Petrogenesis,geochronology, and tectonic significance of granitoids in the Tongshan intrusion,Anhui Province,Middle–Lower Yangtze River Valley,eastern China

The Tongshan copper deposit in Anhui Province is a typical mid-sized skarn and porphyry type deposit in the Anqing–Guichi district along the Middle–Lower Yangtze River Valley, eastern China. The Tongshan intrusion is closely related to this mineralization. The intrusion mainly comprises rocks that are quartz diorite porphyry, quartz monzonite porphyry, and granodiorite porphyry. Plagioclase in these rocks is mostly andesine (An = 31.0–42.9), along with minor oligoclase. Biotite is magnesium-rich [Mg/(Mg + Fe) = 0.52–0.67] and aluminum-poor (Al₂O₃ = 12.32–14.09 wt.%), and can be classified as magnesio-biotite. Hornblende is TiO₂-poor (<1.96 wt.%) and magnesium-rich [Mg/(Mg + Fe) > 0.60], and is magnesio-hornblende or edenite. The SHRIMP zircon U–Pb age of the quartz monzonite porphyry is 145.1 ± 1.2 Ma, which corresponds to the middle Yanshanian period. Whole-rock geochemical results show that the rocks are silica-rich (SiO₂ = 60.23–66.23 wt.%) and alkali-rich (K₂O + Na₂O = 4.97–8.72 wt.%), and low in calcium (CaO = 2.61–5.66 wt.%). Trace element results show enrichments in large ion lithophile element (e.g., K, Rb, and Ba) and depletions in some high field strength elements (e.g., Nb, Ta, P, and Ti). The total rare earth element (REE) content of the rocks is low (ΣREE < 200 μg/g), and they exhibit light REE enrichment [(La/Yb)_N > 10] and small positive Eu anomalies (average δEu = 1.16). These mineralogical, geochronological, and geochemical results show that the intrusion has a mixed crust–mantle source. The Tongshan intrusion was formed by multiple emplacements of crustally contaminated basaltic magma generated by varying degrees of partial melting of enriched lithospheric mantle and lower crust. Hornblende thermobarometry yielded magmatic crystallization temperatures of 652–788 °C and an average crystallization pressure of 1.4 kbar, which corresponds to a depth of approx. 4.7 km. Biotite thermobarometry yielded similar temperatures and lower pressures of 735–775 °C and 0.6 kbar (depth 2.1 km), respectively. The parental magma had a high oxygen fugacity and was produced in a volcanic arc setting related to subduction of the paleo-Pacific plate.     

The age of the oceanic accretionary wedge and onset of continental collision in the Sicilian Maghrebian Chain

New biostratigraphic data from the formations unconformably lying above the tectonic units resulting from the Flysch Basin Domain (FBD) in the Sicilian Maghrebids are here reported. The FBD constituted a southern branch of the western Tethys, separating during the Jurassic to Paleogene a Mesomediterranean Microplate from the African Plate.

The age of the youngest sediments involved in the nappes and that of the unconformable terrains deposited in thrust-top basins on these tectonic units, allow to define both the age of deformation of the oceanic realm and the onset of the continental collision. The deformation migrated from internal to external areas of FBD starting from the latest Burdigalian-Langhian to Serravallian. Therefore, the previously proposed Eocene-Oligocene mesoalpine deformation of the Maghrebian FBD cannot be supported. The continental collision started during the Serravallian and it was accomplished in the late Tortonian, when clastic deposits sealed the boundaries of the tectonic units originated from all the paleogeographic domains of the Maghrebian Chain.

The steps of the tectonic evolution in the Sicilian Maghrebids are now very well constrained and the proposed tectonic evolution may be extended to the whole Maghrebian Chain, as far as to the western Betic Cordilleras and to the southern Apennines, where most of the tectonic events show highly similar features and ages.     

贵州台江中寒武世凯里组中分枝状宏观藻类化石

本文描述了贵州中寒武世凯里组中的分枝状宏观藻类化石5属7种，即：Marpolia spissa Walcott,Marpolia aequalis Walcott,Guizhouella ramulosa Yang(gen.et sp.nov.),Doushantuophyton lineare Chen,Thamnophton formosus Yang(gen.et sp.nov.),Eoulothrix fibrillata Ding,Eoulothrix flabellophyton Yang(sp.mov.)。根据大量的藻类与凯里生物群共生特征，从藻类的生态及生物群分布受到沉积韵律控制等特征分析，认为凯里生物群生活环境的水深应该在30－60m，而埋藏和保存环境的水深是150m左右。另外，将凯里生物群中的宏观藻类化石与震旦纪陡山沱期的藻类化石进行了比较，两者在以分枝状藻类占主要组成上是相似的，从这一方面来说，晚震旦世宏观藻类与寒武纪宏观藻类没有大的演变，但寒武纪宏观藻类以出现钙质珊瑚藻类、分枝更加复杂的类型和具有锯齿状叶状体、生殖托构造的藻类为特征。     

湘中地区微细粒浸染型金矿的找矿标志

本文总结了湘中地区微细粒浸染型金矿的地层岩性、构造、岩浆岩、成矿系列与地球化学等方面的找矿标志,这无疑对今后的找矿工作具有指导意义。     

Refinement of the age of the Middle Miocene Fort Ternan Beds,Western Kenya,and its implications for Old World biochronology

It has become increasingly obvious over the past two decades that the fossiliferous strata at Fort Ternan, Kenya, are probably somewhat younger than 14 Ma, an age which has long been attached to the deposits. This realisation flows from geological and biochronological observations. In order to test the hypothesis, resampling of all the lava flows in the region of Fort Ternan was undertaken in 2003, especially those underlying the Fort Ternan Beds in the Kipchorion Gorge where the sequence is the most complete. Samples obtained from lava flows underlying and overlying the fossil beds were analysed for anorthoclase K/Ar and ⁴⁰Ar/³⁹Ar and biotite ⁴⁰Ar/³⁹Ar age determinations. The results reveal that the age of the fossiliferous sediments is ca $13.7\pm 0.3\text{Ma}$. Since Fort Ternan yielded the ‘core fauna’ that defines Faunal Set IV of the East African biochronological sequence this refinement of its age will impact on age estimates of neighbouring Faunal Sets, as well as on other faunas correlated to Fort Ternan, including those in Europe belonging to MN Zones MN 5, MN 6 and MN 7/8. To cite this article: M. Pickford et al., C. R. Geoscience 338 (2006).     

宁镇中段矽卡岩型矿床的闪锌矿及其地质压力计应用讨论

宁镇山脉中段矽卡岩型铁铜矿床的成矿深度是该地区深部找矿前景分析的重要参考因素,以往多运用地质分析法来定性讨论。通过野外调查,发现这些矿床常有少量闪锌矿伴生。初步研究了该地区伏牛山铜矿、安基山铜矿、团山硫铁矿、盘龙岗铁铜矿以及胄王村多金属矿等代表性矿床（点）所伴生闪锌矿的产出特征、矿物共生组合、常量化学成分及晶体结构,发现该区闪锌矿形成于热液硫化物阶段的中晚期,部分矿区具有至少两个结晶世代,无论其共生矿物、结晶形态、颜色、成分或晶体结构均随产状和矿物共生组合有规律地变化。只有团山硫铁矿和伏牛山铜矿的第一世代闪锌矿与六方磁黄铁矿及黄铁矿平衡共存,符合闪锌矿地质压力计应用条件,用前人修正的闪锌矿压力计获得的成矿压力与地质分析结论吻合,为0．9kPa～1．2kPa,相当于成矿深度2420m～3630m,比照处在相同成矿带的湖北大冶和安徽铜陵深部找矿结果,认为该区仍有深部找矿前景。     

普洱地区中二叠统茅口阶地层及类分带

云南普洱中二叠统茅口阶地层处于古特提斯海云南 老挝海槽 ,沉积物为大套碳酸盐岩夹泥质岩。类化石十分丰富 ,依据垂直分布特征 ,由下而上建立Parafusulinanosonensis带及Neoschwagerinacriticulifera N .douvillei带 ,同时介绍了二化石带中类动物群特征 ,为与邻区中二叠统茅口阶地层的划分和对比提供了新的依据。     

鄂尔多斯盆地拉什仲组遗迹化石组合与古环境

首次对鄂尔多斯盆地西北缘桌子山地区中奥陶世拉什仲组的遗迹化石进行了系统研究。该组遗迹化石共有6属8种,建立了Paleodictyon遗迹化石组合。此组合以被侵蚀、改造呈斑状分布的遗迹大量存在与Paleodictyon的普遍出现为最显著的特征。遗迹化石的形态、行为习性、保存方式等分类特征、埋藏学特征等表明该组合相当于Nereites遗迹相,代表了深海远源浊流沉积环境;而在本组沉积晚期,水体开始变浅,大致为大陆斜坡－陆隆半深海浊流沉积环境。其沉积层序、沉积构造及岩性等特征说明拉什仲组为典型的浊流相沉积,并以远源相浊流沉积为主,其下部近相浊流沉积较发育。据古流向测定,自中奥陶世拉什仲组至公乌素组沉积期,重力流运动方向的变化大致反映了贺兰拗拉槽张裂的幅度在变小并渐呈收敛隆起的趋势。     

新疆天山中段独库公路地质构造

路线横穿天山中段，沿途可先后观察到各时期的侵入岩、火山岩、沉积岩及其变质岩，天山几条大型构造线，北天山由橄榄岩、辉长辉绿岩、枕状玄武岩、放射虫硅质岩组成的蛇绿岩套，哈希勒根断裂附近的超镁铁岩带，伊宁盆地东缘石炭纪火山岩及侏罗系含煤岩系，拉尔敦达坂中元古界眼球状混合片麻岩、阳起石片岩及糜棱岩，哈尔克山志留、泥盆、石炭纪联酸盐岩和碎屑岩及丰富的珊瑚、腕足类、层孔虫、类化石，志留─泥盆系整合接触关系及早泥盆世枕状玄武岩、放射虫硅质岩及铁锰矿层，库车盆地中新生界形成的风蚀地貌及新构造运动痕迹，沿途可观光戈壁绿洲，高山隧道，现代冰川，优美的森林、草原、高山湖泊及天鹅自然保护区风光。     

福建永定地区下、中元古界变质岩基本特征及地层时代依据

闽西永定地区的中深变质岩系经调查主要岩石组合为变粒岩、片岩、变质火山岩及少量石英岩,变质程度达低角闪岩相,构造形变特征明显有别于区域内的震旦纪楼子坝群,获得同位素年龄1825—1628 Ma。据此认为,这套变质岩不属于原划定的楼子坝群,应分属于下、中元古界。对该地层所夹变质火山岩的形成环境,本文亦进行了讨论。