秦岭柞水岩体和东江口岩体的锆石U-Pb 年代学及其意义

柞水岩体和东江口岩体位于秦岭造山带南秦岭构造域, 主要由似斑状花岗闪长岩和二长花岗岩组成。通过LA-ICP-MS 锆石U-Pb 同位素定年, 结合锆石阴极发光图像, 揭示柞水岩体的似斑状二长花岗岩(样品ZS01-01)存在两个谐和年龄, 分别为209±2和199±2Ma;东江口岩体似斑状二长花岗岩(样品ZS04-01)也存在两个谐和年龄, 分别为219±2 和209±2 Ma。结合前人的地球化学和区域构造背景研究, 判定这两个岩体属于同一岩浆事件的不同阶段侵位, 东江口岩体的似斑状二长花岗岩侵位结晶略早于柞水岩体, 柞水岩体主期岩浆侵位时, 东江口岩体也有同期岩浆侵位结晶。这两个岩体年龄的准确测定, 表明在219 ～199 Ma 期间沿商丹断裂有3个阶段的构造-岩浆活动。     

秦岭西坝花岗岩LA-ICP-MS 锆石 U-Pb 年代学及其地质意义

西坝花岗岩位于南秦岭构造带陕西境内, 主要由花岗闪长岩、二长花岗岩和英云闪长岩组成。LA-ICP-MS 锆石U-Pb 原位同位素定年结果表明, 西坝岩体侵位于印支期, 由二长花岗岩样品(XB01-2)得到了219±1 Ma的年龄, 花岗闪长岩样品(XB06-1) 给出的年龄是218±1 Ma, 二者在误差范围内一致, 约218Ma代表了西坝花岗岩体的成岩时代。西坝岩体的年龄结合区域构造背景以及前人研究的地球化学特征, 说明它可能是秦岭主造山期岩浆活动的产物。     

辽北新宾?苇子峪地区太古宙花岗质岩石的形成年代、成因及其地质意义

辽北新宾?苇子峪地区的花岗质岩石主要由英云闪长质?奥长花岗质片麻岩和二长花岗岩?正长花岗岩岩体等组成。为确定其形成年代及成因, 对这些花岗质岩石进行锆石U-Pb-Hf同位素和全岩地球化学分析。锆石LA-ICP-MS U-Pb同位素定年结果表明这些花岗质岩石均形成于新太古代, 英云闪长质和奥长花岗质片麻岩的岩浆结晶年龄分别为2588±4 Ma (MSWD=1.3)和2587±6 Ma (MSWD=1.8), 二长花岗岩?正长花岗岩则侵位于2555±4 Ma (MSWD=0.51)。全岩地球化学和锆石Lu-Hf同位素研究表明, 英云闪长质?奥长花岗质片麻岩形成于俯冲板片的部分熔融, 其原始岩浆在上升过程中受到地幔楔岩石的交代; 而二长花岗岩?正长花岗岩中一部分岩浆起源于变质杂砂岩的部分熔融, 其余形成于以变质玄武岩与变质沉积岩为主要成分的混合源区的部分熔融。结合近年的研究成果, 认为新宾?苇子峪地区的新太古代花岗质岩石可能形成于活动大陆边缘的动力学背景。     

东秦岭沙河湾岩体成因——来自锆石U-Pb定年及其Hf同位素的证据

目的 确定东秦岭沙河湾花岗岩体形成时代、源区性质及其成因.方法 在锆石内部结构的CL图像研究基础上,用LA-ICFMS和MC-ICPMS测定锆石U-Pb年龄及Hf同位素组成,探讨寄主花岗岩、暗色闪长质包体及及围岩中闪长质脉体锆石U-Pb年代学及Hf同位素组成特征.结果 寄主花岗岩、暗色包体及其围岩中闪长质脉体分别存在210 Ma和197 Ma,197 Ma和188 Ma以及230M a和210 Ma两组年龄的锆石;对应的εHf(t)值在一个略微偏正或负的范围内变化,指示该岩体非单一源区岩浆物质所能形成,至少是两个源区岩浆混合作用的结果.结论 该岩体是以新元古带古老地壳物质熔融为主体的壳源岩浆与源自略富集地幔的幔源岩浆高度混合的产物.这一壳、幔岩浆混合作用首先以230Ma的幔源岩浆活动为标志,并可能在210 Ma前就由于幔源岩浆活动热源的持续积累而诱发了该区地壳物质的部分熔融,形成以壳源岩浆为主的岩浆房.此后.约在200 Ma深部幔源基性岩浆进入壳源酸性岩浆房发生岩浆混合,并一直持续到185 Ma左右,证明了秦岭中生代壳、幔岩浆混合作用持续了大约60 Ma.     

广东连平大顶铁矿区石背岩体LA-ICP-MS锆石U-Pb年龄及地质意义

广东连平大顶铁矿被誉为华南第一大铁矿床,为华南地区最为典型的矽卡岩型矿床。对大顶铁矿区与成矿作用有关的石背岩体粗粒斑状黑云母花岗岩和中粒斑状黑云母花岗岩进行LA-ICP-MS锆石U-Pb定年,获得的同位素年龄分别为(174.3±3.6)Ma(MSWD=1.6)和(176.9±4.3)Ma(MSWD=2.6),表明石背岩体侵位时代为早侏罗世晚期-中侏罗世早期,是燕山第一幕岩浆活动之产物。石背岩体形成于早中生代古太平洋板块向欧亚板块俯冲过程中的挤压构造背景,其物源主要来自于地壳,为壳内物质熔融-岩浆固结而成,与佛冈岩体相似,均为陆壳改造型(S-型)花岗岩。     

河南泌阳地区变质花岗岩体锆石铀-铅年龄及其地质意义

华北克拉通为中国最古老的克拉通,基底形成时经历了多期岩浆-构造热事件,前寒武纪基底上发育有大量的不同时代的花岗岩体。为了厘定分布在华北克拉通南缘的河南泌阳地区的前寒武纪变质花岗岩体的形成年龄,采用高精度的激光剥蚀电感耦合等离子质谱仪(LA-ICP-MS)锆石铀-铅(U-Pb)同位素测年方法对其进行精确定年。实验结果表明,变质花岗岩中锆石具有典型的岩浆结晶成因特征,但可能受到后期构造热事件的扰动影响发生同位素的丢失。该变质岩体四个锆石样品的~(206)Pb/~(207)Pb上交点年龄在误差范围内基本一致,给出了2 510～2 556 Ma的年龄,代表了岩体形成年龄。工作表明该地区变质花岗岩形成于新太古代晚期,而不是前人在区调工作中认为的中-新元古代,为华北克拉通南缘的早期岩浆-构造演化研究提供了年代学依据。     

河南泌阳地区变质花岗岩体的锆石铀-铅年龄及其地质意义

华北克拉通为中国最古老的克拉通,基底形成时经历了多期岩浆-构造热事件,前寒武纪基底上发育有大量的不同时代的花岗岩体。为了厘定分布在华北克拉通南缘的河南泌阳地区的前寒武纪变质花岗岩体的形成年龄,采用高精度的激光剥蚀电感耦合等离子质谱仪(LA-ICP-MS)锆石铀-铅(U-Pb)同位素测年方法对其进行精确定年。实验结果表明,变质花岗岩中锆石具有典型的岩浆结晶成因特征,但可能受到后期构造热事件的扰动影响发生同位素的丢失。该变质岩体四个锆石样品的~(206)Pb/~(207)Pb上交点年龄在误差范围内基本一致,给出了2 510～2 556 Ma的年龄,代表了岩体形成年龄。工作表明该地区变质花岗岩形成于新太古代晚期,而不是前人在区调工作中认为的中-新元古代,为华北克拉通南缘的早期岩浆-构造演化研究提供了年代学依据。     

广西大宁岩体和初洞岩体锆石U-Pb年代学 及Hf同位素研究

利用锆石LA-ICP-MS U-Pb定年,获得大宁岩体形成年龄为441.1±3.0 Ma,其包体年龄为439.5±3.6 Ma,初洞岩体形成年龄为423.5~434.2 Ma。结果表明,大宁岩体及其包体几乎同期形成,而初洞岩体是后期的侵入体。Lu-Hf同位素研究结果表明,大宁岩体及其暗色包体与初洞岩体具有相似的Hf同位素组成,在εHf(t)-年龄图上落在1440~1960 Ma的老地壳区间,表明三者的岩浆源区均是早元古代到中元古代地壳,暗色包体是岩浆早期分离结晶的产物,而初洞岩体是岩浆结晶分异晚期的产物。     

四川康定县大雪山超单元地球化学特征

根据花岗岩同源岩浆演化序列,将康定县大雪山超单元花岗岩体划分为3个单元,岩石组合特征为石英闪长岩、花岗闪长岩、二长花岗岩,具有明显的成分-结构演化特征。同位素年龄为104~121 Ma,时代属燕山晚期的Ⅰ型花岗岩。通过对岩石化学、稀土元素、微量元素等数据的分析,论述了折多山岩体的物质来源、构造环境及其成因。     

四川康定折多山超单元地球化学特征

根据花岗岩同源岩浆演化序列,将康定县折多山超单元花岗岩体划分为3个单元,岩石组合特征为粗粒似斑状二长花岗岩、中粒二长花岗岩、细粒二长花岗岩,具有明显的成分-结构演化特征,同位素年龄为3.75~15.4 Ma,时代属喜马拉雅期的S型花岗岩.通过岩石化学、稀土元素、微量元素等数据的分析,论述了折多山岩体的物质来源、构造环境及其成因.     

Indosinian isotope ages of plutons and deposits in southwestern Miaoershan-Yuechengling,northeastern Guangxi and implications on Indosinian mineralization in South China

The Miaoershan-Yuechengling complex pluton is the largest granitoid complex in the western Nanling metallogenic belt with a surface exposure of >3000 km2.The complex pluton is composed of an early stage granitoid batholith and late stage small intrusions.The early stage batholith contains mainly medium-grained porphyritic mica granite and porphyritic monzonite granite,whereas the late stage intrusions are composed of muscovite granite porphyry and muscovite monzonitic granite.There are many W-Sn-Mo-Pb-Zn-Cu ores in the contact zone between the batholith and strata,forming an ore-rich belt around the batholith.Based on zircon LA-ICP-MS U-Pb ages,the southwestern part of the early stage batholith formed at 228.7 ± 4.1 Ma(MSWD = 2.49),with slightly earlier magmatic activity at 243.0 ± 5.8 Ma(MSWD = 2.62).The Yuntoujie muscovite granite was associated with W-Mo mineralization and has a zircon LA-ICP-MS U-Pb age of 216.8 ± 4.9 Ma(MSWD = 1.44).The Re-Os isochron age of molybdenite from the Yuntoujie W-Mo ore was 216.8 ± 7.5 Ma(MSWD = 11.3).Our new isotope data suggest that the late stage intrusive stocks from the southwestern Miaoershan-Yuechengling batholith were closely associated with W-Mo mineralization from the Indosinian period.These new results together with previous isotope data,suggest that South China underwent not only the well-known Yanshanian mineralization event,but also a widespread Indosinian metallogenic event during the Mesozoic period.Therefore,South China has a greater potential for Indosinian mineralization than previously thought such that more attention should be given to the Indosinian ore prospecting in South China.     

Zircon U-Pb ages of granites at Changba and Huangzhuguan in western Qinling and implications for source nature

Mesozoic granitoids are widespread in the Qinling-Dabie-Sulu orogenic belt. Precise U-Pb dating on these granitoids can reveal the evolution of the continental collision orogen and thus provide information on the nature of magma sources. This study presents zircon LA-ICP-MS U-Pb dating and whole-rock geochemical analyses for two intrusions at Changba and Huangzhuguan in western Qinling. Zircon U-Pb ages for central and marginal phases of the Huangzhuguang intrusion are 214±1 Ma and 213±3 Ma, respectively. Zircons from the Changba intrusion yield a dominant cluster with an U-Pb age of 213±2 Ma. Collectively, these ages are younger than ages of 220 to 240 Ma for ultrahigh-pressure metamorphism due to the continental collision between the South China Block and the North China Block, corresponding to syn-exhumation magmatism. Some inherited zircons occur in the Changba intrusion, yielding a weighted mean of ²⁰⁶Pb/²³⁸U ages at 757±14 Ma. This indicates that the Changba intrusion has the crustal source of mid-Neoproterozoic ages and a tectonic affinity to the South China Block. Geochemically, the two intrusuons are both rich in LILE and LREE but depleted in HFSE and HREE, similar to arc-type igneous rocks. The Huangzhuguang intrusion exhibits linear correlations between SiO₂ and the other major oxides, implying chemical evolution from a cognate magma source. It contains mafic enclaves, suggesting possible mixing of felsic-mafic magmas. The Changba granite is rich in Si and K but poor in Fe and Mg as well as has a high value of Fe*, suggesting strong differentiation of granitic magma. Therefore, the two intrusions were derived from the Late Triassic anatexis of the continental crust of different compositions in the northern margin of South China Block. This process may be coupled with exhumation of the subducted continental crust in the stage of late collision.     

SHRIMP zircon U-Pb geochronology of Indosinian granites in Hunan Province and its petrogenetic implications

The structure, magmatism and sedimentation within the South China Block (SCB) related to the Indosinian Orogeny had attracted considerable attention since De-prat[1] and Fromagat[2] proposed the “Indosinian move-ment” based on two unconformities between Pre-Norian and Pre-Rhaetian during Triassic in Vietnam. However, Indosinian tectonic evolution of the SCB has been long debated[3―6]. Some researchers believed that the compli-cated structure-magmatism-sedimentation within the SCB w…     

SHRIMP zircon U-Pb ages and tectonic implications for Indosinian granitoids of southern Zhuguangshan granitic composite,South China

The large southern Zhuguangshan granitic batholith composite consists of granites with ages varying from the Caledonian through Indosinian to Yanshanian. Based on K-Ar dating data, the ages of the major parts of this composite were previously regarded as Yanshanian. In this study, the SHRIMP zircon U-Pb dating method has been adopted for six plutons, Ledong, Longhuashan, Dawozi, Zhaidi, Baiyun and Jiangnan, in the southern Zhuguangshan composite, in which the four plutons other than Baiyun and Jiangnan were previously regarded as Yanshanian granites. Magmatic zircons from these six plutons, dated by this study, have yielded ages of 239±5 Ma (MSWD = 2.5), 239±5 Ma (MSWD = 2.5), 239±2 Ma (MSWD = 1.7), 239±4 Ma (MSWD = 3.2), 231±2 Ma (MSWD = 0.81) and 231±3 Ma (MSWD = 1.8), respectively. The results indicate that these plutons were formed by early Indosinian magmatism. Geochemical characteristics suggest that these granites were formed in an extensional tectonic environment. Therefore, the Indosinian period granites in the southern Zhuguangshan composite were formed by partial melting of the Paleo-Mesoproterozoic crustal components during the collapse of thickened lithosphere after the collision between the South China and Indosinian plates.     

LA-ICPMS zircon U-Pb geochronological constraints on the tectonothermal evolution of the Early Paleoproterozoic Dakendaban Group in the Quanji Block,NW China

The Quanji Block, situated between the northern margin of the Qaidam Block and the South Qilian orogenic belt in the NE Qinghai-Tibet Plateau, China, is thought to represent a remnant continental crust. In this study, LA-ICPMS U-Pb analyses of detrital zircon grains from two mesosomes in the migmatitic Dakendaban Group yield ages of 2467＋28/-26 Ma and 2474＋66/-52 Ma, respectively. Zircon grains from a leucosome give two distinct ages of 2471＋18/-16 Ma and 1924＋14/-15 Ma. Zircon from a granitic pegmatite that intruded into the Dakendaban Group yields an age of 2427＋44/-38 Ma. These data suggest that the Early Paleoproterozoic Dakendaban Group deposited between -2.43 to -2.47 Ga and has been subject to an intrusive event at 2.43Ga, and regional metamorphism-anatexis at 1.92 Ga. The common lower intercept age of -0.9 Ga probably records a significant Early Neoproterozoic event in the Quanji Block.     

Determination of U-Pb age and rare earth element concentrations of zircons from Cenozoic intrusions in northeastern China by laser ablation ICP-MS

Using the in situ zircon U-Pb dating method of LA-ICPMS, we analyzed the 31 Ma old SHRIMP U-Pb age of the Yongsheng nepheline syenite from southern Jilin Province under different spot sizes. The obtained ages are comparable with that of SHRIMP in both accuracy and precision. The age is also identical to that of the Yinmawanshan gabbro from the Liaodong Peninsula within error. Both the Yongsheng nepheline syenite and the Yinmawanshan gabbro represent the youngest known exposed intrusions in northeastern and even eastern China. The results indicate the Eocene mantle-derived magmatic underplating, and the rapid crustal uplifting of this region since 30 Ma. The analyses also document extremely high LREE concentrations and relatively fiat REE patterns for the zircons from the Yongsheng nepheline syenite, which represent a new type of zircon REE pattern.     

U-Pb dating of detrital zircons from the Wudangshan Group in the South Qinling and its geological significance

U-Pb dating was made by the LA-ICP-MS method for detrital zircons from the Wudangshan volcanic-sedimentary succession in the South Qinling. Samples comprise quartz sandstones of the Wudangshan Group collected from the base of the Yangping Formation and an upper layer of the Shuangtai Formation overlain its volcanic sequence, and two river-sand collections from the drainage systems cutting across the two formations, respectively. The results show that the Yangping detrital zircons are dominated by 830–780 Ma grains with a minor population of ~1.0–0.84 Ga and sporadic grains of ~2.6, ~2.4 and 2.0 Ga, whereas the Shuangtai zircons yield an upper intercept age of 763±33 Ma, identical to the timing of the Wudangshan volcanism within error, with few concordant grains of 1.9 and 0.86 Ga. Age spectra for the two river-sand samples are similar to those of the Yangping and Shuangtai Formations, respectively. It thus suggests that the Wudangshan strata are less than 780 Ma, whereas their major detrital zircon populations of 1.0–0.85 Ga and 830–780 Ma are consistent with timing of the Hannan magmatic activities along the northwestern margin of the South China Block. This suggests a Hannan or adjacent area provenance for the Wudangshan strata. The Wudang area is characterized by rift-related igneous events at ~755 and ~680 Ma, respectively, pointing to a tectono- magmatic history different from the Hannan area. It is inferred that the ~755 Ma magmatism is likely to indicate a separation of the South China Block from the supercontinent Rodinia, while the ~680 Ma event suggests a further split between the South Qinling and some unknown continent.