mineralization was most likely related to an underplating event that took place in the northern part of the Taihang Mountain at ca. 140 Ma. The timing of gold mineralization in the area is similar to those observed in other major gold-producing provinces in the NCC. This episode is simultaneous with those in the eastern NCC, indicative of a widespread late Yanshanian metallogenic event that was a response either to the subduction of the Izanagi-Pacific plate beneath eastern China or to the removal of the Early Cretaceous lithosphere in the eastern NCC. The ore-forming material sources may be the Early Precambrian metamorphic basement, instead of intermediate-acid rock bodies and dykes.  相似文献   

2.
吉林夹皮沟金矿带岩脉和蚀变绢云母定年及金矿成矿时代   总被引：6，自引：2，他引：6  
吉林夹皮沟金矿床的矿化年龄一直存在争议。采用先进的SHRIMP测年方法测得夹皮沟二道沟金矿床的花岗闪长岩脉锆石的2 0 6Pb/ 2 3 8U年龄为 (2 2 3± 2 )Ma ;八家子金矿床的石英正长斑岩锆石的2 0 6Pb/ 2 3 8U年龄为 (2 41± 6 )～ (2 18± 6 )Ma。这一结果与前人测得的K Ar年龄基本相符。这两条岩脉与含金石英脉同构造空间 ,形成时代相近 ,因此上述岩脉年龄大体反映了金矿化年龄。同时还测得八家子金矿床蚀变绢云母的 4 0 Ar 3 9Ar等时线年龄为(2 0 3 975± 0 5 2 7)Ma ,进一步证明金矿化发生在中生代印支期。矿石中含有大量的方铅矿 ,还存在矿物及元素的分带 ,这些特征表明夹皮沟金矿床不太可能是新太古代或元古代形成的变质热液矿床 ,更大可能是中生代与岩浆活动有关的岩浆热液矿床  相似文献   

3.
Uranium–lead zircon (laser ablation multi-collector ICP-MS spot analysis) ages from La Caridad porphyry copper deposit in the Nacozari District, Northeastern Sonora, Mexico, suggest a short period of magmatism, between 55.5 and 52.6 Ma. Two U–Pb ages from the mineralized quartz monzonite unit, showing different textural characteristics, yielded indistinguishable crystallization ages (~54 Ma), and indicate that the intrusion responsible for the mineralization occurred as a single large complex unit, instead of multiple pulses of magmatism. Some zircons analyzed also show inherited ages in cores recording dates of 112–124 Ma, 141–166 Ma and 1.4 Ga. The Re–Os molybdenite ages from the potassic and phyllic hydrothermal alteration veins yielded identical ages within error, 53.6±0.3 Ma and 53.8±0.3 Ma, respectively (weighted average of 53.7±0.21 Ma), supporting a restricted period for the mineralization. The geochronological data thus indicate a short-lived magmatic and hydrothermal system. The inherited zircons of Precambrian and Late Jurassic-Mid Cretaceous age found in the intrusive rocks of La Caridad deposit, can be explained considering two possible scenarios within the tectonic/magmatic evolution of the area. The first scenario considers the presence of a Precambrian anorogenic granitic basement that is intruded by Mesozoic (Jurassic–Cretaceous) units present beneath the La Caridad deposit. The second scenario suggests that the Mesozoic Glance Conglomerate Formation of Arizona underlies the Paleocene volcanic-igneous pile in the La Caridad area.  相似文献   

4.
The Dawan Mo–Zn–Fe deposit located in the Northern Taihang Mountains in the middle of the North China Craton (NCC) contains large Mo‐dominant deposits. The mineralization of the Dawan Mo–Zn–Fe deposit is associated with the Mesozoic Wanganzhen granitoid complex and is mainly hosted within Archean metamorphic rocks and Proterozoic–Paleozoic dolomites. Rhyolite porphyry and quartz monzonite both occur in the ore field and potassic alteration, strong silicic–phyllic alteration, and propylitic alteration occur from the center of the rhyolite porphyry outward. The Mo mineralization is spacially related to silicic and potassic alteration. The Fe orebody is mainly found in serpentinized skarn in the external contact zone between the quartz monzonite and dolomite. Six samples of molybdenite were collected for Re–Os dating. Results show that the Re–Os model ages range from 136.2 Ma to 138.1 Ma with an isochron age of 138 ± 2 Ma (MSWD = 1.2). U–Pb zircon ages determined by laser ablation inductively coupled plasma mass spectrometry yield crystallization ages of 141.2 ± 0.7 (MSWD = 0.38) and 130.7 ± 0.6 Ma (MSWD = 0.73) for the rhyolite porphyry and quartz monzonite, respectively. The ore‐bearing rhyolite porphyry shows higher K2O/Na2O ratios, ranging from 58.0 to 68.7 (wt%), than those of quartz monzonite. All of the rock samples are classified in the shoshonitic series and characterized by enrichment in large ion lithophile elements; depletion in Mg, Fe, Ta, Ni, P, and Y; enrichment in light rare earth elements with high (La/Yb)n ratios. Geochronology results indicate that skarn‐type Fe mineralization associated with quartz monzonite (130.7 ± 0.6 Ma) formed eight million years later than Mo and Zn mineralization (138 ± 2 Ma) in the Dawan deposit. From Re concentrations in molybdenite and previously presented Pb and S isotope data, we conclude that the ore‐forming material of the deposit was derived from a crust‐mantle mixed source. The porphyry‐skarn type Cu–Mo–Zn mineralization around the Wanganzhen complex is related to the primary magmatic activity, and the skarn‐type Fe mineralization is formed at the late period magmatism. The Dawan Mo–Zn–Fe porphyry‐skarn ores are related to the magmatism that was associated with lithospheric thinning in the NCC.  相似文献   

5.
华北克拉通东部中生代岩浆岩的主要特征是岩石类型复杂(从辉长质到二长花岗质),显示高钾钙碱性、高Sr-Ba、高Sr/Y和La/Yb比值和高度富集的Sr-Nd同位素成分。锆石SHRIMP定年表明,太行山地区岩浆作用发生在138-127Ma之间。该年代结果与东亚其它地区已经发表的锆石年代数据揭示了中生代岩浆作用的发展具有从日本岛(和朝鲜半岛;210Ma),到胶辽半岛(180Ma),再到大别山-太行山(138Ma)的年轻化趋势。这暗示华北中生代岩浆作用可能与古太平洋板块的俯冲有关,但华北中生代岩浆岩似乎没有明显的向内陆方向的成分变化极性,可能与古太平洋板块在地幔过渡带的水平俯冲有关。地球化学数据表明,华北中生代岩浆岩可能主要形成于壳幔岩浆混合作用和随后的分离结晶过程,而不是形成于基性下地壳部分熔融作用。  相似文献   

6.
The Yanjiagou deposit, located in the central North China Craton (NCC), is a newly found porphyry‐type Mo deposit. The Mo mineralization here is spatially associated with the Mapeng batholith. In this study, we identify four stages of ore formation in this deposit: pyrite phyllic stage (I), quartz–pyrite stage (II), quartz–pyrite–molybdenite stage (III), which is the main mineralization stage, and quartz–carbonate stage (IV). We present sulphur and lead isotope data on pyrite, and rhenium and osmium isotopes of molybdenite from the porphyry deposit and evaluate the timing and origin of ore formation. The δ34S values of the pyrite range from ‐1.1‰ to −0.6‰, with an average of −0.875‰, suggesting origin from a mixture of magmatic/mantle sources and the basement rocks. The Pb isotope compositions of the pyrite show a range of 16.369 to 17.079 for 206Pb/204Pb, 15.201 to 15.355 for 207Pb/204Pb, and 36.696 to 37.380 for 208Pb/204Pb, indicating that the ore‐forming materials were derived from a mixture of lower crust (or basement rocks) and mantle. Rhenium contents in molybdenite samples from the main ore stage are between 74.73 to 254.43 ppm, with an average of 147.9 ppm, indicating a mixed crustal‐mantle source for the metal. Eight molybdenite separates yield model ages ranging from 124.17 to 130.80 Ma and a mean model age of 128.46 Ma. An isochron age of 126.7 ± 1.1 Ma (MSWD = 2.1, initial 187Os = 0.0032 ± 0.0012 ppb) is computed, which reveals a close link between the Mo mineralization and the magmatism that generated the Mapeng batholith. The age is close to the zircon U–Pb age of ca. 130 Ma from the batholith reported in a recent study. The age is also consistent with the timing of mineralization in the Fuping ore cluster in the central NCC, as well as the peak time of lithosphere thinning and destruction of the NCC. We evaluate the spatio‐temporal distribution of the Mo deposits in the NCC and identify three important molybdenum provinces along the northern and southern margins of the craton formed during three distinct episodes: Middle to Late Triassic (240–220 Ma), Early Jurassic (190–175 Ma), and Late Jurassic to Early Cretaceous (150–125 Ma). The third period is considered to mark the most important metallogenic event, coinciding with the peak of lithosphere thinning and craton destruction in the NCC. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

7.
粤东莲花山地区位于我国东南沿海火山岩发育区，是我国重要的钨金成矿远景区。通过对该地区各类花岗岩进行LA-ICP-MS锆石U-Pb定年、岩石地球化学特征、锆石Lu-Hf同位素组成和微量元素研究，结果表明：莲花山地区的岩浆活动至少存在3期，其中石英闪长玢岩形成于中侏罗世（（168.0±2.2）Ma），黑云母二长花岗岩形成于早白垩世早期（（137.5±1.9）Ma），石英斑岩形成于早白垩世晚期（（102.0±1.5）Ma和（98.7±1.8）Ma）；岩石以钙碱性铝质-强过铝质岩浆为主，石英斑岩和流纹斑岩与成矿关系密切；各类岩浆锆石的176Lu/177Hf值均低于0.002，176Hf/177Hf值大多数小于0.282 7，εHf（t）值大多数处于-2.57~1.00之间，fLu-Hf值为-0.99~-0.95，二阶段模式年龄主要介于1.00~0.81 Ga之间，指示成岩物质来源主要来自新元古代古老下地壳变质泥岩和变质砂岩部分熔融，有少量幔源物质加入；锆石结晶温度大多处于650~750℃之间，岩石为I型花岗岩。莲花山地区不同阶段的岩浆活动和成矿作用与区域构造转换事件相关，虽缺少高精度成矿年龄对成矿时限的限制，但根据地质事实和本次研究认为该地区主要的钨金成矿时间应略晚于石英斑岩的形成时间（（102.0~98.7）Ma）。  相似文献   

8.
The Trans-North China Orogen (TNCO), a Paleoproterozoic suture that amalgamates the Western and Eastern Blocks of the North China Craton (NCC), witnessed extensive magmatism and metallogeny during Mesozoic, associated with intraplate tectonics and differential destruction of the cratonic lithosphere. Here we investigate a suite of porphyry dykes surrounding the Mapeng batholith in the Fuping Complex within the TNCO in relation to the Mesozoic gold and molybdenum mineralization. The major element chemistry of these dykes show a range of SiO2 (57.92 to 69.47 wt.%), Na2O (3.20 to 4.77 wt.%), K2O (3.12 to 4.60 wt.%) and MgO (0.51 to 3.67 wt.%), together with high concentration of LREE and LILE, and relatively low contents of HREE and HFSE. The rocks display (La/Yb)N = 13.53–48.11, negative Nb, Ta, Th, U and Zr anomalies, and distinctly positive Ba, K and Sm anomalies. The mineralogy and geochemistry of the porphyry dykes indicate the rocks to be high-K calc-alkaline, and I-type, with adakitic features similar to those of the adjacent Mapeng batholith. The source magma for these rocks was derived from a mixture of reworked ancient continent crust and juvenile mantle materials. The zircon U–Pb data from these rocks show ages in the range of 124 to 129 Ma, broadly coinciding with the emplacement age of the Mapeng intrusion. The inherited zircons of ca. 2.5, 2.0 and 1.8 Ga in the dykes represent capture from the basement rocks during melting. The zircon Lu–Hf isotopic compositions show negative εHf(t) values varying from − 27.8 to − 11.3, with Hf depleted model ages (tDM) ranging from 1228 Ma to 1918 Ma and Hf crustal model ages (tDMC) of 1905 Ma to 2938 Ma, suggesting that the Mesozoic magmatism and associated metallogeny involved substantial recycling of ancient basement rocks of the NCC. We present an integrated model to evaluate the genesis of the porphyry systems and their relation to mineralization. We envisage that these dykes probably acted as stoppers (impermeable barriers) that prevented the leakage and run-off of the ore-bearing fluids, and played a key role in concentrating the gold and molybdenum mineralization.  相似文献   

9.
Whole‐rock geochemistry, zircon U–Pb and molybdenite Re–Os geochronology, and Sr–Nd–Hf isotopes analyses were performed on ore‐related dacite porphyry and quartz porphyry at the Yongping Cu–Mo deposit in Southeast China. The geochemical results show that these porphyry stocks have similar REE patterns, and primitive mantle‐normalized spectra show LILE‐enrichment (Ba, Rb, K) and HFSE (Th, Nb, Ta, Ti) depletion. The zircon SHRIMP U–Pb geochronologic results show that the ore‐related porphyries were emplaced at 162–156 Ma. Hydrothermal muscovite of the quartz porphyry yields a plateau age of 162.1 ± 1.4 Ma (2σ). Two hydrothermal biotite samples of the dacite porphyry show plateau ages of 164 ± 1.3 and 163.8 ± 1.3 Ma. Two molybdenite samples from quartz+molybdenite veins contained in the quartz porphyry yield Re–Os ages of 156.7 ± 2.8 Ma and 155.7 ± 3.6 Ma. The ages of molybdenite coeval to zircon and biotite and muscovite ages of the porphyries within the errors suggest that the Mo mineralization was genetically related to the magmatic emplacement. The whole rocks Nd–Sr isotopic data obtained from both the dacite and quartz porphyries suggest partial melting of the Meso‐Proterozoic crust in contribution to the magma process. The zircon Hf isotopic data also indicate the crustal component is the dominated during the magma generation.  相似文献   

10.
深熔作用是大陆地壳分异、元素迁移富集和混合岩化作用的主要机制和关键地质过程.吉南地区出露的太古宙基底普遍经历了角闪岩相-麻粒岩相变质及深熔作用,长英质淡色体及淡色花岗岩广泛分布.吉南和龙花岗-绿岩地体出露的太古宙变质石英闪长岩及相关的长英质浅色体和含斜方辉石(角闪石)淡色伟晶花岗岩的野外地质特征、相互关系及岩相学特征指...  相似文献   

11.
Migmatite gneisses are widespread in the Dabie orogen, but their formation ages are poorly constrained. Eight samples of migmatite, including leucosome, melanosome, and banded gneiss, were selected for U–Pb dating and Hf isotope analysis. Most metamorphic zircon occurs as overgrowths around inherited igneous cores or as newly grown grains. Morphological and internal structure features suggest that their growth is associated with partial melting. According to the Hf isotope ratio relationships between metamorphic zircon and inherited cores, three formation mechanisms for metamorphic zircon can be determined, which are dissolution–reprecipitation of pre‐existing zircon, breakdown of Zr‐bearing phase other than zircon in a closed system and crystallization from externally derived Zr‐bearing melt. Four samples contain magmatic zircon cores, yielding upper intercept U–Pb ages of 807 ± 35–768 ± 12 Ma suggesting that the protoliths of the migmatites are Neoproterozoic in age. The migmatite zircon yields weighted mean two‐stage Hf model ages of 2513 ± 97–894 ± 54 Ma, indicating reworking of both juvenile and ancient crustal materials at the time of their protolith formation. The metamorphic zircons give U–Pb ages of 145 ± 2–120 ± 2 Ma. The oldest age indicates that partial melting commenced prior to 145 Ma, which also constrains the onset of extensional tectonism in this region to pre‐145 Ma. The youngest age of 120 Ma was obtained from an undeformed granitic vein, indicating that deformation in this area was complete at this time. Two major episodes of partial melting were dated at 139 ± 1 and 123 ± 1Ma. The first episode of partial melting is obviously older than the timing of post‐collision magmatism, corresponding to regional extension. The second episode of partial melting is coeval with the widespread post‐collision magmatism, indicating the gravitational collapse and delamination of the orogenic lithospheric keel of the Dabie orogen, which were possibly triggered by the uprising of the Cretaceous mid‐Pacific superplume.  相似文献   

12.
俞军真  郑有业  许荣科 《地质学报》2020,94(11):3361-3375
双口山金- 银- 铅矿床地处柴北缘西段，赋存在滩间山变基性- 超基性变火山岩中。矿体由金矿体和银铅矿体组成，成矿作用与热液活动密切相关。本文通过对双口山含金矿体赋矿围岩及含金石英脉进行LA- ICP- MS锆石U- Pb年代学分析和研究。结果表明，赋矿围岩形成时代为443±2. 9Ma，与区域滩间山群火山岩形成年代一致(440~490Ma)。含金石英脉热液锆石U- Pb年代为402. 8±4. 2Ma，与区域金矿床成矿年龄以及韧性剪切带年龄相接近(~400Ma)，代表了金矿体热液作用及成矿时代。结合地质特征及前人研究，表明双口山金银铅矿床是柴北缘造山带在不同造山带演化阶段，由不同成矿作用，在不同时期，相互叠加形成的复合型多金属矿床。金矿体具有典型造山型金矿床特征的变质热液型金矿，其成因主要与造山运动过程中的变质和变形作用有关, 成矿物质和流体来源于绿片岩相的滩间山群变基性- 超基性变火山岩。银铅矿体为岩浆热液型，成矿与后碰撞造山作用伸展- 构造转换有关的岩浆作用有关，成矿物质和流体来源于晚泥盆世深部含矿岩浆作用。  相似文献   

13.
胶东地区在晚中生代发生了大规模岩浆活动和"爆发式"成矿作用。为了深入研究岩浆活动的时代及其对成矿的影响,本文在对胶东晚中生代花岗岩类侵入岩及大规模成矿作用进行综合分析基础上,选择福山邢家山钼钨矿区、栖霞香夼铅锌矿区和福山王家庄铜矿区,对成矿岩体进行锆石U-Pb同位素年龄测试。测试结果表明,幸福山斑状二长花岗岩体(邢家山矿区)和香夼花岗闪长斑岩体的SHRIMP锆石U-Pb同位素年龄分别为159.3±1.6Ma和130.4±1.2Ma,养虎山石英闪长玢岩体(王家庄矿区)的LA-ICP-MS锆石U-Pb年龄为116.1±5.1Ma和119.8±1.8Ma,由此确定了三期岩浆活动及与之相对应的三期成矿事件。在晚侏罗世幸福山岩体中测得了前寒武纪残余锆石的年龄信息,三组年龄分别为3548±12Ma、2472.9～2400Ma和2192～1725Ma,指示岩浆物质来源于前寒武纪结晶基底的再循环作用。3548±12Ma是胶东地区迄今为止获得的最大年龄值,指示胶东地区存在古太古代早期的古老结晶基底。综合分析认为,胶东晚侏罗世岩浆活动和160Ma±的成矿事件是华北克拉通与扬子克拉通碰撞造山后续过程的产物,形成于挤压构造背景;早白垩世早期的岩浆活动及130Ma±成矿事件与太平洋板块俯冲有关,形成于挤压向伸展转化背景;早白垩世中晚期岩浆活动形成于拉张环境,与华北克拉通破坏和岩石圈伸展减薄有关,由此产生的胶东热隆-伸展构造体系,为115Ma±的金、银及有色金属等热液矿床大规模爆发式成矿提供了有利成矿条件。  相似文献   

14.
The Gangdese magmatic arc, southeastern Tibet, was built by mantle‐derived magma accretion and juvenile crustal growth during the Mesozoic to Early Cenozoic northward subduction of the Neo‐Tethyan oceanic slab beneath the Eurasian continent. The petrological and geochronological data reveal that the lower crust of the southeastern Gangdese arc experienced Oligocene reworking by metamorphism, anatexis and magmatism after the India and Asia collision. The post‐collisional metamorphic and migmatitic rocks formed at 34–26 Ma and 28–26 Ma respectively. Meta‐granitoids have protolith ages of 65–38 Ma. Inherited detrital zircon from metasedimentary rocks has highly variable ages ranging from 2708 to 37 Ma. These rocks underwent post‐collisional amphibolite facies metamorphism and coeval anatexis under P–T conditions of ~710–760 °C and ~12 kbar with geothermal gradients of 18–20 °C km ? 1, indicating a distinct crustal thickening process. Crustal shortening, thickening and possible subduction erosion due to the continental collision and ongoing convergence resulted in high‐P metamorphic and anatectic reworking of the magmatic and sedimentary rocks of the deep Gangdese arc. This study provides a typical example of the reworking of juvenile and ancient continental crust during active collisional orogeny.  相似文献   

15.
Abstract This paper discusses the relationships between granitic magmatism and gold mineralization and the exhumation history of the Dapinggou gold deposit in northern Altun, NW China based on the geochronological data, including zircon U‐Pb ages, Rb‐Sr isochron age and 40Ar‐39Ar dating and MDD modeling data. The main granitic magmatism age in this area is attained from the ID TIMS U‐Pb geochronology of zircons from the Kuoshibulak granite, the biggest granite in the northern Altun area, which gives a concordant age of 443±5 Ma in the Late Ordovician. Zircon ID TIMS U‐Pb geochronology of the West Dapinggou biotite granite west of the Dapinggou gold deposit gives concordant ages around 485±10 Ma, representing the early stage of Ordovician magmatism. The Rb‐Sr isochron age (487±21 Ma) of 6 quartz inclusion samples from quartz veins in this gold deposit is very close to that of the West Dapinggou granite. MDD modeling of step heating 40Ar‐39Ar data of K‐feldspar from the same West Dapinggou biotite granite gives a rapid cooling history from 300°C to 150°C during 200–185 Ma. According to the age data and the geological setting of this area, we conclude that the Dapinggou gold deposit was formed at the early stage of the Early Paleozoic granitic magmatism in northern Altun, and exhumed in the Early Jurassic due to the normal faulting of the Lapeiquan detachment. The Early Paleozoic magmatism may provide heat source and produce geological fluids, which are very important for gold mineralization. Exhumation in the Mesozoic caused the uplift of the deposit towards the ground surface.  相似文献   

16.
热液石英脉型金矿石中锆石可以来自围岩,也可以由热液活动形成。因此,对其研究有助于揭示成岩成矿信息。中山沟金矿位于河北省张家口—宣化(张宣)地区,主要呈石英脉型产于水泉沟岩体西段,是张宣幔枝构造核部的典型金矿床之一。本文在矿区地质特征基础上,主要开展含金石英脉内锆石形态学特征、LA-ICP-MS U-Pb同位素测年以及Hf同位素研究。研究表明:石英脉内的锆石形态为自形—半自形,环带特征明显,Th/U值较高,平均0.97,具有岩浆锆石特征。锆石稀土元素含量(∑REE)为351×10-6~976×10-6,平均值为690×10-6,呈现出轻稀土(LREE)亏损、重稀土(HREE)富集特征,在稀土元素球粒陨石标准化曲线总体呈现出斜率基本一致的左倾型;17个锆石U-Pb年龄数据获得391±1 Ma的谐和年龄和391±3 Ma的加权平均年龄,两组年龄在误差范围内基本一致,代表了含金石英脉中岩浆锆石的结晶年龄。11个Hf同位素测试数据获得的εHf(t)值位于-21.4~-16.6,TDM1介于1.7~1.9 Ga,平均1.7 Ga,TDM2主要集中于2.4~2.6 Ga,平均2.5 Ga,在Hf图解中投影点均位于亏损地幔和球粒陨石演化线之下,基本靠近2.5 Ga古老地壳的Hf同位素演化线,反应了其源区物质在地壳中平均存留的年龄。结合区域、矿区地质和实验锆石特征,本文认为中山沟金矿成矿时代不早于391±1 Ma,推测可能形成于海西早期,存在燕山期热液叠加成矿。水泉沟岩体的主成岩时代为加里东末期—海西早期。  相似文献   

17.
Abundant gold deposits are distributed along the margins of the North China Craton (NCC). Occurring throughout the Precambrian basement and located in or proximal to Mesozoic granitoids, these deposits show a consistent spatial–temporal association with Late Jurassic–Early Cretaceous magmatism and are characterized by quartz lode or disseminated styles of mineralization with extensive alteration of wall rock. Their ages are mainly Early Cretaceous (130–110 Ma) and constrain a very short period of metallogenesis. Sr–Nd–Pb isotopic tracers of ores, minerals and associated rocks indicate that gold and associated metals mainly were derived from multi-sources, i.e., the wall rocks (Precambrian basement and Mesozoic granites) and associated mafic rocks.Previous studies, including high surface heat flow, uplift and later basin development, slow seismic wave speeds in the upper mantle, and a change in the character of mantle xenoliths sampled by Paleozoic to Cenozoic magmas, have been used to suggest that ancient, cratonic mantle lithosphere was removed from the base of the NCC some time after the Ordovician, and replaced by younger, less refractory lithospheric mantle. The geochemistry and isotopic compositions of the mafic rocks associated with gold mineralization (130–110 Ma) indicate that they were derived from an ancient enriched lithospheric mantle source; whereas, the mafic dikes and volcanic rocks younger than 110 Ma were derived from a relatively depleted mantle source, i.e., asthenospheric mantle. According to their age and sources, relation to magmatism and geodynamic framework, the gold deposits were formed during lithospheric thinning. The removal of lithospheric mantle and the upwelling of new asthenospheric mantle induced partial melting and dehydration of the lithospheric mantle and lower crust due to an increase of temperature. The fluids derived from the lower crust were mixed with magmatic and meteoric waters, and resulted in the deposition of gold and associated metals.  相似文献   

18.
大别造山带北大别超高压变质带是研究秦岭-大别-苏鲁造山带古老基底演化过程的关键区域,其内广泛发育的混合岩长期被认为主要形成于中生代。本文对北大别团风一带新识别出的一套混合岩开展了锆石U-Pb定年和Hf同位素组成分析,结果显示,混合岩第一类锆石核部具有岩浆锆石特点,组成的不一致线上交点年龄为2850±86 Ma,该年龄代表了混合岩原岩年龄。第二类锆石具有变质深熔锆石特点,其加权平均207Pb/206Pb年龄为2011±12 Ma,代表了混合岩化的时间。岩浆锆石多数具有负的εHf(t)值(-8.1~2.2),对应两阶段Hf同位素模式年龄(TDM2)为3.6~3.0 Ga,表明原岩可能为大别造山带内古太古代地壳物质重熔形成,并可能在形成过程中伴有少量幔源物质加入。与之相比,变质锆石均具有正的εHf(t)值(0.3~8.2),对应TDM2为2.7~2.2 Ga,说明在混合岩化变质深熔过程中锆石Lu-Hf同位素体系完全开放,导致了锆石Hf同位素组成的升高。本文研究表明,大别造山带除了中生代混合岩化作用以外,还存在古元古代与Columbia超大陆聚合过程相关的一期混合岩化作用,为目前已知的大别造山带内最早一期混合岩化作用。此外,该套混合岩原岩为太古宙岩石,且对应模式年龄高达3.6 Ga,这扩展了目前已知的大别造山带最古老岩石信息范围,表明大别造山带内太古宙古老地壳物质可能不仅局限于黄土岭一带,还在北大别更广泛地区出露。  相似文献   

19.
An integrated study of petrology, mineralogy, geochemistry, and geochronology was carried out for contemporaneous mafic granulite and diorite from the Dabie orogen. The results provide evidence for granulite‐facies reworking of the ultrahigh‐pressure (UHP) metamorphic rock in the collisional orogen. Most zircons from the granulite are new growth, and their U‐Pb ages are clearly categorized into two groups at 122–127 Ma and 188.2 Ma. Although these two groups of zircons show similarly steep HREE patterns and variably negative Eu anomalies, the younger group has much higher U, Th and REE contents and Th/U ratios, much lower εHf(t) values than the older group. This suggests their growth is associated with different types of dehydration reactions. The older zircon domains contain mineral inclusions of Grt, Cpx and Qz, indicating their growth through metamorphic reactions at high pressures. In contrast, the young zircon domains would have grown through peritectic reaction at low to medium pressures. The younger granulite‐facies metamorphic age is in agreement not only with the adjacent diorite at 125.1 Ma in this study but also the voluminous emplacement of coeval mafic and felsic magmas in the Dabie orogen. Mineral separates from both mafic granulite and its adjacent diorite show uniformly lower δ18O values than normal mantle, similar to those for UHP eclogite‐facies metaigneous rocks in the Dabie orogen. In combination with major‐trace elements and zircon Lu‐Hf isotope compositions, it is inferred that the protolith of mafic granulites shares with the source rock of diorites, both being a kind of mafic metasomatites at the slab‐mantle interface in the continental subduction channel. This provides a direct link in petrogenesis between the granulitic, migmatic and magmatic rocks in the collisional orogen to active continental rifting, whereby high heat flow was transferred from the asthenospheric mantle into the thinned orogenic lithosphere for partia melting.  相似文献   

20.
本文主要报道内蒙古中部白乃庙地区侵入古生界徐尼乌苏组沉积地层中的石英二长闪长岩脉的锆石LA-ICP-MS 法U-Pb定年结果。测试结果显示大量锆石为捕获锆石并获得了从古元古代1.9Ga到中元古代1.26Ga左右的谐和年龄。其中中元古代年龄可划分为1.7Ga, 1.6~1.47Ga和1.26Ga等三个不同阶段;前两阶段年龄分别与华北克拉通化之后初始裂谷和非造山岩浆作用以及白云鄂博裂谷中火成碳酸盐的侵位时代相对应;而1.26Ga的年龄则与全球格林威尔构造-岩浆热事件时代相吻合。结果表明华北北缘存在中元古1.26Ga左右岩浆热事件。该结果为进一步认识华北北缘地壳演化及华北板块是否参与过罗迪尼亚超大陆演化提供了重要线索。  相似文献   

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