云南思茅盆地江城上白垩统勐野井组稀土微量元素特征及地质意义

沉积盆地中碎屑岩的地球化学成分主要受物源区控制,因此,通过分析碎屑岩的化学成分可以揭示盆地沉积岩的源区构造背景和物源属性。思茅盆地上白垩统勐野井组（K2me）细碎屑岩的稀土元素组成分析结果表明,研究区沉积物具有轻稀土元素富集,较平坦的重稀土元素分布模式,以及中等程度 Eu 负异常的总体特征。根据样品的（Hf-La/Th、La/Sc-Co/Th和REE-La/Yb）图解,特征性微量元素比值（La/Sc、Sc/Th、Cr/Th 和 Co/Th）,并结合岩矿薄片分析,认为勐野井组细碎屑岩具有典型的上陆壳特征,源区母岩以长英质岩石为主。微量元素 Cr/Co 结合岩相古地理的分析显示勐野井组细碎屑沉积物应属于近源沉积。通过与不同构造背景下杂砂岩的稀土元素特征对比及主元素（K2O/Na2O-SiO2/Al2O3和SiO2-K2O/Na2O）判别图解,勐野井组细碎屑岩源区构造背景应属被动大陆边缘环境,这与思茅盆地所处的三江造山带构造背景相符。     

Evolution in the provenance of a tectonically controlled Plio–Pleistocene alluvial system between the Variscan Iberian Massif and the Atlantic margin, Portugal

Geochemical and mineralogical data from a Pliocene to Pleistocene alluvial sequence are integrated to access the factors that control rare earth elements (REE) geochemistry and the evolution and spatial differences in provenance. The studied alluvial system is situated in a tectonic active setting at the contact between the Variscan Massif, with several Paleozoic and Precambrian units that support a coastal range, and the Atlantic margin. REE and HREE abundances are generally higher in swamp-lake than in floodplain sediments. The majority of the REE in floodplain sediments is hosted by Y and Th-bearing minerals and illite; in swamp-lake sediments is also probable an association with organic matter. The high Gd/Yb, Eu/Eu* and kaolinite content in older sediments suggest that during the earlier phases provenance was mainly from the hinterland (weathered granitic rocks and its sediment cover). The subsequent illite (Mg-rich) clay assemblages and REE patterns indicate mainly lateral input from the eastern basin edge (Palaeozoic and Precambrian metapelitic rocks). These sediments tend to have lower Gd/Yb and La/Sm than their source rocks. The analysis of the chemical index of alteration (CIA) indicates that although a north-directed fluvial axis existed at that time the “mature” basin edge units found to the south (Silurian) had a limited role in supplying sediments. This shift in provenance is attributed to the uplift of the coastal range. Afterwards, the contribution of recycled Cretaceous and Cenozoic sedimentary units increased progressively. This is demonstrated by the increase is SiO₂/TiO₂, CIA and kaolinite/illite when the climatic conditions are expected to have become less chemically aggressive.     

Anomalous lead isotope ratios and provenance of offshore sediments,Gulf of Carpentaria,northern Australia

Anomalous Pb isotope ratios measured by Inductively Coupled Plasma Mass Spectrometry in terrigenous marine sediments (<63 μm fraction) from the Gulf of Carpentaria originated from depositional mixing of clay/silt with average modern crustal Pb isotope ratios and detrital monazite with high ²⁰⁸Pb/²⁰⁶Pb and low ²⁰⁷Pb/²⁰⁶Pb. This interpretation is supported by strong correlations between Pb isotope ratio and Th, U and light rare‐earth element concentrations in the sediments as well as by monazite compositional data. A likely source of the detrital monazite is the western portion of the Georgetown Inlier of mainly Proterozoic S‐type granitic rocks. A clear distinction between Pb isotope ratios in sediments deposited from the Norman and Bynoe Rivers in the southeast Gulf of Carpentaria and the persistence of catchment‐specific Pb isotope ratios 45 km offshore suggest that Pb isotope data are useful in tracing the provenance of terrigenous offshore sediments when the source rocks of catchments show sufficient chemical and/or mineralogical variation.     

Sources of stream sediments in the granulite terrain of the Walawe Ganga Basin,Sri Lanka,indicated by rare earth element geochemistry

Thirty-eight samples of stream sediments draining high-grade metamorphic rocks in the Walawe Ganga (river) Basin, Sri Lanka, were analysed for their REE contents, together with samples of metamorphic suites from the source region. The metamorphic rocks are enriched in light REE (LREE) compared to heavy REE (HREE) and are characterised by high La/Lu ratios and negative Eu anomalies. The chondrite-normalised patterns for these granulite-grade rocks are similar to that of the average post-Archaean upper crust, but they are slightly enriched with La and Ce. The REE contents of the <63-μm fraction of the stream sediments are similar to the probable source rocks, but the other grain size fractions show more enriched patterns. The <63-μm stream sediments fraction contains lower total REE, more pronouncd negative Eu anomalies, higher Eu_N/Sm_N and lower La _N/Lu_N ratios relative to other fractions. The lower La _N/Lu_N ratio is related to the depletion of heavy minerals in the <63-μm fraction. The 63–125-μm and 125–177-μm grain size fractions of sediments are particularly enriched in LREE (average ΣLREE=2990 μg/g and 3410 μg/g, respectively). The total HREE contents are surprisingly uniform in all size fractions. However, the REE contents in the Walawe Ganga sediments are not comparable with those of the granulite-grade rocks from the source region of the sediments. The enrichment of REE is accounted for by the presence of REE containing accessory mineral phases such as zircon, monazite, apatite and garnet. These minerals are derived from an unknown source, presumably from scattered bodies of granitic pegmatites.     

Secular variations of the upper crust composition: Implication of geochemical data on the Upper Precambrian shales from the Southern Urals western flank and Uchur-Maya region

In the mid-1980s, it was concluded based on geochemical study that Th, Sc, La concentrations and ratios Th/Sc, La/Sc and Eu/Eu* did not wary significantly in the post-Archean time. It was impossible to judge about compositional variations of upper crust during the Riphean and Vendian, because data of that time characterized a limited number of samples from the post-Archean basins of Australia, New Zealand, and Antarctic. Considered in this work are variations of Eu/Eu*, LREE/HREE, Th/Sc, and La/Sc ratios in Upper Precambrian fine-grained siliciclastic rock of the Southern Urals western flank (Bashkirian meganticlinorium) and Uchur-Maya region (Uchur-Maya plate and Yudoma-Maya belt). As is established, only the Eu anomaly in the studied siliciclastic rocks is practically identical to this parameter of the average post-Archean shale. Three other parameters plot on the Riphean-Vendian variation curves with positive and negative excursions of diverse magnitude, which do not coincide always in time. It is assumed that these excursions likely mark stages of local geodynamic activity, destruction of pre-Riphean cratons, and progressing recycling of sedimentary material during the Riphean.     

松辽盆地钱家店地区姚家组赋矿砂岩的组成、地球化学特征及其构造背景

松辽盆地钱家店地区姚家组砂岩矿物、地球化学成分与源区岩石性质和沉积构造环境密切相关。岩相学观察和矿物化学分析表明,所研究的岩石主要碎屑矿物由石英、岩屑和长石组成,含少量的黄铁矿、炭屑和重矿物等矿物。地球化学特征上,这些岩石普遍具有高SiO2含量(68.4%~79.61%)、相对高的K2O/Na2O比值(1.83~2.03)和较低的Fe2O3T+MgO含量(1.48%~4.22%),稀土元素标准化配分曲线呈现轻稀土富集,重稀土平坦和弱Eu、Ce负异常特征。较低的CIA(57~63)和PIA(60~71)指数、A-CN-K以及AK-C-N分布模式还说明源区经历了相对较弱的风化作用。Zr/Sc和Th/Sc比值共同表明姚家组的碎屑组成不具备沉积再旋回的特征,说明其为近源沉积,具有较差的分选性。砂岩物源区组成判别图研究表明,姚家组砂岩的物源区主要出露长英质岩浆岩。砂岩形成构造环境判别图解及特征指数分析表明,姚家组主要形成于被动大陆边缘沉积环境。     

Behavior of accessory phases and redistribution of Zr,REE, Y,Th, and U during metamorphism and partial melting of metapelites in the lower crust: an example from the Kinzigite Formation of Ivrea-Verbano,NW Italy

This study is aimed at understanding the behavior of monazite, xenotime, apatite and zircon, and the redistribution of Zr, REE, Y, Th, and U among melt, rock-forming and accessory phases in a prograde metamorphic sequence, the Kinzigite Formation of Ivrea-Verbano, NW Italy, that may represent a section from the middle to lower continental crust. Metamorphism ranges from middle amphibolite to granulite facies and metapelites show evidence of intense partial melting and melt extraction. The appearance of melt controls the grain size, fraction of inclusions and redistribution of REE, Y, Th, and U among accessories and major minerals. The textural evolution of zircon and monazite follows, in general, the model of Watson et al. (1989). Apatite is extracted from the system dissolved into partial melts. Xenotime is consumed in garnet-forming reactions and is the first source for the elevated Y and HREE contents of garnet. Once xenotime is exhausted, monazite, apatite, zircon, K-feldspar, and plagioclase are progressively depleted in Y, HREE, and MREE as the modal abundance of garnet increases. Monazite is severely affected by two retrograde reactions, which may have consequences for U-Pb dating of this mineral. Granulite-grade metapelites (stronalites) are significantly richer in Ti, Al, Fe, Mg, Sc, V, Cr, Zn, Y, and HREE, and poorer in Li, Na, K, Rb, Cs, Tl, U, and P, but have roughly the same average concentration of Cu, Sr, Pb, Zr, Ba, LREE, and Th as amphibolite-grade metapelites (kinzigites). The kinzigite-stronalite transition is marked by the sudden change of Th/U from 5–6 to 14–15, the progressive increase of Nb/Ta, and the decoupling of Ho from Y. Leucosomes were saturated in zircon, apatite, and (except at the lowest degree of partial melting) monazite. Their REE patterns, especially the magnitude of the Eu anomaly, depend on the relative proportion of feldspars and monazite incorporated into the melt. The presence of monazite in the source causes an excellent correlation of LREE and Th, with nearly constant Nd/Th ≈ 2.5–3. The U depletion and increase in Th/U characteristic of granulite facies only happens in monazite-bearing rocks. It is attributed to enhancement of the U partitioning in the melt due to elevated Cl activity followed by the release of a Cl-rich F-poor aqueous fluid at the end of the crystallization of leucosomes. Halide activity in partial melts was buffered by monazite and apatite. Since the U (and K) depletion does not substantially affect the heat-production of metapelites, and mafic granulites maintain similar Th/U and abundance of U and Th as their unmetamorphosed equivalents, it seems that geochemical changes associated to granulitization have only a minor influence on heat-production in the lower crust.     

Geochemistry of clastic sediments from Sargur supracrustals and Bababudan group,Karnataka: Implications on Archaean Proterozoic Boundary

The sediments from three stratigraphic levels in the Bababudan schist belt of Dharwar craton exhibit great diversity in major, trace and rare earth element (REE) geochemistry and thus interpreted to represent significant compositional variation in the source rocks. Detailed geological and geochemical studies have been carried out on clastic rocks constituting the Archaean Sargur supracrustals and the Bababudan belt of Dharwar craton (DC), southern India for understanding the geochemical characteristics and to define the Archaean-Proterozoic Boundary (APB/QPC) in southern India. There is significant contrast in the geochemical signatures for the sediments from these stratigraphic levles. The Sargur enclave population is characterised by slight LREE enrichment with (La/Sm)_N ranging from 1.45 to 3.58, almost flat HREE with (Gd/Yb)_N ranging from 0.65 to 1.29 with Eu/Eu* ranging from 0.49 to 0.91 suggesting mafic-ultramafic source rocks in the provenance. On the other hand, the Post QPC (PQPC) rocks are characterised by LREE enrichment with (La/Sm)_N ranging from 2.66 to 7.07, nearly flat HREE with (Gd/Yb)_N ranging from 0.58 to 0.95 and significant depletion of Eu with Eu/Eu* ranging from 0.34 to 0.85, indicating felsic province in the source area. The conglomerates and quartzites representing the QPC are showing mixed nature of these, reflecting the transitional character in depositional environment. Increase in abundance of REE, K₂O/Na₂O, Th/Sc, La/Sc, Th/U, Hf/Ta and Zr/Y ratios are characteristic of the QPC. The PQPC sediments are enriched in Th, U and HFSE like Hf, Nb, Zr and Y, and depleted in Co and Eu than their older counterparts. These geochemical signatures signify the dominance of mafic-ultramafic rocks in the source area for Sargur rocks and the existence of granite-granodiorite for PQPC clastics. Thus, the unconformity related oligomictic quartz pebble conglomerates (QPC) and quartzites at the base of Bababudan Group resembling the QPC of Witswaterand, South Africa signifies that a stable continental crust had already developed in southern India prior to ∼3.0Ga.     

Trace elements and REE fractionation in subsoils developed on sedimentary and volcanic rocks: case study of the Mt. Vulture area,southern Italy

There is an increasing interest in the distribution of rare earth elements (REEs) within soils, primarily as these elements can be used to identify pedogenetic processes and because soils may be future sources for REE extraction, despite much attention should be paid to the protection and preservation of present soils. Here, we evaluate the processes that control the distribution of REEs in subsoil horizons developed over differing lithologies in an area of low anthropogenic contamination, allowing estimates of the importance of source rocks and weathering. Specifically, this study presents new data on the distribution of REEs and other trace elements, including transition and high-field-strength elements, in subsoils developed on both Quaternary silica-undersaturated volcanic rocks and Pliocene siliciclastic sedimentary rocks within the Mt. Vulture area of the southern Apennines in Italy. The subsoils in the Mt. Vulture area formed during moderate weathering (as classified using the chemical index of alteration) and contain an assemblage of secondary minerals that is dominated by trioctahedral illite with minor vermiculite. The REEs, high-field-strength elements, and transition metals have higher abundances in subsoils that developed from volcanic rocks, and pedogenesis caused the Mt. Vulture subsoils to have REE concentrations that are an order of magnitude higher than typical values for the upper continental crust. This result indicates that the distribution of REEs in soils is a valuable tool for mineral exploration. A statistical analysis of inter-elemental relationships indicates that REEs are concentrated in clay-rich fractions that also contain significant amounts of low-solubility elements such as Zr and Th, regardless of the parent rock. This suggests that low-solubility refractory minerals, such as zircon, play a significant role in controlling the distribution of REEs in soils. The values of (La/Yb)_N and (Gd/Yb)_N fractionation indices are dependent on the intensity of pedogenesis; soils in the study area have values that are higher than typical upper continental crust ratios, suggesting that soils, especially those that formed during interaction with near neutral to acidic organic-rich surface waters, may represent an important source of both light REEs and medium REEs (MREEs). In comparison, MREE/heavy REE fractionation in soils that form during moderate weathering may be affected by variations in parent rock lithologies, primarily as MREE-hosting minerals, such as pyroxenes, may control (La/Sm)_N index values. Eu anomalies are thought to be the most effective provenance index for sediments, although the anomalies within the soils studied here are not related to the alteration of primary minerals, including feldspars, to clay phases. In some cases, Eu/Eu* values may have a weak correlation with elements hosted by heavy minerals, such as Zr; this indicates that the influence of mechanical sorting of clastic particles during sedimentary transport on the Eu/Eu* values of siliciclastic sediments needs to be considered carefully.     

Geochemical signature of provenance in sand-size material in soils and stream sediments near the Tobacco Root batholith, Montana, U.S.A.

Trace-element geochemistry of sandstones are being used to determine provenance. We have conducted preliminary and limited experiments to determine to what extent daughter sands retain the geochemical signature of parent rocks. Six sets of first-order stream sediments, soils from adjacent slopes, and a variety of parent rocks were collected from southwestern Montana, U.S.A. Sampling in a low-relief area ensured that climate and residence time of soils on slopes could be eliminated as variables. Sand-size fractions of stream sediments and soils, and the corresponding parent rocks (granodiorite, quartz monzonite, granite gneiss, biotite-tonalite gneiss and amphibolite) were analyzed for most major elements and selected trace elements. Petrologic modal analysis of the parent rocks and the 0.25–0.50-mm fraction of each sand was done to monitor major mineralogic control, if any, on chemical compositions of the samples.

Our data show that the abundances of the Si and Al in sediments do not discriminate provenance. Abundances of Ca, Mg, Fe and Ti may broadly distinguish between sands derived from metamorphic and igneous source rocks, at least in the area studied. Differences in abundances of the Ba and Th, and the ratio of La/Lu between granitic, tonalitic and amphibolitic parent rocks are preserved in the daughter sediments that we studied. However, the size of the Eu anomaly in the REE patterns of different daughter sediments is not diagnostic of parent rocks. Abundances of Co and Sc distinguish between sediments derived from felsic and mafic rocks. A better provenance discrimination is obtained if the ratios La/Sc, Th/Sc, La/Co, Ba/Sc and Ba/Co are used.

Petrologic modal data show that mineral contents and chemical compositions of parent rocks are compatible with each other. The chemical composition of the sands may be roughly correlated to the petrological modal data but the abundances of some minor and trace elements of sediments cannot be inferred from modal mineralogy. This is expected because these elements may concentrate in accessory minerals and/or may weather out into aqueous or clay mineral fractions; it is also compatible with conclusions of previous studies that some of these elements do not reside in sand-size fractions of siliciclastic sediments.     

北部湾东部海域表层沉积物稀土元素组成及物源指示意义

对北部湾东部海域70个表层沉积物样品的稀土元素(REE)分析结果表明,研究区沉积物 REE 呈现轻稀土元素(LREE)富集、重稀土元素(HREE)平坦以及中等程度的 Eu 异常等特征.REE 组成受沉积物粒度和生物碳酸盐含量的制约,具有典型风化上陆壳 REE 特征,其源岩以上陆壳的长英质岩石为主.根据研究区沉积物 REE 分布规律,研究区可划分为4个地球化学分区,各区域上陆壳标准化曲线明显的不同.物源判别显示研究区的西部、海南岛西南侧(Ⅰ区)呈多源沉积特征,来自以下几个物源区:(1)海南岛西南侧河流沉积物和沿岸侵蚀物;(2)由南向北输入的外海沉积物(冬季);(3)夏季或冬季由北部湾西北部和西部搬运来的沉积物.研究区中部粗粒沉积区(Ⅱ区)与北部湾西部沉积物来源是相同的,主要来源于红河输砂.东北部砂质区(Ⅲ区)沉积物可能来源于雷州半岛西北部近岸基岩侵蚀.研究区东北部(Ⅳ区)沉积物主要来自北部湾北部沿岸侵蚀、琼州海峡和雷州半岛西部的沿岸侵蚀.此外,部分沉积物还可能来自珠江流域以及南海北部陆架区和北部湾西北部     

REE geochemistry of the recent playa sediments from the Thar Desert, India: An implication to playa sediment provenance

The playas (saline lakes) situated in the Thar Desert, north-west India, provide prominent examples of alkaline brine and varying assemblages of detrital and evaporite mineralogy. The eastern margin of the desert is relatively semi-arid, whereas the central to western region is arid to hyper-arid in nature. Rare earth elements (REEs) systematics in the sediments of nine different playas of the Thar Desert were studied to understand the provenance of the sediments and the intensity of chemical weathering in the region. Based on the REE patterns, fractionation of light REE (LREE) (La/Sm)_N and heavy REE (HREE) (Gd/Yb)_N, and Eu anomaly (Eu/Eu*), the upper continental crust normalised playa sediments are divided into two different groups. The eastern margin playa sediments show homogeneous REE contents, relatively positive Eu anomaly and depleted HREE values, whereas the western arid core playa sediments have highly variable REE contents, relatively negative Eu anomaly and similarly fractioned LREE and HREE patterns. The dissimilarity in the degree of HREE fractionations both in the eastern and western playa sediments is attributed to the differential distribution of minerals, depending upon their resistance to chemical weathering. It is believed that the relatively higher abundance of REE bearing heavy minerals and the presence of higher amounts of evaporites influence the large variation of REE distribution and enriched HREE in the western playa sediments. Apart from the relatively higher abundance of heavy minerals, the presence of rock fragments of variable petrographic character and roundness mirror the lower rock–water interaction in the arid western region. The presence of well-rounded metamorphic rock fragments and minerals, sourced from the eastern margin Aravalli mountains, indicates that the playas of the entire desert get the detrital and dissolved material mainly from the Aravalli mountains. Additionally, the western playas receive sediments from their surrounding Proterozoic and Mesozoic formations. This interpretation is supported by the presence of angular rock fragments of basalt, rhyolite and limestone in the western playas.     

Provenance,tectonic setting and source-area weathering of the lower Cambrian sediments of the Parahio valley in the Spiti basin,India

The geochemical study of siliciclastic rocks from the Lower Cambrian of Parahio Valley has been studied to describe the provenance, chemical weathering and tectonic setting. The K₂O/Al₂O₃ ratio and positive correlation of Co (r=0.85), Ni (r=0.86), Zn (r=0.82), Rb (r=0.98) with K₂O reflects that the presence of clay minerals control the abundances of these elements and suggests a warm and humid climate for this region. The chondrite normalized REE pattern of the samples is equivalent to upper continental crust, which reflects enriched LREE and flat HREE with negative Eu anomaly. The tectonic setting discriminant diagram log[K₂O/Na₂O] vs. SiO₂; [SiO₂/Al₂O₃] vs. log[K₂O/Na₂O]; [SiO₂/20] – [K₂O+Na₂O] – [TiO₂+Fe₂O₃+MgO] indicates transitional tectonic setting from an active continental margin to a passive margin. The discriminant function plot indicates quartzose sedimentary provenance, and to some extent, the felsic igneous provenance, derived from weathered granite, gneissic terrain and/or from pre-existing sedimentary terrain. The CIA value indicates low to moderate degree of chemical weathering and the average ICV values suggests immature sediments deposited in tectonically active settings. The A–CN–K diagram indicates that these sediments were generated from source rocks of the upper continental crust.     

北京平原沉积物稀土元素地球化学特征及物源意义

文中总结了北京平原永定河、潮白河流域钻孔沉积物中稀土元素分布特征,两流域沉积物稀土元素总量∑REE、轻重稀土比(LREE/HREE)及轻(La/Sm)N、重(Gd/Yb)N稀土分馏特征差异较为显著。粒度对沉积物稀土分布(总量、轻重稀土比及分馏特征)有一定影响;各流域沉积物均表现为轻稀土相对富集、弱Eu负异常的球粒陨石标准化曲线。细颗粒沉积物稀土分馏特征(La/Yb)N有较好的物源示踪意义。根据沉积物(La/Yb)N值对永定河、潮白河交互沉积区不同深度沉积物进行了物源示踪,不同深度上沉积物来源不同。此外,同一流域上、中、下游沉积物稀土分馏特征不同。常量元素Al2O3/Fe2O3与稀土元素(La/Yb)N划分结果相符,但精度低于稀土元素物源分析。     

Implications of geochemistry in support of Palaeo-Proterozoic tectonothermal evolution of bhopalpatnam Granulite Belt, Bastar Craton, Central India

Bhopalpatnam Granulite Belt which occur along SW margin of Bastar Craton and NE shoulder of Pranhita-Godavari Rift comprise of charnockite (enderbitic variety), garnet-sillimanite-biotite gneiss, quartzo-feldspathic gneiss and corundum bearing aluminous gneiss. High La/Yb ratio, low Eu anomaly (Eu/Eu*=1.0), high LREE/HREE ratio with uniform REE pattern, high La/Sc ratio (0.53–6.43), high Th/Sc ratio (0.03–2.56), low Ni (5.52–20.95), low Cr (31.05–117.05) and uniform Zr/Hf distribution pattern indicate a Proterozoic character. Distribution pattern of K₂O, Na₂O and CaO in ternary diagram show quartz-monzonite-granodiorite trend for the bulk rocks indicating that the bulk rock composition is close to TTG of early Archaean, which might have supplied the sediments for the rocks of Bhopalpatnam Granulite Belt. Geochemical and mineralogical evidence indicate an argillaceous protolith for garnet — sillimanite — biotite gneiss and corundum bearing aluminous gneiss, whereas an arkosic protolith for quartzo-feldspathic gneiss. The geochemical signatures also suggest an active continental margin setting for the rocks of Bhopalpatnam Granulite Belt with prominent Nb and Ta anomaly favouring a subduction environment between Bastar Craton and East Dharwar Craton. This is in conformity with the finding of the earlier workers suggesting a clockwise P-T path based on the combined fluid inclusion and mineral phase equilibria. The LILE geochemistry of charnockite suggests a bi-phase evolution. High LREE/HREE ratio portrays a highly evolved nature of the charnockitic melt generated through partial melting of the continental crust at the final stage of the granulite facies metamorphism during collision between Bastar and East Dharwar Cratons.     

Provenance and tectonic setting of the metapelites deposits in the Bulfat Complex,NE-Iraq

Major and trace elements including rare earth elements (REEs) chemistry of the metapelitic rocks of Bulfat Complex (Iraqi Zagros Suture Zone) indicate their enrichment in large-ion Lithophile, light rare earth (LREE) elements, and relative depletion of high field strength and heavy rare earth (HREE) elements. The linear correlation coefficients between TiO₂, K₂O, and Al₂O₃ and total REE reveal that phyllosilicates (e.g., mica) and accessory minerals mainly Ti-bearing phases (e.g., ilmenite) are likely the dominant hosts for REEs. Chondrite-normalized REE patterns typical of continental margin settings with significant enrichment of LREE, prominent negative Eu anomalies, and nearly flat HREE are positively correlated with post-Archean Australian shale (PAAS) and upper continental crust (UCC) patterns. Additionally, their consistent elemental La/Sc, Th/Sc, La/Co, Th/Co, Cr/Th, and Eu/Eu* values suggest that sediments may have been originally derived from an old post-Archean upper continental crust composed chiefly of granitic component. It seems most likely that the felsic source rocks were originated by a process of intra-crustal differentiation such as partial melting and/or fractional crystallization involving fractionation of Ca-plagioclase. The geochemical evidences particularly REEs evaluation show that deposition of clasts occurred in an active continental margin setting during lower–upper Cretaceous period contemporaneous with the igneous activities. It is evident therefore that the clasts source is from the north–northeast side, i.e., from the active margin of Iranian microcontinent (Sanandaj–Sirjan Zone).     

广西南部凭祥中三叠世沉积盆地构造环境——来自岩相学和碎屑岩地球化学的证据

岩相学特征表明,广西凭祥盆地砾岩可分为颗粒支撑和基质支撑2种,砾石成分主要为生物碎屑灰岩,其次为砂岩和泥岩。盆地砂岩主要由成分成熟度和结构成熟度较低的亚岩屑(杂)砂岩和岩屑(杂)砂岩组成,物源区为碰撞造山带或再旋回造山带。碎屑岩地球化学特征表明,凭祥中三叠世盆地中的砂岩和泥岩样品SiO2含量为61.71%~74.85%,接近于上地壳的平均值。具有高的K2O/Na2O值(6.50~0.51)和高的TFe2O3+MgO含量(7.29%~10.31%),TFe2O3/K2O值为2.05%~5.54%,矿物稳定性较差。稀土元素标准化配分曲线呈现出轻稀土元素富集、重稀土元素平坦和明显的Eu、Ce负异常特征,类似于上地壳和典型的太古宙页岩,具有海相沉积的特征。砂岩风化蚀变指数CIA高(71~88),Th/U值为3.68~9.53,表明砂岩和泥岩经历了较强的风化作用。砂岩物源区判别图表明,凭祥盆地物源与酸性岛弧具明显的亲缘性,增生楔和活动陆缘是主要的物源区。这些特征综合表明,凭祥盆地是一个伴随古特提斯分支洋盆闭合、经强烈构造改造的残余弧前盆地。     

Geochemistry and Provenance of Maastrichtian Clastic Rocks in the Dikmendede Formation of Orhaniye in Kazan-Ankara-Turkey Region

An integrated petrographic and geochemical study of the sandstones of the Maastrichtian-aged in the Orhaniye (Kazan-Ankara-Turkey) was carried out to obtain more information on their provenance, sedimentological history and tectonic setting. Depending on their matrix and mineralogical content, the Maastrichtian sandstones are identified as lithic arenite/wacke. The Dikmendede sandstones derived from types of provenances, the recycled orogen and recycled transitional. The chemical characteristics of the Dikmendede sandstones, i.e., fairly uniform compositions, high Th/U ratios (>3.0), negative Eu anomalies (Eu/Eu* 0.72–0.99) and Th/Sc ratios (mostly less than 1.0), favor the OUC (old upper continental crust) provenance for the Dikmendede sandstones. The SiO2/Al2O3, Th/Sc (mostly <1.0) and La/Sc (<4.0) ratios are; however, slightly lower than typical OUC, and these ratios may suggest a minor contribution of young arc-derived material. The rare earth element (REE) pattern, and La/Sc versus Th/Co plot suggests that these sediments were mainly derived from felsic source rocks. The Dikmendede sandstones have high Cr (123–294 ppm) and Ni (52–212 ppm) concentrations, Cr/Ni ratio of 1.93, and a medium correlation coefficient between Cr and Ni and corresponding medium to high correlation of both (Cr and Ni, respectively) elements with Co. These relationships indicate a significant contribution of detritus from ophiolitic rocks. As rare earth element data are available for the Dikmendede sandstones, the Eu/Eu* is compared with LaN/YbN. Samples plot in the area of overlapping between continental collision, strike-slip and continental arc basins. The predominantly felsic composition of the Dikmendede sandstones is supported by the REE plots, which show enriched light REE, negative Eu anomaly and flat or uniform heavy REE. The Dikmendede sandstones have compositions similar to those of the average upper continental crust and post-Archean Australian shales. This feature indicates that the sediments were derived mainly from the upper continental crust. The Dikmendede sandstones have chemical index of alteration (CIA) values of 28–49, with an average of 40 indicating a low degree of chemical weathering in the source area. The compositional immaturity of the analyzed sandstone samples is typical of subduction-related environments, and their SiO2/Al2O3 and K2O/Na2O ratios and Co, Sc, Th and Zr contents reflect their oceanic and continental-arc settings. The Dikmendede sandstones were developed as flysch deposits derived from mixed provenance in a collision belt.     

Zr, Hf, U, Th and REE-Fertile Lower Proterozoic Potassic Granite from Parts of Andhra Pradesh, South India

The medium- to coarse-grained and porphyritic granitoid of Dharmawaram, Karimnagar district, Andhra Pradesh, south India is a biotite-hornblende granite with notable contents of rare metal (Zr, Hf, Th) and rare earth (including Y) minerals like zircon, thorite, allanite, monazite and xenotime. Chemically, it is metaluminous (average A/ C+N+K = 0.95)-type, potassic (av. 5% K2O) granite, with dominantly sub-alkaline characters. It shows up to 8 times enrichment of rare metals (Zr, Hf, U, Th) and rare earths (including Y, Sc), with reference to their abundances in normal unevolved granite, and hence, fertile for some of these elements. Field, petrological, geochemical and isotopic data of potassic granite (PG) indicate involvement of silica-rich metasedimentary-basic crustal rocks (amphibole-quartzite, amphibolite, hornblende-biotite gneiss, etc.) in its genesis, at a depth range of 30 km. Further, chondrite-normalized REE patterns demonstrate that low-degree partial melting of source rocks is the major con