Exhumation history of the NW Indian Himalaya revealed by fission track and 40Ar/39Ar ages

New fission track and Ar/Ar geochronological data provide time constraints on the exhumation history of the Himalayan nappes in the Mandi (Beas valley) – Tso Morari transect of the NW Indian Himalaya. Results from this and previous studies suggest that the SW-directed North Himalayan nappes were emplaced by detachment from the underthrusted upper Indian crust by 55 Ma and metamorphosed by ca. 48–40 Ma. The nappe stack was subsequently exhumed to shallow upper crustal depths (<10 km) by 40–30 Ma in the Tso Morari dome (northern section of the transect) and by 30–20 Ma close to frontal thrusts in the Baralacha La region. From the Oligocene to the present, exhumation continued slowly.Metamorphism started in the High Himalayan nappe prior to the Late Oligocene.High temperatures and anatexis of the subducting upper Indian crust engendered the buoyancy-driven ductile detachment and extrusion of the High Himalayan nappe in the zone of continental collision. Late extrusion of the High Himalayan nappe started about 26 Ma ago, accompanied by ductile extensional shearing in the Zanskar shear zone in its roof between 22 and 19 Ma concomitant with thrusting along the basal Main Central Thrust to the south. The northern part of the nappe was then rapidly exhumed to shallow depth (<10 km) between 20 and 6 Ma, while its southern front reached this depth at 10–5 Ma.     

Tethyan and Indian subduction viewed from the Himalayan high- to ultrahigh-pressure metamorphic rocks

The Himalayan range is one of the best documented continent-collisional belts and provides a natural laboratory for studying subduction processes. High-pressure and ultrahigh-pressure rocks with origins in a variety of protoliths occur in various settings: accretionary wedge, oceanic subduction zone, subducted continental margin and continental collisional zone. Ages and locations of these high-pressure and ultrahigh-pressure rocks along the Himalayan belt allow us to evaluate the evolution of this major convergent zone.

(1) Cretaceous (80–100 Ma) blueschists and possibly amphibolites in the Indus Tsangpo Suture zone represent an accretionary wedge developed during the northward subduction of the Tethys Ocean beneath the Asian margin. Their exhumation occurred during the subduction of the Tethys prior to the collision between the Indian and Asian continents.

(2) Eclogitic rocks with unknown age are reported at one location in the Indus Tsangpo Suture zone, east of the Nanga Parbat syntaxis. They may represent subducted Tethyan oceanic lithosphere.

(3) Ultrahigh-pressure rocks on both sides of the western syntaxis (Kaghan and Tso Morari massifs) formed during the early stage of subduction/exhumation of the Indian northern margin at the time of the Paleocene–Eocene boundary.

(4) Granulitized eclogites in the Lesser Himalaya Sequence in southern Tibet formed during the Paleogene underthrusting of the Indian margin beneath southern Tibet, and were exhumed in the Miocene.

These metamorphic rocks provide important constraints on the geometry and evolution of the India–Asia convergent zone during the closure of the Tethys Ocean. The timing of the ultrahigh-pressure metamorphism in the Tso Morari massif indicates that the initial contact between the Indian and Asian continents likely occurred in the western syntaxis at 57 ± 1 Ma. West of the western syntaxis, the Higher Himalayan Crystallines were thinned. Rocks equivalent to the Lesser Himalayan Sequence are present north of the Main Central Thrust. Moreover, the pressure metamorphism in the Kaghan massif in the western part of the syntaxis took place later, 7 m.y. after the metamorphism in the eastern part, suggesting that the geometry of the initial contact between the Indian and Asian continents was not linear. The northern edge of the Indian continent in the western part was 300 to 350 km farther south than the area east of the Nanga Parbat syntaxis. Such “en baionnette” geometry is probably produced by north-trending transform faults that initially formed during the Late Paleozoic to Cretaceous Gondwana rifting. Farther east in the southern Tibet, the collision occurred before 50.6 ± 0.2 Ma. Finally, high-pressure to ultrahigh-pressure rocks in the western Himalaya formed and exhumed in steep subduction compared to what is now shown in tomographic images and seismologic data.     

SERPENTINIZATION OF THE MANTLE WEDGE BY FLUIDS DERIVED FROM CONTINENTAL CRUSTAL MATERIAL: EVIDENCE FROM Nd ISOTOPIC SIGNATURES OF SERPENTINITES (TSO MORARI DOME,ELADAKH)

SERPENTINIZATION OF THE MANTLE WEDGE BY FLUIDS DERIVED FROM CONTINENTAL CRUSTAL MATERIAL: EVIDENCE FROM Nd ISOTOPIC SIGNATURES OF SERPENTINITES (TSO MORARI DOME,ELADAKH)1　deSigoyerJ ,GuillotS .Glaucophane bearingeclogitesintheTsoMoraridome (easternLadakh ,NWHimalaya) [J] .Euro peanJournalofMineralogy ,1997,9:10 73～ 10 83. 2　deSigoyerJ,ChavagnacV ,VillaIM ,etal.DatingtheIndiancontinentalsubductionandcollisionalthicke…     

Seismic crustal structure between the Transylvanian Basin and the Black Sea, Romania

In order to study the lithospheric structure in Romania a 450 km long WNW–ESE trending seismic refraction project was carried out in August/September 2001. It runs from the Transylvanian Basin across the East Carpathian Orogen and the Vrancea seismic region to the foreland areas with the very deep Neogene Focsani Basin and the North Dobrogea Orogen on the Black Sea. A total of ten shots with charge sizes 300–1500 kg were recorded by over 700 geophones. The data quality of the experiment was variable, depending primarily on charge size but also on local geological conditions. The data interpretation indicates a multi-layered structure with variable thicknesses and velocities. The sedimentary stack comprises up to 7 layers with seismic velocities of 2.0–5.9 km/s. It reaches a maximum thickness of about 22 km within the Focsani Basin area. The sedimentary succession is composed of (1) the Carpathian nappe pile, (2) the post-collisional Neogene Transylvanian Basin, which covers the local Late Cretaceous to Paleogene Tarnava Basin, (3) the Neogene Focsani Basin in the foredeep area, which covers autochthonous Mesozoic and Palaeozoic sedimentary rocks as well as a probably Permo-Triassic graben structure of the Moesian Platform, and (4) the Palaeozoic and Mesozoic rocks of the North Dobrogea Orogen. The underlying crystalline crust shows considerable thickness variations in total as well as in its individual subdivisions, which correlate well with the Tisza-Dacia, Moesian and North Dobrogea crustal blocks. The lateral velocity structure of these blocks along the seismic line remains constant with about 6.0 km/s along the basement top and 7.0 km/s above the Moho. The Tisza-Dacia block is about 33 to 37 km thick and shows low velocity zones in its uppermost 15 km, which are presumably due to basement thrusts imbricated with sedimentary successions related to the Carpathian Orogen. The crystalline crust of Moesia does not exceed 25 km and is covered by up to 22 km of sedimentary rocks. The North Dobrogea crust reaches a thickness of about 44 km and is probably composed of thick Eastern European crust overthrusted by a thin 1–2 km thick wedge of the North Dobrogea Orogen.     

Growth of the Namche Barwa Syntaxis and associated evolution of the Tsangpo Gorge: Constraints from structural and thermochronological data

The eastern syntaxis of the Himalaya, Namche Barwa, is dominated by a north-plunging antiform which began to decompress/grow at approximately 4 Ma. New fission-track analyses on both apatite and zircon, combined with previous geochronological ages, indicate that the Namche Barwa Dome also extended laterally while growing vertically. Zircon fission-track ages range from 17.6 to 0.2 Ma and have a strong relationship to the main faults of the region, including the Tertiary Tsangpo Suture, with the younger ages inside the fault bounds towards the syntaxis core on the Indian Plate and the older ages away from the fault. Apatite ages reveal that the dome has grown laterally and now impinges over the older faulted margin onto the Asian Plate. The dome is traversed by the Tsangpo which has followed the trace of the Suture for over 1300 km from its source to the entrance of the dome near Dania. As the Tsangpo crosses the dome it departs from the Suture but rejoins it some 60 km northeastwards. We construe that the Suture has been displaced by the growing antiform and as a consequence, the antecedent river has been “dragged” in a left-lateral sense along the exhuming north-plunging dome. Restoring the Suture to its position prior to 4 Ma reveals a path of the Tsangpo eastwards across the present southwestern position of the Namche Barwa indentation. This geometric reconstrunction implies that the Tsangpo and the Brahmaputra were always one and the same river. In addition, the Tsangpo was tectonically forced into juxtaposition with a tributary of the Jiali-Parlung which it probably then captured. The capture was due to tectonic forcing, in the last 4 Ma, rather than headward retreat of the paleo-Brahmaputra as has been previously suggested.     

Time scale of an early to mid-Paleozoic orogenic cycle of the long-lived Central Asian Orogenic Belt, Inner Mongolia of China: Implications for continental growth

We present a detailed, new time scale for an orogenic cycle (oceanic accretion–subduction–collision) that provides significant insights into Paleozoic continental growth processes in the southeastern segment of the long-lived Central Asian Orogenic Belt (CAOB). The most prominent tectonic feature in Inner Mongolia is the association of paired orogens. A southern orogen forms a typical arc-trench complex, in which a supra-subduction zone ophiolite records successive phases during its life cycle: birth (ca. 497–477 Ma), when the ocean floor of the ophiolite was formed; (2) youth (ca. 473–470 Ma), characterized by mantle wedge magmatism; (3) shortly after maturity (ca. 461–450 Ma), high-Mg adakite and adakite were produced by slab melting and subsequent interaction of the melt with the mantle wedge; (4) death, caused by subduction of a ridge crest (ca. 451–434 Ma) and by ridge collision with the ophiolite (ca. 428–423 Ma). The evolution of the magmatic arc exhibits three major coherent phases: arc volcanism (ca. 488–444 Ma); adakite plutonism (ca. 448–438 Ma) and collision (ca. 419–415 Ma) of the arc with a passive continental margin. The northern orogen, a product of ridge-trench interaction, evolved progressively from coeval generation of near-trench plutons (ca. 498–461 Ma) and juvenile arc crust (ca. 484–469 Ma), to ridge subduction (ca. 440–434 Ma), microcontinent accretion (ca. 430–420 Ma), and finally to forearc formation. The paired orogens followed a consistent progression from ocean floor subduction/arc formation (ca. 500–438 Ma), ridge subduction (ca. 451–434 Ma) to microcontinent accretion/collision (ca. 430–415 Ma); ridge subduction records the turning point that transformed oceanic lithosphere into continental crust. The recognition of this orogenic cycle followed by Permian–early Triassic terminal collision of the CAOB provides compelling evidence for episodic continental growth.     

The S-type Ladybird leucogranite suite of southeastern British Columbia: Geochemical and isotopic evidence for a genetic link with migmatite formation in the North American basement gneisses of the Monashee complex

The 62–52 Ma Ladybird granite (LBG) suite is a peraluminous, leucocratic, S-type, quartz monzonitic to granitic suite which occurs as batholiths, stocks, dikes, sills, and pegmatite veins predominantly in the high-grade rocks of the Shuswap complex, in southeastern British Columbia. The emplacement of the LBG was synchronous with the production of abundant migmatites within Thor–Odin dome of the Monashee complex, an exposure of North American basement, exhumed from depths of ca. 26–33 km by Eocene extensional faults. The LBG and the leucosome in migmatites from Thor–Odin dome have similar major and trace element patterns, and are both characterized by zircons which have inherited Precambrian cores. Whole rock Nd isotope compositions show a range of values for the LBG with εNd_{(55 Ma)} values from − 5.0 to − 17.2. The εNd_{(55 Ma)} for the leucosome samples range from − 9.5 to − 23.6, overlapping with those of the granitic suite. These data support the interpretation of a genetic link between formation of the LBG suite and melting of North American basement rocks, such as those exposed in the core of Thor–Odin dome. The leucosome samples have lower high field strength element (HFSE) concentrations and positive Eu anomalies, whereas the LBG samples have higher HFSE concentrations and negative Eu anomalies. The similar trace element characteristics suggest that the leucosome from the migmatites and the LBG are related, whereby most of the leucosome samples are cumulates and the LBG samples represent evolved or residual melts. The initial ⁸⁷Sr/⁸⁶Sr isotope values for both the LBG and leucosome samples have a large range. However, the initial Sr isotopic ratios for the LBG suite are lower than those of the leucosome samples, with ⁸⁷Sr/⁸⁶Sr_{(55 Ma)} ranging from 0.70603 to 0.73688 and 0.74256 to 0.76593, respectively. This isotopic discrepancy suggests either: a) isotopic disequilibrium during partial melting in the mid- to lower crust where the leucosome formed, b) the distribution of Sr during partial melting was controlled by different melt-producing reactions, and/or c) isotopic heterogeneity in the source rocks. At least part of the LBG suite likely formed via melting of North American basement rocks that were dominantly of sedimentary origin. Melting of the Proterozoic supracrustal metasedimentary rocks overlying North American basement may also have contributed to the formation of the different phases of the suite found at the regional scale. However, the abundant leucosomes in the basement rocks of Thor–Odin dome may mark the paths along which anatectic melt migrated in the structurally overlying Ladybird granites of the South Fosthall pluton.     

喜马拉雅西部雅鲁藏布江缝合带地壳尺度的构造叠置

陆陆碰撞过程是板块构造缺失的链条。印度板块与亚洲板块的碰撞造就了喜马拉雅造山带和青藏高原的主体。然而,人们对印度板块在大陆碰撞过程中的行为尚不了解。如大陆碰撞及其碰撞后的大陆俯冲是如何进行的、印度板块是俯冲在青藏高原之下还是回转至板块上部(喜马拉雅造山带内)以及两者比例如何,这些仍是亟待解决的问题。印度板块低角度沿喜马拉雅主逆冲断裂(MHT)俯冲在低喜马拉雅和高喜马拉雅之下已经被反射地震图像很好地揭示。然而,关于MHT如何向北延伸,前人的研究仅获得了分辨率较低的接收函数图像。因而,MHT和雅鲁藏布江缝合带之间印度板块的俯冲行为仍是一个谜。喜马拉雅造山楔增生机制,也就是印度地壳前缘的变形机制,反映出物质被临界锥形逆冲断层作用转移到板块上部,或是以韧性管道流的样式向南溢出。在本次研究中,我们给出在喜马拉雅造山带西部地区横过雅鲁藏布江缝合带的沿东经81.5°展布的高分辨率深地震反射剖面,精细揭示了地壳尺度结构构造。剖面显示,MHT以大约20°的倾斜角度延伸至大约60 km深度,接近埋深为70~75 km的Moho面。越过雅鲁藏布江缝合带运移到北面的印度地壳厚度已经不足15 km。深地震反射剖面还显示中地壳逆冲构造反射发育。我们认为,伴随着印度板块俯冲,地壳尺度的多重构造叠置作用使物质自MHT下部的板块向其上部板块转移,这一过程使印度地壳厚度减薄了,同时加厚了喜马拉雅地壳。     

DIFFUSION MODELLING IN GARNET FROM TSO MORARI ECLOGITE AND IMPLICATIONS FOR EXHUMATION MODELS

DIFFUSION MODELLING IN GARNET FROM TSO MORARI ECLOGITE AND IMPLICATIONS FOR EXHUMATION MODELS1　ChakrabortyS ,GangulyJ.ContribMineralPetrol,1992 ,111:74～ 86 . 2　ChemendaAI ,BurgJ P ,MattauerM .EarthPlanetSciLett ,2 0 0 0 ,174:397～ 40 9. 3　ChemendaAI ,MattauerM ,MalavieilleJ ,etal.EarthPlanetSciLett ,1995 ,132 :2 2 5～ 2 32 . 4　GirardM ,BussyF .TerraNostra ,1999,99/ 2 ,5 7～ 5 8. 5　GuillotS ,SigoyerdeJ ,LardeauxJM ,etal.Contr…     

Age and emplacement of late-Variscan granites of the western Bohemian Massif with main focus on the Hauzenberg granitoids (European Variscides, Germany)

The Variscan Hauzenberg pluton consists of granite and granodiorite that intruded late- to postkinematically into HT-metamorphic rocks of the Moldanubian unit at the southwestern margin of the Bohemian Massif (Passauer Wald). U–Pb dating of zircon single-grains and monazite fractions, separated from medium- to coarse-grained biotite-muscovite granite (Hauzenberg granite II), yielded concordant ages of 320 ± 3 and 329 ± 7 Ma, interpreted as emplacement age. Zircons extracted from the younger Hauzenberg granodiorite yielded a ²⁰⁷Pb–²⁰⁶Pb mean age of 318.6 ± 4.1 Ma. The Hauzenberg granite I has not been dated. The pressure during solidification of the Hauzenberg granite II was estimated at 4.6 ± 0.6 kbar using phengite barometry on magmatic muscovite, corresponding to an emplacement depth of 16-18 km. The new data are compatible with pre-existing cooling ages of biotite and muscovite which indicate the Hauzenberg pluton to have cooled below T = 250–400 °C in Upper Carboniferous times. A compilation of age data from magmatic and metamorphic rocks of the western margin of the Bohemian Massif suggests a west- to northwestward shift of magmatism and HT/LP metamorphism with time. Both processes started at > 325 Ma within the South Bohemian Pluton and magmatism ceased at ca. 310 Ma in the Bavarian Oberpfalz. The slight different timing of HT metamorphism in northern Austria and the Bavarian Forest is interpreted as being the result of partial delamination of mantle lithosphere or removal of the thermal boundary layer.     

Crustal architecture of the Himalayan metamorphic front in eastern Nepal

The Himalayan Metamorphic Front consists of two basinal sequences deposited on the Indian passive margin, the Mesoproterozoic Lesser Himalayan Sequence and the Neoproterozoic–Cambrian Greater Himalayan Sequence. The current paradigm is that the unconformity between these two basinal sequences coincides with a crustal-scale thrust that has been called the Main Central Thrust, and that this acted as the fundamental structure that controlled the architecture of the Himalayan Metamorphic Front. Geological mapping of eastern Nepal and eight detailed stratigraphic, kinematic, strain and metamorphic profiles through the Himalayan Metamorphic Front define the crustal architecture. In eastern Nepal the unconformity does not coincide with a discrete structural or metamorphic discontinuity and is not a discrete high strain zone. In recognition of this, we introduce the term Himalayan Unconformity to distinguish it from high strain zones in the Himalayan Metamorphic Front. The fundamental structure that controls orogen architecture in eastern Nepal occurs at higher structural levels within the Greater Himalayan Sequence and we suggest the name; High Himal Thrust. This 100–400 m thick mylonite zone marks a sharp deformation discontinuity associated with a steep metamorphic transition, and separates the Upper-Plate from the Lower-Plate in the Himalayan Metamorphic Front. The high-T/moderate-P metamorphism at  20–24 Ma in the Upper-Plate reflects extrusion of material between the High Himal Thrust and the South Tibet Detachment System at the top of the section. The Lower-Plate is a broad schistose zone of inverted, diachronous moderate-T/high-P metamorphic rocks formed between  18 and 6 Ma. The High Himal Thrust is laterally continuous into Sikkim and Bhutan where it also occurs at higher structural levels than the Himalayan Unconformity and Main Central Thrust (as originally defined). To the west in central Nepal, the Upper-Plate/Lower-Plate boundary has been placed at lower structural levels, coinciding with the Himalayan Unconformity and has been named the Main Central Thrust, above the originally defined Main Central Thrust (or Ramgarh Thrust).     

Two stages of granite formation in the Sredinny Range, Kamchatka: Tectonic and geodynamic setting of granitic rocks

The newly formed continental crust in southern Kamchatka was created as a result of the Eocene collision of the Cretaceous-Paleocene Achaivayam-Valagin island arc and the northeastern Asian margin. Widespread migmatization and granite formation accompanied this process in the Sredinny Range of Kamchatka. The tectonic setting and composition of granitic rocks in the Malka Uplift of the Sredinny Range are characterized in detail, and the U-Pb (SHRIMP) zircon ages are discussed. Two main stages of granite formation—Campanian (80–78 Ma ago) and Eocene (52 ± 2 Ma ago) have been established. It may be suggested that granite formation in the Campanian was related to the partial melting of the accretionary wedge due to its under-plating by mafic material or to plunging of the oceanic ridge beneath the accretionary wedge. The Eocene granitic rocks were formed owing to the collision of the Achaivayam-Valagin ensimatic island arc with the Kamchatka margin of Eurasia. In southern Kamchatka (Malka Uplift of the Sredinny Range), the arc-continent collision started 55–53 Ma ago. As a result, the island-arc complexes were thrust over terrigenous sequences of the continental margin. The thickness of the allochthon was sufficient to plunge the autochthon to a considerable depth. The autochthon and the lower portion of the allochthon underwent high-grade metamorphism followed by partial melting and emplacement of granitic magma 52 ± 2 Ma ago. The anomalously rapid heating of the crust was probably caused by the ascent of asthenospheric magma initiated by slab breakoff, while the Eurasian Plate plunged beneath the Achaivayam-Valagin arc.     

Fluid inclusion evidence for deep burial of the Tertiary accretionary wedge of the Carpathians

Hydrothermal quartz from mineralized joints of the Carpathian accretionary wedge contains immiscible aqueous, oil‐condensate, methane and carbon dioxide‐rich fluid inclusions. Distribution patterns of the inclusion trapping PT parameters point to a crack‐seal mechanism during upward and lateral migration of hot methane‐rich fluids from overpressured sediments at the base of the accretionary wedge. A simple equation is proposed to calculate depths from densities and trapping pressures of the buoyant inclusion fluids. In the Carpathian accretionary wedge, the paleofluid pressures of 52–306 MPa correspond to a 5‐ to 11‐km‐thick overburden. Prior to exhumation, thickness of the wedge must have attained 10–25 km, of which only c. 50% was preserved until recently. Anomalously high methane densities (up to 0.43 g cm^?3) recorded in the lowermost nappe sheets are provisionally interpreted as a result of supralithostatic overpressure due to thermal cracking of oil and kerogen to methane and pyrobitumen at temperatures above 200 °C.     

Early cretaceous granitoids and their implications for the collapse of the Dabie orogen, eastern China: SHRIMP zircon U–Pb dating and geochemistry

Two stages of early Cretaceous post-orogenic granitoids are recognized in the Dabie orogen, eastern China, which recorded processes of extensional collapse of the orogen. The early stage granitoids ( 132 Ma) are foliated hornblende quartz monzonites and porphyritic monzogranites. They are of high-K calc-alkaline series and metaluminous to weakly peraluminous, with high K₂O and low MgO contents (Mg^# values: 32.0–46.0), they contain high Sr, low Y and heavy rare earth elements (HREE), and have high Sr/Y and (La/Yb)_N ratios, without clear negative Eu, Sr and Ti anomalies. The early stage deformed granitoids have adakitic geochemical compositions and are equilibrated with residues rich in garnet and poor in anorthite-rich plagioclase, and thus indicate the existence of an over-thickened (> 50 km) crustal root beneath the orogen at  132 Ma. The later stage granitoids ( 128 Ma) are undeformed fine-grained monzogranites, fine-grained K-feldspar granites and coarse-grained K-feldspar granite-porphyry. They belong to a peraluminous and high-K calc-alkaline to shoshonite series, and display a flat HREE pattern and have strong negative Eu, Sr and Ti anomalies, with low Sr/Y and (La/Yb)_N ratios. The late stage granitoids are equilibrated with residues rich in anorthite-rich plagioclase, hornblende, ilmenite/titanite and poor in garnet, indicating that the crust of the Dabie orogen became thinner (< 35 km) at  128 Ma. SHRIMP zircon U–Pb ages and changing compositional trends for these two stages of granitoids indicate that the over-thickened crust formed by the Triassic continental subduction/collision under the Dabie orogen remained until the early Cretaceous, and collapsed quickly in a few million years during the early Cretaceous.     

Signature of Himalayan orogenic features in Brahmaputra River sediments,Bangladesh: Evidence from single-grain heavy mineral chemistry

The present study describes results obtained from the chemistry of detrital heavy minerals i.e. pyroxene, amphibole, biotite, garnet, epidote and Fe-Ti oxides in fluvial sediments of the northern Brahmaputra River (Bangladesh) with an aim to determine conditions of their petrogenesis and provenance. The primary and secondary genera of ferromagnesian minerals occurred in calc-alkaline and peraluminous subduction zone. In which, the garnets are Fe-rich, indicating mostly almandine component (Alm₆₅–Pyp₁₆–Grs₈–Sps₆ averagely), occurred in medium to high grade metasedimentary rocks in the Lesser Himalaya (LH), along the Main Central Thrust (MCT) and the eastern Himalayan syntaxis. Besides, the fingerprint of omphacite and actinolite owe to ascertain the co-existence of garnet developed in ultrahigh-pressure (UHP) eclogites that may also be drained from the Tso Morari massif. Augite to aegirine-augite pyroxenes emphasizes Fe enrichment in basaltic systems and high to ultrahigh grade metamorphic rocks, which are exposed in the LH, Shillong Plateau, Mikir Hills, South Tibetan Detachment System (STDS), eastern Himalayan syntaxis and Tso Morari massif. Geochemistry and thermobarometry of the primary magmatic amphiboles and biotites manifest the source of granitoid and granodiorite like bodies, and their windows are exposed in the Bomi–Chayu, Gangdese arcs and the western Arunachal Himalaya. Again, metamorphosed Fe-Ti oxide minerals are well-exposed along the NE Lesser Himalaya, where magmatic derivative of Fe-Ti oxide minerals were modified through the diffusional processes in low-grade metamorphism (534–562 °C with 10^–22.1–10^?21.5 fo₂). Integrating the aforementioned discussion with the thermochronology, it is evident that the eastern Himalayan syntaxis is the major source of sediment flux, which is carried mostly by the upper Himalayan tributaries i.e. Yigong, Parlung, Dibang and Lohit. Also, the lower Himalayan tributaries i.e. Subansiri and Manas drain the sequestered derivatives dominantly from the Arunachal Himalayan. Tso Morari eclogites (NW Himalaya) have also contribution somewhat of dense minerals to the Tsangpo-Brahmaputra River system. Thus, scrutinizing the fingerprint of single-grain detrital minerals provides key information regarding the source terrains and tectonics of the Himalayan sequences.     

A counterclockwise PTt path of high-pressure/low-temperature rocks from the Coastal Cordillera accretionary complex of south-central Chile: constraints for the earliest stage of subduction mass flow

Within the metamorphic basement of the Coastal Cordillera of central Chile, the Western Series constitutes the high-pressure (HP)/low-temperature (LT) part (accretionary prism) of a fossil-paired metamorphic belt dominated by metagreywackes. In its eastern part, blocks derived from small lenses of garnet amphibolite with a blueschist facies overprint are locally intercalated and associated with serpentinite and garnet mica-schist. Continuously developed local equilibria were evaluated applying various independent geothermobarometric approaches. An overall anticlockwise PT path results. The prograde path evolved along a geothermal gradient of 15 °C/km, passing the high-pressure end of greenschist facies until a transient assemblage developed within albite-epidote amphibolite facies transitional to eclogite facies at peak metamorphic conditions (600–760 °C, 11–16.5 kbar; stage I). This peak assemblage was overprinted during an external fluid infiltration by an epidote blueschist facies assemblage at 350–500 °C, 10–14 kbar (stage II) indicating nearly isobaric cooling. The retrograde equilibration stage was dated with a Rb–Sr mineral isochron at 305.3±3.2 Ma, somewhat younger (296.6±4.7 Ma) in an adjacent garnet mica-schist. Localized retrograde equilibration continued during decompression down to 300 °C, 5 kbar. The retrograde evolution is identical in the garnet amphibolite and the garnet mica-schist.

The counterclockwise PT path contrasts the usual clockwise PT paths derived from rocks of the Western Series. In addition, their ages related to stage II are the oldest recorded within the fossil wedge at the given latitude. Its “exotic” occurrence is interpreted by the path of the earliest and deepest subducted material that was heated in contact with a still hot mantle. Later accreted and dehydrated material caused hydration and cooling of the earliest accreted material and the neighbouring mantle. After this change also related to rheological conditions, effective exhumation of the early subducted material followed at the base of the hydrated mantle wedge within a cooler environment (geothermal gradient around 10–15 °C/km) than during its burial. The exotic blocks thus provide important time markers for the onset of subduction mass circulation in the Coastal Cordillera accretionary prism during the Late Carboniferous. Continuous subduction mass flow lasted for nearly 100 Ma until the Late Triassic.     

A 1.78 Ga large igneous province in the North China craton: The Xiong'er Volcanic Province and the North China dyke swarm

The 1.78 Ga Xiong'er Volcanic Province (XVP) and coeval North China giant mafic Dyke Swarm (NCDS) are the most important magmatic events occurring after the amalgamation of the North China craton (NCC). The XVP consists of 3–7 km of extrusive volcanics and some feeder dykes/sills located along the southern margin of the NCC and extending over an area > 0.06 M km². Compositions vary from basalt to rhyolite, but are predominantly intermediate in terms of silica content. There are also minor sedimentary intercalations and pyroclastic units. The sedimentary interlayers indicate an environment changing from continental-facies to oceanic-facies up-section. The XVP is characterized by fractional crystallization from an EM I type mantle source, and both continental arc (Andean-type) and rift environments have been proposed. The NCDS is widespread in the central NCC with an outcrop area > 0.1 M km², and are exposed at variable depths up to 20 km (deepest in the north). Dyke compositions vary from basalt to andesite and dacite, but are dominantly mafic, and comprise two series of magmatism. Previous studies revealed that the NCDS recorded assimilation and fractional crystallization of an EM I type magma source, with a minor DM contribution in the younger magmas. Both syn-collisional and intra-continental anorogenic environments have been proposed. Spatial and petrogenic correlations suggest a cogenetic relationship between the NCDS and XVP, and considered together, they define a Large Igneous Province (LIP) of > 0.1 M km² in area and > 0.1 M km³ in volume, which is also notable for its continuous compositional range from mafic to felsic (with no gap at intermediate compositions). The petrology is explained by a common magma source that undergoes a silica-poor and iron-enriched fractionation trend at depth followed by a silica-rich and iron-poor fractionation trend in shallow-level magma conduits (dykes) and surface lavas. A mantle plume is favored as the cause of this  1.78 Ga North China LIP.     

Ar–Ar ages of intrusions in East Greenland: Rift-to-drift transition over the Iceland hotspot

Sixteen ⁴⁰Ar–³⁹Ar ages are presented for alkaline intrusions to appraise prolonged post-breakup magmatism of the central East Greenland rifted margin, the chronology of rift-to-drift transition, and the asymmetry of magmatic activity in the Northeast Atlantic Igneous Province. The alkaline intrusions mainly crop out in tectonic and magmatic lineaments orthogonal to the rifted margin and occur up to 100 km inland. The area south of the Kangerlussuaq Fjord includes at least four tectonic lineaments and the intrusions are confined to three time windows at 56–54 Ma, 50–47 Ma and 37–35 Ma. In the Kangerlussuaq Fjord, which coincides with a major tectonic lineament possibly the failed arm of a triple junction, the alkaline plutons span from 56 to 40 Ma. To the north and within the continental flood basalt succession, alkaline intrusions of the north–south trending Wiedemann Fjord–Kronborg Gletscher lineament range from 52 to 36 Ma.

We show that post-breakup magmatism of the East Greenland rifted margin can be linked to reconfiguration of spreading ridges in the Northeast Atlantic. Northwards propagation of the proto-Kolbeinsey ridge rifted the Jan Mayen micro-continent away from central East Greenland and resulted in protracted rift-to-drift transition. The intrusions of the Wiedemann Fjord–Kronborg Gletscher lineament are interpreted as a failed continental rift system and the intrusions of the Kangerlussuaq Fjord as off-axis magmatism. The post-breakup intrusions south of Kangerlussuaq Fjord occur landward of the Greenland–Iceland Rise and are explained by mantle melting caused first by the crossing of the central East Greenland rifted margin over the axis of the Iceland mantle plume (50–47 Ma) and later by uplift associated with regional plate-tectonic reorganization (37–35 Ma). The Iceland mantle plume was instrumental in causing protracted rift-to-drift transition and post-breakup tholeiitic and alkaline magmatism on the East Greenland rifted margin, and asymmetry in the magmatic history of the conjugate margins of the central Northeast Atlantic.     

Late Quaternary basin evolution of the Gulf of Corinth: Sequence stratigraphy, sedimentation, fault–slip and subsidence rates

The Gulf of Corinth is a graben, which has undergone extension during the Late Quaternary. The subsidence rate is rapid in the currently marine part whereas uplift now affects a large part of the initially subsiding area in the North Peloponnese. In this paper, we document the rates of subsidence/uplift and extension based on new subsurface data, including seismic data and long piston coring in the deepest part of the Gulf. Continuous seismic profiling data (air gun) have shown that four (at least) major oblique prograding sequences can be traced below the northern margin of the central Gulf of Corinth. These sequences have been developed successively during low sea level stands, suggesting continuous and gradual subsidence of the northern margin by 300 m during the Late Quaternary (last 250 ka). Subsidence rates of 0.7–1.0 m kyr^− 1 were calculated from the relative depth of successive topset to foreset transitions. The differential total vertical displacement between the northern and the southern margins of the Corinth graben is estimated at about 2.0–2.3 m kyr^− 1.

Sequence stratigraphic interpretation of seismic profiles from the basin suggests that the upper sediments (0.6 s twtt thick) in the depocenter were accumulated during the last 250 ka at a mean rate of 2.2–2.4 m kyr^− 1. Long piston coring in the central Gulf of Corinth basin enabled the recovery of lacustrine sediments, buried beneath 12–13.5 m of Holocene marine sediments. The lacustrine sequence consists of varve-like muddy layers interbedded with silty and fine sand turbidites. AMS dating determined the age of the marine–lacustrine interface (reflector Z) at about 13 ka BP. Maximum sedimentation rates of 2.4–2.9 m kyr^− 1 were calculated for the Holocene marine and the last glacial, lacustrine sequences, thus verifying the respective rates obtained by the sequence stratigraphic interpretation. Recent accumulation rates obtained by the ²¹⁰Pb-radiometric method on short sediment box cores coincide with the above sedimentation rates. Vertical fault slip rates were measured by using fault offsets of correlated reflector Z. The maximum subsidence rate of the depocenter (3.6 m kyr^− 1) exceeds the maximum sedimentation rate by 1.8 m kyr^− 1, which, consequently, corresponds to the rate of deepening of the basin's floor. The above rates indicate that the 2.2 km maximum sediment thickness as well as the 870 m maximum depth of the basin may have formed during the last 1 Ma, assuming uniform mean sedimentation rate throughout the evolution of the basin.     

Low-temperature constraints on the Alpine thermal evolution of the Western Carpathian basement rock complexes

The Cretaceous to Palaeogene Alpine exhumation of previously buried Variscan basements is recorded in the southern portion of the Western Carpathians in the Gemeric and Veporic units. The Meso-Cenozoic collisional processes resulted in basement exhumation of the Tatric Unit from Palaeogene to Neogene times. According to zircon and apatite fission track data, the Gemeric Unit, an uppermost thick-skinned thrust sheet, cooled from depth levels of ∼10 up to 2.5 km (temperature interval of ∼250–60 °C) about 88–64 Ma ago, after the collapse of overlying Meliata-Turňa-Silica Mesozoic accretionary prism. The middle and lower thick-skinned thrust sheets, Veporic and Tatric units, cooled from the depths of ∼10 up to 2.5 km ∼110–40 Ma ago. The process was controlled by unroofing of footwall from beneath the Gemeric Unit. About 50–20 Ma ago, the internal zone of Tatric Unit gradually exhumed to depth of <2 km and some parts of the unit appeared at the surface level. However, the external zone of Tatric Unit was buried beneath the Eocene to Lower Miocene sedimentary successions and exhumed to the subsurface level at ∼21–8 Ma ago, as a result of oblique collision of the Western Carpathians with the European Platform.