Archaean–Proterozoic crust, atop a thick (180 km), cold (40 mW/m
2), melt-depleted mantle keel, characterised the North China Craton (NCC) at the end of the Precambrian. Differing ages for ...Pre-Cambrian crust and underlying mantle reveal decoupling brought about by repeated orogenic events over the history of the NCC. The most recent thermo-tectonic episode in the Mesozoic–Cenozoic virtually replaced/transformed all of the Precambrian lithosphere. Whether this was caused by “top-down” rapid delamination (<
5 Ma) or “bottom-up” more protracted thermal/chemical erosion (ca. 100 Ma) depends on the interpretation of Jurassic to Cretaceous geological events. The eastern part of the craton east of the North–South Gravity Lineament lithospheric boundary has experienced the most re-activation. In the Palaeozoic–Mesozoic this region was intruded by kimberlitic magmas and cross-cut by the Tan-Lu fault zone and in the Mesozoic–Cenozoic, the eastern craton was the site of major mafic igneous activity. By the end of the Cenozoic the eastern craton was characterised by thermal highs >
64 mW/m
2, thin continental lithosphere (<
50 km) and thin crust (<
32 km) adjacent to the intra-cratonic Bohai Sea.
Unravelling the generation of compositionally and thermally zoned magma reservoirs is important to our understanding of the dynamic processes operating in magmatic systems. Here, we present new major ...and trace element data for volcanic glasses from the classically zoned Laacher See Tephra and suggest that mafic recharge may play an important role in producing the observed compositional gradient. Mafic phonolite glass from the upper part of the Laacher See Tephra records the addition of ca. 30% basanite magma, which is recognised by an increase in REE + Y and a decrease in Th, U and Zr relative to glasses from more evolved units. We suggest that the Laacher See magmatic system was sustained by repeated episodes of basanite recharge and calculate a recharge magma flux of between 2 × 10
–5
and 1 × 10
−4
km
3
y
−1
in the 20 kyr leading up to the eruption. Basanite addition would have provided heat required to generate the strong compositional and thermal gradients that are recorded in crystals ejected during the Laacher See Tephra eruption.
Volcanic activity at Phlegraean Fields, Italy, produced several major marker tephras over a 50ka period. The caldera forming eruptions of the Campanian Ignimbrite (CI) and Neapolitan Yellow Tuff ...(NYT) are of particular importance for tephrostratigraphy in Europe. Other key eruptions from this source include the Pomici Principali (PP) and the Tufi Biancastri eruptions. We combine analyses of fresh glasses from proximal locations (i.e., juvenile clasts in proximal flow and fall deposits) with data for key tephra layers from Lago Grande di Monticchio, 120km to the east. The micron-beam major (EMPA) and trace (LA-ICP-MS) element glass dataset allows us to: (a) distinguish between tephra units produced from the Phlegraean Fields before and during the CI eruption (CI-series), and before and during the NYT and PP eruptions (NYT-series/PP); (b) discriminate between the CI and the geochemically similar Pre-CI pyroclastic deposits; (c) separate the NYT from Pre-NYT tephra units, although both major and trace elements do show significant overlap. The complex compositional overlap between Pre-NYT tephras may present a problem for tephra correlations in the 14–39ka time window and may have resulted in incorrect proximal–distal and distal–distal correlations. The diagnostic chemical criteria detailed herein permits more accurate matching of distal tephras with their proximal equivalents and hence will improve chronostratigraphy of distal settings and give insight into tephra dispersal. We show that the dispersal of PP tephra was more limited than previously thought. The surge/fall (Lower Member) and subsequent pyroclastic density current (Upper Member) phases of the NYT eruption can be recognised in distal settings. Both the NYT Lower and Upper Members are found in distal localities to the east of the Phlegraean Fields, however the Lower Member is found in the absence of the Upper Member in locations to the far north of Phlegraean Fields. Chemical compositions of the Plinian and ignimbrite phases of the CI eruption overlap extensively, but can be distinguished on a plot of Zr–Th.
Unraveling the eruptive history of the Island of Ischia (southern Italy) is problematic due to its burial, caldera collapse, resurgent uplift and erosion. Here, we present new major and trace element ...glass data for 39–75ka proximal tephra deposits, including those of the caldera-forming Monte Epomeo Green Tuff (MEGT) eruption. Correlations with the distal tephra archive preserved at Lago Grande di Monticchio (LGdM) are used to constrain the timing of as yet undated eruptive events. Out of 13 LGdM tephras analysed from the 39–104ka time window, glass geochemical data show that all are compositionally consistent with the explosive volcanic eruptions of Ischia, whilst 5 of them can be correlated with specific proximal deposits.
Pre-MEGT pyroclastic sequences comprise three compositional groups, these groups occur repeatedly in sucessive eruptions. Proximal-distal correlations indicate that the Porticello eruption occurred at 59±2ka and the Tisichiello eruption probably occurred at 76±3ka. The MEGT eruption is correlated with LGdM TM-19, which has been directly dated at 55±2ka. Post-MEGT tephras form compositional groups that overlap with the pre-MEGT but are displaced to lower FeO and TiO2 and lower incompatible element contents. Proximal-distal correlations indicate that the Schiappone and Pietre Rosse eruptions occurred at 50.6±2.0ka and 45±6ka, respectively.
Tephra from the MEGT eruption span a wide compositional range, broadly overlapping the three pre-MEGT compositional groups but are displaced to higher Nd and Y and contain an additional less evolved glass population. Glass geochemistry is used to recognise and confirm distal equivalents of the MEGT at LGdM (TM-19) and in the Ionian (Y-7), Adriatic (PRAD 1870) and Tyrrhenian (C-18, MD 28) seas. Distal occurences of MEGT tephra define a dispersal axis to the south-southeast and are found as far as 540km from Ischia, making the MEGT one of the most widely dispersed late Quaternary pyroclastic deposit erupted in the Campanian region. We estimate a volume of approximately 40km3 for the fallout portion of the MEGT pyroclastic sequence on the basis of proximal and distal deposit thicknesses.
•We provide major and trace element micron-beam data 39–75ka Ischia tephra.•We correlate 5 distal tephras with proximal deposits.•High resolution ages are provided the varved distal stratigraphy of Lago Grande di Monticchio.•Isopach maps are provided for the caldera-forming MEGT eruption.•MEGT fall is dispersed to the SSE and had a volume of ca. 40km3.
Volcanic ash (<2mm) erupted from the Aeolian Islands is reported distally as layers in sedimentary archives from across the central Mediterranean region. Here we present volcanic glass geochemistry ...of proximal tephra deposits from explosive eruptions on the islands of Vulcano, Lipari, Salina and Stromboli spanning approximately the last 50ka using grain-specific EMPA and LA-ICP-MS. This comprehensive database of volcanic glass compositions (>1000 analyses) provides a basis for proximal-distal and distal-distal tephra correlations. Tephra deposits from the different Aeolian Islands are geochemically diverse; with some individual eruptions showing diagnostic geochemical heterogeneity recognised both stratigraphically and/or spatially. Major element glass analyses reveal that Vulcano (0–21ka) and Stromboli (4–13ka) have erupted potassic (shoshonitic and K-series) tephra with broadly overlapping compositions, but data presented here demonstrates that their eruptive products can be distinguished using either TiO2 contents or their HFSE/Th ratios. Whilst individual volcanic sources often produce successive tephra deposits with near identical major and minor element compositions through time (i.e., Lipari, Vulcano), trace element glass data can help to decipher successive eruptions. Changes in LREE and Th concentrations of volcanic glasses erupted spanning approximately the last 50ka greatly enhance the potential to discriminate successive eruptive units on Lipari. The new proximal glass database has been used to verify new (Ionian Sea; core M25/4-12) and existing distal occurrences of Aeolian Island derived tephra enabling the reassessments of past ash dispersals. Finally, proximal and distal data have been used to establish an integrated proximal-distal eruptive event stratigraphy for the Aeolian Islands.
•Glass characterisation (EMPA and LA-ICP-MS) of Aeolian Island tephra units•Geochemical database•Proximal-distal tephra correlations•Proximal-distal composite event stratigraphy
The increasing application of cryptotephra studies is leading the identification of new tephra marker layers the sources of which in many cases may not be known or may be ambiguous. In this ...contribution, we discuss the controls on tephra geochemistry in the context of establishing the provenance of an unknown tephra layer. We use the RESET database (https://c14.arch.ox.ac.uk), which contains major and trace element data for a number of European silicic tephra erupted in the period 100ka to ca 10ka, to define new and modify existing tectonic setting discrimination diagrams for use with volcanic glass analyses. Bivariate plots of the elements Rb, Nb, Ta, Y and Th and K2O, SiO2, FeO and MgO can be used to identify tephra from different tectonic settings. New, detailed glass chemistry shows that tephra from the productive Neapolitan volcanic centres, Somma-Vesuvius (22–4ka activity), Campi Flegrei (60–15ka) and Ischia (75–20ka), can be separated using major elements, CaO–SiO2, Na2O/K2O–CaO and CaO–MgO. In each of these centres, the tephrostratigraphic record is characterized by the repeated occurrence of similar glass compositions, punctuated by significant changes in magma chemistry. The glass compositions of successive eruptions from Campi Flegrei are similar but there is a significant change in the composition following the Campanian Ignimbrite, and there are comparable compositional changes at Ischia following the Monte Epomeo Green Tuff eruption and at Somma-Vesuvius following the Verdoline event. Distinguishing different tephras from a single volcanic centre is more problematic, and in some instances even impossible, without good chronological and stratigraphic control and/or high-resolution trace element glass data. At Somma-Vesuvius certain major elements can be used to separate glasses from the major chronological phases (Group 1 – Pomici di Base and Verdoline; Group 2 – Mercato and Avellino), but separating tephras within a single group on the basis of glass composition can be problematic.
•Large major and trace element dataset for central and eastern Mediterranean tephras.•Discriminating diagrams for anorogenic and active and post subduction settings.•Diagrams for discriminating between Ischia, Campi Flegrei and Somma-Vesuvius tephra.•Present and compare data for 22–4ka tephra from Somma-Vesuvius.•Discuss causes of compositional variation in tephra.
Miocene to Recent volcanism in northwestern Arabia produced the largest intraplate volcanic field on the Arabian plate (Harrat Ash Shaam, Jordan). The chemically and isotopically diverse volcanic ...field comprises mafic alkali basalts and basanites. The magmas underwent limited fractional crystallization of ol ± cpx ± plag and rare samples have assimilated up to 20% of Late Proterozoic crust en route to the surface. However, there are subtle Sr–Nd–Pb isotopic variations (87Sr/86Sr = 0·70305–0·70377, 143Nd/144Nd = 0·51297–0·51285, 206Pb/204Pb = 18·8–19·2), which exhibit marked correlations with major elements, incompatible trace element ratios and abundances in relatively primitive basalts (MgO >8·5 wt %), and cannot be explained by fractional crystallization and crustal contamination alone. Instead, the data require polybaric melting of heterogeneous sources. Semi-quantitative melt modelling suggests that this heterogeneity is the result of small degree melts (2–5%) from spinel- and garnet-facies mantle, inferred to be shallow Arabian lithosphere, that mixed with smaller degree melts (<1%) from a predominantly deep garnet-bearing asthenospheric(?) source with ocean island basalt characteristics. The latter may be a ubiquitous part of the asthenosphere but is preferentially tapped at small degrees of partial melting. Volcanism in Jordan appears to be the result of melting lithospheric mantle in response to lithospheric extension. With time, thinning of the lithosphere allowed progressively deeper mantle (asthenosphere?) to be activated and melts from this to mix with the shallower lithospheric mantle melts. Although Jordanian intraplate volcanism is isotopically similar to examples of Late Cenozoic volcanism throughout the Arabian peninsula (Israel, Saudi Arabia), subtle chemical and isotopic differences between Yemen and Jordan intraplate volcanism suggest that the Afar plume has not been channelled northwestwards beneath the Arabian plate and played no role in producing the northern Saudi Arabian and Jordan intraplate volcanic fields.
Palaeoclimate records in East Asia offer significant potential to further our understanding of monsoon dynamics and can serve as a link between North Atlantic and tropical climate systems. The ...sedimentary core from Lake Kushu, Rebun Island, provides the first high-resolution palaeoclimate record from northern Japan. In order for this regionally significant archive to be synchronised to other records, and to generate a more detailed Holocene tephra lattice for East Asia, we present the first cryptotephra stratigraphy for northern Japan using the Kushu RK12 core. The detailed RK12 tephrostratigraphy integrates local and far-travelled tephras originating from Japan, Russia, China/North Korea and most likely Indonesia. Five key cryptotephra layers have been identified, precisely dated and correlated to the specific eruptions or the source region (B-Tm tephra – Changbaishan volcano; SH#12 tephra – Shiveluch volcano; Ko-g tephra – Komagatake volcano; Ma-f ∼ j tephra – Mashu volcano and RK12-0819 tephra with possible Indonesian origin). These tephra horizons are very widely dispersed, providing opportunities to synchronise distant palaeoclimate records from the polar region, through high northern latitudes to the tropics, which facilitate interregional comparison of palaeoclimate and environmental data. In addition, a number of the geochemically analysed horizons contain other minor numbers of compositionally distinct glass, which can also be grouped and correlated to their source volcanoes. These minor analyses are of interest since they provide new insight into regional tephra dispersal (e.g., ash dispersal potential of Aira and Towada), and could suggest that there are other potential eruptions that have yet to be identified in the geological record (e.g., potential Changbaishan eruptions). The integrated Lake Kushu cryptotephra record extends the ash dispersal of several key tephra horizons in the region. The presence of the Shiveluch SH#12 tephra in Lake Kushu (ca. 1900 km away), documents the first example of a Russian tephra reaching the Japanese Archipelago. Furthermore, glass compositions suggest that the core could preserve an eruption event derived from Indonesia, highlighting the future possibility to significantly extend and interlink the tephra lattice across the entirety of Asia. This is an essential step for the understanding of how climate changes propagate over large geographical areas. Indeed, several of these tephra markers coincide with significant ecological changes reflected in the pollen proxy record at Lake Kushu. Using this high-resolution palaeoenvironmental record, we however find no significant ecological impact following the large late Holocene “Millennium Eruption” from Changbaishan, China/North Korea.
•First high-resolution Holocene cryptotephra stratigraphy for the northernmost Japan.•First identification of a Russian tephra onshore in Japan.•Tephras from Japan, Russia, China and Indonesia are integrated within the record.•Ash dispersal limits & potential eruption events revealed by cryptotephra study.•Updated Holocene tephra lattice for East Asia based on cryptotephra results.
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