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The geochemical characteristics of sediments are important for reconstructing paleoclimatic and paleoenvironmental conditions in the Asian summer monsoon marginal area. However, robust reconstructions require an understanding of the key factors and mechanisms governing the spatial variations in the composition and ratio of chemical elements in the modern sediments of the Asian summer monsoon marginal area. In this study, 128 surface sediment samples were collected from the Bashang area, which is situated in the Asian summer monsoon marginal area, and examined for their major and trace element compositions and grain size. Principal component analysis (PCA) and redundancy analysis (RDA) were used to analyse the relationship between geochemical data and modern temperature and precipitation data. The results showed that the CIA values of sediments in the Bashang area are mainly affected by temperature rather than precipitation and the Rb/Sr value in the study area reflects the level of precipitation in the corresponding period and the temperature controlling the leaching and weathering. In addition, SiO2/Al2O3 and Zr/Ti ratios have good positive relationships with the coarse-grained fraction of sediments and thus can be used as grain size proxies. We propose that the exact environmental significance indicated by these proxies should be stated explicitly before using them as proxies for paleoenvironmental reconstructions of the Asian summer monsoon marginal area.

Pedogenic weathering of aeolian materials plays an essential role in global nutrient and carbon cycling. A quick and effective approach for temporally high‐resolution and spatially large‐scale pedogenic investigations has long been needed. Here, we used visible and near‐infrared, mid‐infrared and sensor‐fused data to predict pedogenesis‐related soil properties (i.e., grain‐size distribution, clay‐mineral properties and geochemical ratios) in a thick loess sequence in central China. Sensor fusion was achieved at three different levels: (1) direct combination of spectral parameters (low‐level fusion; Fusionpara); (2) combination of spectral features selected by principal component analysis (middle‐level fusion; FusionPCA) and (3) fusion using outer product analysis (high‐level fusion; FusionOPA). Sensor‐fusion generally improves the model predictions for all soil properties, with increases in the values of the model efficiency coefficient (MEC) of 8% and the performance‐to‐interquartile range of 12%. Whole‐soil properties are optimally predicted with the Fusionpara dataset using the random forest algorithm, yielding a mean MEC of 0.85. Spectral parameters D2200/D1900 and AS2200 are demonstrated as promising new pedogenic proxies, with higher values indicating more intense hydrolysis during pedogenesis. Spectral proxies along the loess sequence suggest that intense soil formation occurred during warm and humid interglacial periods when the East Asian summer monsoon intensified. The sensor‐fusion technique improved model performance for assessing mineral transformations and chemical weathering intensity, providing a quick and efficient means of interpreting pedogenic evolution, especially in the case of spatially large‐scale soil investigations. Highlights: Fusion of VNIR and MIR spectra to model loess pedogenesis.Spectral modeling provides a robust surrogate for pedogenic evolution studies.Sensor fusion improves the performance of chemometric models.Sensor‐fusion models can reconstruct loess pedogenesis. [ABSTRACT FROM AUTHOR]

Geological, mineralogical–petrographic, and geochronological studies (U/Pb, Rb/Sr, and Ar/Ar isotope dating) of igneous complexes of the Dalat Zone identified two stages, which reflect a change in the geodynamic regime. The first, Late Jurassic, stage corresponded to a suprasubduction setting with formation of volcanic sequences of the Deobaoloc complex: calc-alkali basaltic andesites, andesites, dacites, their tuff breccias, and tuffs. The second, Albian–Coniacian, stage of the transform setting was related to a sliding zone of tectonic plates, activation of general left-lateral shear deformations at the continent–ocean boundary, and formation of paleovolcanic structures and related Dinhquan granitic batholiths (113 ± 0.6 Ma), Ancroet granites (97 ± 0.4 Ma), Deoca monzogranodiorites (90.4 ± 0.3 Ma), and Cana leucogranite–alaskites (86.8 ± 1.5 Ma). The thermochronological analysis and mathematical modeling indicate that the live period of parental granitic magma in a transform geodynamic setting was Δt of ~27 Ma and differentiation in the deep source resulted in origination of the final Cana leucogranite-alaskitic intrusive stocks with Au–Mo ± Cu mineralization. [ABSTRACT FROM AUTHOR]

Multi-grain isotope dilution and secondary ion microprobe zircon U-Pb as well as wholerock Rb-Sr isotope dilution data on the late Paleoproterozoic Suomenniemi rapakivi granite complex (exposed on the northern flank of the Wiborg batholith in southeastern Finland) are discussed in the light of point-specific errors on Pb/U and proposed new values of the decay constant of 87Rb, λ87. U-Pb zircon data on hornblende granite and biotite granite of the main metaluminous-marginally peraluminous granite fractionation series of the Suomenniemi batholith indicate crystallization in the 1644-1640 Ma range, with a preferred age at 1644±4 Ma. A cross-cutting hornblende-clinopyroxene-fayalite granite is probably slightly younger, as are quartz-feldspar porphyry dikes (1634±4 Ma) that cut both the main granite series and the metamorphic Svecofennian country rocks of the Suomenniemi batholith. Recalculation of whole-rock Rb-Sr data published on the main granite series of the batholith by Rämö (1999) implies errorchron ages of 1635±10 Ma and 1630±10 Ma and a magmatic 87Sr/86Sri of 0.7062±0.0024. This relatively high initial ratio is indicative of a major Proterozoic crustal source component in the granites of the batholith. The main granite series of the batholith probably cooled relatively rapidly to and below the closure temperature of the Rb-Sr isotope system, with little subsequent subsolidus adjustment. The three discrete silicic magmatic phases of the batholith (the main granite series, the hornblende-clinopyroxene-fayalite granite, and the quartz-feldspar porphyry dikes) were all probably emplaced before the main volume of rapakivi granite (the Wiborg batholith proper) in southeastern Finland. The Suomenniemi batholith thus represents an early magmatic precursor to the classic Wiborg batholith and was emplaced clearly before the massive rise of isotherms associated with the ascent and crystallization of the magmas that formed the bulk of the Wiborg batholith system.

The mid-Proterozoic, locus classicus Wiborg rapakivi granite batholith of southeastern Finland and adjacent Russia comprises a varying, bimodal (silicic-basic) sequence of plutonic, subvolcanic, and volcanic rocks. At the current level of erosion silicic rocks are dominant, the most prominent of which are wiborgites and dark wiborgites (that have been considered to mark the main build-up stage of the batholith) and pyterlites. New observations and optical microscopy data from the dark wiborgite-dominated Ristisaari Island in the southern, off-shore part of the Wiborg batholith show that dark plagioclase megacrysts in dark wiborgite are calcic xenocrysts. They were probably incorporated into wiborgite magma from consanguineous massif- type anorthosite magmas in the course of the evolution of the bimodal magmatic system. Our new ID-TIMS U-Pb zircon age of the Ristisaari Island dark wiborgite, 1627±3 Ma, is the youngest isotopic age so far determined for the plutonic rocks of the Wiborg batholith. This, combined with preexisting U-Pb zircon data, implies a minimum duration of 12 m.y. (1642–1630 Ma) for the emplacement of the plutonic rocks of the batholith. Combined with data on high- level dike rocks, a window of at least 20 m.y. (1642–1622 Ma) is implied. Furthermore, as the batholith grew, the overall locus of magmatism may have shifted southwards. New whole-rock Nd isotope data on the dark wiborgite of the Ristisaari Island and three further granites of the batholith, as well as Nd (whole-rock) and Sr (whole-rock, plagioclase) isotope data on a spectrolite massif-type anorthosite from the east-central part of the batholith, are also presented. These data suggest that the lithosphere across the Wiborg batholith area in the southeastern part of the Svecofennian orogen may vary slightly in overall mantle separation age.

We inferred moisture variations from the early 1930s to the early 2010s in the southwestern Mu Us Desert of China using Rb/Sr ratio, chemical index of alteration (CIA), and organic matter (OM) content in a nebkha profile. Our results showed that the variations in moisture may have been the main factor that controlled vegetation recovery or degradation, and we believe that gradual vegetation recovery was notable throughout the study area during the past 80 years, despite two notable degradation stages during the mid-1950s and the mid-1980s. The Rb/Sr ratio, CIA, and OM content revealed that moisture levels increased during the study period, though with large interannual variations. During the early stage of nebkha formation, the moisture variations were controlled by unusually low precipitation. Thereafter, the precipitation, pan evaporation and temperature determined together moisture variations, but the key factor determining moisture variations was different during different periods. The moisture variations trend revealed in this study may not be restricted to this region as it was similar with the adjacent Mongolian Plateau. [ABSTRACT FROM AUTHOR]

A method to estimate the 87Sr/86Sr ratio of a rock based on its age and Rb/Sr ratio is presented. This method, together with data from the Rock Geochemical Database of Finland (n=6544) is used to estimate the 87Sr/86Sr ratios in the Precambrian of Finland and in its different major units. A generalization to cover the whole area of Finland is achieved by smoothing of estimation points. The estimation method is evaluated by comparing its results to published Rb-Sr isotope analyses (n=138) obtained on the Finnish Precambrian. The results show correspondence to different geological units of Finland, but no systematic difference between Archaean and younger areas is evident. Evaluation of the method shows that most of the estimates are reliable and accurate to be used as background material for provenance studies in archaeology, paleontology and sedimentology. However, some granitic rocks may have large (>1.0 %) relative errors. Strontium concentration weighted average of the estimates differs only by 0.001 from the average 87Sr/86Sr ratio (0.730) of the rivers on the Fennoscandian shield.

Multi-grain isotope dilution and secondary ion microprobe zircon U-Pb as well as whole-rock Rb-Sr isotope dilution data on the late Paleoproterozoic Suomenniemi rapakivi granite complex (exposed on the northern flank of the Wiborg batholith in southeastern Finland) are discussed in the light of point-specific errors on Pb/U and proposed new values of the decay constant of 87Rb, λ87. U-Pb zircon data on hornblende granite and biotite granite of the main metaluminous-marginally peraluminous granite fractionation series of the Suomenniemi batholith indicate crystallization in the 1644-1640 Ma range, with a preferred age at 1644±4 Ma. A cross-cutting hornblende-clinopyroxene-fayalite granite is probably slightly younger, as are quartz-feldspar porphyry dikes (1634±4 Ma) that cut both the main granite series and the metamorphic Svecofennian country rocks of the Suomenniemi batholith. Recalculation of whole-rock Rb-Sr data published on the main granite series of the batholith by Rämö (1999) implies errorchron ages of 1635±10 Ma and 1630±10 Ma and a magmatic 87Sr/86Sri of 0.7062±0.0024. This relatively high initial ratio is indicative of a major Proterozoic crustal source component in the granites of the batholith. The main granite series of the batholith probably cooled relatively rapidly to and below the closure temperature of the Rb-Sr isotope system, with little subsequent subsolidus adjustment. The three discrete silicic magmatic phases of the batholith (the main granite series, the hornblende-clinopyroxene-fayalite granite, and the quartz-feldspar porphyry dikes) were all probably emplaced before the main volume of rapakivi granite (the Wiborg batholith proper) in southeastern Finland. The Suomenniemi batholith thus represents an early magmatic precursor to the classic Wiborg batholith and was emplaced clearly before the massive rise of isotherms associated with the ascent and crystallization of the magmas that formed the bulk of the Wiborg batholith system. [ABSTRACT FROM AUTHOR]

The mid-Proterozoic, locus classicus Wiborg rapakivi granite batholith of southeastern Finland and adjacent Russia comprises a varying, bimodal (silicic-basic) sequence of plutonic, subvolcanic, and volcanic rocks. At the current level of erosion silicic rocks are dominant, the most prominent of which are wiborgites and dark wiborgites (that have been considered to mark the main build-up stage of the batholith) and pyterlites. New observations and optical microscopy data from the dark wiborgite-dominated Ristisaari Island in the southern, off-shore part of the Wiborg batholith show that dark plagioclase megacrysts in dark wiborgite are calcic xenoc-rysts. They were probably incorporated into wiborgite magma from consanguineous massif-type anorthosite magmas in the course of the evolution of the bimodal magmatic system. Our new ID-TIMS U-Pb zircon age of the Ristisaari Island dark wiborgite, 1627±3 Ma, is the youngest isotopic age so far determined for the plutonic rocks of the Wiborg batholith. This, combined with preexisting U-Pb zircon data, implies a minimum duration of 12 m.y. (1642-1630 Ma) for the emplacement of the plutonic rocks of the batholith. Combined with data on high-level dike rocks, a window of at least 20 m.y. (1642-1622 Ma) is implied. Furthermore, as the batholith grew, the overall locus of magmatism may have shifted southwards. New whole-rock Nd isotope data on the dark wiborgite of the Ristisaari Island and three further granites of the batholith, as well as Nd (whole-rock) and Sr (whole-rock, plagioclase) isotope data on a spect- rolite massif-type anorthosite from the east-central part of the batholith, are also presented. These data suggest that the lithosphere across the Wiborg batholith area in the southeastern part of the Svecofennian orogen may vary slightly in overall mantle separation age. [ABSTRACT FROM AUTHOR]

The Suomusjärvi shear zone in the West Uusimaa area in the Proterozoic Svecofennides of SW Finland belongs to a group of late, post-peak metamorphic structures comprising vertical shear zones and folds with vertical fold axes. Field and microscopical evidence suggest that these structures can be correlated with a shear zone cutting the Bodom granite with a known U-Pb zircon age of 1641 ± 13 Ma. This paper presents the results of a pilot Rb-Sr whole-rock and biotite dating of the Suomusjärvi shear zone. The shear zone cuts the Suomusjärvi tonalite and is locally developed as a 5 meter thick ultramylonite in which the biotite is completely recrystallized. A sample of undeformed tonalite yields a Rb-Sr biotite age of 1644 ± 16 Ma, the ultramylonite a biotite age of 1533 ± 23 Ma. The tonalite age is interpreted as a cooling age, while the ultramylonite age represents resetting due to the mylonitization process (deformation, recrystallization and fluid flow) below the biotite Rb-Sr blocking temperature of 300‒350°C. The whole-rock data give a meaningless age of 1760± 108 Ma, which is the result of partial whole-rock resetting at the scale of the ultramylonitic banding. It is concluded that the results of the pilot-dating are compatible with the expectations based on other data. This indicates that this group of late deformation structures in the studied area is the result of an important post-Svecofennian event which was previously hardly recognized in south Finland. Structural, isotopical, petrological and fluid inclusion data on the cooling history of the West Uusimaa area are internally consistent, but conflicting with other evidence from southern Finland.

[Display omitted] • Ores formed during multi-episodic hydrothermal events in Devonian-Carboniferous times. • Ophiolite-related rocks do not exhibit typical mantle isotopic signatures. • Ore fluids scavenged elements from a number of isotopically different crustal sources. • Brannerite inclusions in arsenides controlled their Pb and Nd isotope behavior. The Bou Azzer district in Morocco has a long mining history since the beginning of the XXst century during which it has become the only world producer of Co from primary, hydrothermal Co arsenide ores. Orebodies are structurally controlled, and mainly distributed along fault contacts between Cryogenian ophiolite-related serpentinite bodies and intrusive quartz diorite or, locally, ophiolitic gabbros or Ediacaran volcanic rocks. Ore formation took place through a multi-stage mineralizing process that included an early stage composed by gold, quartz, chlorite, muscovite and calcite, followed by the main arsenide and sulfarsenide stage (subdivided into three substages, IIa: Ni-rich, Co ores, IIb: Co-Fe ores and IIc: Fe-Co ores), and ending with an epithermal stage characterized by the precipitation of sulfides along with quartz and calcite. Field relations and most previous geochronologic dating pointed to a post Pan-African age of ore formation, mainly coincident with the Hercynian orogeny. The isotopic study presented in this paper includes S, Pb, Rb/Sr and Sm/Nd data of a set of ore mineral samples from three deposits (Aghbar, Tamdrost and Aït Ahmane), as well as of regional samples representative of the different lithologies occurring in the Bou Azzer area. The isotope data set was completed with S isotope analyses of arsenide and sulfarsenide minerals from five ore deposits (Filon 7/5, Aghbar, Tamdrost, Ightem and Aït-Ahmane) and of some whole-rock regional samples. Results show that ores formed during multi-episodic hydrothermal events connected with hercynian reactivation of Devonian-Carboniferous faults, supporting previous geochronologic dating. The obtained Pb, Sr, Nd and S isotopic signatures of ore minerals and regional rocks further show that ophiolite-related lithologies became isotopically modified by interaction with crustal material and afterwards acted as the main source of ore-forming elements. Nevertheless, isotopic data do not fully concur with such a simple scenario but are quite consistent with a rather complex interpretation based on multi-source origin of some elements and isotopes scavenged from a number of isotopically different lithologies both from the inferred basement and the volcanic and sedimentary cover. [ABSTRACT FROM AUTHOR]

A detailed Sm/Nd, epsilon Nd and Rb/Sr profile through a 30-cm thick section of Silurian (Llandovery) interbedded turbiditic and hemipelagic mudrocks from the central Wales Basin shows well-marked chemical and isotopic trends. The variations reflect an interplay of depositional mode and diagenetic fractionation. Sm and Nd values are substantially higher and Sm/Nd ratios tend to be lower in the organic-rich hemipelagite layers due to diagenetic concentration in the hemipelagites. There is a corresponding depletion in the turbidite mudstones. Epsilon Nd values range from −0·8 to −7·1 and this is attributed to diagenetic modification of Sm/Nd ratios causing scatter in back-calculated epsilon values. Rubidium–strontium ratios in this succession fall within a narrow range, due to homogenization during diagenesis. By contrast, data from a hemipelagite-dominated (condensed) succession near the northern margin of the Welsh Basin show a lower range of epsilon Nd values and a higher scatter of Rb/Sr values, consistent with less fluid throughput during burial compaction and hence less diagenetic redistribution in these rocks. These patterns demonstrate the sensitivity of mudrock trace element and isotope compositions to both small-scale sedimentary structure and large-scale basin architecture. [ABSTRACT FROM AUTHOR]

Abstract: Room-temperature reactions of the atomic cations Sr+ and Rb+ have been surveyed systematically with a variety of gases using an Inductively-Coupled Plasma/Selected-Ion Flow Tube (ICP/SIFT) tandem mass spectrometer. Rate coefficients and product distributions have been measured in He buffer gas at 0.35Torr and 295K for reactions of Sr+ and Rb+ with CH3F, CH3Cl, N2O, CO2, CS2, SF6, D2O and NH3. Rb+ (s0) is seen to be quite inert with these molecules and reacts either slowly by molecule addition or not at all, while Sr+ (s1) is much more reactive with all these 8 molecules, especially with CH3F, CH3Cl, N2O and SF6. Sr+ reacts with CH3F and SF6 by F-atom transfer, with CH3Cl by Cl-atom transfer and with N2O by O-atom transfer, and the reaction rate coefficients are all quite high, k ≥1.4×10−11 cm3 molecules−1 s−1. The extreme differences in reactivity with CH3F, SF6, CH3Cl and N2O provide a chemical basis for the separation of isobaric interferences of 87Rb+ and 87Sr+ often encountered in ICP–MS. Among these four molecules, SF6 exhibits the largest difference in reactivity, almost a factor of 104, and so is identified as the kinetically recommended reagent for the chemical resolution of the isobaric interference of 87Rb+ and 87Sr+. [Copyright &y& Elsevier]

Abstract: The Honam shear zone, dextrally running along the southern margin of the Ogcheon belt, Korea, has drawn much attention in reconstructing the Mesozoic tectonic framework of northeastern Asia. Here we present Rb–Sr data for the middle to southwestern part of the Honam shear zone, in an attempt to directly determine ages of deformation. In the middle part, the younger limit of deformation is constrained to be 162±11 Ma by feldspar–biotite Rb–Sr dating of the deformed Sunchang granodiorite. On the other hand, an early Cretaceous deformation age is estimated for synkinematic fibers in ultramylonites from the southwestern part by two reproducible Rb–Sr errorchrons at 138±4 and 139±23 Ma. This deformational time scale is consistent with earlier interpretations based on field evidence, magnetic susceptibility data, and age data for Jurassic plutons within the shear zone. Our data demonstrate that the Honam shear zone is not a Permian to Triassic tectonic feature related to the Chinese continental collision. [Copyright &y& Elsevier]

Based on the principle that the present is the key to the past, detailed analyses, such as AMS 14C dating, grain size, component and morphology of heavy minerals, micro-morphology of zircon, Rb/Sr, magnetic susceptibility and total organic carbon (TOC), were conducted to identify paleoflood sediments archived in Zhongba Site. The results indicate that the plaeoflood sediments bear great similarities with modern flood sediments in the following aspects: (1) probability cumulative curves mainly show a pattern of 3–4 segments; (2) grain-size distribution of suspended matter ranges between 3 and 10Φ; (3) the sediments are well-sorted, most of which are suspended matter (>50%); (4) the same species, quantity and morphology of heavy minerals; (5) scanning electronic microscope images show that shapes of zircon are mainly oval and nearly spheral, rounded due to long-distance transport; (6) higher Rb/Sr values (0.55–0.66)than those of sediments from cultural layers (0.03–0.26); (7) magnetic susceptibility values (133.73–433.05 10-6m³/kg) are lower than those of sediments from cultural layers (959.25–2442.44 10-6 m³/kg); (8) TOC (0.14%–0.33%) are lower than those of sediments from cultural layers (1.13%–2.95%). Our results demonstrate that, except for the 1981 flood, there are at least six paleoflood events that occurred during the Qing Dynasty, the middle of Song Dynasty, the early Warring States (400BC–350BC), the West Zhou Dynasty (920BC–900BC), the Xia Dynasty (2070BC–1600BC), and the late Neolithic Age (3000BC–2300BC), respectively. [ABSTRACT FROM AUTHOR]

Multimineral Rb/Sr internal isochrons from eclogite facies rocks of the Eclogite Zone (Tauern Window, Eastern Alps) consistently yield an Early Oligocene age of 31.5±0.7 Ma. This age has been obtained both for late-prograde, dehydration-related eclogitic veins, and for rocks variably deformed and recrystallized under eclogite facies conditions (2.0–2.5 GPa, 600°C). Initial Sr-isotopic equilibria among all phases indicate absence of significant post-eclogitic isotope redistribution processes, therefore the ages date eclogite facies assemblage crystallization. Equilibria also prove that no prolonged pre-eclogite facies history is recorded in the rocks. Instead, subduction, prograde mineral reactions, and eclogitization proceeded rapidly. Fast exhumation immediately after eclogitization, with minimum rates >36 mm/a is inferred from a 31.5±0.5 Ma internal mineral isochron age of a post-eclogitic greenschist facies vein assemblage. Such rates equal typical subduction rates. Late Eocene to Early Oligocene subduction of the European continental margin, with subsequent rapid exhumation of high-pressure nappe complexes has previously been recognized only in the Western Alps. The new data signify synchronous continental collision all along the Alpine belt. Our results demonstrate the unique potential of Rb/Sr assemblage ‘system analysis’ for precise dating of both eclogite facies and post-eclogitic events, thus for precisely constraining exhumation rates of deep-seated rocks, and for straightforward linkage of petrologic evidence with isotopic ages. [ABSTRACT FROM AUTHOR]

Sr and Nd isotopic data from the anorthosite-mangerite-charnockite (AMC) suite of the Late-Sveconorwegian (ca. 0.93 Ga) Rogaland anorthosite province of SW Norway are discussed. The study focuses on new data obtained from three distinct rock occurrences: (1) primitive (=MgO-rich and K2O-poor) jotunites that represent the parental magmas of leuconorite and mafic plutons (87Sr/86Sr0.93 Ga=ca. 0.704–0.707, &epsiv;Nd(0.93 Ga)=+3.6 down to +1.2); (2) evolved jotunites that differentiated from the primitive jotunites and constitute the starting components of dyke-scale fractionation trends (87Sr/86Sr0.93 Ga=ca. 0.705–0.713, &epsiv;Nd(0.93 Ga)=+0.4 down to −2.0); and (3) felsic plutons (87Sr/86Sr0.93 Ga=ca. 0.707–0.723, &epsiv;Nd(0.93 Ga)=+1.4 down to −1.7). A comparison of the Sr and Nd isotopic compositions with available geochemical data (major and trace elements) is also made. Fractionation of the primitive to the evolved jotunites, below the intrusion level of the anorthosite province, is shown to have involved crustal contamination. A case of fractional crystallization and simultaneous contamination/assimilation is substantiated in the felsic cap of a layered intrusion (the Bjerkreim-Sokndal intrusion). It is further proposed that the Sr and Nd isotopic compositions of the various felsic occurrences result from fractional crystallization of primitive jotunitic melts, with or without contamination/assimilation; this strengthens the possibility for large volumes of silica-rich magmas to have been produced by fractionation, through evolved jotunites, of primitive jotunites. The entire range in Sr and Nd isotopic compositions of the Rogaland anorthosite province is interpreted as reflecting a mixing of crustal contaminants, having variable 87Sr/86Sr0.93 Ga ratios and (negative) &epsiv;Nd(0.93 Ga) values, with a more isotopically primitive source. The crustal end members of that mixing array are represented by moderately to strongly LILE-enriched high-grade gneisses from the Pre-Sveconorwegian basement of southernmost Norway, that have a crustal history extending back to 1.5–1.9 Ga in the surroundings of the anorthosite province. The primitive end member is either an unusual LREE-depleted and Rb-enriched component, possibly corresponding to an originally depleted source subsequently modified by metasomatic fluids, or a more classical depleted component; it corresponds to a gabbronoritic rock of the deep crust, as shown by recent experimental data, with a quite short crustal residence time (<0.4–0.2 Ga). If that mafic end member is the lower granulitic crust itself, this would imply the presence in the deep continental crust of southwesternmost Norway of a crustal material strongly different from the 1.7- to 1.9-Gyr-old, moderately LILE-enriched component that is supposed to constitute the largest volume of the present deep continental crust in southern Norway. [Copyright &y& Elsevier]

Kinematic data from the internal zones of the Western Alps indicate both top-to-SE and top-to-NW shearing during synkinematic greenschist facies recrystallisation. Rb/Sr data from white micas from different kinematic domains record a range of ages that does not represent closure through a single thermal event but reflects the variable timing of synkinematic mica recrystallisation at temperatures between 300 and 450 °C. The data indicate an initial phase of accretion and foreland-directed thrusting at ca. 60 Ma followed by almost complete reworking of thrust-related deformation by SE-directed shearing. This deformation is localised within oceanic units of the Combin Zone and the base of the overlying Austroalpine basement, and forms a regional scale shear zone that can be traced for almost 50 km perpendicular to strike. The timing of deformation in this shear zone spans 9 Ma from 45 to 36 Ma. The SE-directed shear leads to local structures that cut upwards in the transport direction with respect to tectonic stratigraphy, and such structures have been interpreted in the past as backthrusts in response to ongoing Alpine convergence. However, on a regional scale, the top-to-SE deformation is related to crustal extension, not shortening, and is coincident with exhumation of eclogites in its footwall. During this extension phase, deformation within the shear zone migrated both spatially and temporally giving rise to domains of older shear zone fabrics intercalated with zones of localised reworking. Top-NW kinematics preserved within the Combin Zone show a range of ages. The oldest (48 Ma) may reflect the final stages of emplacement of Austroalpine Units above Piemonte oceanic rocks prior to the onset of extension. However, much of the top-to-NW deformation took place over the period of extension and may reflect either continuing or episodic convergence or tectonic thinning of the shear zone.40Ar/39Ar data from the region are complicated due to the widespread occurrence of excess 40Ar in eclogite facies micas and partial Ar loss during Alpine heating. Reliable ages from both eclogite and greenschist facies micas indicate cooling ages in different tectonic units of between 32 and 40 Ma. These ages are slightly younger than Rb/Sr deformation ages and suggest that cooling below ca. 350 °C occurred after juxtaposition of the units by SE-directed extensional deformation.Our data indicate a complex kinematic history involving both crustal shortening and extension within the internal zones of the Alpine Orogen. To constrain the palaeogeographic and geodynamic evolution of the Alps requires that these data be integrated with data from the more external zones of the orogen. Complexity such as that described is unlikely to be restricted to the Western Alps and spatially and temporally variable kinematic data are probably the norm in convergent orogens. Recognising such features is fundamental to the correct tectonic interpretation of both modern and ancient orogens. [Copyright &y& Elsevier]

Time must be integrated with other geologic parameters such as pressure–temperature (P-T), composition or structural–textural information in order to quantify the dynamics of geologic processes like mountain building, faulting, metamorphism or magmatism. In the past, this connection was weak due to large sample sizes required in geochronology; however, recent developments open up exciting new possibilities. Texturally controlled in situ dating of minerals utilizing UV–laser ablation 40Ar/39Ar or Rb–Sr microsampling facilitates the crucial link between ages and textures at high spatial resolution. In situ U–Pb ages of accessory minerals can now be linked to the corresponding P-T evolution via their characteristic trace elemental signatures, indicative of mineral reactions in rocks. Garnet dating by Sm–Nd, and more recently Lu–Hf, can greatly benefit from both laser ablation inductively coupled plasma mass spectrometry (ICPMS) screening and improved leaching strategies, improving the link between time and P-T. Such integrated approaches can yield the duration and rates of deformation in shear zones, the rates of burial and exhumation of subducted rocks or the duration of entire metamorphic loops, to name a few. Potential for further development is identified in diverse areas. Dating of carbonate minerals related to brittle faulting using U–Pb could provide previously unavailable constraints on rates and duration of brittle deformation in the Earth’s upper crust. In situ Rb–Sr dating applicable to micas could become available using either laser ablation dynamic reaction cell-ICPMS or microbeam accelerator mass spectrometry. Other future developments and trends, and their limitations, are discussed briefly. [Copyright &y& Elsevier]

New structural and metamorphic data coupled with U–Pb SHRIMP zircon and Rb–Sr step-leach biotite ages help constrain a period of Early Palaeozoic (Pan-African) deformation recognised in the northern Prince Charles Mountains, east Antarctica. This period of deformation is accommodated along discrete northeast trending mylonites that preserve up-dip reverse kinematics with dominantly southeast over northwest vergence. Ambient P–T conditions of 524±20°C and 7.6±4 kbar accompanied deformation. This phase of deformation post-dated the intrusion of planar felsic dykes that yield ages of c. 550 Ma and pre-dated Rb–Sr biotite ages of c. 475 Ma that record cooling of the terrane below c. 300°C. These mylonites are identical in age to continental collisional events recognised in the southern Prince Charles Mountains and Prydz Bay, which lie to the south and east of the northern Prince Charles Mountains, and similar in age to orogenesis recognised to the west in Lu¨tzow-Holm Bay. These belts represent sutures between the component lithospheric blocks of east and west Gondwana. The northern Prince Charles Mountains lie between these sutures. Consequently, the mylonites we report here are interpreted to have formed in an intraplate setting and developed in response to stresses applied along the plated margins as a consequence of continental collision during the amalgamation of Gondwana. [Copyright &y& Elsevier]