Tectonic Period Research Articles

Petrographic characteristics and zircon UPb geochronology of granitogneiss rocks in the Chu Lai - Kham Duc area (Quang Nam province)

The early Palaeozoic granitogneiss association in the Chu Lai - Kham Duc area (Quang Nam) is a large area of hundreds of km2, along southern of the East – West ductile deformation zones (Tam Ky – Phuoc Son fault zone), which is studied in detail in different geologic maps scales by the geologists, which is named Chu Lai complex. The five samples studied in detail are composed mainly of granitogneiss and biotite gneiss from the Chu Lai - Kham Duc area. The samples were crushed and large zircons were extracted. The in-situ zircon U–Pb geochronology was conducted on five samples (60 zircons in total) of age between 444 Ma and 426 Ma. These ages indicated the prolonged magmatic – tectonic period between the late Ordovician and middle Silurian in Kon Tum massif.

Detrital zircon U–Pb geochronology of Permian strata in the Galilee Basin, Queensland, Australia

ABSTRACTThe late Carboniferous to Triassic tectonic history of eastern Australia includes important periods of regional-scale crustal extension and contraction. Evidence for these periods of tectonism is recorded by the extensive Pennsylvanian (late Carboniferous) to Triassic basin system of eastern Australia. In this study, we investigate the use of U–Pb dating of detrital zircons in reconstructing the tectonic development of one of these basins, the eastern Galilee Basin of Queensland. U–Pb detrital zircon ages were obtained from samples of stratigraphically well-constrained Cisuralian and Lopingian (early and late Permian, respectively) sandstone in the Galilee Basin. Detrital zircons in these sandstones are dominated by a population with ages in the range of 300–250 Ma, and ages from the youngest detrital zircons closely approximate depositional ages. We attribute these two fundamental findings to (1) appreciable derivation of detrital zircons in the Galilee Basin from the New England Orogen of easternmost Australia and (2) syndepositional magmatism. Furthermore, Cisuralian sandstone of the Galilee Basin contains significantly more >300 Ma detrital zircons than Lopingian sandstone. The transition in detrital zircon population, which is bracketed between 296 and 252 Ma based on previous high-precision U–Pb zircon ages from Permian ash beds in the Galilee Basin, corresponds with the Hunter–Bowen Orogeny and reflects a change in the Galilee Basin from an earlier extensional setting to a later foreland basin environment. During the Lopingian foreland basin phase, the individual depocentres of the Galilee and Bowen basins were linked to form a single and enormous foreland basin that covered >300 000 km2 in central and eastern Queensland.

Influence of Rift Superposition on Lithospheric Response to East African Rift System Extension: Lapur Range, Turkana, Kenya

AbstractThe Turkana Depression of northern Kenya lies at the intersection of the NW‐SE trending late Mesozoic‐early Paleogene South Sudan and Anza rifts and the N‐S trending late Paleogene‐Recent East African Rift System (EARS). A low‐temperature thermochronology study in the Lapur Range reveals a complex tectonothermal evolution related to multiple periods of regional and local tectonism. Zircon (U‐Th)/He data from Precambrian basement record rapid Early Cretaceous denudational cooling. Coeval subsidence in the adjacent Anza and South Sudan rifts (Morley, Bosworth, et al., 1999; Schull, 1988) suggests that the northern Turkana region acted as a basement high separating the grabens, as well as an axial source of sediment. Between ~95 and 90 Ma, a period of reheating commenced with burial of Lapur basement beneath ~500 m of Late Cretaceous‐Eocene Lapur Sandstone and ~1.5–3.5 km of latest Eocene‐early Miocene Turkana volcanics. Apatite fission track (AFT) and apatite (U‐Th‐Sm)/He data record a transition to rapid denudational cooling in the mid‐Miocene (~14 Ma) in response to EARS‐related extension in the northern Turkana Basin. Thermal history models indicate that the Lapur Range experienced ~90–100°C of mid‐Miocene to Plio‐Pleistocene cooling, yielding the first Neogene AFT ages reported from Kenya related to EARS exhumation. We attribute the larger magnitude of cooling in the Lapur Range compared to other regions of the EARS to the attenuated crustal thickness and elevated heat flow of the Turkana Depression, crustal properties inherited from earlier Cretaceous‐Paleogene rifting. The resulting low effective elastic thickness of the Turkana lithosphere allowed for increased isostatic footwall uplift in response to EARS extension.

Structural Geology Analysis In A Disaster-Prone Of Slope Failure, Merangin Village, Kuok District, Kampar Regency, Riau Province

The geological disaster of landslide has occurred in Merangin Village, Kuok Subdistrict, Kampar Regency, Riau Province which located exactly in the national road of Riau - West Sumatra at Km 91. Based on the occurrence of landslide, this research was conducted to study geological structure and engineering geology to determine the main factors causing landslides. Based on measurement of the structural geology found on research area, there were fractures, faults and fold rocks which having trend of stress N 2380 E, plunge 60, trending NE-SW direction. Several faults that found was normal faults directing N 2000 E with dip 200 trending from northeast-southwest and reverse fault impinging N 550 E with dip 550, pitch 200 trending to the northeast. Fold structures showing azimuth N 2010 E trending southeast-northwest. From geological engineering analysis, the results of scan line at 6 sites that have RQD value ranges 9.4% - 78.7 % with discontinuity spacing 4 - 20 cm. So, It can be concluded that the formed structure was influenced by the extensive northeast-southwest tectonic phase, then continued through north-south tectonic phase, and ended by a tectonic period with directing from northeast-southwest. Rock Mass Rating classification showing value 62 – 76, Which also resulted that rocks in the study area have weathered on the outside but still in good condition (good rock). However, This condition of structure has caused the formation rocks producing weak zone that became one cause of the occurrence of landslides.

The control of deformation partitioning and strain localization on porphyroblast behaviour in rocks and experiments

Multiple generations of sub-vertical and sub-horizontal foliations preserved as inclusion trails in garnet in mylonitic rocks from the hanging wall of the Main Central Thrust in the Himalayas indicate that these porphyroblasts did not rotate during thrusting. This result is predicated by (i) a consistent succession of 5 changes in FIA trend (foliation inflection/intersection axes in porphyroblasts) for samples where the orientation changes from porphyroblast cores to rims; (ii) sub-vertical and sub-horizontal foliations occur as inclusion trails around each of the 5 FIAs in the succession, which would not be the case if the garnet porphyroblasts rotated during subsequent phases of deformation as tectonism continued; (iii) a change in inclusion trail asymmetry immediately prior to the commencement of mylonitzation indicates top to the south thrusting only if the porphyroblasts had not rotated as they grew; (iv) the latter asymmetry matches truncated crenulation relics preserved within the mylonitic matrix foliation that indicate top to the south thrusting as the latter foliation formed. Partitioning of deformation into shortening and shearing components stops rotation of porphyroblasts during their growth and during following periods of ductile tectonism. This can be replicated via computer modelling by duplicating the crenulation-hinge-like coaxial environment in which porphyroblasts nucleate and grow before the strain intensifies. This was done using Drucker-Prager constitutive models with temperature-dependent strain softening behaviour and resulted in no porphyroblast rotation when followed by non-coaxial deformation no matter how intense. Furthermore, strain localization in the model containing competent objects of variable size, shape and orientation, produced no rotation during deformation involving components of shortening and shearing. These approaches to modelling mechanically resolve the sub-vertical/sub-horizontal foliations defined by inclusion trails and consistent FIA trend successions obtained from the Main Central Thrust rocks as well as in orogens elsewhere.

Magmatic zircon Lu–Hf isotopic record of juvenile addition and crustal reworking in the Gawler Craton, Australia

New in situ zircon Lu–Hf isotopic data are presented from magmatic rocks distributed across the Gawler Craton, Australia. These rocks range in composition from granite to gabbro, with the majority being granite or granodiorite and moderately peraluminous in composition. The new Lu–Hf isotopic data, together with previously published data, provide insight into the magmatic evolution of the craton and crust and mantle interaction through time. Increased juvenile content of magmatic rocks correlate with periods of extensional tectonism, in particular basin formation and associated magmatism during the Neoarchean to earliest Paleoproterozoic (c. 2555–2480Ma), Middle Paleoproterozoic (c. 2020–1710Ma) and Late Paleoproterozoic (c. 1630–160Ma). In contrast, magmatic rocks associated with periods of orogenic activity show greater proportions of crustal derivation, particularly the magmatic rocks generated during the c. 1730–1690Ma Kimban Orogeny. The final two major magmatic events of the Gawler Craton at c. 1630–1604Ma and c. 1595–1575Ma both represent periods of juvenile input into the Gawler Craton, with εHf(t) values extending to as positive as +8. However, widespread crustal melting at this time is also indicated by the presence of more evolved εHf(t) values to −6.5. The mixing between crust and mantle sources during these two youngest magmatic events is also indicated by the range in two stage depleted mantle model ages (TDMc) between 1.76Ga and 2.51Ga. Significant mantle input into the crust, particularly during formation of the c. 1595–1575Ma Hiltaba Suite and Gawler Range Volcanics, likely facilitated the widespread crustal magmatism of this time period. Viewed spatially, average εHf(t) and TDMc values highlight three of the major shear zones within the Gawler Craton as potentially being isotopic as well as structural boundaries. Differences in isotopic composition across the Coorabbie Shear Zone in the western Gawler Craton, the Middle Bore Fault in the northern Gawler Craton and, to a lesser extent, the Kalinjala Shear Zone in the southern Gawler Craton, broadly correspond to crustal and even lithospheric-scale discontinuities evident in geophysical studies. Therefore, these shear zones may approximate some of the first order crustal domains within the Gawler Craton.

Mass‐transport complexes as markers of deep‐water fold‐and‐thrust belt evolution: insights from the southern Magdalena fan, offshore Colombia

AbstractMass wasting is an important process in the degradation of deep‐water fold‐and‐thrust belts. However, the relationship between mass‐transport complex (MTC) emplacement and the timing and spatial progression of contractional deformation of the seabed have not been extensively studied. This study uses high‐quality, 3D seismic reflection data from the southern Magdalena Fan, offshore Colombia to investigate how the growth of a deep‐water fold‐and‐thrust belt (the southern Sinú fold belt) is recorded in the source, distribution and size of MTCs. More than nine distinct, but coalesced MTCs overlie a major composite basal erosion surface. This surface formed by multiple syn‐ and post‐tectonic mass‐wasting events and is thus highly diachronous, thereby recording a protracted period of tectonism, seascape degradation and associated sedimentation. The size and source location of these MTCs changed through time: the oldest ‘detached’ MTCs are relatively small (over 9–100 km2 in area) and sourced from the flanks of growing anticlines, whereas the younger ‘shelf‐attached’ MTCs are considerably larger (more than 200–300 km2), are sourced from the shelf, and post‐date the main phase of active folding and thrusting. Changes in the source, distribution and size of MTCs are tied to the sequential nucleation, amplification and along‐strike propagation of individual structures, showing that MTCs can be used to constrain the timing and style of contractional deformation, and seascape evolution in time and space.

The Litchfield Pluton in South-Central Maine: Carboniferous Alkalic Magmatism in northern New England, USA

The Litchfield pluton is a poorly exposed 7 km2 composite alkalic intrusive complex that cuts previously deformed and metamorphosed Silurian turbidites in south-central Maine. The pluton includes a variety of alkaline syenites, including the type locality of “litchfieldite”, a coarse-grained cancrinite, sodalite, and lepidomelane bearing nepheline syenite first recognized over 150 years ago and common in many petrologic collections. A new U-Pb zircon age of 321 ± 2 Ma from the nepheline syenite is interpreted to represent the crystallization age of the plutonic complex. A new biotite 40Ar/39Ar age of 239 ± 1 Ma from the syenite is similar to previously published mica ages from the surrounding country rocks and dates the time of regional cooling in the area below ~ 300°C. Whole rock geochemical analyses from rocks of the Litchfield pluton are compatible with strongly alkaline A-type granitoid rocks that formed in a within plate or continental rift tectonic setting. The age and geochemical characteristics of the alkalic igneous rocks near Litchfield are consistent with a model that invokes the generation of a small volume of alkalic magma beneath south-central Maine during a period of Carboniferous transcurrent tectonism in the northern Appalachian orogen.

Study on Karst Features and its Influence on the Project of Wudongde Hydropower Station of Jinsha River

Wudongde canyon where the hydropower station will be built is deeply cut by the river with the height of more than 800m. Three type of rocks (sedimentary, metamorphic and volcanic rocks) outcrop at the project area. The complexity of the lithology of the Mesoproterozoic Huili Group Luoxue Formation (the limestone, marble, dolomite, marble lithification dolomite, quartzite and phyllite parallel to each other) combined with the complexity metamorphic process (including marble lithification, dolomization and sericitization) and the multiphase tectonic movement and multiphase transgressive period and regressive period formed the Wudongde canyon unique hydro-geological structures. The complexity of the geological conditions (complex lithology, tectonic structures, Neotectonics movement) combined with the dry-hot canyon meteorological conditions formed the complexity of the Wudongde caynon Karst features. The different karst types have developed such as the karst fissures, karst holes, horizontal caves and karst oblique caves. Based on the detailed geological data, the karst and hydro-geology features and the karst controlling factors have been systematically analyzed, meanwhile the karst influence on the project have been evaluated and the suggested measures have been taken to avoid the disadvantage conditions. The experience of Wudongde Hydropower station karst research can be as reference for other similar projects.

Geochronological (U–Pb, U–Th–total Pb, Sm–Nd) and geochemical (REE, 87Sr/86Sr, δ18O, δ13C) tracing of intraplate tectonism and associated fluid flow in the Warburton Basin, Australia

The Warburton Basin of central Australia has experienced a complex tectonic and fluid-flow history, resulting in the formation of various authigenic minerals. Geochemical and geochronological analyses were undertaken on vein carbonates from core samples of clastic sediments. Results were then integrated with zircon U–Pb dating and uraninite U–Th–total Pb dating from the underlying granite. Stable and radiogenic isotopes (δ18O, Sr and eNd), as well as trace element data of carbonate veins indicate that >200 °C basinal fluids of evolved meteoric origin circulated through the Warburton Basin. Almost coincidental ages of these carbonates (Sm–Nd; 432 ± 12 Ma) with primary zircon (421 ± 3.8 Ma) and uraninite (407 ± 16 Ma) ages from the granitic intrusion point towards a substantial period of active tectonism and an elevated thermal regime during the mid Silurian. We hypothesise that such a thermal regime may have resulted from extensional tectonism and concomitant magmatic activity following regional orogenesis. This study shows that the combined application of geochemical and geochronological analyses of both primary and secondary species may constrain the timing of tectonomagmatic events and associated fluid flow in intraplate sedimentary basins. Furthermore, this work suggests that the Sm–Nd-isotopic system is surprisingly robust and can record geologically meaningful age data from hydrothermal mineral species.

ACTIVE CHARACTERISTICS OF SAM NUA FAULT ZONE DURING NEOTECTONIC STAGE

The Sam Nua fault zone lies in the Sop Cop fault zone (in the NW of Vietnam). In Laos, the Sam Nua fault zone composed of two fault branches, which are the main branch called Na Vine - Nam and Tham Pong - Na Ham fault. The first part of fault zone is NW-SE directed extension while the southeastern end turns gradually to latitude direction and sloping NW. In the present - day tectonic period, it has been undergone two stages of motion: right lateral slips in the Miocen - Pliocen time and left lateral slip in the latter phase (Pliocen - Quatylity). The amplitude of horizontal movement is estimated approximately 1200m at a slip - rate of 4mm/year and the vertical is 50m. Recently, this fault zone has been reactivated with a magnitude 5.5 Richter by earthquake recorded. This study will attribute to reveal the process of displacement in Sop Cop fault zone.ReferencesNguyễn Văn Hùng, 2002. Đặc điểm cơ bản đứt gãy hoạt động khu vực tây bắc. Luận án Tiến sỹ Địa chất. Lưu trữ tại Thư viện Quốc gia.Nguyễn Văn Hùng, Hoàng Quang Vinh, 2004. Về hoạt động của các đới đứt gãy Tân kiến tạo ở Tây Bắc Bộ Việt Nam. Tạp chí Địa chất, loạt A số 285, tr.38-48.Bùi Văn Thơm, 2002. Một số đặc điểm đứt gãy tân kiến tạo khu vực Bắc Trung Bộ. Luận án Tiến sỹ. Lưu trữ tại Thư viện Quốc gia.Nguyễn Đình Xuyên (chủ biên), 2003. Nghiên cứu động đất và dao động nền lãnh thổ Việt Nam. Báo cáo Đề tài cấp Nhà nước Viện Vật lý Địa cầu, Hà Nội.Nguyễn Trọng Yêm (chủ biên), 2005. Thiên 107 tai nứt đất lãnh thổ Việt Nam và các giải pháp phòng tránh giảm nhẹ thiệt hại. Đề án điều tra cơ bản. Viện Khoa học và Công nghệ Việt Nam.Daninovich DN, 1961. The method of the study of crack zones associated with faults. Methodical rukovostvo, Irkursk.Nikolaev P. N., 1992. Methods of analysis tectono-dynamics Science. Mockva.Semensky KK, 1991. A new aproach to study the tectonic fractures in discontinuous zones. Geology and Geophysics N0 5 , Novosibirsk.Sherman SI, Dneprovskiy YI, 1968. stress field of the Earth's crust and the geological - structural methods of study Novosibirsk.

Oligocene to Lower Pliocene deposits of the Norwegian continental shelf, Norwegian Sea, Svalbard, Denmark and their relation to the uplift of Fennoscandia: A synthesis

This study provides the results of the first integrated study of Oligocene–Pliocene basins around Norway.Within the study area, three main depocentres have been identified where sandy sediments accumulated throughout the Oligocene to Early Pliocene period. The depocentre in the Norwegian–Danish Basin received sediments from the southern Scandes Mountains, with a general progradation from north to south during the studied period. The depocentre in the basinal areas of the UK and Norwegian sectors of the North Sea north of 58°N received sediments from the Scotland–Shetland area. Because of the sedimentary infilling there was a gradual shallowing of the northern North Sea basin in the Oligocene and Miocene. A smaller depocentre is identified offshore northern Nordland between Ranafjorden (approximately 66°N) and Vesterålen (approximately 68°N) where the northern Scandes Mountains were the source of the Oligocene to Early Pliocene sediments. In other local depocentres along the west coast of Norway, sandy sedimentation occurred in only parts of the period. Shifts in local depocentres are indicative of changes in the paleogeography in the source areas.In the Barents Sea and south to approximately 68°N, the Oligocene to Early Pliocene section is eroded except for distal fine-grained and biogenic deposits along the western margin and on the oceanic crust. This margin was undergoing deformation in a strike-slip regime until the Eocene–Oligocene transition. The Early Oligocene sediments dated in the Vestbakken Volcanic Province and the Forlandssundet Basin represent the termination of this strike-slip regime.The change in the plate tectonic regime at the Eocene–Oligocene transition affected mainly the northern part of the study area, and was followed by a quiet tectonic period until the Middle Miocene, when large compressional dome and basin structures were formed in the Norwegian Sea. The Middle Miocene event is correlated with a relative fall in sea level in the main depocentres in the North Sea, formation of a large delta in the Viking Graben (Frigg area) and uplift of the North and South Scandes domes. In the Norwegian–Danish Basin, the Sorgenfrei-Tornquist Zone was reactivated in the Early Miocene, possibly causing a shift in the deltaic progradation towards the east. A Late Pliocene relative rise in sea level resulted in low sedimentation rates in the main depositional areas until the onset of glaciations at about 2.7 Ma when the Scandes Mountains were strongly eroded and became a major source of sediments for the Norwegian shelf, whilst the Frigg delta prograded farther to the northeast.

How was the Anatolian Side of Istanbul Formed? A Geomorphologic Assessment (NW Turkey)

This study investigates the Geomorphological evolution of Anatolian side of Istanbul. This area is one of the most problematic and most discussed areas in the Near East geography. There is no detailed contemporary geological study undertaken in the area although there are various publications regarding the study area in terms of geomorphology. Current study aims to explicated the geomorphologic features of the study area. In addition to examining the related literature in terms of subject and field, topography maps scaled 1/25.000 were utilized in the study as main materials. Geological characteristics were compiled from geological maps with various scales and reports generated by different researchers. Mapping phase of the study was undertaken with the help of Geographical Information Systems (GIS) software ArcGIS/ArcMAP 10 package program. Obtained data were checked in situ via field surveys and missing points were completed. It was observed that Anatolian side of Istanbul was a product of elements and processes that completely developed in the new tectonic period. The field was observed to be the product of various morphological transformations, different developments and different elements and processes with a topography which has various landforms and polycyclic features due to a lengthy and discontinuous process. Time concept which started with the first lithological storage in Lower Ordovician continued with the deformation related to the right lateral heave around the Marmara Sea and with the clockwise rotation of the study area in Middle-Upper Miocene. The distortion caused by relief inversion during the geomorphologic development caused the formation of embedded valleys in places as a result of drainage gaining a new energy. The study area has obtained its contemporary geomorphologic form.

Inversion-Phase Tectonic Styles and its Oil and Gas Geological Significance in Hailar Basin

In hailaer basin as an example, the paper discusses the types, characteristics, forming conditions and petroleum geological significance of the inversion-phase structures. It is summarized that the characteristics of the three structural types. Non-superimposed newborn extrusion structures, positive inversion structures, and twisting inversion structures, forming in tectonic inversion period of the basin. It also analyzes the forming conditions of the three. The forming conditions of former is the existence of strong extrusion stress field, has not suffered deformation or slight deformation of rock zone in synrift period, and that there are deep and shallow slip planes in the basin. Points out that the inversion-phase structures are the main trap types in extensional basin,that the tectonic inversion period is the mass period of oil and gas migration, which have good matching relationship with inversion-phase structures. Therefore, the traps provided by the tectonic inversion as the most favorable oil and gas gathering place.

Leaf wax stable isotopes from Northern Tibetan Plateau: Implications for uplift and climate since 15 Ma

The growth of Tibetan Plateau is considered to have played a key role during the evolution of Asian climate. Our understanding of the relationship between the plateau growth and Asian climate changes is limited, however, due to the scarcity of well-dated sedimentary sequences that could provide parallel information of the evolution of elevation and climate. Here, we report a high-resolution time series record of the stable hydrogen isotopic composition of leaf-wax n-alkanes (δDn-alk) from a continuous Neogene stratigraphic sequence (15–1.8 Ma) from the Qaidam basin on the northern Tibetan Plateau. These data are used to reconstruct the isotopic composition of meteoric waters (δDm) and subsequently applied to interpret the history of paleotopography and climate in Qaidam.Our results indicate four stages in the evolution of hydrology in the Qaidam basin. In Stage I (15 Ma to 10.4 Ma), δDm gradually decreases from −24.9‰ to −75.5‰, synchronous with a period of active tectonism. The estimated topographic growth of 2.1±0.3 km is comparable to the height of Qaidam basin relative to the foreland Hexi Corridor. We note that C3 plants were dominant in this region since the Miocene; we take this as independent evidence that this area was mountainous before the C4 expansion in late Miocene and Pliocene. δDm variability in subsequent stages appears to be related to shifts in dry and moist conditions and independent of topographical changes — a conclusion supported by other independent climatic records on the Tibetan Plateau. High δDm values in Stage II (10.4 Ma to 6.9 Ma) are related to severe aridity, and Stage III (6.9 Ma to 4.1 Ma) is marked by low δDm values, suggestive of moist conditions related to the strengthening East Asia Summer Monsoon. High δDm values in Stage IV (4.1 Ma to 1.8 Ma) reflect a climate, drier than the present.

Deep structure of a stretched lithosphere: Magnetotelluric imaging of the southeastern Borborema province, NE Brazil

Abstract Magnetotelluric data were collected at 25 stations along a NNW–SSE linear profile deployed perpendicularly to the main structures in the southeastern portion of the Borborema province, northeast Brazil. The geotectonic scenario is characterized by a broad range of tectomagmatic events including periods of compressive tectonism associated with amalgamation of lithospheric blocks during the Brasiliano orogeny in the Late Neoproterozoic, superimposed by extensional events related to the continental break-up and plate drift that led to the formation of the southern Atlantic Ocean in the Early Cretaceous. Strike analysis and distortion decomposition show that most of the data are two-dimensional (2D) but sensitive to distant off-profile structures. Data fit an ENE regional geoelectric strike direction, consistent with the geological and tectonic setup. A joint 2D inversion of the TE and TM modes defined by this strike direction was undertaken and the obtained model exhibits signatures of the different tectonic events in the area. The model suggests that the SE Borborema province is electrically separated into two parts. The first, comprising the southern domain of the province (Sergipano belt and Pernambuco–Alagoas block), has a highly heterogeneous crust and an anomalously conductive upper mantle. The second, comprising the transversal domain of the province (Alto Moxoto terrain), displays crust and upper mantle predominantly homogeneous and resistive. A deep Neoproterozoic lithospheric shear zone (Pernambuco lineament) marks the limit between the two contrasting domains. Also, the region where the Jatoba basin is located in the southern domain presents a striking conductor at upper- to mid-crustal depths beneath the basin. These results correlate well with seismic refraction data that indicate thicker crust for the transversal domain than for the southern domain, with the thinnest crust coinciding with the location of the Jatoba basin. The data support the conclusion that the lithosphere of the southern domain of the Borborema province was significantly stretched in the Cretaceous during the opening of the South Atlantic Ocean, allowing refertilization of depleted upper mantle with incompatible elements from enriched deeper mantle material and reactivation of older crustal fabrics. The conductivity increase below the Jatoba basin is associated with ionic conduction in a currently reactivated fracture zone filled with high salinity fluid. Apparently, the Alto Moxoto terrain worked as a region of higher resistance to stretching, causing the crustal thinning and geoelectric effects to be concentrated to the south of the Pernambuco lineament.

Fault gouge analyses: K–Ar illite dating, clay mineralogy and tectonic significance—a study from the Sierras Pampeanas, Argentina

We introduce a method for the detailed interpretation of K–Ar illite fine-fraction ages of fault gouges from non-sedimentary host rocks. Ages are cross-evaluated with several independent parameters, e.g. illite crystallinity, illite polytype quantification, grain size, mineralogical observations, K–Ar muscovite and biotite host-rock cooling ages as well as low-temperature thermochronological data (AFT, AHe, ZHe). This interpretation approach is applied to a regional study in order to constrain the ‘deformation path’ of the Eastern Sierras Pampeanas in NW Argentina. In the course of this study, a large number of gouge-bearing fault zones were systematically sampled and analysed. Obtained K–Ar illite fine-fraction ages range from Devonian to Cretaceous times, documenting a long-lasting brittle fault activity in this region. Ages >320 Ma are synchronous with a period of intra-Carboniferous compressional tectonism, whereas Permo-Triassic ages are contemporaneous to a flat-slab subduction episode of the Farallon plate beneath the South American plate. Middle to Late Permian and Early Triassic ages as well as Early Jurassic to Middle Cretaceous ages correlate with extensional tectonics in this region. Additionally, K–Ar illite ages reveal a propagation of brittle deformation from north to south in the Sierras de Cordoba and San Luis. Data integrity and consistency with other chronometers and geological evidence show that the here suggested interpretation is valid and can provide a powerful tool to evaluate cooling and deformation histories. Despite of that, we could show that the reliability of fault gouge data strongly depends on the regional cooling.

Glacioeustatic control on the origin and cessation of the Messinian salinity crisis

The desiccation of the Mediterranean during the Messinian salinity crisis (MSC) is one of the most intriguing geological events of recent Earth history. However, the timing of its onset and end, as well as the mechanisms involved remain controversial. We present a novel approach to these questions by examining the MSC from the Atlantic, but close to the Gibraltar Arc, analysing the complete Messinian record of the Montemayor-1 core of the Guadalquivir Basin (SW Spain). Flexural backstripping analysis shows a tectonic uplift trend that would have reduced the depth of the Rifian Corridors considerably. Nonetheless, the rate of tectonic uplift was insufficient to account for the close up of the corridors. At 5.97Ma, a global cooling and associated glacioeustatic sea-level drop, estimated in 60m, is observed. This would have been sufficient to restrict the Rifian Corridors and to trigger the MSC. The later flooding of the Mediterranean occurred during a sea-level rise associated with global warming during a stable tectonic period. We postulate a two-step flooding event: 1) A glacioeustatic sea-level rise during interglacial stage TG 11 (5.52Ma) led to subtropical Atlantic waters entering the west-central Mediterranean through pathways south of the Gibraltar Strait, probably the Rifian Corridors. 2) A global sea-level drop at 5.4Ma, that might have favoured intensification of regressive fluvial erosion in the Gibraltar threshold, along with the subsequent global sea-level rise would have generated the Gibraltar Strait leading to complete Mediterranean refilling during the earliest Pliocene.

Types, characteristics, and time–space distribution of molybdenum deposits in China

Molybdenum exploration activity in China has accelerated tremendously during the past decade owing to the continuous, increasing demand for Earth resources. China possesses the largest Mo reserves in the world (exceeding 19.6 Mt). The major ore deposits are of porphyry, porphyry–skarn, skarn, vein, and sedimentary types. Porphyry molybdenum deposits contain 77.5% of the Chinese Mo reserves, with lesser amounts in porphyry–skarns (13%), skarns (5.1%), and veins (4.4%). Exploitation of sedimentary-type molybdenum deposits thus far has been uneconomical. The six Mo provinces are in the Northeast China, Yanliao, Qinling–Dabie, middle–lower Yangtze River Valley, South China, and Sanjiang areas. We recognize six ore-forming periods: (1) Precambrian (>541 Ma), (2) Palaeozoic (541–250 Ma), (3) Triassic (250–200 Ma), (4) Jurassic–Early Cretaceous (190–135 Ma), (5) Cretaceous (135–90 Ma), and (6) Cenozoic (55–12 Ma). The abundance of Mo ore deposits in China reflects the occurrence of multiple periods of tectonism, involving interactions between the Siberian, North China, Yangtze, India, and Palaeo-Pacific plates. Precambrian molybdenum deposits are related to Mesoproterozoic volcanism in an extensional setting. Palaeozoic Cu–Mo deposits are related to calc-alkaline granitic plutons in an island arc or a continental margin setting. Triassic Mo deposits formed in the syn-collision–postcollision tectonic setting between the Siberian and North China plates and between the North China and Yangzi plates. Jurassic–Early Cretaceous molybdenum deposits formed along the eastern margin of Asia and are associated with the palaeo-Pacific plate-subduction tectonic setting. Cretaceous Mo deposits are related to high-K calc-alkaline granitic rocks and formed in a lithospheric thinning setting. Cenozoic molybdenum deposits formed in a collision setting between the Indian and Eurasian continents and the subsequent extensional setting.

Tectonic Setting of the Cu-Ni Sulfide-Bearing Mafic-Ultramafic Complexes in Northern Jilin Province, NE China

There are series of Cu-Ni sulfide-bearing mafic-ultramafic intrusions widespread in north JilinProvince,Northeastern China. The intrusions formed in Xing’an-Mongolian Orogenic Belt near to the northeastern margin of North China Craton. The complexes were formed in almost same period according to the zircon U-Pb dating reported recently, which means that the complexes were formed in same tectonic period and belong to one tectonic magmatic event. The rock assemblages are different from the ophiolite type and Yidun type in orogenic belt. The mafic-ultramafic complexes formed in the range from 217 Ma to 232 Ma coeval with A-type granites in the area, which formed bimodal igneous rock assemblage. According to the regional angular unconformities, there were existed the orogenies of Caledonian, Hercynian, Early Indosinian, Late Indosinian and Yanshanian. The Early Indosinian coeval with orogenic I-type granites and sanukitie that suggesting the lithosphere thickening in the extrusion tectonic setting of orogenic processes, however the Late Indosinian coeval with bimodal igneous rock assemblage that suggesting the lithosphere thinning in the extension tectonic setting of post-orogenic processes in the Xing’an-Mongolian Orogenic Belt. Chemical composition of the mafic-ultramafic rocks has the characteristics of high-Mg and low-K tholeiites related with inter-continental post-orogenic tectonic setting. The trace elements indicate their formed in conditions of continental extension belt or initial rift and has the characteristics of revolution from oceanic island arc, volcanic arc of continental margin to continental extended belt. The low initial Sr isotopic ratios and positive εNd(t) values suggest that the initial magma of the complexes come from the parting melting of depleted lithospheric mantle. The depleted ithospheric mantle was new formed supported by zircon Hf isotope in Hongqiling complex. The depleted lithospheric mantle may be caused by the asthenosheric mantle upwelling and underplating in the tectonic setting of extension during the Late Indosinian post-orogenic processes.