Hercynian plutonic rocks of Voras Mountain,Macedonia, Northern Greece: their structure,petrogenesis, and tectonic significance

We studied the structural, petrological, and geochemical characteristics, as well as the geotectonic setting, of the Hercynian (300 ± 3 Ma) Voras plutonic rocks intrusive into the lower part of the Pelagonian nappe pile (East Pelagonian Zone, EPZ). These rocks are compared with the neighbouring Hercynian Varnountas and Kastoria plutons intruding the tectonic upper Pelagonian part (Korabi West Pelagonian Zone, KoWPZ). Based on modal and chemical compositions, four rock-types can be distinguished for the Voras ploutonic rocks: (1) hornblende-biotite granodiorite to granite (HbBtGrd), (2) biotite granite (BtGr), (3) leucogranite (LGr), and (4) mafic microgranular enclaves (MMEs) occurring typically in HbBtGrd and BtGr. Aplites intrude HbBtGrd and BtGr whereas xenoliths are rare. The MMEs are metaluminous, while all the other rock-types are slightly peraluminous. Crystallization pressures range from 2.4 to 2.9 kbar for the HbBtGrd and 3.0 kbar for the MME. Field observations, chemical, mineralogical, and petrographical data suggest that theMME and HbBtGrd + BtGr formed as a result of a two-step evolution process. In the first step, a mantle-sourced basic magma with composition similar to the more basic MMEs fractionated (F = 0.40, 60% crystallization) and concurrently mixed with an acid magma, of composition similar to the more acid BtGr. The crystallized mineral assemblage is Qtz_38.27Pl_27.83Hb_14.84Bt_10.61Kf_6.13Ap_2.30Zrn_0.02. The process evolved with a low r-value (r = 0.3) giving the more basic HbBtGrd. In the second step, evolved magma (more basic HbBtGrd) fractionated, while simultaneously mixing with the same acid magma, but with higher r-value (r = 0.8), giving the more evolved HbBtGrd and the BtGr after 50% crystallization (F = 0.50) to the phase assemblage Qtz_30.07Pl_27.75Hb_5.59Bt_3.33Kf_23.26Tit_5.86Ap_1.91Zrn_0.04Mt_2.19. We interpret the evolution of the LGr through fractional crystallization; it formed by partial melting of gneisses or felsic charnokites and granoulites. The less evolved MME (basic end-member) had a mantle origin, whereas for the more evolved BtGr (acid end-member) we favour partial melting of gneisses or mafic charnokites. Detailed structural analysis shows a strong, polyphase Alpine deformation which affected the Hercynian Voras ploutonic rocks and is thoroughly imprinted on the host Pelagonian metamorphic basement rocks. No evidence of relict Hercynian structures has been recognized, possibly due to intense reworking by the younger Alpine deformation. We have identified five tectonic events (D1–D5) from the Late Jurassic to recent, that evolved progressively from ductile, synmetamorphic (D1, D2) to semi-ductile (D3), and finally brittle (D4, D5) conditions. Voras plutonic rocks in the EPZ, and Varnountas and Kastoria plutons in the KoWPZ, have similar major and trace element geochemistries, as well as structural evolution; they coevally intruded (Carboniferous) the Pelagonian continent as a single unit. They show similar crystallization pressures and mantle contributions for their genesis; both are related to a volcanic arc geotectonic setting, associated with the subduction of the Palaeotethys Ocean beneath the Pelagonian continental fragment, the latter possibly of Gondwana origin.     

西昆仑大同西岩体成因：矿物学、地球化学和锆石U-Pb年代学制约

大同西岩体出露于西昆仑造山带西段,主要岩性为高钾钙碱性的石英闪长岩和石英二长岩-二长花岗岩。石英闪长岩中普遍发育椭球形或卵形暗色镁铁质包体,包体岩性主要为闪长岩,石英闪长岩的SiO₂的含量为56.6%~65.3%,Mg^#为0.45~0.46,包体SiO₂的含量为52.9%左右,Mg^#为0.48。相对于石英闪长岩,石英二长岩-二长花岗岩具有较高SiO₂的含量(SiO₂=65.0%~73.3%)和较低Mg^# (Mg^#=0.36~0.44)。微量元素分析数据表明,石英闪长岩与暗色包体的REE球粒陨石标准化图呈右倾型,Eu负异常不明显,富集大离子亲石元素,亏损高场强元素。石英二长岩-二长花岗岩具有明显的Eu负异常,强烈亏损Nb-Ta、Ti等元素。温压计算显示石英闪长岩为相对低温(638~768℃)的中-深成岩体(平均深度为8.8km),石英二长岩-二长花岗岩具有相对高的结晶温度(752~771℃)。锆石U-Pb年代学研究表明,石英二长岩形成年龄为470±1.2Ma,略晚于前人报道的石英闪长岩侵位年龄。石英二长岩-二长花岗岩与石英闪长岩来源于不同的岩浆,二者之间不存在分异关系。结合区域构造演化历史,早期的石英闪长岩为大洋板片俯冲过程中地幔楔部分熔融岩浆的分异产物,晚期的石英二长岩-花岗岩则来源于碰撞后伸展阶段由于软流圈地幔物质上涌加热导致变泥质岩石熔融的结果。大同西复式岩体的成因指示了西昆仑造山带在早奥陶纪经历了由俯冲向碰撞后伸展的构造体制转换。     

甘肃省龙首山成矿带芨岭岩体闪长岩特征及其与铀成矿关系

芨岭岩体是龙首山铀成矿带加里东期岩浆岩,其闪长岩侵位于加里东早期,是芨岭岩体主要岩石类型之一。闪长岩主要有两期侵入,分别为早期灰色、深灰色中粒闪长岩以及晚期深灰色细粒闪长岩,且出露面积较小,集中分布于新水井、芨岭地区。采用LA ICP MS方法对研究区内中粒闪长岩进行锆石U Pb测年,得到年龄值为(4856±14) Ma。研究表明,闪长岩对后期铀成矿起重要作用：破碎蚀变闪长岩作为一种优质赋矿岩石,为含矿热液提供了卸载空间,蚀变后矿物成分主要为钠长石、绿泥石、方解石、赤铁矿等蚀变矿物,同时随着U含量的增加蚀变闪长岩中SiO2含量略有增加,Na2O明显增加,K2O、FeO 和P2O5有下降的趋势,CO2含量先增后减。综合研究分析认为,闪长岩本身是钠交代型铀矿的有利赋矿岩石,而其与花岗岩的接触面为花岗岩内接触带铀矿富集提供了物理化学环境突变的成矿结构面     

江西灵山杂岩体地质特征及成因探讨

江西灵山花岗岩体位于钦杭结合带南带之怀玉拗陷,呈环形岩基状产出;SiO2含量69.16%~76.45%, K2O+Na2O为 6.41%~9.44%,属酸性-超酸性、高钾钙碱性-钾玄岩系岩石,里特曼指数平均为2.42;富集Rb、Th、U、Nd、Hf、Zr、 Y 、Nb、Ta等元素,亏损Ba、Sr、P、Ti等元素;稀土元素总量为79.08×10-6~629.88×10-6,La/Yb比值为4.66~20.86,δEu= 0.11~0.45,显示出强烈的Eu负异常。作者在《江西省灵山地区矿产地质调查》工作中收集到杂岩体各侵入体之间的侵入接 触构造,研究发现岩体受北东和北西向断裂交汇点控制,认为属陆内局部伸展环境下具有两次以上由南西向北东上侵呈非 对称的气球膨胀式定位的“A”型、混熔型花岗岩,成岩成矿时代均为早白垩世;葛源至樟村是寻找与灵山岩体相类似的 矿床有利地段。     

Petrogenesis of highly fractionated I-type granites in the Zayu area of eastern Gangdese,Tibet: Constraints from zircon U-Pb geochronology,geochemistry and Sr-Nd-Hf isotopes

The Cretaceous granitoids in the middle and northern Gangdese, Tibet are generally interpreted as the products of anatexis of thickened deep crust genetically associated with the Lhasa-Qiangtang collision. This paper reports bulk-rock major element, trace element and Sr-Nd isotopic data, zircon U-Pb age data, and zircon Hf isotopic data on the Zayu pluton in eastern Gangdese, Tibet. These data shed new light on the petrogenesis of the pluton. Our SHRIMP zircon U-Pb age dates, along with LA-ICPMS zircon U-Pb...     

北祁连造山带东段老虎山石英闪长岩成因及其地质意义

以北祁连造山带东段老虎山石英闪长岩体为研究对象,进行了锆石U-Pb年龄及全岩元素与Sr-Nd同位素组成的系统 测定,据此探讨了岩石的成因及其对北祁连构造演化的启示。锆石LA-ICP-MS U-Pb定年结果表明,石英闪长岩体的形成 年龄为440 Ma。岩石具有亚碱、准铝以及贫钙、镁、铁的特征,碱铝指数（AKI值） 均低于0.85,铝饱和指数（A/NKC 值） 多小于1.0,属钙碱性I型花岗岩类岩石。在稀土和微量元素组成上,岩石富集轻稀土和大离子亲石元素（如Rb、Cs、 Th和U）,亏损高场强元素（如Nb和Ta）,显示弧岩浆岩的地球化学特征。岩体具有相对均一的Sr-Nd同位素组成,初始Sr同 位素值为0.7058~0.7071,εNd(t)值为-1.06~-0.31。综合分析表明,老虎山石英闪长岩应起源于玄武质下地壳物质的部分熔 融,并在成岩过程中有少量幔源物质的混入。对区内火成岩地质地球化学特征与产出背景的全面分析,表明受北祁连洋俯 冲及随后岛弧与祁连—柴达木陆块碰撞拼贴影响,弧后盆地的北向俯冲消减作用可能是诱发民乐窑沟和老虎山弧岩浆岩以 及导致毛藏寺—老虎山花岗岩带内埃达克质岩石侵位的基本动力机制。     

新疆东天山旱草湖环状岩体锆石U-Pb年龄、地球化学特征及成因

以新疆东天山旱草湖地区中酸性环状岩体为研究对象,进行LA-ICP-MS锆石U-Pb年龄和全岩地球化学研究,探讨其成因和地质意义。结果表明,侵入英云闪长岩的最老年龄为275.0±2.9Ma(MSWD=4.8),侵位时代为二叠纪。岩体Al_2O_3含量为14.46%～17.05%,A/CNK为0.93～1.09,属准铝质和弱过铝质系列,较富集K_2O,MgO含量较低,为0.71%～2.84%,Mg~#值为33.3～48.6。微量元素高Sr、低Y,Sr含量为217×10~(-6)～740×10~(-6),Y含量为4.26×10~(-6)～21.4×10~(-6),Sr/Y值为16.87～145.07,富集大离子亲石元素Rb、Sr、Ba,亏损高场强元素Nb、Ta、Ti。稀土元素配分模式图呈现平坦右倾的轻稀土元素富集、重稀土元素亏损,表明岩体来源于石榴子石和金红石较稳定而斜长石不稳定的区域,属于角闪岩相向榴辉岩相过渡阶段,可能是同时期底侵的产物。地球化学特征表明岩体不是一期岩浆事件结晶分离演化的结果,不同岩性的岩体之间没有发生结晶分离。部分熔融程度和新生幔源组分的不同导致了旱草湖环状花岗质岩体的形成,二叠纪旱草湖地区存在较强烈的中酸性岩浆活动,是东天山二叠纪构造-岩浆演化的响应。     

冀东晚古生代东湾子岩体的岩石成因研究

冀东晚古生代东湾子岩体由角闪石岩、少量辉石岩和辉长岩组成.典型的堆晶结构、全岩和镁铁质矿物(透辉石、角闪石)的上凸型稀土分布模式、相容元素含量低且变化范围大(如:角闪石岩中V=296×10-6～673×10-6)的特征表明了岩体的堆晶成因.计算得到的与辉石岩中的透辉石相平衡的熔体具有很高的稀土含量,轻重稀土分馏较为明显,富集大离子亲石元素(如:Sr,Ba,K),亏损高场强元素(如:Nh,Zr,Ti),具有典型的弧岩浆特征.透辉石和角闪石的矿物成分也具有弧岩浆的特征.高钙透辉石、大量的角闪石与黑云母的存在说明母岩浆富水.透辉石在高PH2O的状态下与熔体反应,生成角闪石的结构特征也证明了这一点.结合岩体的球化学特征,认为岩浆来源于富集的含有角闪石的尖晶石橄榄岩的部分熔融,母岩浆具有富水的特征(>3%).考虑到岩体形成时代(～300Ma;Zhao et al.,2007)和地质背景,认为东湾子岩体与位于华北北缘的其它晚石炭-早二叠世的岩体形成于同一构造背景下,都是晚古生代时期古亚洲洋向华北板块之下俯冲的产物.     

锆石铀含量与岩体成矿能力相关性研究——以诸广南部花岗岩为例

为初步探讨锆石铀含量在花岗岩型铀矿远景区预测方面的应用前景,以勘探研究程度较高的诸广南部花岗岩为样本,经花岗岩类样品概率统计显示产铀岩体锆石平均铀含量略大于贫铀岩体,总体差别不明显;样品分期次、岩性对比分析表明产铀岩体锆石平均铀含量也并非普遍高于贫铀岩体,印支期产铀岩体二云母花岗岩锆石平均铀含量甚至低于贫铀岩体;统计发现产铀岩体花岗岩岩脉中具有超高的锆石铀含量(平均铀含量3000×10-6以上)。初步分析认为依据花岗岩类锆石铀含量暂不能有效判别诸广山复式岩体成矿能力;岩脉锆石铀含量超高可能是铀矿找矿的重要标志,因而具超高锆石铀含量的花岗岩岩脉是否发育可能是该区域寻找工业铀矿床的关键。     

Age,nature, and origin of early cretaceous plutons in the Dabie Mo Mineralization belt: the Xinxian example

The Mesozoic granitoids in the Dabie Orogen are of particular geological interest as indicators for Mesozoic lithospheric evolution and because of their close association with porphyry Mo mineralization. Here, we present a study using zircon laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) U–Pb dating, petrogeochemistry, and Hf isotopic data to constrain the timing of the magmatism and petrogenesis of the Xinxian granites in the Dabie Mo mineralization belt (DMB), Henan Province, China. Field investigations combined with previously published data show that the Xinxian pluton mainly consists of four phases. Zircon LA-ICP-MS U–Pb dating yielded ages from 153.4 ± 1.1 Ma for Phase 1 to 146.4 ± 1.6 Ma for Phase 2, 131.6 ± 1.8 Ma for Phase 3, and 125.5 ± 1.5 Ma for Phase 4. The Xinxian granites have high SiO₂ contents of 74.94–78.70 wt.% (average: 76.63 wt.%), Al₂O₃ contents of 11.59–13.68 wt.% (average: 13.01 wt.%), and K₂O contents of 3.85–4.86 wt.% (average: 4.36 wt.%) with Na₂O/K₂O ratios of 0.78–1.03 (average: 0.92) and low MgO (0.04–0.15 wt.%), TiO₂ (0.03–0.13 wt.%), and P₂O₅ (0.006–0.07 wt.%) contents. They are enriched in Rb, U, K, and Hf, but depleted in Ba, Nb, Ta, Sr, P, and Ti. The zircon ε_Hf(t) values for Phases 1, 2, 3, and 4 vary as follows: from – 22.8 to – 20.3 with T_DM2 values from 2682 to 2869 Ma, from – 24.2 to – 21.2 with T_DM2 values from 2738 to 2925 Ma, from ?24.5 to ?21.5 with T_DM2 values from 2722 to 2915 Ma, and from ?22.9 to ?19.4 with T_DM2 values from 2421 to 2643 Ma, respectively. By integrating previous geological, geochronological, and geochemical data for the DMB, we propose that the Xinxian pluton was dominantly sourced from the crust. The granites were most likely derived from the partial melting of the Northern Dabie Complex (NDC) with some Yangtze lower crust and Southern Dabie Complex (SDC). The Xinxian pluton may have formed in a post-collision extensional setting.