Geochemistry of Granitoid Rocks from Zhejiang Province and Crustal Evolution—Ⅰ.Phanerozoic Granitoid Rocks

The Phanerozoic granitoid rocks include the Caledonian,Indosinian and Yenshanian granitoid rocks.The existence of Caledonian and Indosinian granites was evidenced by zircon U-Pb ages,The study of the characteristics of major,trace and rare-earth elements,isotopic composition and petrogenesis for the granitoid rocks has been made,The Caledonian and Indosinian granites were derived from partial melting of the Proterozoic basement rocks and the two tectonic activities were weak,The Yenshanian grantoid rocks were derived from mixing of mantle and crustal materials,It implies that the crustal accretion took place in Mesozoic time.     

Discussion on Induan—Olenekian Boundary in Chohu,Anhui Province, China

This paper proposes a scheme for the definition of the Lower Triassic Induan-Olenekian boundary(IOB) based on investigation of sections in Chaohu, Anhui Province, China as well as data accunulated from other studies elsewhere. The conodont Neospathodus waageni is suggested as the index fossil of the boundary. According to the FAD of N.waageni, the IOB is at the base of bed 25-2 of the West Pingdingshan Section in Chaohu,42.19 m above the Permian-Triassic boundary, and it is slightly higher than the base of the Flemingites-Euflemingites Ammonoid Zone at the section.     

Discovery of Pyrrhotite-Chalcopyrite-Bearing Amphibole Megacrysts in Tongling Area, Anhui Province

Some pyrrhotite-chalcopyrite-bearing amphibole megacrysts (including pyroxene megacrysts) were discovered in Mesozoic augite diorite-porphyrite at Caoshan in Tongling area, Anhui Province. The amphibole megacrysts, belonging mainly to pargasite and magnesiohastingsite, are characteristic of the amphibole composition derived from mantle and crystallized in lower crust. In general, the aggregates of pyrrhotite-chalcopyrite take the shapes of cylinder and sphere. Three occurrences have been recognized in the amphibole megacrysts: parallel linear, bunchy and scattered. The unique cylinder-like shape of the aggregates and remarkable Ni-poor sulfides in Caoshan are distinctively different from the spherical Ni-rich sulfides in pyroxene megacrysts and any other kinds of megacrysts. In terms of composition, the amphibole megacrysts and their sulfides in Caoshan are similar to those in the pyroxenite xenoliths in Qilin, Guangdong Province. In terms of origin, the pyrrhotite-chalcopyrites as exsolution products resulted from the subsolidus re-equilibration of sulfide solid solution within amphibole megacrysts.amphibole megacrysts were first discovered inside and outside China. This discovery is important for the study of regional magma evolution and its associated mineralizations and ore sources as well.     

Grain Coarsening of Hematite in the Gushan Iron Deposit,Anhui Province,China

The iron ores of the Gushan mine occur in the contact zone of a Mesozoic diorite intrusion and are composed primarily of hematite microcrystallites and chalcedony,The hematite microcrystallites have undergone post-mineralization recrystallization and coarsening with resultant formation of lath-shaped hematite porphyroblasts.Microscopic investigation reveals that recrystallization and coarsening of the hematite ores of the Gushan mine took place without the formation of new nuclei,due to the coalescence of the microcrystallites.The whole process could have begun with the mutual approach of the microcrystallites,followed by grain rotation to realize paralleism and ending by the welding of these grains to form optically homogeneous porphyroblastic hematite.     

Rare—Earth Elements and Genesis of Lamprophyres in the Laowangzhai Gold Orefield,Yunnan Province

The Laowangzhai super-large gold orefield,which is situated in northern Mt.Ailao tectonic zone,Yunnan Province,is a typical gold orefield where lamprophyres are temporally and spatially related to gold mineralization.Major element data show that lamprophyres in the orefield are of alkalic series and can be divided into potassic and K-rich calc-alkaline lamprophyres.The rocks are enriched in rare-earth elements as compared with the primary mantle and mid-ocean ridge basalts(MORB).Modelled calculations by the least squares method of Petrological Mixing show that the mantle-source for the lamprophyres in enriched in rarc earth elemeots.The geotectonic development of western Yunnan,Sr and Nd isotopic compositions,incompatible element patterns and linear programing calculations indicate that the fluids were derived from dehydration of submaine sediments which are enriched in ALK,LREE and incompatible elements and then were carried to mantle wedges as a result of plate subduction.That is the main factor leading to the formation of a metasonatic fertile mantle in the area studied.     

Granulite—facies Middle—Lower Crustal Xenoliths from Nueshan Alkali Basalt in Northeastern Anhui Province, China

Metamorphic xenoliths within the Nushan alkali basalt of northeastern Anhui (NEA),China ,are from the middle-lower crust.They could be divided into two end-members:basic and acid.Interme-diate xenoliths are scarcely found.Basic two-pyroxene granulites(pyriclasites) were formed at 720-810℃ and 7-8kb.Petrological and geochemical studies indicate that the primary magma of the protoliths of basic granulites was derived from the metasomatized upper mantle, while the pa-rental magma of the acid end-member was probably produced by partial melting of the basic rocks. The protoliths of charnockites and grey gneisses represent respectively the early and late crystallization products of the granitic magma.The Nushan granulites are much different in many aspects from the granulites exposed in the northern part of North China ,which implies the inhomogeneity regarding to the early evolution of the North China terranc.     

Symplectite of Pyrite and Magnetite in the Massive Sulphide Ore of the Mashan Mine,Anhui Province

A symplectite of pyrite and magnetite in the massive sulphide ore of the Mashan mine,Anhui Province,is interpreted to have been formed by their replacing earlier pyrrhotite.The compositions of pyrrhotite,pyrite and magnetite related to this texture are given by electron microprobe analysis.Such a texture is likely to be formed when the ore-forming system reaches the three-phase point of pyrrhotite,pyrite and magnetite from the pyrrhotite stability field.The very small probability for the system to reach this point could be used to account for the rare occurrence of such symplectite in natural ores.     

Morphological Variation of Conodonts Platyvillosus from Yinkeng Formation in Chaohu, Anhui Province, China

A preciously undescribed Lower Triassic sequence of a series of multiple cycles of mud-lime rocks, with the argillaceous content decreasing upward while limestone becomes the dominant lithology in the upper part, contains abundant fossils such as conodonts, ammonoids and bivalves. The Yinkeng Formation is the oldest Triassic unit represented, and it conformably overlies dark-gray thin-bedded argillaceous silicalite and intercalated grayish illite clay interbeds of the Upper Permian of Dalong Formation.Conodont samples collected from west Pingdingshan Section, one of four measured sections in Chaoha,yielded abundant Lower Triassic conodonts from the middle part of the Yinkeng Formation. Most interesting and unmaml is the abundant occurrence of Platyvillosus in seven samples from the Flemingites-Euflemingites bearing (Smithian) mudstone, rhyolitic clay and limestone part of the section. The associated conodonts are Neospathodus dieneri type 1, N. dieneri type 2. N. dieneri type 3, N. cristagalli, N. waagenieowaageni (nov. subsp. ), N. waagenielongata (nov. subsp. ), N. waageniwaageni,N. sp. G (nov. sp. ), N. sp. L (nov. sp. ), N. sp. H (nov. sp. ), N. alberti, N. novaehollandiae,N. peculiaris, N. aff. discretus, N. conservativus, Parachirognathodus sp. and ramiform elements.The species Platyvillosus. which is restricted to a 1.32 m interval, reveals great variety in shape and denticle ornamentation pattern on the platform. The morphological study of the samples indicates that all speciemens with denticles on the upper surface can be included in intraspecific variation in Platyvillosus costatus (Staesche). Platyvillosus hamadai (Koike), marked by smooth upper surface, also appears to be connected by transitional forms in some samples. The fauna corresponds closely with that of the Taho limestone in Japan, although the depositional environments differ. The associated lithologies of the Yinkeng Formation within Chaohu area reflect a deeper and low energy remaining basin of the northern edge of the Lower Yangtze block.     

Characteristics of Compositional Migration in Mylonites from the Ductile Shear Zones of the Southern Tancheng-Lujiang Fault Belt, Eastern Anhui Province

On the basis of field geology, three typical ductile shear zones in the southern part of the Tancheng-Lujiang fault belt have been chosen for a detailed study. Altogether ten samples of the tectonites have been collected for this study. The paper is focused on a comprehensive study of the tectonites in the medium-lower horizons of the ductile shear zones. The mineral compositions of the rocks are analyzed with EPMA and some typical whole-rock samples analyzed by chemical and ICP methods. Based on the comprehensive study of the characteristics of the deformation, the mineral assemblages and the changes of chemical composition of the bulk rocks, this paper presents a discussion on the relationship between the volume loss, the fluid flow and compositional changes during mylonitization of the ductile shear zones in this region. Our study shows that there are a large amount of fluids flowing through the shear zones during the process of mylonization, accompanied by the loss of rock volume and migration of el     

安徽洪镇地区董岭群片麻岩独居石SIMS U-Th-Pb定年

本文报道了安徽洪镇地区董岭群片麻岩中高精度的独居石SIMS U-Th-Pb定年结果,以~(207)Pb含量为基准对普通Pb进行校正后得到~(206)Pb/~(238)U的加权平均年龄为128.4±0.7 Ma(MSWD=1.6),~(208)Pb/~(232)Th年龄的加权平均值为128.6±0.4 Ma(MSWD=1.4)。作者认为独居石的SIMS U-Th-Pb年龄(128.4±0.7 Ma)代表了董岭群片麻岩的前进变质年龄。综合区域地质资料,提出董岭群片麻岩为新元古代沉积物在中生代经岩浆热动力接触变质的产物。这一发现不仅否定了前人提出的董岭群为前寒武纪区域变质地体的观点,而且否定了这一地区的"洪镇变质核杂岩",对进一步研究中国东部零星出露的中高级片麻岩的大地构造属性和构造演化具有借鉴意义。     

广东英德白沙佛冈花岗岩风化壳地下水中的稀土元素

广东省英德市白沙镇花岗岩风化壳地下水主要属于HCO3-Ca·Na型。水样的pH值在4.3～6.6之间。与世界其他花岗岩地区地下水相比,白沙地区花岗岩风化壳地下水的稀土元素(REE)总浓度偏高,在1.1～114μg/L之间,变化范围较大。地下水中的REE浓度与水的pH值呈弱的负相关关系,并且受母岩风化程度的影响。由于pH值、氧化还原状态及水中主要离子组成的差异,使得可溶态REE在水中的赋存状态存在差异。地下水与母岩、风化壳REE的PAAS标准化分布模式基本相似,呈LREE富集型,母岩中无Ce异常,而水样中有Ce负异常,表明Ce在水岩作用过程中发生了明显的分异。     

Origin and geochemistry of Pan-African granitoid rocks in the Gabal Um Shomer area,Southwestern Sinai,Egypt

Geological, petrological and geochemical studies indicated that there are two distinct types of granitoid rocks: older quartz diorites to granodiorite assemblage and younger granitoids, the latter occurring in two phases. The older granitoids have a meta-aluminous chemistry and a calc-alkaline character, with high MgO, Fe2O3, TiO2, CaO, P2O5, Sr and low SiO2, K2O, and Rb. Their major and trace elements data, together with low 87Sr/ 86Sr ratios (0.7029±0.0008) are indicative of I-type affinities. The second-...     

Deep-crustal granulites with migmatitic and mylonitic fabrics from the Zambezi Belt, northeastern Zimbabwe

Abstract High- P granulites contained in two allochthonous tectonic units were thrust southwards onto the northern margin of the Zimbabwe craton during the Pan-African Zambezi orogeny. In the lower sheet, the Masoso Metamorphic Suite contains mafic garnet granulite assemblages formed during a high- P-T metamorphic event, although the suite as a whole is predominantly granitic. The garnet granulites occur as relicts within narrow mafic layers characterized by migmatitic and mylonitic fabrics. The annealed mylonites represent surfaces of deep-crustal tectonic imbrication that formed immediately before the Pan-African orogeny. Gabbros which intruded the granulites after the main phase of migmatization have formed corona textures that document a low- P-T metamorphic event at mid-crustal levels. The style of deformation then changed and the Masoso Suite with its mylonitic layers was folded and thrusted southwards onto the Archaean Zimbabwe craton.     

安徽池州地区下蜀组沉积环境及成因探讨

采用磁化率、黏土矿物测试及粒度分析等手段,结合区域第四纪地质特征,从气候演变和岩相古地理等角度探讨了安徽池州地区下蜀组的沉积环境及成因.该区下蜀组磁化率曲线呈波峰、波谷旋回特征;黏土矿物以伊利石为主,个别层位以蒙脱石、高岭石、绿泥石为主;粒度以粉砂为主,个别层位以粉砂及中粗砂为主.下蜀组沉积期间存在多次寒冷干燥到温暖潮湿的气候转换,整体为寒冷干燥气候的风成沉积,受古地理位置影响,沿江局部地区夹温暖潮湿气候条件下的长江水系冲积沉积.     

北京密云典型韧性剪切带特征

北京密云典型韧性剪切带特征黄云波（长春工业高等专科学校,长春１３００２１）关键词北京密云糜棱岩韧性剪切带张家坟群为一套太古宙高级变质岩石,是密怀古隆起的主要组成部分;其变质变形作用的特征是全面研究密怀地区的地壳早期演化历史和铁、金成矿规律的关键［１］...     

安徽怀宁县洪镇变质核杂岩原岩时代与形成机制再认识

大别造山带东侧、扬子板块上安徽怀宁县的洪镇变质核杂岩,以往认为是早白垩世NE—SW拉张形成的科迪勒拉型变质核杂岩,其核部的董岭杂岩长期被认为是变质基底。然而,该核杂岩所指示的拉张方向与中国东部一系列早白垩世伸展构造指示的NW—SE拉张相矛盾,从而需要对这一重要伸展构造进行再研究和认识。本次11个样的锆石定年表明,董岭杂岩内变形—变质岩体的侵位时代为829~812 Ma,而变火山岩的原岩时代为761~754 Ma,后者属于扬子板块上的新元古代南华纪盖层。锆石生长边揭示了董岭杂岩内一期127 Ma的热事件,应为旁侧同期洪镇岩体侵位的热影响结果,并影响了董岭杂岩内韧性剪切带白云母~(40)Ar/~(39)Ar年龄值。该区董岭杂岩两侧在早白垩世发育了两组北东走向、倾向相背的正断层,南侧与西侧分别上叠同期的怀宁和潜山断陷盆地。断层擦痕应力场反演结果表明,这些早白垩世伸展构造是在NW—SE拉张中发育的,而不是前人认为的NE—SW拉张。综合分析表明,该区在早白垩世两组倾向相背正断层活动与洪镇岩体侵位、隆升的共同控制下发育为伸展穹窿构造,并非科迪勒拉型变质核杂岩。     

内蒙古二连浩特北部阿仁绍布地区晚石炭世花岗岩Sr-Yb分类及其成因

对分布在内蒙古二连浩特北部阿仁绍布地区的晚石炭世花岗岩类,依据Sr、Yb含量,划分为低Sr高Yb型、极低Sr高Yb型和低Sr低Yb型花岗岩3种类型。低Sr高Yb型花岗岩类相对低Si、富Al,Na2O>K2O,稀土元素分馏中等,有或无负Eu异常,Sr含量低,平均为183×10-6,Ba含量较高,平均585×10-6,Y含量高,平均30.06×10-6,Rb/Sr比值较低,平均0.97;极低Sr高Yb型花岗岩富Si、REE,低Al、Sr、Ba,高的Rb/Sr比值(平均为7.47),具明显的负Eu异常等;低Sr低Yb型花岗岩富Si,贫Al、Ca、Mg,重稀土元素(Y、Yb)含量低,Y含量在(7.26～10.6)×10-6之间,平均9.76×10-6,Yb含量在(1.04～1.89)×10-6之间,平均1.44×10-6,δEu=0.64～0.94,具弱负Eu异常,微量元素Ba含量高,Rb/Sr比值低。3种类型的花岗岩类过铝指数(A/CNK)多小于1.0,说明它们均源自变质火成岩的部分熔融。由于源区的深度不同(pT条件不同)和残留的主要矿物相不同,它们的岩石地球化学特征存在差异。极低Sr高Yb型花岗岩形成深度最浅(中上地壳),熔融残留相以斜长石为主;低Sr高Yb型花岗岩类形成于中下地壳,熔融残留相为斜长石和辉石;低Sr低Yb型花岗岩形成深度最深,推测可能形成于加厚下地壳(>40km)底部,熔融残留相为石榴子石、斜长石和角闪石。     

黑龙江晨明地区桦皮沟岩体和达里岱岩体LA-ICP-MS 锆石U-Pb 年龄及其意义

前人认为,黑龙江省晨明地区的桦皮沟岩体(花岗质糜棱岩)和达里岱岩体(糜棱岩化黑云母花岗岩）分别由形成于元古宙和海西期的花岗岩组成。LA-ICP-MS 锆石U-Pb测年对2个岩体的定年结果显示,桦皮沟岩体中的花岗质糜棱岩和达里岱岩体中的糜棱岩化黑云母花岗岩的206Pb/238U年龄加权平均值分别为453.5±6.0Ma和454.8±2.6Ma,表明二者均形成于早古生代,应是伊春—延寿构造带早古生代花岗岩带的组成部分,而非形成于元古宙和晚古生代。