Micrometallogeny and hydrothermal fluid evolution of the Iju porphyry Cu deposit,NW Kerman,Iran: Evidence from fluid inclusions,Laser Raman spectroscopy,and SO isotope systematics     

《Chemie der Erde / Geochemistry》2023,83(2):125956

The Iju Cu porphyry is located in the NW part of the Kerman Magmatic Copper Belt (KMCB). It is related to a ~ 9 Ma granodiorite porphyry intrusion, with three main stages of hydrothermal activity. The homogenization temperatures for the fluid inclusions are in the ranges of 200–494 °C, and their salinities vary from 4.0 to 42.8 wt% NaCl equiv., which are typical magmatic-hydrothermal fluids. The δ³⁴S values of sulfides range from −0.4 to +3.2 ‰ (V-CDT), and the δ³⁴S values of anhydrite samples range from +11.6 to +16.8 ‰. The δ³⁴S values of sulfides show a narrow range, implying a homogeneous sulfur source. The oxygen isotopic composition of hydrothermal water in equilibrium with quartz samples ranges from +3.4 to +6.0 ‰ (V-SMOW) consistent with the hydrothermal fluids having a magmatic signature, but diluted with meteoric waters in the main mineralizing stage. The most important factors responsible for metal precipitation in the Iju porphyry deposit are fluid boiling, oxygen fugacity decrease and cooling followed by dilution with meteoric water. The primary fluids of the Iju Cu deposit are characterized by relatively high temperature and moderate salinity, and are CO₂-rich, indicating a typical post-collisional porphyry system.  相似文献   

Petrographic and mineral chemistry investigation of the high-grade chrysotile asbestos-bearing Zvishavane Ultramafic Complex,south central Zimbabwe     

《Chemie der Erde / Geochemistry》2023,83(2):125950

The Zvishavane Ultramafic Complex (ZUC) in the south central part of the Zimbabwe craton is comprised of coarse-grained serpentinites, metadunites and metagabbros and hosts Africa's largest reserves, and largest mine, of high-grade chrysotile asbestos. Magnesiohornblende, actinolite, plagioclase (An_0.6–41.9), augite, diopside and clinozoisite constitute the mineralogy of the ZUC. Forsteritic olivine (>Fo₉₀) was altered to form chrysotile and antigorite minerals, although some primary olivines are preserved. Contents of Al₂O₃ range from <1 to >2.5 wt% at TiO₂ values of <0.7 wt% consistent with an island arc setting for the ZUC that originated from tholeiitic magmas. The Zvishavane Ultramafic Complex was metamorphosed at relatively high temperatures (542-779 °C) and low pressures (1.2-2kbars), consistent with contact metamorphism. Intrusion of several granitic batholiths relatively close to the ZUC likely triggered hydrothermal fluid migration which metamorphosed the ZUC. The associated asbestos deposits likely formed during hydrothermal circulation events. Zoned amphiboles, the occurrence of magnesiohornblende and actinolite, as well as cross-cutting serpentine veins are consistent with at least two stages of alteration and/or metamorphism of the ZUC. The lack of a thrust contact between the ZUC and its country rocks is consistent with the ZUC having intruded into the host Zvishavane Gneiss Complex and possibly acted as a feeder to the nearby Mberengwa greenstone belt (MGB). However, the occurrence of near end-member forsteritic olivine, the presence of zoned amphiboles, and faulting within the ZUC are all suggestive of an ophiolitic origin although forsteritic olivines also occur in intrusive layered complexes. Metamorphism of the ZUC, ascribed to intrusion of multiple batholiths and possibly the MGB, likely led to the formation of ZUC chrysotile asbestos deposits.  相似文献   

Anatomical Study of Cretaceous, Permineralized, Bennettitalean Fossils from Heilongjiang Province, NE China     

LIU Fengxiang  YANG Xiaonan  CHENG Yeming 《《地质学报》英文版》2022,96(5):1495-1501

Well-preserved Cretaceous trunk fragments of Cycadeoidea (Cycadeoidaceae) were recently found in Keshan County, Heilongjiang Province, Northeast China. These fossils represent important evidence of the distribution of this group of plants in East Asia. In these trunk fragments, the stem cortices and leaf bases with cones are preserved. The leaf bases are rhombic with cones infrequently distributed among leaf bases. The cortex is broad and consists of fundamental parenchyma cells, numerous secretory ducts and C-shaped leaf traces with adaxial secondary xylem and abaxial secondary phloem. The genus Cycadeoidea, which is widely distributed in the Cretaceous deposits of East Asia, North America and Western Europe, was an important component of Cretaceous floras. Bennettitalean trunk fossils with well-preserved anatomical structures are rarely known from China. These fossils are important for studies of the evolution of genus Cycadeoidea and for stratigraphic correlation.  相似文献   

Tooth Plates of Ceratodus (Dipnoi, Ceratodontidae) from the Upper Jurassic Shaximiao Formation of Guang’an, Sichuan Province, China     

WANG Zizheng  JIANG Xinsheng  WANG Xiaobing  GAO Jianguo  ZHU Sibao 《《地质学报》英文版》2022,96(3):766-775

Ceratodus is a form genus of ceratodontid lungfishes. Until now, only 14 specimens have been reported from the Mesozoic of China. Detailed measurements and characteristic comparisons based on 15 well-preserved lungfish tooth plates of Ceratodus type, uncovered from the upper member of the Upper Jurassic Shaximiao Formation at Luojiashan, Qianfeng District, Guang''an, Sichuan Province in 2019, allow us to establish a new species, Ceratodus guanganensis sp. nov., on the basis of its small swollen irregular triangular tooth plate with four low and swollen radial crests on the occlusal surface without denticles. Other specimens from the same locality can be referred to C. szechuanensis and C. youngi. This is the first discovery of Ceratodus in the Guang''an region and represents the fifth Ceratodus fossil site in the Sichuan Basin. The discovery indicates that the climate was hot and arid in the Sichuan Basin during the Late Jurassic, and reveals a tectonic paleogeographic relationship between the Yangtze block in southwestern China and the Kola Basin in northern Thailand.  相似文献   

论江苏东海早白垩世地层     

詹瑜 《江苏地质》2015,39(2):207-210

主要论述了江苏东海南古寨村一带产恐龙足印化石地层的岩石地层归属和地质时代,认为这套地层应归于大盛群,而不宜归于青山群或孟疃组,时代为早白垩世晚期。江苏东海南古寨村一带大量恐龙足印化石的发现不仅填补了江苏不产恐龙化石的空白,而且也为该县增添了新的旅游资源。  相似文献   

Predominance of archaea-derived hydrocarbons in an Early Triassic microbialite     

《Organic Geochemistry》2015

We investigated the distribution of lipids in Lower Triassic sedimentary rocks (252–247 myr) from South China, including a shallow water microbialite in the uppermost section of the outcrop. Archaeal derived hydrocarbons were the major constituents of the microbialite from the latest Early Triassic. Among these, we detected (i) abundant C₄₀ acyclic and monocyclic biphytanes (possibly derived from glycerol dialkyl glycerol tetraether lipids) and their degradation products, C_30–39 pseudohomologues and (ii) a C₂₅ head-to-tail linked (regular) isoprenoid hydrocarbon [possibly derived from dialkyl glycerol diether lipids (DGDs)] and its degradation products, C_21–24 pseudohomologues and abundant pristane and phytane. Through combination of compound-specific stable carbon isotope analysis of isoprenoid hydrocarbons, which had average δ¹³C values of −35‰ to −30‰, and their molecular distribution, it was not possible to unambiguously define the archaeal source for the biphytanes in the microbialite. The δ¹³C values for pristane and phytane were similar to those for head-to-tail linked C_21–25 isoprenoids; potential source organisms for these compounds were halophilic archaea. Except for methane seep microbialites, no other ancient or recent phototrophic microbialites have been reported to contain predominantly archaeal isoprenoid hydrocarbons. Our findings suggest the presence of a new type of microbialite.  相似文献   

Complex rift geometries resulting from inheritance of pre-existing structures: Insights and regional implications from the Barmer Basin rift     

《Journal of Structural Geology》2015

Structural studies of the Barmer Basin in Rajasthan, northwest India, demonstrate the important effect that pre-existing faults can have on the geometries of evolving fault systems at both the outcrop and basin-scale. Outcrop exposures on opposing rift margins reveal two distinct, non-coaxial extensional events. On the eastern rift margin northwest–southeast extension was accommodated on southwest- and west-striking faults that form a complex, zig-zag fault network. On the western rift margin northeast–southwest extension was accommodated on northwest-striking faults that form classical extensional geometries.Combining these outcrop studies with subsurface interpretations demonstrates that northwest–southeast extension preceded northeast–southwest extension. Structures active during the early, previously unrecognised extensional event were variably incorporated into the evolving fault systems during the second. In the study area, an inherited rift-oblique fault transferred extension from the rift margin to a mid-rift fault, rather than linking rift margin fault systems directly. The resultant rift margin accommodation structure has important implications for early sediment routing and depocentre evolution, as well as wider reaching implications for the evolution of the rift basin and West Indian Rift System. The discovery of early rifting in the Barmer Basin supports that extension along the West Indian Rift System was long-lived, multi-event, and likely resulted from far-field plate reorganisations.  相似文献   

Notatudiadema and Aegyptiaris: Two new regular echinoids genera with two new species from the Cenomanian of north Sinai,Egypt     

《Cretaceous Research》2015

Revision of the Cenomanian echinoids deposited in the Cairo Geological Museum resulted in the erection of two new genera with two new species of regular echinoids. The first, Notatudiadema rekeibensis gen. and sp. nov. is established for specimens from the Cenomanian of Gabal El-Rekeib, southeast the Maghara massif, north Sinai to accommodate diadematoid echinoids having hemi-crenulate ambital and sub-ambital interambulacral tubercles with the adapical part of platform non-crenulate and the adoral one of same tubercle coarsely crenulate. The second is Aegyptiaris halalensis gen. and sp. nov., erected for material from the lower Cenomanian of Gabal El-Halal, northeast Sinai as an emiratiid echinoid with throughout polyporus ambulacra and extremely reduced adapical ambulacral tubercles. The functional morphology and paleobiology of these taxa are also discussed. A new family is established: family Monodiadematidae fam. nov.  相似文献   

Rajkanella hottingerinaformis n. gen., n. sp., a new larger benthic foraminifer from the middle-upper Cenomanian of Kosovo     

《Cretaceous Research》2015

A new larger benthic porcelaneous foraminifer of soritid affinity is described as Rajkanella hottingerinaformis n. gen., n. sp. from the middle-upper Cenomanian of Kosovo. It occurs in foraminiferal packstones and grainstones, in association with cuneolinids, rhapidionids, chrysalidinids, and other benthic foraminifers. Due to its general morphology and superficial chamber subdivision by exoskeletal elements, Rajkanella n. gen. can be compared with the early Paleogene genus Hottingerina Drobne, 1975, from which it mainly differs in its apertural features, ornamented test, and coiled adult stage. Further differences to coeval Pseudorhapydionina De Castro, 1971, Pseudorhipidionina De Castro, 1971, and to other comparable genera, are discussed. The discovery of Rajkanella hottingerinaformis in the middle-upper Cenomanian is a further witness of the significant radiation and blooming of increasingly complex porcelaneous foraminifers in inner platform, shallow-water depositional settings during that period.  相似文献   

New U–Pb SHRIMP zircon age for the Schurwedraai alkali granite: Implications for pre-impact development of the Vredefort Dome and extent of Bushveld magmatism,South Africa     

《Journal of African Earth Sciences》2006,44(5):537-548

The Schurwedraai alkali granite is one of a number of prominent ultramafic-mafic and felsic intrusions in the Neoarchaean to Palaeoproterozoic sub-vertical supracrustal collar rocks of the Vredefort Dome, South Africa. The alkali granite intruded the Neoarchaean Witwatersrand Supergroup and has a peralkaline to peraluminous composition. A new zircon SHRIMP crystallization age of 2052 ± 14 Ma for the Schurwedraai alkali granite places it statistically before the Vredefort impact event at 2023 ± 4 Ma and within the accepted emplacement interval of 2050–2060 Ma of the Bushveld magmatic event. The presence of the alkali granite and associated small ultramafic-mafic intrusions in the Vredefort collar rocks extends the southern extremity of Bushveld-related intrusions to some 120 km south of Johannesburg and about 150 km south of the current outcrop area of the Bushveld Complex. The combined effect of these ultramafic-mafic and felsic bodies may have contributed to a pronouncedly steep pre-impact geothermal gradient in the Vredefort area, and to the amphibolite-grade metamorphism observed in the supracrustal collar rocks of the Vredefort Dome.  相似文献