bluuebunny/crossref_metadata_2025_split huggingface dataset:
Palaeomagnetism and magnetostratigraphy of the Middle Triassic in the Iberian Ranges (Central Spain)
Authors: Rey D. , Turner P. , Ramos A. 
Published: April 2008

Abstract
The study of the structure and origin of remanence in five sections comprising the Rillo Mudstones and Sandstones and Torete Multicoloured Mudstone and sandstone Formations (Middle Triassic, Central Spain) reveals the presence of several components of magnetization of different ages. Detrital hematite and ilmenohaematite carry a primary magnetization of Triassic origin in the form of a DRM or PDRM. In addition, it is likely that an early CRM also contributes to the primary remanence. Goethite and several textural phases of authigenic hematite are responsible for a recent overprint in the form of a late CRM. Thermal demagnetization allowed the isolation of a characteristic Triassic remanence on which a reliable magnetostratigraphy for Anisian-Ladinian times could be based, and correlated with sections of similar age in North America and Asia. However, it did not succeed in entirely removing the CRM associated with the latest component of the overprint which resulted in the primary remanence being biased by residual components of Recent origin.
Remanence acquisition was controlled by the sedimentary environment and the diagenetic processes that took place during burial and uplift. The sedimentary environment controlled the conditions of deposition and facies distribution which limited the occurrence of a particular diagenetic phase within the rock volume. Acquisition of secondary components of magnetization, and the consequent pervasive Holocene magnetization (in the form of a late CRM) is primarily related to coarser grained horizons. Sand body interconnectivity has also played an important role in the process. Primary remanence is better preserved in the finer-grained horizons. A PTRM associated with the uplift is easily removed during thermal demagnetization. Calculation of mean vectors by integrating data from adjacent magnetozones allows correction for the overprint bias. The corrected directions can then be closely compared with results from stable Europe.
Palaeomagnetism and palaeogeography of Adria
Authors: Channell J. E. T. 
Published: April 2008

AbstractAn ‘African’ Mesozoic apparent polar wander path (APWP) based on rotated North American data is compared with palaeomagnetic data from Adria and surrounding regions. The form of the APWPs from the Southern Alps, Umbria-Marche (Italy) and the Transdanubian Central Range (Hungary) is similar to that of the ‘African’ APWP. The Umbria-Marche and Transdanubian APWPs are rotated relative to the African APWP, and the rotation is best explained by local anticlockwise tectonic rotations of 20° and 30° for the NW Umbria-Marche and Transdanubian regions, respectively. Permian to Cretaceous palaeomagnetic poles from the Southern Alps are not distinguishable from the African APWP. The more recently derived Cretaceous poles from Istria, Cretaceous poles from Iblei (Sicily), Gargano and Apulia are all consistent, within the confidence limits of the data, with the African APWP. Rifting in the Ionian Sea/Eastern Mediterranean either predated the mainly Jurassic-Cretaceous palaeomagnetic dataset or did not produce recognizable rotation of Adria relative to Africa. The Northern Calcareous Alps are often considered to have been contiguous with the Southern Alps during the Mesozoic, however, the NCA (Liassic) poles are closer to coeval poles for Europe, and are rotated in excess of 80° clockwise relative to the African APWP. The Northern Calcareous Alps were probably detached from the Southern Alps during Late Triassic and Jurassic time, and did not undergo the ‘African’ rotation which affected Adria.
The pattern of crustal block rotations in the Italian region deduced from aeromagnetic anomalies
Authors: Fedi M. , Florio G. , Rapolla A. 
Published: April 2008

Abstract
In contrast to palaeomagnetic studies that consider outcropping rocks, the analysis of aeromagnetic anomalies can give averaged information about large volumes of deep-seated rocks. The recognition and analysis of anomalies having an ‘abnormal shape’ in the central Mediterranean area have yielded original and interesting results in recent years. Accurate interpretation of these anomalies gives information on the nature of magnetization of the deep crust and on the geodynamic history of this region. Results suggest that the southern Italian area can be divided into zones which experienced different tectonic rotations in both clockwise and anticlockwise senses. The pattern of rotations deduced in this way agrees well with that determined by standard palaeomagnetic analyses.
A review of palaeomagnetic research in the Troodos ophiolite, Cyprus
Authors: Morris Antony 
Published: April 2008

Abstract

A summary of the most significant results of palaeomagnetic research within the well-known Troodos ophiolite of Cyprus is presented. The studies are broadly divided into those relating to microplate rotation and those which shed light on processes operating during crustal genesis. Early recognition that the Troodos Complex as a whole experienced a 90° anticlockwise rotation generated several attempts to constrain the precise timing of rotation. A series of palaeomagnetic data obtained within the
in situ
Late Cretaceous to Recent sedimentary cover of the ophiolite demonstrate that rotation began in the Campanian, soon after Turonian crustal genesis, and was complete by the Early Eocene. Rotation occurred at an approximately constant rate of
c.
2° Ma
−1
. The most popular rotation mechanism is one involving a combination of oblique subduction to the south of Cyprus and collision of the trench with the Arabian continental margin to the east. A Troodos microplate became detached and rotated in response to the resultant anticlockwise torque exerted upon the supra-subduction zone crust. Detailed palaeomagnetic and structural studies have also revealed details of the Troodos spreading configuration, and specifically the relationships of horizontal and vertical axis rotations to ridge-parallel faulting and transform tectonism. Extension was achieved through a combination of magmatic accretion and amagmatic stretching, the latter producing significant rotations about ridge-parallel, sub-horizontal axes. Dykes and extrusives adjacent to the fossil Southern Troodos transform zone have been rotated clockwise in response to dextral shear along the transform, producing deviations away from the predominant N-S dyke trend within the Sheeted Dyke Complex of the ophiolite. The intersection of the transform with the principal Troodos spreading axis along the Solea graben has been identified, and transform-related rotations are now suggested to have occurred mainly in the active corner of the intersection. On-going palaeomagnetic research is now focused on the relationship between the Troodos Complex and the other major tectonostratigraphic terranes of Cyprus.
Palaeomagnetism of some Cretaceous Nubian Sandstones, Northern Sinai, Egypt
Authors: Kafafy A. M. , Tarling D. H. , El Gamili M. M. , Hamama H. H. , Ibrahim E. H. 
Published: April 2008

Abstract

A total of 23 sites have been sampled from the Nubian Sandstone of Gabal El-Minsherah and Gabal El-Halal, northern Sinai. Isothermal remanent magnetization acquisition showed that hematite is the predominant magnetic mineral carrying the remanence after the destruction of goethite at temperatures of 100–150°C. The
in situ
directions correspond to palaeomagnetic poles at 84°N 257°E (G. El Minsherah) and 78°N 288°E (G. El Halal). A fold-test shows that the magnetizations were acquired later than the Late Cretaceous (Laramide) tectonic disturbance. The presence of both normal and reversed polarities and
in situ
pole positions close to the expected Late Tertiary palaeomagnetic pole suggest that the magnetizations are of Miocene age. They are probably chemical magnetizations acquired during occasional fluid migrations through these permeable beds during arid Miocene climatic phases.
Emplacement temperatures of pyroclastic deposits on Santorini deduced from palaeomagnetic measurements: constraints on eruption mechanisms
Authors: Bardot Leon , Thomas Rick , McClelland Elizabeth 
Published: April 2008

Abstract
In pyroclastic eruptions, explosive fragmentation of magma occurs, breaking up some of the surrounding volcanic edifice, and a clastic deposit is formed containing fragments of juvenile magma and other rock debris. The temperature at which such a deposit is emplaced places important constraints on eruption mechanisms. The palaeomagnetic technique applied to lithic clasts which had cooled and solidified prior to the eruption can provide a quantitative estimate of emplacement temperature if there has been no modification of the magnetic mineralogy of the lithics during emplacement; thermal demagnetization is used to determine the temperature which removes all of the uniformly directed overprint component acquired during cooling in the deposit.
The volcano of Santorini (or Thera) in the Aegean has experienced a series of cataclysmic eruptions over the past 200 ka. We have determined emplacement temperatures for many of these tephra, from plinian airfalls, lag breccias, ignimbrites and phreatomagmatic deposits. The palaeomagnetic technique will give erroneous results if the magnetic mineralogy of a lithic clast altered during the eruption. This would give a CRM overprint which might completely or partially replace the primary remanence in blocking temperature intervals which extend above the actual emplacement temperature. We have carried out palaeointensity experiments on overprinted lithics to assess the magnetic origin of the overprint (pTRM, CRM or a combination) and hence the reliability of the temperature estimates. Results from the co-ignimbrite lithic breccias show they were emplaced hot. The Middle Pumice and Minoan plinian airfalls display equilibrium temperatures that decrease with increasing distance from vent, and provide constraints on the predictions concerning the cooling of tephra during fallout from eruption columns. Emplacement temperatures for the Minoan Phases 2 (phreatomagmatic deposits) and 3 (massive structureless white deposits) are low considering the deposits are principally composed of juvenile material. For Phase 2 this supports the conventional view of such deposits being the products of lateral explosions caused when water entered the plinian vent. The juvenile material of Phase 3 probably cooled as a result of interaction with water in the vent system, and we interpret them as very low grade ignimbrites.
Palaeomagnetic controls on the emplacement of the Neapolitan Yellow Tuff (Campi Flegrei, Southern Italy)
Authors: Gennaro Maurizio De’ , Gialanella Paola R. , Incoronato Alberto , Mastrolorenzo Giuseppe , Naimo Debora 
Published: April 2008

Abstract
Two outcrops of Neapolitan Yellow Tuff at Torregaveta and Posillipo have been investigated palaeomagnetically. Analyses of low blocking temperature components, in association with mineralogical, volcanological and magnetic anisotropy data, suggest the following sequence of events: (i) deposition of pyroclastics at temperatures not lower than 275°C, at least at Torregaveta; (ii) cooling associated with zeolitization and modification of the original positions of the clasts; (iii) further dislocation of the clasts after cooling; and (iv) lithification. Such a model reconciles otherwise conflicting volcanological and palaeomagnetic data.
Archaeomagnetic directions: the Hungarian calibration curve
Authors: Márton P. 
Published: April 2008

Abstract

The first archaeomagnetic dating in Hungary was made using a reference inclination curve derived by interpolation between three inclination curves then available from continental Europe, namely from France, Bulgaria and the Ukraine. As the corresponding declination curves could not be interpolated with confidence, all three declination curves were used only for an estimation of the time interval to which the measured declinations might be assigned. As data accumulated it became feasible for dating to be made exclusively on the basis of archaeomagnetic and direct observational results for Hungary. The results now cover the last 2000 years with relatively short gaps (sixth and thirteenth centuries
ad
), for which data interpolation is plausible. The variation of inclination is fairly sinusoidal and well resolved. It exhibits two maxima (
c.
70°) at approximately
ad
800 and
ad
1500 and three minima at about
ad
300 (
c.
58°),
ad
1300 (
c.
55°) and in the twentieth century (
c.
62°). Although the variation of the declination is twice as large as that of the inclination, the declination record has inherently less resolution (d
D
= d
I
/cos
I
> d
I
). Approximately zero declination values during the first half of the first millennium
ad
were followed by westerly values during the sixth to eighth centuries (
c.
10°). It appears that by
ad
900 the declination was already easterly and rapidly increasing until
ad
1000 when it peaked with a value over 20°E. A newly discovered feature is a short oscillation beginning with 16° at
ad
1300 and ending with 16.5° at
ad
1600 during which the declination became westerly with a minimum of −10° in the first half of the fifteenth century. From
ad
1600 on the declination rapidly decreased and described a negative half circle between about
ad
1620–30 and 1950 with a minimum of −18° at
ad
1800. The general pattern of the directional secular variation for Hungary is in agreement with that for France, Sicily, Britain, the Ukraine and the Balkans.
Continental collision in the Banda arc
Authors: Richardson A. N. , Blundell D. J. , Richardson A. N. 
Published: April 2008

Abstract
Two deep seismic reflection profiles across the zone of convergence between Australia and the Banda arc east of Timor reveal the structures formed during lithosphere deformation in response to continental collision. Australian continental crust is bent down to the north to form the lower lithospheric plate. The immediately overlying upper plate is made up of a former outlier of the Australian continental shelf, now squeezed between the Australian continent to the south and the Banda arc to the north. The ages of metamorphism and of a regional unconformity in Timor indicate that the outlier began to accrete to the upper plate in the late Miocene. Near the Timor trough, at the junction between the two plates, seismic reflection data show the upper plate to be cut by north-dipping structures interpreted as thrusts in an accretionary prism formed since the arrival of the Australian continental shelf at the collision zone at about 2.5 Ma. The northern part of the collision zone is dominated by structures dipping southwards, antithetic to subduction, which penetrate the lithosphere to depths of at least 50 km. Earthquake data indicate that these are active thrust faults which divide the upper plate into imbricate slices. The seismic reflection sections, supported by gravity data and seismicity patterns, have been used to develop a model of plate convergence and continental collision which now consists of a 200 km wide zone in which both oceanic and continental material is being shortened, thickened and uplifted.
Contrasting tectonic styles in the Neogene orogenic belts of Indonesia
Authors: Simandjuntak T. O. , Barber A. J. 
Published: April 2008

Abstract
The recent compilation of a new tectonic map of Indonesia as part of the Geotectonic Map Project of East Asia has prompted a reassessment of the contrasted tectonic styles represented by currently developing orogenic belts. These orogenic styles provide a range of models illustrating the diversity and complexity of tectonic processes which may provide the key to the interpretation of other orogenic belts elsewhere in the world. The following distinctive types of orogenies have been recognized within Indonesia. 1. Sunda Orogeny in Java and Nusa Tenggara: involving subduction of oceanic crust with normal convergence, producing an orogenic belt of Andean type with trench, accretionary complex, forearc basin and Quaternary magmatic arc with active volcanoes built on the margin of the Sundaland continent. 2. Barisan Orogeny in Sumatra: with strongly oblique convergence and major strike slip transcurrent fault movement within the magmatic arc, along which a segment of continental crust is being displaced northwards along the western margin of Sundaland. 3. Talaud Orogeny in the northern Molucca Sea: convergence of the Sangihe and Halmahera oceanic magmatic arcs as the Molucca Sea Plate subsides beneath them. 4. Sulawesi Orogeny in eastern Sulawesi: collision of microcontinental blocks with subduction systems along the eastern margin of Sundaland. 5. Banda Orogeny in the southern Banda Arc between Sumba and Tanimbar: collision of the northern margin of the Australian continent with the subduction system along the southern segment of the Banda Arc. 6. Melanesian Orogeny in Irian Jaya and Papua New Guinea: a more advanced stage in the collision of the northern margin of the Australian continent with a magmatic arc on the Philippine Sea plate, commencing in the early Miocene with a partial reversal of polarity and the subduction of the Caroline plate beneath the collision zone.
The present phase of orogenic activity in most of these occurrences commenced in mid-Miocene times and orogenic processes are still in progress.
Palaeomagnetism of the Sibumasu and Indochina blocks: implications for the extrusion tectonic model
Authors: Richter Bryan , Fuller Michael 
Published: April 2008

Abstract
The Jurassic-Cretaceous Kalaw redbeds of Myanmar yield a prefolding Late Cretaceous to Early Palaeogene magnetization which records c. 25–30° of clockwise (CW) rotation relative to the South China block. This corresponds to 10–15° CW relative to the Lower Cretaceous Khorat Plateau VGP. The data also show 5° of northward transport relative to the 100 Ma South China VGP or 12° relative to the Khorat Lower Cretaceous VGP. Similar CW rotations are measured in remagnetized Palaeozoic carbonates in Peninsular Thailand and Langkawi Island, Malaysia. These block motions most likely took place between the Late Cretaceous and the Late Oligocene. These and other recently published data have several implications for the extrusion tectonic model: (i) Sundaland has only rotated 25–30° CW relative to South China during the Tertiary; (ii) southeastward translation is only 300–500 km; and (iii) Sundaland is composed of smaller sub-blocks, some of which have moved northward. This is interpreted to indicate that deformation of the Sibumasu block is dominated by the oblique subduction of the Indian Ocean Plate while deformation of the Indochina block is dominated by extrusion, in turn driven by convergence between the Indian Craton and Eurasia.
Changes in tectonic stress field in northern Sunda Shelf basins
Authors: Tjia H. D. , Liew K. K. 
Published: April 2008

Abstract
The Tertiary basins of the northern Sunda Shelf are underlain by normal and attenuated continental crust that is characterized by moderate to high average geothermal gradients in excess of 5°C/100 m. In the Malay basin, upper Oligocene and younger sediments are more than 12 km thick; in the other basins, such sediments are between 4 and 8 km thick. The Malay, Penyu and West Natuna basins are aulacogens meeting at a triple junction that marks a Late Cretaceous hot spot in the centre of the Malay Dome. Sub-basins (commonly half-graben) developed as pull-apart basins within regional, north to northwest-striking, wrench fault zones. The NW-striking Three Pagodas fault most probably extends farther southeast as the Axial Malay fault in the basement along the length of the Malay basin. Pre-late Oligocene sinistral slip along this fault developed east-west half-graben that fixed the position and orientation of inverted anticlines that later developed in the basin-filling sediments through strike-slip reversal along the fault. Initial basin subsidence took place during Eocene-Oligocene time. Regional tensional conditions prevailed until the early Miocene. During the middle to late Miocene, regional compressional stresses caused reversals of the sense of motion on the major wrench faults, and structural inversion of the basin-filling sediments. On some of the north-striking wrench faults there are indications of up to 45 km of right-lateral displacement which is possibly post-Miocene. The regional wrench faults have acted as domain boundaries with each tectonic domain characterized by different stress fields. The stress systems evolving during the Cenozoic are attributed to varying degrees of interference of plates coupled with changes in convergent directions and/or rates of motion of the Pacific plate, the Indian Ocean-Australian plate, and continued, differential extrusion of SE Asian crust following the collision of the Indian plate with the Eurasian plate.
Far-field and gravity tectonics in Miocene basins of Sabah, Malaysia
Authors: Clennell Ben 
Published: April 2008

Abstract

At the end of the early Miocene, at
c.
17 Ma, oceanic spreading ceased in the South China Sea Basin, as a series of collisions were initiated between continental blocks derived from the Asian mainland and the northwestern margins of Borneo and Palawan. In the NW Sabah Basin this tectonic event caused a major period of uplift and erosion which produced the so-called ‘Deep Regional Unconformity’. While these mainly compressional events were occurring at the southern margin of the South China Sea, the Sulu Sea was undergoing extension, with rifting in the northwest and oceanic spreading in the southeast.

Recent seismic surveys in the Sabah offshore area show that the Deep Regional Unconformity can be traced through from the South China Sea into the Sulu Sea as a boundary between two contrasting depositional systems that are both represented in sedimentary sections onshore eastern Sabah. Eastern Sabah changed from an environment of deep marine clastic deposition in the Oligocene and early Miocene, to shallow marine and terrestrial sedimentation in the mid to late Miocene, with a major period of sedimentary mélange formation occurring at the time of the Deep Regional Unconformity.
Inversion of the Miocene sequence in eastern Sabah appears to be limited to the edges of basement blocks, which were moved by far-field tectonic stresses. Post Middle-Miocene basin evolution in the onshore (Central Sabah Basin) and adjacent parts of the Sulu Sea offshore (Sandakan Basin) has been strongly influenced by mud diapirism and gravitational sagging of progradational sand-rich sediments into underlying muds and mélange units. These sequences appear to have been decoupled from later tectonic events by the great thickness of underlying muds and mélanges.