Genetic Mechanism of Dolomitization in Fengcheng Formation in the Wu‐Xia area of Junggar Basin,China     

ZHU Shif  ZHU Xiaomin  NIU Huapeng  HAN Xuefang  ZHANG Yueqian  YOU Xincai 《《地质学报》英文版》2012,86(2):449-461

The dolomitic rocks of the Fengcheng Formation are considered to be formed under special geologic conditions, and are significant hydrocarbon reservoir rocks in the Wu-Xia area in the Junggar Basin. Analyses of petrologic characteristics and stable isotope composition indicate that the dolomitizing host rock is volcanic and the dolomitizing fluids probably consists of brine from shore-shallow lakes with great evaporation and salinity in the Fengcheng Formation, which have formed under arid climatic conditions, as well as residual Mg-rich seawater from the underlying Jiamuhe Formation and Carboniferous. Dust tuff in the area has significant plagioclase content. Anorthite and labradorite hydrolysis by CO2 can be coupled with calcite precipitation. Late Mg-rich brine percolated and replaced calcite formed in the early time, which lead to precipitate dolostones with different occurrences, such as graniphyric, random bedded or lumpy. The diagenetic dolostones with different occurrences resulting from particular formation conditions occurred in different tectonic settings. The dolomitizing fluid has been driven by the thermal convection flow generated by volcanic eruptions. At the same time, the overthrusts of the Wu-Xia growth fault?have speeded up the flow of deep Mg-rich water upwards, and induced the water to quickly?penetrate and horizontally migrate in the strata. Fracture is the major and the most important reservoir space in dolomitic reservoir of the Fengcheng Formation. Fracture and fault plays a decisive role in controlling the formation of dolostone and the distribution of favorable reservoirs. The deliverability of oil and gas is determined by the development and match relations of dissolved pores and fractures to a certain degree.  相似文献   

Late Ordovician island‐arc volcanic rocks,northern Capertee Zone,Lachlan Fold Belt,New South Wales     

P. F. Carr  C. L. Fergusson  J. W. Pemberton  G. P. Colquhoun  S. I. Murray  J. Watkins 《Australian Journal of Earth Sciences》2013,60(3):319-330

The Cape Hoskins volcanoes form part of the Quaternary volcanic island arc that extends from Rabaul in the east to the Schouten Islands in the west, and they overlie the northerly dipping New Britain Benioff Zone. The products of the volcanoes range in composition from basalt to rhyolite, and are normative in quartz and hypersthene. They contain phenocrysts of plagioclase and subordinate augite, hypersthene, and in most samples iron‐titanium oxides; some samples also contain olivine or quartz or both, and some pumice contains hornblende and, rarely, biotite.

Chemical analyses of 29 volcanic rocks are presented; 22 were also analysed for 17 minor elements — Rb, Ba, Sr, Pb, Zn, Cu, Zr, Y, Ni, Co, Sc, Cr, V, Ga, B, U, and Th.

Chemically the rocks have many of the characteristics of the ‘island arc tholeiitic series’, but do not show a pronounced relative enrichment in iron and appear to be relatively enriched in Sr. Compared with volcanic rocks from the northern part of the Willaumez Peninsula, they are lower in K (but not Na), Ti, Rb, Ba, Zr, Pb, Th, Ni, and probably also V, Cu, and Zn: these differences are attributed to the greater depth of the Benioff Zone beneath the Willaumez Peninsula. The more basic of the Cape Hoskins rocks are similar in most respects to lavas of comparable composition from Ulawun volcano to the east.  相似文献   

Kenn Plateau off northeast Australia: a continental fragment in the southwest Pacific jigsaw     

N. F. Exon  P. J. Hill  Y. Lafoy  C. Heine  G. Bernardel 《Australian Journal of Earth Sciences》2013,60(4):541-564

The submarine Kenn Plateau, with an area of about 140 000 km², lies some 400 km east of central Queensland beyond the Marion Plateau. It is one of several thinned continental fragments east of Australia that were once part of Australia, and it originally fitted south of the Marion Plateau and as far south as Brisbane. It is cut into smaller blocks by east- and northeast-trending faults, with thinly sedimented basement highs separated by basins containing several kilometres of sediment. In the Cretaceous precursor of the Kenn Plateau, Late Triassic to Late Cretaceous basins probably rested unconformably on Palaeozoic to Triassic rocks of the New England Fold Belt. Rift volcanism was common on the northern plateau and was probably of Early Cretaceous age. Late Cretaceous extension and breakup were followed by Paleocene drifting, and the Kenn Plateau moved to the northeast, rotated 30° anticlockwise and left space that was filled by Tasman Basin oceanic basalts. During these events, siliciclastic sediments poured into the basins from the continental mainland and from locally eroding highs. After a regional Late Paleocene to Early Eocene unconformity, siliciclastic sedimentation resumed in proximal areas. In deep water, radiolarian chalks were widely deposited until biosiliceous sediment accumulation ended at the regional Late Eocene to Early Oligocene unconformity, and warming surface waters led to accumulation of pure biogenic carbonates. Calcarenite formed in shallow water on the margins of the subsiding plateau from the Middle Eocene onward. Some seismic profiles show Middle to Late Eocene compression related to New Caledonian obduction to the east. Hotspots formed parts of two volcanic chains on or near the plateau as it moved northward: Late Eocene and younger volcanics of the Tasmantid chain in the west, and Late Oligocene and younger volcanics of the Lord Howe chain in the east. As the volcanoes subsided, they were fringed by reefs, some of which have persisted until the present day. Other reefs have not kept up with subsidence, so guyots formed. The plateau has subsided 2000 m or more since breakup and is now subject solely to pelagic carbonate sedimentation.  相似文献   

Geochemical and isotopic evidence for the age,orogenic setting and petrogenesis of the Nychum Volcanic association,North Queensland     

J.C. Bailey  W.R. Morgan  L.P. Black 《Australian Journal of Earth Sciences》2013,60(3-4):375-393

Rb‐Sr and K‐Ar age determinations agree with palaeobotanical evidence in assigning an age of 270 Ma (Lower Permian) to the Nychum Volcanics, North Queensland. Geological and geochemical evidence (moderate ‐REE, La/Yb, Th, Zr/Y, Hf/Yb, Sc/Ni) indicate that the volcanics were erupted on a thin, active continental margin. Five magma groups are present: high‐alumina basalts, andesite‐dacites, acid rocks, tholeiitic andesites, and pitchstone with a high La/Yb ratio. The high‐alumina basalts and calc‐alkaline andesites have a parent‐daughter (source rock‐partial melt) relationship. The acid rocks share high HREE, Zr, Hf, Zn, Sc, Fe/Mg and low Al with, and may be fractionated from, the tholeiitic subduction‐zone andesites. Low‐pressure fractional crystallisation is evident in all five magma groups.  相似文献   

The age and tectonic significance of the Warraweena Volcanics and related rocks,southern Thomson Orogen     

A. C. Hack  R. C. Dwyer  G. Phillips  S. Whalan  H.-Q. Huang 《Australian Journal of Earth Sciences》2013,60(7-8):1071-1096

Abstract

Magmatic-textured zircon from medium- to high-K calc-alkaline Warraweena Volcanics (WV) in two drill holes have yielded concordant U–Pb dates of 417?±?3.5 and 414?±?4.0?Ma and are interpreted as maximum emplacement ages. The Warraweena volcanics were previously considered to be either Neoproterozoic or Macquarie arc equivalents. Whole-rock εNd_t values of these volcanics are +4.5 and +4.8. Along strike of the drill holes, Devonian zircon U–Pb ages (411?±?5.5?Ma) were obtained from coherent S-type rhyolite flows that have highly negative εNd_t values (–7.9 and –7.8). These are a component of the Oxley volcanics. The ages of the Warraweena and Oxley volcanics are identical within uncertainty.

The Oxley volcanics (OV) are interbedded with predominantly fine- to medium-grained metasedimentary and so imply a Lower Devonian deposition age for these host rocks. Based on their geophysical characteristics, the metasediments are widely distributed. These metasedimentary rocks yield a wide range of maximum depositional ages, from Early Devonian to earliest Ordovician–latest Cambrian, similar to the Cobar Basin. The absence of complex fabric development typical of Ordovician supracrustal rocks in the region, and conformity with the OV where observable suggest the widespread sedimentation was synchronous with rift-related volcanism in the Early Devonian.

Regionally, the WV is temporally, geochemically and isotopically (εNd values) similar to the calc-alkaline Louth Volcanics located over 100?km to the southwest of the WV. Louth Volcanics define a complexly folded belt in geophysical data. Other potentially correlative Early Devonian igneous rocks occur in the nearby Cobar Superbasin and elsewhere in the eastern Lachlan Orogen and are considered to represent the products of a post-orogenic, nascent continental back-arc rift system.  相似文献   

Geochronology and geochemistry of the Devonian Gumbardo Formation (Adavale Basin): evidence for cratonisation of the Central Thomson Orogen by the Early Devonian     

P. Asmussen  S. E. Bryan  C. M. Allen  D. J. Purdy 《Australian Journal of Earth Sciences》2013,60(7-8):1133-1159

Abstract

The Devonian subsurface Adavale Basin occupies a central position in the Paleozoic central Thomson Orogen of eastern Australia and records its tectonic setting during this time interval. Here, we have focussed on the basal volcanics of the Gumbardo Formation to clarify the tectonic setting of the basin. The approach has been to undertake stratigraphic logging, LA-ICP-MS U–Pb zircon geochronology and whole-rock geochemical analysis. The data indicate that basin initiation was rapid occurring at ca 401?Ma. The volcanic rocks are dominated by K-feldspar phyric rhyodacitic ignimbrites. The whole-rock geochemical data indicate little evidence for extensive fractional crystallisation, with the volcanic suite resembling the composition of the upper continental crust and exhibiting transitional I- to A-type tectonomagmatic affinities. One new U–Pb zircon age revealed an Early Ordovician emplacement age for a volcanic rock previously interpreted to be part of the Early Devonian Gumbardo Formation, and older basement age is consistent with seismic interpretations of uplifted basement in this region of the western Adavale Basin. Five ignimbrites dated from different stratigraphic levels within the formation yield similar emplacement ages with a pooled weighted age of 398.2?±?1.9?Ma (mean square weighted deviation?=?0.94, n?=?93). Significant zircon inheritance in the volcanic rocks records reworking of Ordovician and Silurian silicic igneous basement from the Thomson Orogen and provides insight into the crustal make-up of the Thomson Orogen. Collectively, the new data presented here suggest the Adavale Basin is a cover-type basin that developed on a stabilised Thomson Orogen after the major Bindian deformation event in the late Silurian.  相似文献   

The Southward Extension of Cathaysia Block: Evidence from Zircon UPb Dates of Borehole Volcanics in the Northern South China Sea   总被引：1，自引：0，他引：1  

XU Changhai  QUE Xiaoming  SHI Hesheng  ZHOU Zuyi  MA Changqian 《《地质学报》英文版》2013,87(5):1370-1386

Five Paleogene volcanics sampled from the northern South China Sea were analyzed via LA-ICP-MS zircon U-Pb dating,including basalt and andesite from Borehole SCSV1 and volcanic agglomerate from Borehole SCSV2,respectively.A total of 162 zircon U-Pb dates for them cover an age range from Neoarchean to Eocene,in which the pre-Paleocene data dominate.The Paleogene dates of 62.5±2.2 Ma and 42.1±2.9 Ma are associated with two igneous episodes prior to opening of South China Sea basin.Those pre-Paleocene zircons are inherited zircons mostly with magmatogenic oscillatory zones,and have REE features of crustal zircon.Zircon U-Pb dates of 2518–2481 Ma,1933– 1724 Ma,and 1094–1040 Ma from the SCSV1 volcanics,and 2810–2718 Ma,2458–2421 Ma,and 1850 –993.4 Ma from the SCSV2 volcanics reveal part of Precambrian evolution of the northern South China Sea,well comparable with age records dated from the Cathaysia block.The data of 927.0±6.9 Ma and 781±38 Ma dated from the SCSV2 coincide with amalgamation between Yangtze and Cathaysia blocks and breakup of the Rodinia,respectively.The age records of Caledonian orogeny from the Cathaysia block are widely found from our volcanic samples with concordant mean ages of 432.0±5.8 Ma from the SCSV1 and of 437±15 Ma from the SCSV2.The part of the northern South China Sea resembling the Cathaysia underwent Indosinian and Yanshannian tectonothermal events.Their age signatures from the SCSV1 cover 266.5±3.5 Ma,241.1±6.0 Ma,184.0±4.2 Ma,160.9±4.2 Ma and 102.8±2.6 Ma,and from the SCSV2 are 244±15 Ma,158.1±3.5 Ma,141±13 Ma and 96.3±2.1 Ma.Our pre-Paleogene U-Pb age spectra of zircons from the borehole volcanics indicate that the northern South China Sea underwent an evolution from formation of Precambrian basement,Caledonian orogeny,and Indosinian orogeny to Yanshannian magmatism.This process can be well comparable with the tectonic evolution of South China,largely supporting the areas of the northern South China Sea as part of southward extension of the Cathaysia.  相似文献   

Interpretation of Magnetic Anomalies and Estimation of Depth of Magnetic Crust in Slovakia     

Kamil Rozimant  Aydin Büyüksaraç  Özcan Bektaş 《Pure and Applied Geophysics》2009,166(3):471-484

The magnetic map of Slovakia used in the paper was compiled as part of a project titled Atlas of Geophysical maps and profiles in 2001. The residual magnetic data were analyzed to produce Curie point estimates. To remove distortion of magnetic anomalies caused by the Earth’s magnetic field, reduction to pole transformation was applied to the magnetic anomalies using the magnetization angle of the induced magnetization. Anomalies reduced to the pole tend to be better correlated with tectonic structures. We applied a 3-km upward continuation to the residually compiled magnetic anomalies in order to remove effects of topography. The depth of magnetic dipoles was calculated by an azimuthally averaged power spectrum method for the entire area. Such estimates can be indicative of temperatures in the crust, since magnetic minerals lose their spontaneous magnetization according to Curie temperature of the dominant magnetic minerals in the rocks. The computed Curie point depths in the Slovakia region vary between 15.2 km and 20.9 km. Heat flow higher than 100 mWm⁻² occurs at the central volcanics and eastern part of Slovakia, where the Curie point depths values are shallow. The correlation between Curie point depths, heat flow and crust depth was investigated for two E-W cross sections. Heat flow and Curie point depth values are correlated with each other however, these values could not be correlated with crust depth. The Curie point isotherm, which separates magnetic and non-magnetic parts of the crust, is represented in two cross sections.  相似文献   

昆仑-黄河运动的时代下限:来自塔里木盆地南缘西域砾岩顶部火山岩~(40)Ar/~(39)Ar定年的约束     

黎敦朋  赵越  王瑜  刘健  潘燕兵 《大地构造与成矿学》2017,41(6)

"昆仑-黄河运动"是发生在早、中更新世之交的一次强烈的构造运动,它使青藏高原现代构造地貌格局基本定型。以往对昆仑-黄河运动时限的研究,主要由黄河干流发育的阶地、昆仑山垭口地区羌塘组与望昆冰碛层等古地磁、ESR、TL等分析测试得出,缺少其他年代学约束。在塔里木盆地,昆仑-黄河运动表现为西域砾岩与乌苏群之间的角度不整合接触。本文通过对塔里木盆地南缘西域砾岩顶部的普鲁上层火山岩4个样品的全岩~(40)Ar/~(39)Ar定年,获得~(40)Ar/~(39)Ar坪年龄为1.03±0.05 Ma~1.20±0.05 Ma,加权平均年龄为1.1±0.1 Ma(n=4,MSWD=2.3)。这是首次应用~(40)Ar/~(39)Ar定年方法,获得昆仑-黄河运动的时代下限为1.1±0.1 Ma,与前人确定的昆仑-黄河运动时代下限在误差范围内一致,为我国西部新构造运动提供了重要的年代学约束。  相似文献   

Elemental composition and mineralogical characteristics of coastal marine sediments of Tutuila, American Samoa     

R.J. Morrison  P.J. Peshut 《Marine pollution bulletin》2010,60(6):925-930

Surface sediment samples were collected from 5 pristine coastal areas and 1 potentially contaminated coastal site on Tutuila, the main island of American Samoa, an isolated island group in the South Pacific Ocean. Samples were analysed for total element analysis (15 elements) and mineralogy. The results indicated no evidence of trace element contamination at any site, including Pago Pago Harbour. Inter-site variations could be explained assuming the sediments consisted predominantly of coralline sand and rubble with varying quantities of basaltic materials derived from local catchments.  相似文献