LA-ICP-MS Zircon U-Pb Geochronology of Quartz Porphyry from the Niutougou Gold Deposit in Songxian County,Henan Province

The Niutougou gold deposit, located in the center of the Xiong＇ershan gold district, western Henan Province, is a large gold deposit with many quartz porphyries found in the area. Based on the field geological investigation of quartz porphyry of Niutougou gold deposit and by using the cathodoluminescence （CL） images analysis and in situ LA-ICP-MS U-Pb isotope dating method of zircons, the inner structure, trace element compositions and U-Pb age of the zircons separated from quartz porphyry were analyzed and determined. Cathodoluminescence （CL） images of zircons show clear magmatic zonations. Trace element analyses of zircons reveal that all zircons show high concentrations of Th, U, and HREE, and the REE patterns of depletion in LREE, with a positive Ce anomaly. Zircon LA-ICP-MS U-Pb dating results show that the quartz porphyry in the Niutougou gold deposit was formed at 159.714-0.99 Ma （about 160 Ma）, belonging to the product of magmatic activity in late Middle Jurassic. Combined with the geological characteristics of the Niutougou gold deposit, the formation age of the quartz porphyry and the analysis of the formation age of the granite body exposed in the Niutougou gold deposit, the study suggests that the metallogenic epoch of the Niutougou gold deposit may be Yanshanian in age.

U-Pb Zircon Geochronology and Geochemistry of Granitoids in the Douling Group in the Eastern Qinling

LA-ICPMS U-Pb zircon dating of the Sanpinggou, Gangou and Fengzishan granitoids in the Douling Group of the Eastern Qinling yields ages of 760-685 Ma, which represents a strong tectono-magmatic event in the southern Qinling during the late Neoproterozoic. Geochemical data show that these intrusions have wide compositions ranging from minor gabbros through diorites to granodiorites. They are relatively enriched in LILE, poor in HFSE and strongly depleted in Nb and Ta, displaying affinities of Ⅰ-type granites formed in an active continental margin with oceanic subduction. In contrast to granitoids, gabbros and enclaves in the granitoids have higher REE abundances, relatively flat REE patterns, lower LILE, slightly higher HFSE and more depletion in Nb and Ta. All these suggest that the gabbros were formed by partial melting of the upper mantle above the subduction zone and the granitoids by the partial melting of the lower crust. Combined with regional geological data, the subduction-related granitoids in the Douling Group, together with the Tuwushan A-type granite with an age of 725 Ma and contemporaneous basic dikes in the Wudang Block, provide evidence for local subduction of oceanic basins between different blocks during the rifting in the Southern Qinling in the Neoproterozoic. Thus, the coexistences of various magmatic rocks formed in different tectonic environments indicate a complicated tectonic evolution and variety of tectonic frameworks in the Qinling area in the Neoproterozoic.

Chronology and Crust-Mantle Mixing of Ore-forming Porphyry of the Bangongco: Evidence from Zircon U-Pb Age and Hf Isotopes of the Naruo Porphyry Copper-Gold Deposit

The Naruo porphyry copper-gold deposit （hereinafter referred to as the Naruo deposit） in Tibet is a potentially ultra-large, typical gold-rich porphyry copper deposit, which was recently discovered in the Bangongco-Nujiang metallogenic belt. This study analyzed U-Ph chronology and Hf isotopes of the ore-bearing granodiorite porphyry in the Naruo deposit using the LA-ICPMS dating technique. The results show that the weighted average age is 124.03±0.94Ma （MSWD=1.7, n=20）, and 2±6pb/23SU isocbron age is 126.2±2.7 Ma （MSWD=1.02, n=20）, both of which are within the error. The weighted average age represents the crystallization age of the granodiorite porphyry, which indicates that the ore-bearing porphyry in the Naruo deposit area was formed in the Early Cretaceous and further implies that the Neo-tethys Ocean had not been closed before 124 Ma under a typical island-arc subduction environment. The εGr（t） of zircons from the granodiorite porphyry varies from 2.14 to 9.07, with an average of 5.18, and all zircons have εRf（t） values greater than 0; 176Hf/177Hf ratio is relatively high （0.282725-0.282986）. Combined with the zircon age--Hf isotope correlation diagram, the aforementioned data indicate that the source reservoir might be a region that is mixed with depleted mantle and ancient crust, which possibly contains more materials sourced from depleted mantle. Rock-forming ages and ore-forming ages of the Duolong ore concentrate area are 120-124 Ma and 118-119 Ma, respectively, which indicate 124-118 Ma represents the main rockforming and ore-forming stage within the area. The Naruo deposit is located in the north of the Bangongco-Nujiang suture, and it yielded a zircon LA-ICPMS age of 124.03 Ma. This indicates the Bangongco-Nujiang oceanic basin subducted towards the north at about 124 Ma, and the Neo-tethys Ocean had not been closed before the middle Early Cretaceous. It is possible that the crust-mantle mixing formed the series of large and giant porphyry copper-gold deposits in the Bangongco.

LA-ICPMS Zircon U-Pb Dating for Three Indosinian Granitic Plutons from Central Hunan and Western Guangdong Provinces and Its Petrogenetic Implications

The LA-ICPMS zircon U-Pb geochronology of three typically Indosinian granitic plutons yielded weighted mean ^206pb/^238U ages of 214.1±5.9 Ma and 210.3±4.7 Ma for the biotite monzonitic granites from the Xiema and Xiangzikou plutons in Hunan Province, and 205.3±1.6 Ma for biotite granite from the Napeng pluton, western Guandong Province, respectively, showing a similar late Indosinian age of crystallization. In combination with other geochronological data from Indosinian granites within the South China Block （SCB）, it is proposed that those late Indosinian granites with an age of -210 Ma and the early Indosinian granites （230-245 Ma） have the similar petrogenesis in identical tectonic setting. The Indosinian granites within the SCB might be the products of anatexis of the thickening crust in a compressive regime. These data provide a further understanding for the temporal and spatial distribution of the Indosinian granites and the dynamic evolution of the SCB.

LA-ICPMS Zircon U-Pb Dating in the Jurassic Daohugou Beds and Correlative Strata in Ningcheng of Inner Mongolia

LA-ICPMS Zircon U-Pb dating is applied to volcanic rocks overlying and underlying the Salamander-bearing bed in the Daohugou beds of Ningcheng in Inner Mongola and Reshuichang of Lingyuan and Mazhangzi of Jianping in western Liaoning. The results indicate that the youngest age of the rocks in Daohugou of Ningcheng is 158 Ma, and the oldest one is 164 Ma. Synthesized researches indicate that the salamander-bearing beds in Daohugou of Ningcheng, Reshuichang of Lingyuan and Mazhangzi of Jianping were developed in the same period. The Daohugou beds were formed in the geological age of 164-158 Ma of the middle-late Jurassic. Whilst, the Daohugou beds and its corrdative strata should correspond to the Tiaojishan Formation （or Lanqi Formation） of the middle Jurassic in northern Hebei Province and western Liaoning Province, based on the disconformity between the Daohugou beds and its overlaying beds of the Tuchengzi Formation of Late Jurassic and the Jehol Beds of early Cretaceous, and the disconformity between the Daohugou Beds and its underlying Jiulongshan Formation, which is composed of conglomerate, sandstone, shale with coal and thin coal beds.

Zircon U-Pb geochronology and geochemistry of diorite dikes from Nancha ore deposit in Tonghua area of Jilin and its geological significance

The authors presented geochronology and geochemical data of diorites from Nancha gold deposit in Tonghua region, with the aim to constraining its formation age, magma source and tectonic setting. LA-ICP-MS U-Pb dating results of zircons from the diorites indicate that the rocks were formed in the Middle Jurassic （171 ±2 Ma, MSWD = 1. 19）. Geochemically, these rocks have Si02 concentrations of 52. 52%-54. 90%,K20 of 2. 14%-3.84% , Na20 of 3. 17%-3. 35% , MgO of 7. 43%-9. 34% and high Mg# of 68. 57-72. 57. These rocks are characterized by enrichment in large ion lithophile elements（ LILE,such as K, Ba, Rb and Sr） and light rare earth elements （ LREE） , relatively depletion in high field strength elements （ HFSE, such as Ta, Nb, Ti and Zr） , and heavy rare earth elements （HREE）. These characteristics suggest that primary magma of the rocks were derived from the partial melting of mantle with miner crustal contamination, which may related to partial melting of mantle wedge by addition of sediment melt from subducting oceanic crust. Based on former and present studies, the authors consider that the Nancha ore deposit high-Mg diorites were formed in compres- sional structural setting which is similar to volcanic arc. It could be related to the subduction of the Paleo-Paci- fic plate beneath the Eurasian continent.

Chronology and Genesis of S-type Granites in Hetai District, Guangdong Province: Constraints from LA-ICP-MS Zircon U-Pb Dating and Tourmaline Boron Isotope In-situ Analyses

1 Introduction Hetai district,which is a mountainous area,situated on Guangning and Zhaoqing city,west Guangdong Province.Hetai district is generally located on southwest of South China Caledonian fold belt,east margin of Yunkai post-Caledonian uplift.Multiple type granites are widely distributed in Hetai district,including Caledonian,Indosinian and Yanshanian granites.Based on different

Zircon U-Pb Chronology and Whole-rock Sr-Nd Isotope Compositions of Granite Porphyry in the Kaladaban Area of the Northern Altyn

Objective The Altyn Tagh marks the northern margin of the Qinghai-Tibet Plateau and lies between the Tarim block to the north and the Qaidam block,Qilian Orogen,and Kunlun orogenic belt to the south.The Altyn Tagh region contains ophiolite,high-to ultrahigh-pressure metamorphic rocks,and igneous rocks.Previous research has virified the occurrence of continental rifting,subduction,slab roll-back,and collision between the Tarim block and Proto-Tethys oceanic plate.Moreover,Kaladaban volcanic rocks are mainly distributed in the north Altyn region.Studies of the magmatic evolution of this region have proposed that Altyn oceanic plate was subducted during the Ordovician(Han et al.,2012;Wang et al.,2017).However,the specific timing and other aspects of the subduction are debated,and an investigation of granite porphyry in the Kaladaban area would improve our understanding of this subduction event.In this study,we present new U-Pb zircon dating result and Sr-Nd isotope composition data for granite porphyry from the North Altyn region.The objective is to constrain the timing of subduction of the North Altyn oceanic plate and establish the petrogenesis and magma source of the granite porphyry.

First Report of Zircon U-Pb Chronology and Hf Isotope Evidence of the Heluositan Group Granulite in West Kunlun, Xinjiang

Objective As the uplift belt on the southem margin of the Tarim block, the Tiekelike block consists mainly of a set of Precambrian metamorphic rocks with granulite and gneisses. The Heluositan group-complex is the most ancient rock series in the area, and is a key area for studying the formation and evolution of the Precambrian basement of the Tarim craton. LA-ICP-MS zircon U-Pb dating and Hf isotopic analysis of granulite in this area provide new evidence for revealing the formation and evolution of the Precambrian basement in the Tarim Basin.

Sedimentary Facies, Provenance and Geochronology of the Heshangzhen Group: Implications for the Tectonic Evolution of the Eastern Jiangnan Orogen, South China

The Neoproterozoic Jiangnan orogen plays an important role in the study of the Precambrian tectonic evolution of South China. The tectonic nature of the Neoproterozoic sedimentary basins is still controversial, due to poor understanding of the sedimentary sequences and the lack of geochronological data. Here, we present sedimentological, provenance and geochronological data from the Heshangzhen Group in the eastern Jiangnan orogen. Sedimentological analysis shows that the Luojiamen Formation was deposited in a submarine fan, and the overlying Hongchicun Formation was deposited in front of a fan delta. The youngest detrital zircons constrain the lower Luojiamen and Hongchicun formations with ages of 827.3 ± 8.4 Ma and 825 ± 12 Ma, respectively. The sandstones of the Luojiamen Formation are characterized by a large number of intermediate to felsic volcanic grains, suggesting a volcanic arc source. In contrast, quartz and sedimentary lithic grains increase in the Hongchicun Formation, showing a new input from a collisional orogenic source. Detrital zircon from six sandstone samples in the Luojiamen and Hongchicun formations yield similar age spectra of 930–820 Ma with a peak at ca. 845–860 Ma, with one main cluster at 930–820 Ma. Detrital zircons of 930–845 Ma show a positive value of εHf(t)(+2.4 to +11, mean +7.6), which is similar to the volcanic arc of the nearby Shuangxiwu Group. There are a minor group of zircons with U-Pb ages ranging from 820 Ma to 845 Ma from the middle part of the Luojiamen Formation and Hongchicun Formation, with εHf(t) values between-20 to +2.4, which are consistent with the characteristics of the Shuangqiaoshan Group. within light of the bidirectional paleocurrents in the Luojiamen Formation, it is speculated that the zircons of 820–845 Ma were recycled from the Shuangqiaoshan Group, which is derived from a continental arc to the northwest. Our data suggests that the Luojiamen Formation was formed in an inter-arc basin, while the Hongchicun Formation was formed in an accretionary wedge-top basin. When juxtaposed with the conglomeratic characteristics at the bottom of the Luojiamen Formation, it is believed that the unconformity represented by the ‘Shen Gong Movement' reflects the rapid erosion and accumulation process of island arc volcanic material. The disconformity between the Luojiamen and Hongchicun formations is the imprint of transition from inter-arc basin to accretionary wedge-top basin,which represents the collision between the Shuangxiwu arc and the Yangtze Plate.

辽宁本溪地区新太古代晚期钾质花岗岩的发现及其地质意义

辽宁本溪地区位于华北克拉通东部陆块东北部,区内广泛发育新太古代深成侵入岩和变质表壳岩,尚无钾质花岗岩的报道。钾质花岗岩的形成过程是早期陆壳发育成熟和稳定的重要标志,本次钾质花岗岩的发现对系统的研究华北克拉通早期陆壳的形成与演化具有重要的价值。本文对本溪地区马家沟的钾质花岗岩进行了岩石学、成岩年代学、岩石地球化学的研究,探讨了岩石成因和形成的构造背景。马家沟岩体为片麻状中细粒黑云母二长花岗岩。锆石U-Pb测年数据显示,岩石^(207)Pb/^(206)Pb加权平均年龄为(2490±21)Ma,形成于新太古代晚期。该岩体属弱过铝质、高钾钙碱性系列钾质岩石;主要富集高场强元素La、Zr、Th及大离子亲石元素K、Nd等元素,亏损P元素、高场强元素Nb和大离子亲石元素Sr、Ti等;REE曲线为右倾型,负Eu异常,属于S型花岗岩。研究区钾质花岗岩岩浆主要来源于地壳,是变质泥岩部分熔融的产物,形成于活动大陆边缘碰撞造山后的伸展环境,代表华北太古宙克拉通固结基底形成之前的最后一次岩浆活动,标志着在新太古代晚期本溪地区微陆块已拼贴完成,并与其他地区一起构成稳定的华北太古宙克拉通。

皖南解带山铅锌矿成矿岩体锆石U-Pb年代学研究及地质意义

解带山铅锌矿位于皖南铅锌成矿区,本文对解带山花岗闪长斑岩含矿岩体开展了岩相学和锆石U-Pb年代学研究,获得锆石U-Pb年龄为136.4±1.4 Ma,形成于早白垩世,属燕山晚期岩浆活动产物,花岗闪长斑岩相对较低的结晶温度和相对中等的氧逸度有利于铅锌沉淀成矿。

内蒙古半沟地区紫苏碱长花岗岩的年代学、同位素地球化学及构造意义

为进一步探讨华北克拉通古-中元古代构造演化过程,本文对位于华北克拉通北缘孔兹岩系与怀安片麻岩接触界限附近、侵入TTG片麻岩的紫苏碱长花岗岩进行了地质年代学及地球化学研究。锆石U-Pb测年结果表明,该紫苏碱长花岗岩的结晶年龄为1792±19Ma;此外,分析样品的主量元素显示高硅、贫镁铁、准过铝质-弱过铝质特征,属高钾钙碱性I型花岗岩;同时,微量元素具有右倾式稀土配分模式、Eu呈正异常、富集大离子亲石元素、亏损高场强元素的特征。锆石εHf(t)呈负值(-12.1~-6.2),εNd(t)=-4.5~-9.4,具有相对富集的同位素组成。锆石Hf和Nd同位素单阶段模式年龄分别为2.41~2.62Ga、2.40~2.61Ga,与年龄为~2.5Ga的TTG片麻岩对应值一致。岩石地球化学及Nd-Hf同位素证据指示紫苏碱长花岗岩源自碰撞后伸展抬升阶段TTG片麻岩的重熔,标志着华北克拉通古元古代造山运动结束。

赣东北牛角坞钨多金属矿床地质、年代学和地球化学

牛角坞矿床位于江南造山带东段,是近年来赣东北地区钨多金属矿产勘查取得重要进展的矿区,钨矿体主要赋存于花岗闪长斑岩与元古界板桥组变质砂岩内外接触带,目前探获钨资源量已达到中型规模(WO_(3)平均品位为0.26%),且其深部资源潜力巨大。该矿床以浅部石英脉型钨矿和深部细脉浸染型钨矿分带共生为特色,区别于典型的石英脉型“五层楼”模式,故对其赋矿岩体开展年代学和地球化学研究、对不同类型白钨矿进行矿物学工作和构建成矿模式具有重要意义。本文在矿床地质调查和钻孔编录的基础上,首先厘定了牛角坞矿床矿物组合及其矿化分带特征;获得了花岗闪长斑岩锆石U-Pb年龄为149.1±0.6Ma,判断其为华南东部燕山期大规模岩浆热液成矿作用的产物;赋矿花岗质岩浆岩表现为明显的过铝质钙碱性特征,其稀土元素则为明显的右倾型配分模式,具有弱负Eu异常,富集Rb、Th、U等大离子亲石元素,亏损Nb、Ti等高场强元素特征;锆石εHf(t)集中在-15.2~-3.2,指示其成矿岩浆来源于古元古代壳源物质重熔;白钨矿稀土元素特征指示两类含矿热液均主体源自深部花岗质岩浆。综合年代学、矿物学和地球化学研究,建立了牛角坞石英脉型与细脉浸染型共生钨矿床成矿模式,为华南地区大规模钨成矿作用研究和深部勘查工作提供了新的理论依据。

大兴安岭中南段哈力黑坝岩体的年代学、地球化学及其构造拆沉作用

【研究目的】在区域地质调查基础上,本文探讨了大兴安岭中南段哈力黑坝岩体早白垩世花岗岩成岩年代、岩石成因类型、源区性质及地球动力学背景。【研究方法】本文基于显微镜、XRF和(LA-)ICP-MS等手段对哈力黑坝岩体早白垩世花岗岩进行了岩相学、锆石U-Pb年代学、地球化学及Hf同位素组成研究。【研究结果】哈力黑坝早白垩世花岗岩主要包括中细粒黑云母花岗岩和细粒斑状黑云母花岗岩,LA-ICP-MS锆石U-Pb定年结果分别为(139.1±0.7)Ma和(138.4±1.0)Ma。岩石主量元素具有高硅(74.09%~77.19%)、富碱(7.92%~8.46%),低CaO(0.35%~1.14%)和低MgO(0.15%~0.47%)的特征,属高钾钙碱性系列;其A/CNK值介于0.95~1.08,为准铝质—弱过铝质岩石。岩石相对富集轻稀土元素,(La/Yb)N=3.69~13.17,稀土配分模式图呈右倾海鸥型,具有较为明显的负铕异常(δEu=0.11~0.47)。岩石微量元素组成显示岩石富集Rb、U、Th、Zr、Hf等元素,强烈亏损Sr、Ba、Ti、P等元素。岩石具有高正的ε_(Hf)(t)值(+5.0~+11.2)和年轻的二阶段Hf模式年龄(408~731 Ma)。【结论】哈力黑坝岩体早白垩世花岗岩为铝质A型花岗岩,其源区主要为年轻地壳物质,并有老地壳物质的贡献,形成于伸展的大地构造背景,受控于岩石圈拆沉减薄过程。

内蒙古黄土窑地区古元古代辉石正长岩的锆石U-Pb年代学、Nd-Hf同位素地球化学及岩石成因

华北克拉通中部造山带古元古代构造演化一直是前寒武纪地质研究的热点问题,尤其是最后一期造山碰撞的性质,一直存在多种解释。本文对出露于黄土窑地区、侵入怀安片麻岩中的古元古代辉石正长岩进行了锆石U-Pb年代学、Nd-Hf同位素地球化学及岩石地球化学研究。辉石正长岩侵位时代为~1830Ma,并捕获了围岩中~1.92Ga的变质锆石及~2.4Ga的岩浆锆石。辉石正长岩贫硅、高钠钾,轻重稀土分馏明显,无Eu异常,Rb、Ba、K等大离子亲石元素相对富集,Th、U、Nb、Ta等高场强元素相对亏损。辉石正长岩εNd(t)-5.2~-5.9,Nd亏损地幔模式年龄(t DM)为2.56~2.61Ga,所有锆石的Hf同位素一阶模式年龄为~2.5Ga,二阶段模式年龄为~2.7Ga,其中~1824Ma岩浆锆石的Hf同位素相对富集(εHf(t)-11.3~-2.1)。岩石地球化学及同位素证据指示辉石正长岩源自与其围岩TTG源区类似的中下地壳的部分熔融,并较少受到地幔物质的影响。本文研究为限定华北克拉通古元古代最后一期碰撞挤压-抬升的时限、规模及形式提供了新的证据。

华北克拉通辽宁兴城玄武岩脉LA-ICP-MS U-Pb年龄及其地质意义

华北克拉通中生代期间受古太平洋板块俯冲作用的影响,岩石圈发生大规模的减薄,导致其物理化学性质明显改变.揭示克拉通减薄的机制并约束克拉通破坏时限是地学界的重大科学问题.华北克拉通广泛发育中生代玄武岩,玄武岩作为岩浆作用的产物,所蕴含的年代学信息可以为岩石圈演化过程提供重要的时间约束.辽宁兴城地区位于华北克拉通的北缘,其内发育的太古宙—中新生代岩浆岩是研究华北克拉通破坏的理想对象.尽管前人对这些玄武岩做了大量的研究,但是对其结束时间仍然存在争论.本文选取兴城地区出露的玄武岩脉为研究对象,采用LA-ICP-MS锆石U-Pb年代学和金红石U-Pb年代学方法,探讨成岩年代学及其地质意义.锆石U-Pb定年结果表明,辽宁兴城玄武岩脉年龄为104.8±6.5Ma,而华北克拉通中生代岩石圈减薄的结束年龄也可推到105Ma左右.此年代学信息为早白垩世晚期华北克拉通大规模岩石圈减薄过程的时限提供了约束.

松辽盆地南部开鲁坳陷姚家组砂岩物源示踪研究——来自岩石地球化学及锆石U-Pb年代学的制约

针对可地浸砂岩型铀矿潜在铀储层预测和铀资源评价而言,明确赋矿砂体的物源是关键。文章以松辽盆地南部开鲁坳陷上白垩统姚家组砂岩为研究对象,通过岩石地球化学及锆石年代学分析工作,探讨姚家组沉积物来源,结果表明:姚家组砂岩稀土元素含量为100.08×10^(-6)~134.06×10^(-6),以轻稀土富集、重稀亏损、铕负异常为特征;所有样品稀土元素配分模式曲线高度一致,表明姚家组砂岩来自于同一物源体系;利用∑REE-La/Yb、HfLa/Th、Zr/Sc-Th/Sc和Cr/Th-Th/Sc图解结合砂岩镜下特征综合判断,姚家组砂岩的源岩为长英质岩石;碎屑锆石UPb测年显示姚家组砂岩年龄主要集中分布在3个年龄区间,分别为110~180 Ma,230~280 Ma,1695~2171 Ma。结合地层划分、岩石微量和稀土元素特征、盆缘岩浆岩年代以及区域构造演化,指出姚家组沉积物来源于大兴安岭南段乌兰浩特地区。

刚果盆地西南缘Inkisi组碎屑锆石U-Pb年代学:对地层时代及物源的约束

Inkisi组是泛非运动之后刚果盆地最早的沉积地层之一。确定Inkisi组地层时代、物源及恢复构造演化过程,对研究刚果盆地的演化具有重要地质意义。本文通过对Inkisi组碎屑锆石进行U-Pb年代学研究,深入探讨了其形成时代,对泛非运动进行了约束,并进一步探讨了其物源。研究发现,Inkisi组下段与上段碎屑锆石最小年龄分别为526±6 Ma和534±14 Ma,最年轻的4颗锆石的加权平均年龄为532±9.4 Ma,由此限定了Inkisi组的最大沉积时代。因此将其时代划归早寒武世,并将其从新元古界Xisto-Gresoso群解体。另外,Inkisi组岩石并未发生变质变形,也说明其形成于泛非运动之后。碎屑锆石年龄谱结果显示,Inkisi组碎屑锆石的年龄变化范围较广,整体呈现五个年龄峰值:>2800 Ma、2800~2400 Ma、2100~1750 Ma、1500~900 Ma、850~500 Ma。通过将年龄峰值及周围地质体进行对比,认为西刚果造山带、卡赛克拉通、安哥拉克拉通是其主要的物源,卢弗里安构造带等是其次要物源。

胶西北大泽山岩体地球化学、锆石U-Pb年代学及Lu-Hf同位素特征

胶东金矿集区是我国最重要的金矿集区,大规模金成矿作用发生于125~110 Ma。本文选择了与成矿作用同期的早白垩世晚期大泽山岩体为研究对象,通过详细的岩相学、岩石地球化学、锆石LA-ICP-MS U-Pb年代学研究,识别出中粒二长花岗岩和细粒二长花岗岩两种主要的侵入岩类型,它们具有相似的岩相学和岩石地球化学特征,呈现同源岩浆演化特征。定年结果表明,中粒二长花岗岩中锆石U-Pb年龄分别为119.8±0.8 Ma和119.3±0.9 Ma,细粒二长花岗岩中锆石U-Pb年龄分别为109.2±0.7 Ma和109.9±0.7 Ma。岩石地球化学研究表明,二长花岗岩具有高的全碱(K_(2)O+Na_(2)O=8.14%~8.72%),高的Al_(2)O_(3)(12.42%~15.32%),属过铝质高钾钙碱性系列,轻稀土(LREE)富集、重稀土(HREE)相对亏损(LREE/HREE=8.46~18.87),具明显的稀土元素分馏((La/Yb)_(N)=8.52~24.08)和较强的Eu负异常(δEu=0.33~0.58)。大泽山岩体锆石ε_(Hf)(t)值为-26.4~-16.2,亏损地幔二阶段模式年龄(T_(DM2))为2812~2173 Ma,物源主要是古元古代和新太古代陆壳的部分熔融,有少量幔源物质的加入。大泽山岩体成岩期与胶东金矿的主成矿期一致,暗示岩浆活动与金成矿具有统一的地球动力学背景。