LA-ICPMS Data Research Articles

Trace Elements in Ancient Gold Products with PGE Microinclusions from Archaeological Sites of the Urals and North Black Sea Region: LA–ICP–MS Data

Many archaeological gold products of the Urals and North Black Sea region contain microinclusions of platinum group minerals (PGMs). The trace element composition of these products was studied using LA–ICP–MS to reveal their microgeochemical features, the differences in the trace element composition of PGM‐bearing and PGM‐free products, and the source of gold. Owing to the presence of microinclusions of ruthenium, osmium and iridium, the gold products from the Filippovka I grave field and the Phanagoria site are enriched in Os, Ru, Ir and Rh. Among the platinum group elements (PGEs), Pt exhibits the highest contents in the gold products. The gold products are characterized by individual assemblages of Ag and base metals. The gold products with both PGEs and base metals were manufactered from two types of gold: placer‐derived and gold from oxidation zones of polymetallic volcanic‐hosted massive sulphide deposits. It is suggested that cupellation was most common technique of gold refinement.

The First U–Pb Isotopic Systematics of Natural Aeschynite and Coexisting Monazite

We have been the first to study in situ the U–Pb isotopic system of aeschynite identified in the gold-bearing magnetite–chlorite–dolomite rocks of the Karabash serpentine massif in the Southern Urals. In the concordia diagram, the U–Pb LA–ICP–MS data on aeschynite are characterized by a considerable discordance, which is consistent with the regression line, the lower crossing of which with the concordia corresponds to an age of 298 ± 18 Ma, whereas the figurative ellipses of coexisting monazite reveal an almost concordant cluster corresponding to the U–Pb age of 317.3 ± 3.3 Ma. It has been established that the closure temperature of the aeschynite system is lower than that of the coexisting monazite.

First data on Early Carboniferous intrusive magmatism of the eastern margin of the Middle Urals: Geodynamic conditions and U–Pb isotope constraints

U–Pb LA ICP–MS dating of zircon from rocks of the Nekrasov gabbro–granitoid complex within the eastern margin of the Middle Urals was performed. The average U–Pb age calculated from three concordant measurements (326 ± 8 Ma) shows that their intrusion occurred at the Serpukhov Stage of the Early Carboniferous. According to the ideas on periodization of magmatic processes within the eastern sector of the Middle Urals, the formation of this complex corresponds to the final episodes of the continental marginal (supersubduction) magmatism.

Kinematics and timing of continental block deformation from margins to interiors

AbstractDuring the deformation of continental blocks, the magnitude of tectonic stress generally decreases with increasing distance from the margin of the block. However, the timing and kinematics of stress transmission from the margins to the interiors of continents are poorly resolved, even though this information is critical to our understanding of the dynamics of continental deformation. Here, we present a case study of Mesozoic deformation of the North China Craton (NCC). Field investigations of Mesozoic thrust faults and folds, granitic intrusions and dykes, combined with zircon SHRIMP and LA–ICP–MS dating and muscovite 40Ar/39Ar plateau ages, reveal the age of the NE–SW‐trending tectonic belts as ~180–155 Ma, where the deformation of the craton margin occurred 10–20 Ma earlier than that of the craton's interior. Although the kinematics of deformation are similar for the interior and the margin of the NCC, strain decreases with increasing distance from the margin. Notably, the bulk of the strain in the cratonic interior was focused in zones of pre‐existing weakness. Overall, we determined that the NCC deformed under conditions of uniaxial compression, a conclusion that is compatible with simple rheological models, and that the stress magnitude attained in the cratonic interior was much less than that along its margin.

Tracking an upper limit of the “Carnian Crisis” and/or Carnian stage in the Western Carpathians (Slovakia)

The Late Triassic timescale, especially the Carnian–Norian boundary, is poorly constrained mainly due to a paucity of high-precision radio-isotopic ages that can be related accurately to contradictions between the biostratigraphic and magnetostratigraphic correlations. LA ICP-MS dating of detrital zircons from five samples of the Lunz Formation—the Upper Triassic siliciclastic sediments from the Western Carpathians (Slovakia)—provided a wide spectrum of ages that vary from Late Archaean (ca. 2582 Ma) to Triassic (ca. 216 Ma). These marine delta sediments represent a typical product of the “Carnian Crisis”—a major climate change and biotic turnover that occurred during the Carnian stage in the Tethys Ocean within the carbonate shelf and intrashelf basins in the Northern Calcareous Alps and the Western Carpathians. The supply of clastic material in the studied Lunz Formation was derived from several sources, especially: (i) from the recycled Variscan orogen; (ii) from the remote East European Platform; and (iii) from the contemporaneous Triassic volcanic sources. Syn-sedimentary volcanic zircons with a concordia age of 221.2 ± 1.6 Ma (calculated from 12 single analyses) represent the maximum age of deposition of the Lunz Formation, and demonstrate that the upper limit of the “Carnian Crisis” and/or the Carnian stage in the Alpine-Carpathians realm is younger than the current age of the Carnian–Norian boundary at ca. 227 Ma listed on the International Chronostratigraphic Chart (International Commission on Stratigraphy 2016/12 Edition).

Texture and chemistry of pyrite at Chah Zard epithermal gold–silver deposit, Iran

Gold mineralization at Chah Zard, Iran, is mostly concentrated in breccia and veins, and is closely associated with pyrite. Optical and scanning electron microscopy-backscattered electron observations indicate four different pyrite types, each characterized by different textures: porous and fractured py1, simple-zoned, oscillatory-rimmed, framboidal and fibrous py2, colloform py3, and inclusion-rich py4. Laser ablation ICP–MS analysis and elemental mapping reveal the presence of invisible gold in all pyrite types. The highest concentrations (161–166ppm Au) are found in py2 and py4, which correlate with the highest As concentrations (73,000–76,000ppm). In As-poor grains, Au concentrations decrease by about two orders of magnitude. Copper, Pb, Zn, Te, Sb, and Ag occur with invisible gold, suggesting that at least part of the gold occurs in nanoparticles of sulfosalts of these metals and metalloids. Gold distribution patterns suggest that only negligible Au was originally trapped in py1 from the initial ore fluids. However, most, if not all, Au was transported and deposited during subsequent overprinting hydrothermal fluid flow in overgrowth rims around the margins of the py2 and within microfractures of py4 grains. Oscillatory zonation patterns for Co, Ni, Sb, Cu, Pb, and Ag in pyrite reflect fluctuations in the hydrothermal fluid chemistry. The LA-ICP–MS data reveal that Cu, Pb and Ag show systematic variations between different pyrite types. Thus, Cu/Pb and Pb/Ag ratios in pyrite may provide a potentially powerful exploration vector to epithermal gold mineralization at Chah Zard district and elsewhere.

LA-iMageS: a software for elemental distribution bioimaging using LA-ICP-MS data.

The spatial distribution of chemical elements in different types of samples is an important field in several research areas such as biology, paleontology or biomedicine, among others. Elemental distribution imaging by laser ablation inductively coupled plasma mass spectrometry (LA–ICP–MS) is an effective technique for qualitative and quantitative imaging due to its high spatial resolution and sensitivity. By applying this technique, vast amounts of raw data are generated to obtain high-quality images, essentially making the use of specific LA–ICP–MS imaging software that can process such data absolutely mandatory. Since existing solutions are usually commercial or hard-to-use for average users, this work introduces LA-iMageS, an open-source, free-to-use multiplatform application for fast and automatic generation of high-quality elemental distribution bioimages from LA–ICP–MS data in the PerkinElmer Elan XL format, whose results can be directly exported to external applications for further analysis. A key strength of LA-iMageS is its substantial added value for users, with particular regard to the customization of the elemental distribution bioimages, which allows, among other features, the ability to change color maps, increase image resolution or toggle between 2D and 3D visualizations.Electronic supplementary materialThe online version of this article (doi:10.1186/s13321-016-0178-7) contains supplementary material, which is available to authorized users.

Geologic evolution of a Cretaceous tectonometamorphic unit in the Franciscan Complex, western California

ABSTRACTThe Franciscan Yolla Bolly terrane of the NE California Coast Ranges consists mainly of quartzose metagreywackes containing sparse high-pressure/low-temperature (HP/LT) neoblastic minerals, including ubiquitous lawsonite. Some Yolla Bolly rocks also contain one or more of the newly grown phases, pumpellyite, aragonite, glaucophane, and/or jadeitic pyroxene. These blueschist-facies metasandstones recrystallized under physical conditions of ~200–300°C and ~8 kbar at subduction-zone depths approaching 30 km. Petrologically similar Franciscan metaclastic-rich map units – Yolla Bolly terrane-like rocks, here designated the ‘YB’ unit – crop out in the central and southern California Coast Ranges. Recently published detrital zircon U‒Pb SIMS and LA-ICPMS data for 19 ‘YB’ metagreywackes indicate maximum ages of formation as follows: ~110–115 Ma (8) in the NE California Coast Ranges; ~95–107 Ma (7) in the San Francisco Bay area + Diablo Range; and ~85–92 Ma (4) in the dextrally offset Nacimiento Block. These fault-bounded ‘YB’ strata do not constitute coeval parts of a single tectonostratigraphic unit. Instead the term tectonometamorphic is proposed for such time-transgressive map units. Based on the current and likely Cretaceous 30° angular divergence between NS-palaeomagnetic stripes of the Farallon oceanic plate and the NNW-trending California convergent margin, I infer that arrival at the arc margin and underflow of a relatively thick segment of oceanic crust and its largely clastic sedimentary blanket may have resulted in progressive southeastward migration of an accreted, subducted, then exhumed HP/LT metagreywacke section. During the ~30 million year interval, ~115–85 Ma, the locus of ‘YB’ accretion, underflow, and tectonic regurgitation evidently moved SE along an ~1000 km stretch of the accretionary margin of western California.

First U–Pb isotopic data on zircon from andesite of the Saf’yanovka Cu-bearing massive sulfide deposit (Middle Urals)

New results of U–Pb LA ICP–MS dating of zircon from andesite samples cropping out on the western wall of the Saf’yanovka quarry (57°22′58.88″ N, 61°31′50.85″ E) in the synonymous Cu–Zn-bearing massive sulfide deposit of the Urals type are considered. The position of data points of the U–Pb systematics in the 207Pb/235U–206Pb/238U plot determines a cluster practically corresponding to the concordant U–Pb age: 422.8 ± 2.0 Ma. This date indicates for the first time the presence of Pridolian volcanogenic rocks in the East Urals megazone of the Middle Urals.

Results of U–Pb LA–ICP–MS dating of detrital zircons from Ediacaran–Early Cambrian deposits of the eastern part of the Baltic monoclise

Here we present the results of U–Pb LA–ICP–MS dating of detrital zircons from the Ediacaran–Early Cambrian deposits of the eastern part of the Baltic monoclise (Leningrad Region). The obtained age spectra of the detrital zircons suggest that, in the Ediacaran–Early Cambrian, the main clastic material source to the northwest of the Russian Platform was the Baltic Shield. Then in the Early Cambrian along with the Baltic Shield provenance, a clastic source from the Timanian margin of Baltica (northeast in modern coordinates) contributed to the deposits. The obtained data either somewhat set limits of the Timanian orogen formation as older than the previously suggested Middle Cambrian (about 510 Ma), based on the “absence of a Proto–Uralian–Timanian provenance signal” in the Sablino Formation rocks in the south Ladoga, or suggest another rearrangement of detritus transportation paths at the end of Stage 3 (Atdabanian).

Inglés

New field data, geochemical analyses and zircon U-Pb LA-ICP MS data were obtained on plutonic and volcanic rocks of the Mocoa Batholith and Saldana Formation in southern Colombia Putumayo region. Results suggest that the plutonic and volcanic activities are closely related to a common magmatic history. This volcano-plutonic association presents a well-defined LILE and LREE enrichment and negative Nb and Ti negative anomalies characteristic of continental magmatic arcs. Volcanic and plutonic rocks crystallized between 180-186 Ma as revealed by U-Pb zircon geochronology. The magmatic activity is temporally and chemically correlatable with other magmatic arc exposures in Colombia and Ecuador. These units may represent the remnants of a single belt which includes several units from 4°N in Colombia and 5°S in Ecuador. This arc is related to the widespread Jurassic continental magmatic arc setting that characterized the continental margins of the Americas after Pangea break-up.

U–Pb, Lu–Hf and trace element characteristics of zircon from the Felbertal scheelite deposit (Austria): New constraints on timing and source of W mineralization

Combined in-situ U–Pb, Lu–Hf and trace element LA–ICP–MS analyses were performed on zircons from the W-mineralized K1–K3 orthogneiss and associated aplite gneiss from the Felbertal scheelite deposit. The textural and trace element characteristics suggest the presence of magmatic and hydrothermal zircon. Magmatic zircons have low concentrations of W (0.108–3.77ppm), Nb (5.04–48ppm), U (691–3079ppm), B (0.26–6.57ppm), and REE+Y (640–4576ppm) and form euhedral CL-bright cores with distinct oscillatory zoning (zone a). Saturation of P in the granitic melt causing apatite crystallization explains the presence of two sub-types of CL-bright zircon cores distinguished by distinct P and Ca concentrations and variable positive Ce-anomalies. Higher trace element abundances and lower Zr/Hf ratios occur in CL-dark zircons with weak oscillatory zoning (zone b) overgrowing the zircon cores and in granular textured zircons restricted to the aplite gneiss. The increase in trace elements in zircon can be linked to the differentiation of the granitic melt and prolonged zircon crystallization during the transition from the late magmatic to the hydrothermal stage. CL-dark unzoned (texture-less) domains (zone b′) in K1–K3 orthogneiss zircons and granular textured zircons from the aplite gneiss have supra-chondritic Y/Ho ratios (29–62) indicating zircon growth in the presence of F-rich hydrothermal fluids exsolved from the evolved K1–K3 melt. Zone b′ zircons have the highest concentrations of W (4.3–11.4ppm), Nb (63–405ppm), B (7.3–135ppm), REE+Y (0.31–1.87 mass%) and U (1.23–5.56mass%); they are interpreted as hydrothermal and related to W-mineralizing fluids. Magmatic and hydrothermal zircon has identical U–Pb and Lu–Hf isotopic signature indicating the same source. The in-situ U–Pb concordia ages of zircons of four K1–K3 orthogneisses and one aplite gneiss confine the emplacement period of this granitic series between 341.0Ma and 336.2Ma. The initial ɛHft values ranging from −7.6 to −4.3 indicate a crustal protolith. The Felbertauern augengneiss is similar; it yielded a U–Pb concordia age of 338.5±1.3Ma and initial ɛHft between −6.8 and −5.3. On the contrary, zircons from the Granatspitz gneiss yielded discordant U–Pb ages (Late Carboniferous to Early Permian) and the ɛHft values scatter between −3.1 and +2.5 excluding any relation with the K1–K3 orthogneiss. Our new LA–ICP–MS data corroborate the genetic relationship of the W-mineralization at Felbertal with the Early Carboniferous K1–K3 orthogneiss series. The K1–K3 orthogneiss was part of a larger magmatic suite that developed during the Variscan orogeny in the pre-Alpine basement of the Tauern Window in the Viséan.

Characterization and origin of the Taishanmiao aluminous A-type granites: implications for Early Cretaceous lithospheric thinning at the southern margin of the North China Craton

Late Mesozoic magmatic rocks from the Taishanmiao Batholith were collected for LA–ICP–MS dating, Sr–Nd–Hf isotope systematics, and whole-rock major and trace element geochemistry to help understand the nature of collisional and extensional events along the southern margin of the North China Craton. The batholith consists of three texturally distinguishable phases of a 125 ± 1 Ma medium- to coarse-grained syenogranite, a 121 ± 1 Ma fine- to medium-grained syenogranite, and a 113 ± 1 Ma porphyritic monzogranite. Most of the units in the batholith are syenogranitic in composition with high levels of silica (70–78 wt% SiO2), alkalis (8.0–8.6 wt% Na2O + K2O), Fe* (FeOT/(FeOT + MgO) = 0.76–0.90), and depletion in CaO (0.34–1.37 wt%), MgO (0.12–0.52 wt%), TiO2 (0.09–0.40 wt%), and A/CNK (Al2O3/(Na2O + K2O + CaO)) molar ratios of 1.00–1.11. All samples have high proportions of Ga, Nb, Zr, Ga/Al, and REE, and depletions in Ba, Sr, Eu, and compatible elements, indicating that the batholith consists of A-type granites. The zircon saturation temperature for these units yields a mean value of 890 °C, and zircons with Early Cretaceous magmatic ages have eNd(t) values of −14.0 to −12.0, eHf(t) values ranging from −18.7 to −2.1, and corresponding Hf model ages of 2339–1282 Ma. These geochemical and isotopic characteristics allowed us to conclude that the primary magma for the Taishanmiao Batholith originated from partial melting of Precambrian crustal rocks in the medium-lower crust. However, the high Nb and Ta contents and low normalized Nb/Ta values for the Taishanmiao granites are due to fractionation in Nb- and Ta-rich amphibole (or biotite). It is further proposed that these aluminous A-type granites were generated in an extensional tectonic setting during the Early Cretaceous, which was induced by lithospheric thinning and asthenospheric upwelling beneath eastern China toward the Paleo-Pacific Plate.

In situ LA–ICP–MS dating of monazite from aluminous gneisses: insights on the tectono-metamorphic history of a granulite-facies domain in the central Grenville Province

In situ U–Pb dating of monazite from granulite-facies anatectic aluminous gneisses of the hinterland of the Grenville Province (Manicouagan area) is used to constrain the age of metamorphic events. Matrix grains in these rocks show complex internal textures consistent with extensive corrosion and overgrowths which are attributed to partial dissolution of earlier monazite in anatectic melt followed by new growth during melt crystallization or subsequent fluid infiltration. The new monazite data show the following: (i) inherited “pre-Grevillian” ages up to ca. 1400 Ma in some rocks; (ii) “main Grenvillian” ages in the general range of ca. 1070–1020 Ma, with a variable spread in individual samples and a general cluster at 1070–1050 Ma; and (iii) “late Grenvillian” ages at ca. 1010–990 Ma, mostly restricted to backscatter electron (BSE)-bright rims of matrix grains. The wide age range of the main Grenvillian metamorphism suggests episodic growth of monazite over a wide time span, consistent with protracted residence of the host rocks under high-temperature conditions. The clusters in the age distribution likely represent major episodes of melt crystallization in the respective rocks, following the granulite-facies metamorphism. In contrast, the growth of the late Grenvillian monazite at ca. 1000 Ma is attributed to late fluid infiltration of the host rocks under greenschist-facies conditions, coeval with ultrapotassic magmatism. It is the first report of a late Grenvillian metamorphic overprint on granulite-facies mineral assemblages in the hinterland and is consistent with the model of extensional collapse of the orogen.

Geochemical features of ilmenites from the alkaline complexes of the Ukrainian Shield: LA-ICP MS data

LA-ICP MS data are presented for ilmenites from different rocks of the alkaline complexes of the Ukrainian Shield (Chernigovka carbonatite, Oktyabr’skii, Malaya Tersa, and Southern Kal’chinskii gabbrosyenite massifs). Ilmenites from the early intrusive phases (alkaline pyroxenites, gabbroids, and ultramafic rocks) have the elevated contents of Cr, Co, Ni, and V, while ilmenites from later alkaline and nepheline syenites, monzonites, and carbonatites are significantly enriched in Nb and Ta, which is caused by change in the alkalinity of the mineral-forming medium. Zr shows the more intrinsic behavior: its content is higher in the ilmenites from basic and ultrabasic rocks than in those from the nepheline syenites and carbonatites. This is mainly caused by temperature conditions of the formation of differentiated alkaline complexes. The carbonatites contain magnesian ilmenite (up to 22 mol % MgTiO3). Variations of Mg contents in ilmentes are correlated with Mg number of mafic minerals and depend also on the iron oxidation state (amount of magnetite) in the carbonatites. In the alkaline massifs of the Ukrainian Shield, ilmenites usually have the low contents of hematite end member (3–7 mol %). Ilmenite serves as a sensitive indicator of temperature, oxygen fugacity, and alkalinity of the mineral-forming medium during crystallization.

Metallogenic and Metamorphic Age of the Hongtoushan Copper–Zinc Massive Sulfide Deposit, Liaoning Province, China

AbstractThe Hongtoushan copper–zinc deposit is the only large Archean volcanogenic massive sulfide (VMS) deposit in China. This paper presents new information on the timing of metallogenesis and metamorphism of the deposit, including new cathodoluminescence (CL) images, and Th U−1 and LA–ICP–MS U–Pb dating on zircons of the biotite–plagioclase gneiss and plagioclase–amphibole gneiss that host the deposit. The CL images and Th U−1 ratios indicate that the zircons within the gneiss are of metamorphic origin. LA–ICP–MS dating of the plagioclase–amphibole gneiss yielded the upper intercept ages of 2549 Ma, and the biotite–plagioclase gneiss yielded the upper intercept ages of 2552 Ma and 2550 Ma correspondingly, indicating that the mineralization of the deposit occurred at around 2550 Ma. The rims of zircons within these host rocks yielded younger U–Pb ages at 2529, 2520 and 2515 Ma, identical to the age of felsic intrusive rocks in the study area. This suggests that the Hongtoushan VMS deposit underwent initial metamorphism and deformation at around 2520 Ma by the intrusion of granite magmas.

Geology and geochronology of magnetite–apatite deposits in the Ning-Wu volcanic basin, eastern China

The Ning-Wu volcanic basin is an important part of the Middle-Lower Yangtze River Valley metallogenic belt in eastern China, where magnetite–apatite deposits are common. These magnetite–apatite deposits can be classified into two types. The first type includes the Washan, Taocun, Heshangqiao and Dongshan deposits, which are hosted in diorite porphyry and adjacent volcanic rocks. The second type includes Gushan, Baixiangshan and Hemushan deposits, developed at the contact between gabbro–diorite and sedimentary rocks. We used 40Ar–39Ar dating on phlogopite and U–Pb LA-ICP MS dating of zircon in ore-related diorite porphyry and gabbro–diorite to determine the timing of iron mineralization in the basin. The ages of the magnetite–apatite deposits such as Washan, Taocun, Heshangqiao Gushan Baixiangshan Hemushan deposits are from 130Ma to 131Ma. Thus the magnetite–apatite deposits in the Ning-Wu volcanic basin all formed at about 130Ma, later than the skarn and porphyry Cu–Au deposits in the adjacent fault-uplift areas such as Edongnan, Jiu-Rui, Anqing-Guichi and Tongling clusters that are between 146Ma and 135Ma. Based on available petrological and geochemical data, the magnetite–apatite deposits in the Ning-Wu volcanic basin are interpreted to have formed under regional lithospheric extension and thinning, and ore-forming elements were derived from basaltic melts sourced from enriched lithospheric mantle and the crust.

U-Pb zircon geochronology of northern metamorphic massifs in the Biga Peninsula (NW Anatolia-Turkey): new data and a new approach to understand the tectonostratigraphy of the region

Metamorphic massifs of the Biga Peninsula can be divided into two approximately ENE–WSW-trending belts. It is believed that these two belts represent two different tectonic zones separated by a NE-trending Alpine ophiolitic suture. The Sakarya Zone lies to the S–SE of this Alpine suture, and consists of the Kazdağ metamorphic complex which is tectonically overlain by the Permo-Triassic Karakaya Complex. The metamorphic rocks, as an Alpine edifice located N–NW of the suture, have been assigned to the Rhodope and Serbo-Macedonian massifs of Bulgaria and Greece. The northern metamorphic belt is represented by the Karadağ Massif in the west, which has been evaluated as a different unit from the others, the Karabiga Massif in the east and the Çamlıca Massif between them. All three massifs are mapped in detail in light of previous studies and LA–ICP–MS U-Pb zircon dating was applied to stratigraphically compare them. Contrary to previous studies, our data indicate that the basement metamorphic associations in these three areas show similar characteristics concerning their stratigraphical and lithological aspects and also spatial distribution of their outcrops. U-Pb LA–ICP–MS dating of zircons from the three individual metamorphic massifs yielded the following data: maximum sedimentation ages of the protolith of mica schists in the range of 559 ± 17 to 582 ± 30 Ma; crystallisation age of the protolith of metavolcanic rocks of 577 ± 20 Ma; and crystallisation age of the protolith of eclogites at 565 ± 9 Ma. These ages clearly show that the metamorphic units of the northern massifs are comparable to each other. Also, the U-Pb zircon concordia diagrams from these three metamorphic massifs show remarkably similar patterns. In addition to the similar maximum sedimentation ages for all mica schists with crystallisation ages of the protoliths of the metabasic rocks, there are two major complex tectono-thermal overprints (episodic lead loss events), at c. 330–300 Ma (Variscan?) and c. 100–10 Ma (Alpine and late Alpine?), respectively. Field mapping and analytical data indicate that the basement rocks of the northern massifs in the Biga Peninsula have a correlative Late Ediacaran to Early Cambrian stratigraphic range. In part, Permian strata unconformably overlie basement rocks in the Karadağ Massif. Both tectono-thermal events are demonstrated by coeval episodic lead loss of many zircons in all samples from all areas. Finally, the results of this research do not support an Alpine suture between the two metamorphic belts of the Biga Peninsula. Therefore, the geological evolution of the region might require reevaluation.

Obsidian Source Use in Tongan Prehistory: New Results and Implications

ABSTRACT The article presents results of an obsidian sourcing study on artifacts from Tonga and Fiji. New LA-ICPMS data on obsidian source locations on Tafahi in northern Tonga are discussed in relation to inter-island mobility during two important phases in the Central Pacific: the late-Lapita phase in Fiji-West Polynesia at 2700–2600 cal. BP and during the time of the rise of Polynesian chiefdoms at ∼1000–400 cal. BP. The sourcing results indicate that two sources of obsidian were exploited during Tongan prehistory. It is suggested that different modes of interaction were responsible for obsidian movement during the early and late phases of Tongan prehistory.

Late Carboniferous syn-tectonic magmatic flow at the northern margin of the North China Craton—Evidence for the reactivation of cratonic basement

Syn-tectonic magmatic flow, which typically occurs along continental margins or in orogenic belts deformed by tectonic stresses, may indicate the re-melting of middle–lower crust, tectonic setting of the magmatic plutons or the reactivation of cratonic basement. The northern margin of the North China Craton hosts Late Carboniferous plutons that show evidence of magmatic flow. The plutons were emplaced at 320–300Ma, as indicated by zircon U–Pb SHRIMP and LA–ICP–MS dating, rather than high-grade metamorphic rocks such as Archean or Paleoproterozoic gneiss, as previously thought. These granitic plutons, composed of granite and granodiorite, contain a south-vergent shallow-dipping transposition foliation and recumbent folds. Features of magmatic flow are overprinted by a north-dipping foliation and solid-state thrusting and shearing deformation. Aluminum-in-hornblende geobarometry shows that magmatic flow occurred in the middle to lower crust at a depth of approximately 19±5km. The occurrence of southward magmatic flow at 320–300Ma at the northern margin of the North China Craton indicates the reactivation of cratonic basement.