Petrology and geochemical characteristics of Precambrian granitic basement complex rocks in the southernmost part of North-Central Nigeria

The Precambrian basement complex in the southernmost part of North-Central Nigeria is underlain by migmatitic banded gneisses, granitic intrusions and dykes of dolerite, rhyolite porphyry and pegmatite. The rocks are generally felsic, containing modal and normative hypersthene, as well as normative corundum. The basement complex has experienced high-grade regional metamorphism as indicated by the presence of hypersthene and plagioclase of andesine composition. Anatectic melting is suggested by the occurrence of ptygmatic folds, folded gneissose foliation, numerous quartzo-feldspathic veins and lenses of dark-colured, micaceous schistose rocks. Geochemically, the rocks have magnesian, calc-alkalic and strongly peraluminous characteristics. Their overall characteristics suggest derivation from progressive (fractional) partial melting of pelitic rocks during high-grade regional metamorphism, possibly associated with intense hydrothermal activities. The magnesian characteristics reflect close affinity to relatively hydrous, oxidizing melts and source regions in settings broadly related to subduction.     

云南楚雄盆地西部高精度重磁电特征及基底特征

楚雄盆地是滇黔桂地区面积最大的含油气盆地,油气勘探进展缓慢,关键问题是基底和沉积盖层展布不清。重磁电是认识和了解盆地基底展布的重要手段。本研究在楚雄盆地西部实施2条区域重磁电测线,并对其进行基底结构的综合解译。结果表明：楚雄盆地西部上三叠统底界的最大埋藏深度为7 km,盆地总体走向北西,结晶基底在平川、云南驿、红河断裂以东,猛虎、舍资一线以西地区深度最大为9 km;在大姚县和南华县之间形成楚雄盆地最大的磁基底凹陷区,面积达到1 200 km²。     

赣南九龙嶂火山盆地铀矿地质特征与成矿条件分析

九龙嶂火山盆地位于南岭成矿带安远热隆的西部,面积120余km2,盆地基底为元古代变质岩,盖层为上侏罗统鸡笼嶂组火山岩系.在盆地边缘火山岩中分布3个铀矿点或矿化点.其中银坑山矿点受发育于流纹质熔结凝灰岩中的近SN向碎裂带控制.盆地基底岩石碱交代蚀变明显,火山期后浅成-超浅成侵入岩浆活动频繁,火山构造与区域线性构造交接复合并形成派生构造,使盆地具有良好的铀矿形成的源-运-聚条件.盆地南(东)部银坑山一带是找矿方向和勘查重点所在.     

Primordial geodynamics of Southern Carpathian-Balkan basements (Serbo-Macedonian Mass): Avalonian vs. Cadomian arc segments

This review deals with a highly complex set of dismembered peri-Gondwanan exotic polymetamorphic basement systems accommodated outside of the well-explored European Variscides, extending from the controversial Serbo-Macedonian hinterland up to the East Moesian Alpine foreland. The isotopic and limited detrital zircon ages are coupled with the lithotectonic and palinspastic record in order to restore the earliest peri-Gondwanan developments in modern-day South-east Europe (Carpatho-Balkanides and surrounding areas). The results suggest that these rather bewildering, occasionally underexplored tectonometamorphic suites exhibit Cadomian arc inheritance in a flanking part of this belt, whilst inferior Avalonian are positioned more internally.     

A hidden suture within the northern Paleotethyan margin: Paleogeographic/paleo-tectonic constraints on the late Paleozoic 'Veles Series' (Vardar Zone,North Macedonia)

There is little consensus in characterizing the effects of the migrated late Pan-African/Lower Paleozoic configuration (western Paleotethys and precursory Paleozoic oceans) and its Variscan, late Variscan, and Eo-Cimmerian involvement. Constrained by a limited choice of the geological, biostratigraphical, and paleogeographical constraints, the focus of this regional geological synthesis is the little-known Devonian – Lower Carboniferous polymetamorphic 'Veles Series' (southern Vardar-Axios Zone, Northeast Mediterranean). Kinematic reconstructions indicate that the drifted carbonate platform assemblage of the 'Veles Series' including its Lower Carboniferous collision occurred along an active margin of southwestern Moesia, Laurussian foreland. Despite the fact that the dominant, low-grade metamorphic imprint across the 'Veles Series' is compatible with the ‘soft’ Eo-Cimmerian docking (i.e. Triassic), the documented Lower Carboniferous age suggests a Variscan involvement.A distinctive Late Paleozoic age is consistent with the north Gondwana and Variscan developments, reflected by the peculiar protoliths pallet portraying the presence of the oceanic crust to deep-marine equivalents. Accommodated to the west (paleo-south) of the late Cadomian Serbo-Macedonian Unit (a segment of the former peri-Gondwanan terrane assembly) and to the north of the Cimmerian Minoan system (East Mediterranean), the 'Veles Series' reflects a migrated rift to carbonate platform system. Despite the significant Alpine overprinting, based on this regional geological synthesis we propose that the 'Veles Series' is a 60 km-long suture segment documenting a so far rather poorly explored Variscan segment of the Paleotethyan lithosphere exposed within Balkans/Northeast Mediterranean.     

地下室抗浮设防水位标高取值的讨论以及抗浮措施

地下水勘察是岩土工程勘察的一项重要任务。近年来,带有深基坑的高层建筑和地下广场式建筑大量兴建,一旦地下水可能高于地下室基础底板时,必须提供合理的抗浮设计水位,并对地下室抗浮有关问题提出建议。因此,抗浮水位的合理确定问题,它直接涉及到工程的安全性和成本问题,而实际中抗浮水位情况是比较复杂的,抗浮水位的标高取值尤其对一些水位变化大的地方,一直纠结于业内人士。抗浮水位取高了则造成浪费,估算低了则容易出事故,危险性很大。本文结合了不同的地貌地质和水文地质等条件探讨并总结了如何合理的确定地下室的抗浮水位以及相应抗浮措施,运用工程实例区别于传统的“拉压抗浮”设计方法,倡导节能绿色技术以“疏”代“抗”的疏水降压方法及时的降低地下水位,满足地下室抗浮要求。为相应的勘察与设计、施工单位确定抗浮水位或抗浮措施提供参考依据。     

The You Yangs batholith in Southeastern Australia,the sources of its magmas and inferences for local crustal architecture

The 365-Ma You Yangs batholith is a mainly I-type monzogranitic body, containing rocks with both clinopyroxene and hornblende, but with a 2–2.5?km-wide rim of S-type rocks. In places, the margins of the intrusion wedge out laterally. A laccolithic shape may explain there being only low-grade contact metamorphism of the Ordovician metasedimentary wall rocks. The chemical and isotopic characteristics of the granitic rocks suggest that the magmas formed by partial melting of a source that contained some meta-igneous rocks but was dominated by chemically immature metasedimentary types, to impart an evolved Sr isotope signature (⁸⁷Sr/⁸⁶Sr_t?=?0.70877–0.71066 for the main monzogranitic rocks), combined with relatively non-radiogenic εNd_t (–2.4 to –1.9). Crystal fractionation played little role in shaping the compositions of the granitic magmas, with the main variations interpreted to be source-inherited. Igneous-textured microgranular enclaves (IMEs) are prominent in the monzogranitic rocks. The IMEs probably had an ultimate enriched-mantle source, and their magmas did not mix significantly with the crustally derived granitic host magmas. The characteristics of the monzogranitic rocks hosting the enclaves suggest the possibility that an unrecognised metasediment-dominated terrane of ancient arc crust may be present beneath the Bendigo Zone.     

西藏南拉萨地块西部鸭洼地区侵入岩的锆石年代学和Hf同位素特征

拉萨地块南缘发育了广泛的中、新生代岩浆作用,然而与中、东部地区相比,南拉萨地块西部地区的研究程度还相对偏低,尤其是缺乏中生代以前岩浆活动的发现和研究。本文对南拉萨地块西部鸭洼地区新发现的中、新生代侵入岩开展了详细的锆石U-Pb定年和Hf同位素研究,发现鸭洼地区发育了晚三叠世(210～208Ma)辉长岩和闪长玢岩、晚侏罗世(约155Ma)似斑状二长花岗岩和始新世(约50Ma)花岗斑岩。晚三叠世辉长岩和闪长玢岩具有相对亏损的锆石Hf同位素组成,ε_(Hf)(t)值分别是+1.9～+6.2和-3.0～+7.4。晚侏罗世似斑状二长花岗岩和始新世花岗斑岩则具有明显富集的锆石Hf同位素组成,其ε_(Hf)(t)值分别是-10.0～-5.2和-7.9～-2.7,对应的地壳模式年龄分别是1534～1836Ma和1297～1624Ma,分别反映了古元古代和中元古代古老陆壳物质为主的再循环作用。结合区域文献数据,鸭洼-打加错地区中生代以来由于新特提斯洋的俯冲而发生了明显的地壳增生作用,新生地壳的生长从中生代到新生代早期逐渐进行,并且具有从陆内向海沟逐渐增加的趋势。     

上扬子北缘川北地区结晶基底晶质石墨矿数据集

上扬子北缘川北地区出露的基底地层发育双层结构,其中上层的褶皱基底早已发现尖山、坪河、庙坪等中—大型、超大型石墨矿;但是直到最近,才在下层的结晶基底后河岩群汪家坪岩组细粒石英岩中发现了石墨矿。该矿体长约200米,宽约6.7米,矿体平均厚度4.9米,矿石平均品位5.13%。矿物组合为：石英+石墨+云母+黄铁矿+赤铁矿。该成果在上扬子北缘地区的发现,扩大了该区域的找矿前景,为区内晶质石墨矿的找矿工作提供了新的方向,同时为四川巴中地区超大型晶质石墨矿基地建设提供了新的资源潜力保障。数据集包括Excel表格数据,2个*.xls类型文件,记录了样品固定碳测试结果和氧化物测试数据。     

准噶尔盆地深层地质结构叠加演变与油气赋存

根据地表露头、地震、钻井、测年资料,应用地层回剥方法,对准噶尔盆地深层结构进行了解剖。现今的构造区划是石炭系顶面隆坳格局的反映,深、浅层地层沉积隆坳格局和构造变形特征存在差异。石炭纪末的构造事件导致盆地褶皱变形、隆升剥蚀,形成了北西向为主的背向斜构造。早二叠世-中二叠世,沉积在南部,存在多沉积中心、多构造应力环境,形成了二叠纪早中期重要的烃源岩层系。晚二叠世-侏罗纪存在两期大型湖进坳陷盆地沉积,将下伏盆地埋藏,为盆地重要的区域盖层。早侏罗世-中侏罗世西山窑组含煤岩系是盆地内重要的烃源岩层系,中侏罗统头屯河组沉积前,盆地内形成西南高、北东低的大型车莫古隆起,并遭受了强烈剥蚀。白垩系沉积前,盆地受深层断裂活动控制,在侏罗系形成雁列组合正断层构造。白垩纪-新生代,盆地发生翘倾构造作用,北天山山前强烈沉降,褶皱变形,北部隆升。盆地深层存在石炭系、二叠系和侏罗系富含有机质的烃源岩,与叠合连片发育的三叠系、侏罗系、白垩系、新生界泥岩、煤系、膏泥岩等构成了盆地内多套源盖组合,成为盆地油气富集的基础。盆地深层油气围绕构造变动后的富烃中心区赋存。