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.     

西准噶尔别鲁阿嘎希花岗闪长岩年代学、地球化学特征及岩石成因

为更深入了解西准噶尔晚古生代岩浆活动和构造背景,对位于西准噶尔中部的别鲁阿嘎希岩体开展了年代学、地球化学以及Sr-Nd同位素研究,讨论了岩石成因、源区性质和构造背景.别鲁阿嘎希花岗闪长岩为钙碱性系列岩石,岩浆锆石结晶年龄为318.7±3.3 Ma.其具相对高的MgO(Mg#=49~59)、Ni、Cr含量,富集大离子亲石元素(如K、Rb、Sr和Ba)、亏损高强场元素(如Nb、Ta、Ti),轻重稀土元素分异不明显.Sr-Nd同位素特征显示,其有较低的初始Sr比值(0.704 297~0.704 399),较高的ε_Nd(t)值(5.8~6.5).通过综合分析,认为在晚石炭世早期,达尔布特洋壳(板片)俯冲至地幔楔下部,俯冲洋壳板片脱水所产生的流体在上升过程中与地幔楔共同作用,底侵加热由亏损地幔形成不久的年轻地壳(由洋壳和岛弧组成),使其部分熔融形成了别鲁阿嘎希分异I型花岗岩.      

鹅婆复式深成岩体成岩时代初探

本文以１：５万青塘幅、黄石幅区调资料为依据,对鹅婆复式深成岩体的成岩时代从地质特征、岩石学特征、岩石化学特征、同位素年龄等多方面进行了分析,认为鹅婆复式深成岩体形成于加里东晚期。     

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.     

西藏南部晚始新世打拉埃达克质花岗岩及其构造动力学意义

打拉二云母花岗岩岩体位于雅拉香波穹隆的东南,侵入到中生代以前的变质岩系(眼球状花岗质片麻岩和石榴黑云母片麻岩)和特提斯沉积岩(页岩和砂岩)中,主要由石英、斜长石、钾长石、黑云母和白云母组成,形成于～44.3Ma。打拉二云母花岗岩地球化学特征表明:打拉花岗岩具有高Al_2O_3(16.0%～17.0%)、Na_2O/K_2O(1.2)以及A/CNK比值(1.05),表明打拉花岗岩为富钠过铝质花岗岩;轻稀土(LREE)富集,重稀土(HREE)相对亏损,HREE中的Ho到Lu元素有变平的特征((Ho/Lu)_N=1.11～1.46);具有微弱或无Eu异常,Eu/Eu~*=0.87～0.95;较高的初始Sr同位素比值(~(87)Sr/~(86)Sr(i)=0.71754～0.71785)和较低的初始Nd比值(ε_(Nd)(i)=-9.15～-12.4)。打拉花岗岩具有高Sr含量(为355×10~(-6)～416×10~(-6))和Sr/Y的比值(59.1～71.5)、高La/Yb比值、低Y及HREE亏损的特征,与埃达克质花岗岩类似。上述特征表明打拉花岗岩是在较高压力条件下,以角闪岩为主的深部岩石部分熔融的结果。     

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。     

Geochemistry,zircon U–PB ages and HF isotopes of the Muong Luan granitoid pluton,Northwest Vietnam and its petrogenetic significance

The Indosinian Orogeny plays a significant role in tectonic background and magmatic evolution in Indochina and surrounding regions. Being a part product of the Indosinian magmatism in northwest Vietnam during late Permian–middle Triassic period, Muong Luan granitoid pluton dominantly consists of granodiorite, less diorite and granite. This pluton is located in the Song Ma suture and assigned to the Dien Bien complex. Geochemically, the Muong Luan granitoid rocks are characterized by a wide range of SiO₂ contents (59.9–75.1 wt%) and high K₂O contents. They display typical features of I‐type granites. The presence of hornblende and no muscovite and cordierite in the rocks further supports for I‐type character of granitoids. The emplacement age of the Muong Luan pluton obtained by LA–ICP–MS U–Pb zircon is at 242–235 Ma, corresponding to Indosinian time. Zircon ε_Hf values of –5.6 to –10.4, in combination with moderate Mg values of 34–45 suggested that the Muong Luan granitoid was derived from partial melting of mafic crustal source rocks, which are probably Paleoproterozoic in age as revealed by Hf model ages (T_DM2 = 1624–1923 Ma).     

湘南尖峰岭岩体锆石U-Pb年龄、地球化学特征及成因

香花岭锡多金属矿田处于南岭西段中_晚侏罗世形成的花山_西山_香花岭_骑田岭NE向的富碱侵入岩带上,是湘南地区矿化类型最为完整的锡矿区。尖峰岭岩体为矿田内主要的成矿母岩之一。为了进一步明确尖峰岭黑云母花岗岩的岩石成因及成岩年龄,笔者对尖峰岭黑云母花岗岩开展了LA_ICP_MS锆石U_Pb测年及岩石地球化学特征分析。锆石LA_ICP_MS U_Pb测年获得206Pb/238U年龄介于(158.6±2.3)Ma~(164.8±4.5)Ma之间,加权平均年龄为(160.7±2.2)Ma(MSWD=0.8),这与香花岭锡多金属矿田的成矿时限(154~161 Ma)相吻合,表明岩体的侵位与区内多金属成矿作用均发生于中_晚侏罗世。尖峰岭岩体的主量、微量元素研究显示,尖峰岭黑云母花岗岩具有富硅、富碱及成矿元素,富LILE及Zr、Ga等部分高场强元素(HFSE),贫Ca、Mg、P、Eu特征,指示尖峰岭黑云母花岗岩属于过铝质A型花岗岩(A2型)。综合研究表明,尖峰岭黑云母花岗岩体与其周缘钨锡多金属矿床在时间、空间及成因上有密切关系。结合区域上已有的同位素年代学数据,香花岭矿区的成岩成矿作用与南岭西段同时代的其他钨锡多金属矿床形成于同一岩石圈伸展的地球动力学背景下。     

湘南骑田岭岩体菜岭超单元花岗岩侵位年龄和物质来源研究

湘南骑田岭岩体菜岭超单元花岗岩以角闪石黑云母二长花岗岩为主,其全岩Rb-Sr等时线年龄为159±1.2Ma,单颗粒锆石熔融法U-Pb年龄为161±2Ma,Sr同位素初始比值偏低(0.70854),Nd同位素初始比值偏高(-5.4～-5.8),Nd模式年龄偏低(0.94～1.49Ga)。在岩石化学和微量元素方面,属钙碱系列,准铝,富含K、Rb等大离子亲石元素和Th、REE、Nb等高场强元素。常见较多具有岩浆混合特征的微花岗岩类暗色包体。这些同位素、岩石学和微量元素特征,总体上反映了菜岭超单元花岗岩的成岩组成中有明显的地幔物质的参与。该花岗岩可能是在燕山早期华南地壳开始拉张减薄的构造背景下定位的,壳幔相互作用对本区大陆地壳物质的重熔和花岗岩浆的形成和演化起了重要的作用。     

江南隆起带幕阜山岩体新生代剥蚀冷却的低温热年代学证据

江南隆起位于扬子与华夏地块的碰撞汇聚带,是研究华南大地构造演化的关键地质单元.本文采用磷灰石裂变径迹及(U-Th-Sm)/He年龄分布特征定性分析与径迹长度分布数据定量模拟相结合,主要研究了幕阜山岩体新生代的隆升与剥蚀过程,并在此基础上结合区域构造背景, 对其构造-热演化之间的关系进行了探讨.自晚白垩世持续隆升以来,幕阜山岩体经历的平均剥蚀厚度约4800 m.在不同岩体间,隆升过程及幅度存在差异,空间上具有非均匀性.热史结果显示幕阜山岩体经历了3期剥蚀, 其中两期快速剥蚀分别发生在晚白垩世-古近纪(80~50 Ma)和10 Ma以来,而这之间为一期缓慢剥蚀过程.研究区古近纪的快速剥蚀反映了中-下扬子喜山期大规模伸展断陷作用造成的肩部块体快速剥蚀事件; 约10 Ma以来的快速剥蚀是对太平洋板块向西运动的响应.幕阜山岩体自燕山晚期以来的隆升剥蚀作用具有良好的盆地沉积响应, 三期隆升剥蚀事件与研究区构造演化的动力学背景相吻合.