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Radiometric dates of key rock units indicate that a remnant Late Mesozoic ocean of the Huatung Basin is still preserved today east of the South China Sea (SCS). We integrate regional geology with a Cretaceous oceanic basement in the vicinity of the Huatung Basin to reconstruct the Huatung Plate east of the Eurasian continent. Results of geophysical investigations, four expeditions of deep-sea drilling and a renaissance of regional geology allow us to propose a hypothesis that the mechanism responsible for the SCS opening was raised from strike-slip fault on the east. The hypothesis suggests that the SCS opening could highly relate to the strike-slip faults inherited from Late Mesozoic structures onshore–offshore the SE Cathaysia Block to develop rhombic-shaped extensional basins en echelon on the thinned Eurasian continental crust in the Early Cenozoic. It was followed by sinistral strike-slip movements along the boundary between the Eurasian Plate and the Huatung Plate driven by oblique subduction of the Huatung Plate to the northwest coupled with slab-pull force by southward subduction of the Proto-SCS to open up the triangle-shaped oceanic East Sub-basin in the Early Oligocene (33/34 Ma). The spreading ridge then propagated southwestward in the step-over segment between the Zhongnan-Lile and the Red River strike-slip fault systems to open the triangle-shaped oceanic Southwest Sub-basin by 23 Ma. The plate boundary fault was subsequently converted into the Manila Trench when the Eocene Sierra Madre arc of the Huatung Plate had moved from the south to its present latitude by the Middle Miocene.

Greater India comprises a part of the Indian plate that subducted under Asia to help form the Tibetan Plateau. Defining the size of the Greater India is thus a key constraint to model the India-Asia collision, growth of the plateau, and the tectonic evolution of the Neo-Tethyan realm. We report Early Cretaceous paleomagnetic data from the central and eastern Tethyan Himalaya that yield paleolatitudes consistent with previous Early Cretaceous paleogeographic reconstructions. These data suggest Greater India extended at least 2,675 +/- 720 and 1,950 +/- 970 km farther north from the present northern margin of India at 83.6 degrees E and 92.4 degrees E, respectively. An area of lithosphere >= 4.7 x 10(6) km(2) was consumed through subduction, thereby placing a strict limit on the minimum amount of Indian lithosphere consumed since the breakup of Gondwanaland. Plain Language summary Greater India is part of the Indian plate, subsequently subducted under Asia, that helped create the Tibetan Plateau. The amount of Greater Indian crust therefore plays a critical role to address key problems in continental geodynamics. To what extent can continental crust be subducted? How much crust was derived from horizontal shortening of existing crust? How much of Tibet was created by subducted buoyant, continental crust? We provide paleomagnetic evidence that defines the minimum size of Greater India. Our data show that a lithospheric area of >= 4.7 x 10(6) km(2) was subducted, which supports the notion that the growth of Tibetan Plateau in the Cenozoic occurred by adding buoyant material to its base.

The paleomagnetic record during the middle Neoproterozoic (~825-780 Ma) displays rapid apparent polar wander variations leading to large discrepancies in paleogeographic reconstructions. Some authors propose that these data may represent true polar wander events, which correspond to independent motion of the mantle and lithosphere with respect to Earth’s rotation axis. An alternative explanation might be a perturbation of the geomagnetic field, such as a deviation from a predominantly dipole field or a hyper-reversing field. To test these hypotheses, we sampled 1200 oriented cores over a stratigraphic height of 100 metres in sedimentary rocks of the 820-810 Ma Laoshanya Formation in South China. We will present preliminary paleomagnetic and rock magnetic analyses together with results of petrologic and geochemical experiments to better understand the origin of the paleomagnetic signal.

We investigated the (paleo)latitudinal dependence of angular dispersion sets of virtual geomagnetic poles (VGPs) for the Permian-Carboniferous Reversed Superchron (PCRS: 262-318 Ma). In order to analyze the paleosecular variation during this period we prepared different paleomagnetic datasets from scientific databases and recent literature, based on selection criteria which provided high degree of refinement. Model G of McFadden et al. (1988) was fitted to the VGP dispersion data, providing the shape parameters a and b, which were further compared with similar results for the Cretaceous Normal Superchron (CNS) and other periods of different geomagnetic reversal rates throughout the last 3 Ga. Our results indicate high similarity between the angular VGP dispersion from the PCRS and CNS (a low VGP dispersion at low paleolatitudes, and strong paleolatitudinal dependence), in contrasting difference for periods of higher reversal rates (the last 5 Ma). Despite the geodynamic differences related to both Phanerozoic superchrons, such evidence could point out similar heat flux conditions in the CMB, which may favor compatible stability conditions throughout these magnetozones. Notably, two additional observations which arose from the shape parameters relations for both Phanerozoic superchrons and Precambrian datasets demand further investigation: (i) a pattern of increase for the b/a ratio throughout the 0.5-1.6 Ga interval was observed, which could be partially explained by the Maya Superchron, recently proposed by Gallet et al. (2012); (ii) the b × a relationship for both Phanerozoic superchrons and the 2.45-2.82 Ga interval pointed to the presence of one or more long-term magnetozones throughout the Paleoproterozoic.

Ocean Drilling Program Site 1143 of Leg 184 in the southern South China Sea (SCS) recovered a continuous sedimentary sequence since the Late Miocene (~ 10 Ma), which provides a unique record for better understanding the tectonic, environmental, and climatic evolution in the southern part of the SCS. In this study, we conducted a detailed rock magnetism and paleomagnetism study on 637 discrete samples taken from 512.1 m cores of Hole 1143C. Rock magnetic measurements indicate that the main magnetic mineral is single domain magnetite for samples from the upper 200 mcd (meter composite depth). All samples were subjected to stepwise alternating field demagnetization. The demagnetization behaviors of the samples below 200 mcd were erratic and unstable, owing to very weak remanent magnetization. A total of 15 reliable magnetic reversal events were identified in the upper 190 mcd cores of Hole 1143C based on the declination variations of the characteristic remanent magnetization, which can be correlated very well with the Geomagnetic Polarity Time Scale 2012 in combination with biostratigraphic data and astronomical time scales. Our new magnetostratigraphic results provide a more confident age framework for the southern SCS since the Early Pliocene.

A detailed magnetic analysis has been done on sedimentary core of the International Ocean Discovery Program (IODP) Site U1433A during Leg 349 in the South China Sea (SCS). Results show that dominant carriers of the natural remanent magnetization are greigite and (titano) magnetite. The major shift in both declination and inclination at ~ 185 mbsf is assigned to the Matuyama-Brunhes reversal boundary (~ 0.773 Ma). Constrained by biostratigraphic ages, variations in magnetic parameters of the core can be well correlated to the marine oxygen isotope record at glacial/interglacial cycles. Low values of concentration-dependent magnetic parameters correspond to the interglacials, and vice versa. During the interglacial periods, the dominant magnetic minerals are detrital (titano) magnetite and have relatively coarser grain sizes, while fine-grained greigites dominate the glacial periods. This indicates that during the glacials, greigite prevails at the anoxic condition with amount of terrigenous iron oxide caused by the disconnection between the SCS and the Indian Ocean and the exposure of shelf, but digenesis is suppressed at the opposite environment by the high sea level (interglacials). Thus, the preservation/sulfide process of (titano) magnetite is intimately related to the transformation of sea level changes with the monsoon-related rainfall caused by the glacial/interglacial variation.

Deep-sea hydrogenetic ferromanganese crusts are both potential polymetallic resources and records of long-term environmental changes. For palaeoceanographic studies, it is important to construct a detailed and reliable chronological framework. Here, we report the results of a detailed magnetostratigraphic and rock magnetic study of four hydrogenetic Fe-Mn crusts from the Pacific Ocean (PO-01), South China Sea (SCS-01, SCS-02) and Indian Ocean (IO-01). Two groups of characteristic remanent magnetization directions were defined with nearly antipodal normal and reversed polarities for samples PO-01, SCS-01 and SCS-02, indicating a primary record of the Earth’s magnetic field. The magnetostratigraphic framework, established via correlation with the Geomagnetic Polarity Time Scale 2012, implies growth rates of 4.82 mm/Ma, 4.95 mm/Ma, 4.48 mm/Ma and 11.28 mm/Ma for samples PO-01, SCS-01, SCS-02 and IO-01, respectively. Rock magnetic measurements revealed that the Fe-Mn crust samples from the Pacific Ocean and Indian Ocean were dominated by low coercivity, non-interacting, single-domain (SD) magnetite particles, whereas the South China Sea samples were dominated by SD/pseudo-single-domain (PSD) particles. Multidomain (MD) magnetite may also be present in all samples.

We have conducted a paleomagnetic investigation on the Middle–Upper Jurassic marine strata exposed in the hanging wall of the Tanggula Thrust system near the Yanshiping area, northern Tibet. Progressive demagnetization experiments successfully isolated stable magnetization over a broad spectrum of demagnetization temperatures. The mean direction of the characteristic remanent magnetizations for the Middle–Late Jurassic Yanshiping Group in stratigraphic coordinates (D/I (Declination/Inclination) = 5.6°/60.3°, k = 22.9, α95 = 12.9°, N = 7 s) is much more clustered than the mean direction in geographic coordinates (D/I = 345.5°/37.2°, k = 2.5, α95 = 48.4°), indicating magnetization was not acquired after folding. Although the conventional fold test is positive, incremental untilting test on the characteristic remanent magnetization reveals that a maximum value of precision parameter k occurs at 82.1 ± 4.6% untilting (D/I = 3.3°/57.8°, k = 43.9, α95 = 9.2°), which indicates the ChRMs are probably acquired during Late Cretaceous folding. This synfolding magnetization component is therefore secondary. The corresponding pole position (84.4°N, 119.4°E with dp/dm = 13.5/9.9°) is inconsistent with Jurassic–Early Cretaceous paleopoles of the region, but the paleolatitude is consistent with the Late Cretaceous paleolatitude observed in the Qiangtang terrane and its periphery. The synfolding component is carried by both magnetite and hematite, which were identified by isothermal remnant magnetization acquisition experiments, unblocking temperatures of stable magnetic components, and Curie temperature determination and correlated with observed hydrothermal veins. Available geological evidences indicate that the synfolding magnetization is probably the result of chemical remagnetization caused by orogenic fluids or hydrothermal sources during the early uplift of the Tibetan Plateau.

Widespread Cenozoic sediments in and around the Tibetan Plateau (TP) are thought to have played an important role in explaining the process of the India-Asia collision as well as its interactions with global and regional paleoclimate. However, high-resolution temporal frameworks of sedimentary sequences and controls on geological and climatic events are still absent. To study the abovementioned issues, we investigate the Oligocene-Miocene lacustrine sequences (the Dingqinghu Formation) of the Lunpola Basin, central TP. In this work, cyclostratigraphic analyses are conducted with gamma ray log and pollen data to establish a high resolution temporal framework ranging from ca. 25.4 to 18.0 Ma for the sections. Along these sections, sediment accumulation rates are calculated with orbital signals to monitor clastic input of the lake basin; elemental, palynological, and isotopic data are summarized to depict the paleoclimate and paleoelevation evolution of this drainage system. Integrating all these clues together, we sort out a chronological list of events including lake basin, tectonics, and paleoclimate: regional uplift took place at 23.7 Ma; simultaneously, a distinct lake-basin transition characterized by accelerated sediment accumulation rate is recognized; about 0.2 Ma later at 23.5 Ma, catchment scale drought occurred and maintained to the end of the sections. Our results demonstrate that paleoclimate did not impose decisive influence on the late Oligocene-early Miocene evolution of the lake basin; instead, regional uplift and its associated accelerated exhumation of the source area resulted in the lake-basin transition and paleoclimatic drought. After reviewing the Oligocene-Miocene sedimentary records distributed in and around the TP, we argue that the 23.7 Ma geological event of the Lunpola Basin is probably not a single case but a regional effect of a dramatic tectonic transition of the plateau.

The timing of the Palaeo-Pacific Plate (PPP) subduction in East Asia, following the amalgamation of the North and South China Blocks (NCB and SCB), remains equivocal despite several investigations ...

Understanding the dynamics of double-thickening and uplifting of the Tibetan crust requires constraints on the magnitude and timing of crustal shortening. New elongation/inclination (E/I)-corrected paleomagnetic data from similar to 26-22 Ma sediments indicate that the latitude of southern Tibet in the early Miocene was 31.1/+6.8/+ 5.2 degrees N, not significantly different from today. This implies that the southern margin of Asia, which was at 21-24 degrees N latitude from the Late Cretaceous to the early Eocene, advanced 8-10 degrees northward between the early Eocene and the latest Oligocene. Our results therefore suggest that at least 900-1100 km of continental shortening and significant regional uplift of the plateau occurred between the early Eocene and late Oligocene. Our results suggest that N-S intra-Asian convergence was considerably reduced around 26 Ma, corresponding to a transition from compression to extension within the Tibetan Plateau. Plain Language Summary Two critical questions involving the geodynamic evolution of the Tibetan plateau are (i) when did a compression-dominated tectonic regime change to an extension-dominated tectonic regime on the plateau and (ii) how does this timing correlate with double thickening of the crust? Here we provide paleomagnetic evidence for the timing, magnitude, and partitioning of intra-Asian convergence. Our results imply a first-order constraint of 900-1100 km north-south shortening concentrated within the interval from 53 to 26 Ma. This suggests that a fundamental change at similar to 26 Ma occurred in the geodynamics of the Tibetan Plateau marked by a reduction in large-scale convergence and compressive deformation. The implication is that significant regional uplift of the proto-Tibetan Plateau occurred within the similar to 55-26 Ma interval. The paleolatitude, paleoclimate, and topography of south central Tibet seen at present were likely established around 26 Ma.

The destructive nature of subduction erosion poses challenges to fully understanding the evolution of erosive convergent margins that are critical to understanding crustal recycling and seismogenesis. Forearc deformation holds important clues to the evolution of erosive convergent margins. Here we present detailed paleomagnetic and structural analyses of IODP Site U1380 cores from the middle slope of the forearc of the Costa Rican erosive convergent margin. The analyses reveal a strong deformation zone from ~490 to ~550 mbsf that is characterized by abundant fissility/foliations shallower than the bedding. Similar relatively strong deformation zones are recognized from the frontal prism and upper slope sites, and are broadly correlative, forming a zone of strong deformation across the forearc. This zone spans ~2.0 to 1.83 Ma and the deformation likely occurred briefly at ~1.80 Ma. The widespread, short-lived, and strong deformation is interpreted as a result of intense subhorizontal shear following the rapid forearc subsidence driven by the dramatic subduction erosion associated with the abrupt onset of the Cocos Ridge subduction. Given the typical occurrence of forearc subsidence by subduction erosion, similar styles of deformation are probably common in other erosive convergent margins as well.

To better constrain the Late Triassic paleolatitude of the Qiangtang block and the closure of the Paleo-Tethys Ocean, a combined paleomagnetic and zircon U/Pb geochronological study has been conducted on the Upper Triassic Jiapila Formation volcanic rocks on the northern edge of the Qiangtang block of Central Tibet (34.1°N, 92.4°E). These rocks are dated to 204–213 Ma. Progressive thermal or alternating field demagnetization successfully isolated stable characteristic remanent magnetizations (ChRM) that pass both the fold and reversal tests, consistent with a primary magnetization. These are the first volcanic-based paleomagnetic results from pre-Cretaceous rocks of the Qiangtang block that appear to average secular variation well enough to yield a reliable paleolatitude estimate. Based on our new paleomagnetic data from Upper Triassic lavas, we conclude that the Late Triassic pole of the Qiangtang block was located at 64.0°N, 174.7°E, with A 95 = 6.6 ° ( N = 29 ). We compile published paleomagnetic data from the Qiangtang block to calculate a Late Triassic latitude for the Qiangtang block at 31.7 ± 3.0°N. The central Paleo-Tethys Ocean basin was located between the North China (NCB) and Tarim blocks to the north and the Qiangtang block to the south during Late Paleozoic–Early Mesozoic. A comparison of published Early Triassic paleopole from the Qiangtang block with the coeval paleopoles from the NCB and Tarim indicates that the Paleo-Tethys Ocean could not have closed during the Early Triassic and that its width was approximately ∼32–38° latitude (∼3500–4200 km). However, the comparison of our new combined Late Triassic paleomagnetic result with the Late Triassic poles of the NCB and Tarim, as well as numerous geological observations, indicates that the closure of the Paleo-Tethys Ocean at the longitude of the Qiangtang block most likely occurred during the Late Triassic.

International audience; Coring/logging data and physical property measurements from International Ocean Discovery Program Expedition 349 are integrated with, and correlated to, reflection seismic data to map seismic sequence boundaries and facies of the central basin and neighboring regions of the South China Sea. First-order sequence boundaries are interpreted, which are Oligocene/Miocene, middle Miocene/late Miocene, Miocene/Pliocene, and Pliocene/Pleistocene boundaries. A characteristic early Pleistocene strong reflector is also identified, which marks the top of extensive carbonate-rich deposition in the southern East and Southwest Subbasins. The fossil spreading ridge and the boundary between the East and Southwest Subbasins acted as major sedimentary barriers, across which seismic facies changes sharply and cannot be easily correlated. The sharp seismic facies change along the Miocene-Pliocene boundary indicates that a dramatic regional tectonostratigraphic event occurred at about 5 Ma, coeval with the onsets of uplift of Taiwan and accelerated subsidence and transgression in the northern margin. The depocenter or the area of the highest sedimentation rate switched from the northern East Subbasin during the Miocene to the Southwest Subbasin and the area close to the fossil ridge in the southern East Subbasin in the Pleistocene. The most active faulting and vertical uplifting now occur in the southern East Subbasin, caused most likely by the active and fastest subduction/obduction in the southern segment of the Manila Trench and the collision between the northeast Palawan and the Luzon arc. Timing of magmatic intrusions and seamounts constrained by seismic stratigraphy in the central basin varies and does not show temporal pulsing in their activities..

The surface uplift history of the Tibetan Plateau (TP) offers a key testing ground for evaluating models of collisional tectonics and holds important implications for processes ranging from global cooling to the onset of the Asian monsoon. Various models have been proposed to reveal the surface uplift history of the TP, but controversies remain. We evaluate these models using data from sedimentology and stratigraphy, structural geology, magmatism, exhumation, and paleoaltimetry studies. Structural analyses indicate that thrust belts, which spread from the central TP outward toward its surrounding margins, accommodated most of the India–Asia convergence, and facilitated crustal shortening and thickening in the central TP. Eocene adakitic rocks located in the Qiangtang and the Lhasa blocks likely were generated by partial melting of an eclogitic source. Paleogene (50–30 Ma) potassic rocks only occur in the Qiangtang block, whereas Late Oligocene–Late Miocene (26–8 Ma) potassic rocks occur both in the Qiangtang and Lhasa blocks. Low-temperature thermochronologic ages in the central TP are older than 40–35 Ma, whereas those in the margins are younger than 20 Ma (mostly Late Miocene, and Pliocene/Pleistocene in age). Independent paleoaltimetry estimates suggest that the Lhasa and Qiangtang terranes attained their current elevations during the Eocene, most likely due to the initial collision between India and Lhasa, whereas the Hoh Xil basin area to the north and Himalayas to the south were still low, even below sea level in the latter case. We argue for an inside-out growth pattern for the Tibetan Plateau. The TP grew southward and northward from a nucleus of high topography and is likely to continue expanding along the Mazar Tagh fault to the northwest, the Kuantai Shan-Hei Shan-Longshou Shan to the northeast, the Longquan Shan to the east and the Shillong plateau to the south if the northward force of India would not diminished.

New reliable palaeomagnetic data from the Siberian platform help in deciphering its palaeogeography during ∼450–400 Ma. Geochronology of late Devonian mafic sills provides time constraints for tectonic deformation along the southern margin of the Siberian Platform and thus a minimum age for the regional magnetic overprint. From a late Ordovician–Silurian sedimentary section of the Nyuya syncline in the southern part of the Siberian platform with the Devonian sills hosted nearby in early Palaeozoic sediments, pre-folding presumably primary magnetization was isolated from the sediments during stepwise thermal cleaning. High unblocking temperatures imply that haematite is the main carrier of magnetization. The sample-mean direction for 37 Ordovician samples from nine sites in stratigraphic coordinates is Ds = 168.5, Is = −5, ks = 22.3 and α 95 = 5.1 and for 77 Silurian samples from six sites is Ds = 193.9, Is = 20.9, ks = 16 and α 95 = 4.2. Another component recorded in both the Silurian and Ordovician samples is pre-folding, with a sample-mean direction of Ds = 204.4, Is = 37.9, ks = 27.2 and α 95 = 2.7 for 104 samples from eight sites. This component was probably formed during a regional remagnetization event, which took place in post-early Silurian time. Putting this secondary component into a framework with available Palaeozoic data and geochronology further constrains its age to be early Devonian.The isolated components yield new late Ordovician, early Silurian and early-middle Devonian palaeomagnetic poles. The revised middle Palaeozoic segment of the apparent polar wander path (APWP) for the Siberian platform provides new palaeogeographic constraints. Our data suggest that in late Ordovician the platform was situated in equatorial latitudes and was rotated 180° with respect to its present position. During middle-late Ordovician time, the platform did not experience any notable latitudinal drift. It started drifting to the north in the late Ordovician, and by the late Silurian it had travelled ∼1500 km northwards and had rotated ∼30° counter-clockwise (CCW). During late Silurian time, the platform continued northward drift and CCW rotation, and by the early Devonian it had drifted ∼1100 km northwards and rotated 10° CCW relative to its Silurian position. After that, the rotation of the platform changed to clockwise (CW), and by the late Devonian had drifted another 1500 km to the north and had rotated ∼60° CW.We evaluated palaeomagnetically viable positions from 450–400 Ma of the three largest Laurasian cratons, Siberia, Baltica and Laurentia, based on the new data and previously published APWPs. Contrary to several published reconstructions, the Siberian platform could not have been situated to the north of the Caledonian suture in mid-Silurian time, but was probably located either at the eastern or the western side of Laurussia. The new data are compatible with an early Devonian position of Siberia similar to the modern Eurasian configuration. They also support the post- early or middle Devonian relative rotation between the Aldan and Angara blocks of the Siberian platform.

The driving mechanism that is responsible for the uplift of intracontinental mountains has puzzled geologists for decades. This study addresses this issue by using receiver function images across the Chinese Tianshan Mountains and available data from both deep seismic profiles and surface structural deformation. The near-surface structural deformation shows that the Tianshan crust experienced strong shortening during the Cenozoic. The receiver function image across the Tianshan Mountains reveals that the lithosphere of the Junggar Basin to the north became uncoupled along the Moho and the mantle below the Moho subducted southwards beneath the northern part of the Tianshan Mountains, thereby thickening the overlying crust. Similar deep structures, however, are not observed under the Tarim Basin and the adjacent southern Tianshan Mountains. This difference in the deep structures correlates with geomorphological features in the region. Thus, a new model of mantle subduction, herein termed M-type subduction, is proposed for the mountain-building processes in intracontinental compressional settings. The available geomorphological, geological and seismic data in the literatures show that this model is probably suitable for other high, linear mountains within the continent.

article i nfo The Wuyishan metallogenic belt, a part of the circum-Pacific tectonomagmatic belt, is considered one of the 19 key metallogenic belts in China because of its abundant mineral resources and vast prospecting potential. Specifically, the North Wuyi area is an important Cu-Pb-Zn polymetal ore-concentrated district in East China. We report new geochronological dates in this area, which suggest that the formation of mineralization- related magmatic rocks have mainly occurred during the Paleozoic and Mesozoic in four stages: the Caledonian (530 Ma to 430 Ma), Early-Middle Jurassic (183 Ma to 160 Ma), Early Cretaceous (140 Ma to 110 Ma), and Late Cretaceous (63 Ma to 85 Ma). The mineralization events are either coeval or slightly post- date the related magmatic activities. Nappe structures are widespread in the North Wuyi area and play an im- portant role in the formation and preservation of ore deposits, as determined from field observations and structural analyses of mining tunnels. The regional distribution and structural styles of the thrust faults in the North Wuyi area and new 40 Ar- 39 Ar dating results (415 Ma to 390 Ma) confirm that intensive tectonic activity during the Early Paleozoic, when the South China Block was about to separate from Gondwana, has wiped out evidence of Caledonian mineralization. All nappe structures with regional scales (several thousand meters) were formed during the Early Cretaceous period, with an 40 Ar- 39 Ar age of 120 Ma to 129 Ma. The thrust direction of the nappe structures is mainly southeast during the Early Cretaceous in the main body and north piedmont of the Wuyi Mountain. These early thrust faults have not only broken or reformed the existing ore deposits, but have also provided hydrothermal ore-forming channels and spaces for metallogen- ism that are coeval or posterior to the thrust. The subsequent nappe structures thrust mainly from southeast to northwest and overprint the previous southeastward thrust faults. Using 40 Ar- 39 Ar dating of the structural belt, U-Pb SHRIMP zircon dating of the wall rocks, and Re-Os dating of the ore formation, we analyze the ge- netic connection between the structures and ore bodies in different ore fields. Our results serve as useful in- formation on prospecting for the latent ore body in the North Wuyi area, especially the ore bodies destroyed by faulting activities.

The surface uplift of the Tibetan Plateau is the key boundary condition in many Cenozoic geological events ranging from global cooling to changes of Asian environments during Cenozoic. However, poorly constrained timing for the uplift of Tibetan Plateau makes these interpretations highly debatable. Here we report results from sedimentology, detrital zircon U–Pb and Lu–Hf isotopic compositions, and paleomagnetic signatures from both the eastern and western Hoh Xil basins of north-central Tibetan Plateau. Sedimentary lithofacies and facies associations analyzed in the western Hoh Xil basin indicate they were deposited in a braided fluvial system and alluvial fan, similar with the Fenghuoshan Group, eastern Hoh Xil basin. Provenance analyses from conglomerate clast compositions, paleocurrent orientations, and detrital zircon U–Pb and Lu–Hf isotopic compositions document sediments in both western and eastern basins were derived from the Qiangtang and Lhasa blocks. These observations, in combination with comparative paleomagnetic results, imply that Hoh Xil basin was a single, wide basin during Paleogene. The period of Hoh Xil basin deposition was coeval with significant period of the early Cenozoic uplift and erosion of the Qiangtang and Lhasa blocks. These observations not only reinforce the suggestion that the Qiangtang and Lhasa blocks were uplifted during Eocene to form a proto-Tibetan Plateau, but also imply that the proto-Tibet Plateau is vast in areal extent. The large dimension and high elevation of the proto-Tibetan Plateau probably contributed to the global cooling during the early Eocene.

The characteristic remanent magnetizations (ChRMs) of the late Paleozoic in the Lhasa Terrane reported previously were not widely used for paleogeographical reconstructions because the rocks have been obliterated significantly by multiphase orogeny. This study reports the paleomagnetic data of 131 samples collected from 17 sites in the Permian and the late Triassic rocks from the Zhakang section of the Xainza area, where the relative undeformed Paleozoic strata were preserved. Consequently, the ChRMs of high temperature with the different paleomagnetic directions were isolated from the Permian sandstones, limestones, dolomites and the late Triassic silicalites. Without the constraints with the spatial and temporal limitation of the chemical remagnetization derived from the fluids driven by the Neogene strike-slip faults and the Paleogene thrusting faults in the study area, the ChRMs carried by hematite in early Permian sandstones away the faults have potentially preserved a primary magnetization, which has a paleomagnetic direction of D = 46.6°, I = − 31.2°, κ = 69.0, α95 = 9.3°, N = 5 sites after tilt correction, corresponding to a pole at 24.5°N, 219.3°E with A95 = 7.8°. The new corresponding paleomagnetic pole with the former Carboniferous poles shows the Lhasa Terrane drifted into the middle-lower latitude and isolated in the Paleo-Tethys Ocean rather than adjacent to the northern margin of Gondwanaland during the early Permian after being rifted from the Australian continent in the late Carboniferous.

The northern dimension of Greater India, defined as the continental part of India from which the Himalayan fold–thrust belt was derived, is difficult to determine due to major tectonic deformations of the Himalaya during the Tertiary caused by the India–Eurasian collision. Paleomagnetic data from the Tethyan Himalaya can potentially help determine this dimension. However, the tectonic deformations also led to widespread remagnetization of rocks there and thus previously published paleomagnetic poles from the lower Mesozoic Himalayan rocks may not accurately reflect their original paleomagnetic directions. To better understand the Triassic history of India in a Gondwana configuration, we report new paleomagnetic data (after tilt correction D = 345.5°, I = −43.0°, α95 = 12.0°, k = 17.3, N = 10 sites and the corresponding paleopole at 34.5°N, 282.2°E with A95 = 11.7°) of Triassic limestone and sandstone from the Tulong Group in the Tethyan Himalaya. The primary features of the magnetization are supported by the positive fold test. Our new Triassic paleomagnetic pole overlaps with 230–250 Ma poles from India, suggesting the close affinity between the Tethyan Himalaya and cratonic India since the Triassic. Assuming that the Tethyan Himalaya was a part of the Great India since Triassic, the differences between the Tethyan Himalaya paleolatitude obtained by this study and those previously reported for the cratonic India imply ∼1300 km dimension of the Tethyan Himalaya has been absorbed after the Eurasia–India collision.

SUMMARY Palaeomagnetic results from upper Palaeogene volcanics from three localities in the Qiangtang terrane of Central Tibet record a maximum likelihood palaeolatitude of 28.7 ± 3.7°N. These are the first volcanic-based palaeomagnetic results from the plateau interior that appear to average secular variation well enough to yield a reliable palaeolatitude estimate. This palaeolatitude estimate is significantly lower than the ∼36 ± 3°N predicted for Central Tibet by late Palaeogene Eurasia reference poles, consistent with the so-called Central Asia inclination anomaly, but it is consistent with values predicted from upper Palaeogene reference poles for Mongolia. The mean inclination of coeval sedimentary rocks from Central Tibet is ∼15 ± 5° shallower than our volcanic results, similar to the magnitude of sedimentary inclination shallowing estimated from Elongation/Inclination analysis of remanent directions in clastic rocks from the same region. We conclude that most of the inclination anomaly observed in volcanic rocks and that which remains after removal of sedimentary flattening in clastic rocks probably is due to the combined effect of reference poles that are not representative of stable Asia and by Cenozoic intracontinental shortening within Central Asia on the order of several hundred (not more than 1000) kilometers. Our compilation of palaeomagnetic data from the Qiangtang terrane further suggest that the southern margin of the Lhasa terrane (the southern margin of pre-India Asia) was located as far south as 20°N throughout Eocene time. These palaeolatitudes, in conjunction with the upper crustal shortening record for Asia, indicate that only approximately one third of the post-50 Ma India–Asia convergence is partitioned in Asian lithosphere. Low latitudes also imply that much of the proto-Tibetan plateau occupied southerly, tropical to subtropical latitudes, which has important implications for the weathering and erosion of the Tibetan plateau, palaeoaltimetry proxies and early Cenozoic climate dynamics.

The Jurassic to Cretaceous magmatism in the South China Block (SCB) has important geological significance for its tectonic evolution, particularly, the tectonic regime change. We report here new SHRIMP zircon U–Pb ages, geochemical and Sr–Nd isotopic results from the Early Jurassic magmatic rocks in eastern Nanling region of southern Jiangxi and northern Guangdong provinces, SE China. The SHRIMP zircon U–Pb analyses yield consistent Early Jurassic ages of 193 ± 2 Ma for granodiorite and 196 ± 1 Ma for gabbro-diabase from the Hanhu complex of southern Jiangxi Province. Field observation indicates that the gabbro-diabase coexists with syenite in granodiorite, and that the mafic components infiltrate into the syenite. Combined with the SHRIMP zircon U–Pb ages of 196 ± 2 Ma for granites and 195 ± 1 Ma for gabbros of the Xialan complex of northern Guangdong province, these contemporary ages represent an earliest tectono-magmatic events during the Yanshanian orogeny. These results reveal that there are tectonic extension and the post-collisional and intraplate magmatism events at or before 196 Ma, in contrast to the wide believed quiescent stage (205–180 Ma) of magmatic activity in SE China. The confirmation of these tectono-magmatic events in the eastern Nanling area thus sheds new light on the quiescent stage of magmatic activity in SE China during 205–180 Ma and provides new constraints to understand the Early Jurassic tectonic evolution of SE China.

Cretaceous lava flows overlie Jurassic to Early Cretaceous oceanic crust in the Nauru Basin of the western equatorial Pacific, but their exact age and origin is controversial. In one model, they are generically related to volcanism forming the Ontong Java Plateau. However, paleomagnetic data from basalts recovered by ocean drilling in the Nauru Basin have been interpreted as recording numerous geomagnetic reversals, suggesting the Nauru Basin basalts are older than the Early Aptian flows on the Ontong Java Plateau, and the correlative volcanism seen in the western equatorial and southwestern Pacific Ocean basin. Here, we examine the magnetic fidelity of the Nauru Basin basalts through rock magnetic and paleomagnetic approaches. We find the magnetic carriers in the lavas are unlike most basaltic units recovered by oceanic drilling in that they are magnetically soft. This quality makes the rocks especially prone to the acquisition of secondary magnetic components induced during drilling. We demonstrate that the reversed polarity intervals are illusory, and instead record subtle changes in magnetic hardness that result in partial and complete overprinting by the magnetic field associated with the drill string (e.g., the core barrel, drill pipe and bit). The recognition of these magnetic overprints, the identification of only normal polarity in the Nauru Basin basalts, and a critical consideration of the available radiometric and biostratigraphic age data lead us to conclude that coeval formation of the Nauru Basin basalts and Ontong Java Plateau in Aptian times remains a viable hypothesis.

Our Earth is a dynamic planet, changing on temporal scales ranging from millions of years required to complete a solid Earth cycle, or to form mountain ranges, to the few seconds required for a devastating earthquake or explosive volcanic eruptions. The Cretaceous was a period of great unrest in geologic history. It included a series of extraordinary global geological events—a significant increase of marine water temperature and the deposition of black shales; oceanic anoxia events (OAEs); biotic turnovers and mass extinctions; and the formation of many mountain ranges (California's Sierra Nevada and the Rockies in the western United States, the Andes in South America, and the Alps). Sea level rose during the mid-Cretaceous, covering about a third of the land area. Sea level was up to 250 m higher than at present.

In order to better understand the Mesozoic tectonic evolution of Southeast China Block (SECB in short), this paper describes geological features of Mesozoic basins that are widely distributed in the SECB. The analyzed data are derived from a regional geological investigation on various Mesozoic basins and a recently compiled 1:1,500,000 geological map of Mesozoic–Cenozoic basins. Two types of basin are distinguished according to their tectonic settings, namely, the post-orogenic basin (Type I) and the intracontinental extensional basin (Type II); the latter includes the graben and the half-graben or faulted-depression basins. Our studies suggest that the formation of these basins connects with the evolution of geotectonics of the SECB. The post-orogenic basin (Type I) was formed in areas from the piedmont to the intraland during the interval from Late Triassic to Early Jurassic; and the formation of the intracontinental extensional basin (Type II) connects with an intracontinental crustal thinning setting in the Late Mesozoic. The graben basin was generated during the Middle Jurassic and is associated with a bimodal volcanic eruption; and the half-graben or faulted-depression basin, filled mainly by the rhyolite, tuff and sedimentary rocks during Early Cretaceous, is occupied by the Late Cretaceous–Paleogene red-colored terrestrial clastic rocks. We noticed that the modern outcrops of numerous granites and basins occur in a similar level, and the Mesozoic granitic bodies contact with the adjacent basins by large normal faults, suggesting that the modern landforms between granites and basins were yielded by the late crustal movement. The modern basin and range framework was settled down in the Cretaceous. Abundant sedimentary structures are found in the various basins, from that the deposited environments and paleo-currents are concluded; during the Late Triassic–Early Jurassic time, the source areas were situated to the north and northeast sides of the outcrop region. In this paper, we present the study results on one geological and geographical separating unit and two separating fault zones. The Wuyi orogenic belt is a Late Mesozoic paleo-geographically separating unit, the Ganjiang fault zone behaves as the western boundary of Early Cretaceous volcanic rocks, and the Zhenghe–Dapu fault zone separates the SE-China Coastal Late Mesozoic volcanic-sedimentary basins and the Wuyi orogenic belt. Finally, we discuss the geodynamic mechanisms forming various basins, proposing a three-stage model of the Mesozoic sedimentary evolution.

The voluminous volcanic eruptions in the Nauru Basin, Western Pacific, have long been regarded as important research targets for tectonic history of the Pacific Plate and for the widespread Cretaceous volcanic activity in the Western Pacific. The Nauru Basin volcanic rocks were recovered at Site 462 by Deep Sea Drilling Project (DSDP) Legs 61 and 89, where more than 600 m of lavas and sills were drilled, thereby making it the deepest penetration into crust of Cretaceous age in the Pacific Ocean. For paleomagnetism, this section represents a unique possibility for averaging out secular variation to obtain a reliable paleolatitude estimate. However, previous paleomagnetic studies have only been subjected to alternating field (AF) demagnetization on several core samples, thus, unable to provide comprehensive understanding on the paleolatitude of the basin. The work reported here aims to determine the Cretaceous paleomagnetic paleolatitude for the Pacific Plate and define the magnetostratigraphy for the basaltic sections drilled in the Nauru Basin. A total of 391 basaltic rock samples were carefully re-sampled from DSDP Sites 462 and 462A. Stepwise thermal and AF demagnetizations have isolated characteristic components in the majority of the samples. The most important findings from this study include: (1) Two normal and one reversed polarity intervals are identified in Site 462, and six normal and six reversed polarity intervals are found in Site 462A, although possible erroneous markings of the opposite azimuth for some reversed polarity cores during the DSDP coring cannot be completely ruled out. (2) Based on previous radiometric ages, the magnetostratigraphic correlations with the Geomagnetic Polarity Time Scale (GPTS) indicate that the lower-basaltic flow unit in Site 462A began to erupt at least before 130 Ma. No correlation is available for the upper-sill unit. (3) Paleosecular variation for the lower-flow unit has been sufficiently averaged out; whereas bias may exist for that of the upper-sill unit; (4) The calculated mean inclination of ∼ − 50° for the lower-flow unit yields a paleolatitude of 30.8°S for the Nauru Basin at the time of emplacement. This value is well to the north of suggested location in plate reconstruction models, suggesting that there has been a significant amount of apparent polar wander of the Nauru Basin and Pacific plate since 130 Ma. In addition, the paleolatitude for the Nauru Basin is ∼ 7° further south and the basin's age is more than 10 my older than those of the Ontong Java Plateau (OJP), which suggest that the volcanic eruptions of the lower flows in the Nauru Basin are unlikely related to the emplacement of the Ontong Java Plateau.

The near-flat subduction of the Cocos Ridge (CR) along the Middle American Trench (MAT) plays a pivotal role in governing the geodynamic evolution of the central American convergent margin. Elucidating the onset of its subduction is essential to understand the tectonic evolution and seismogenesis of the Costa Rican convergent margin, a typical erosive convergent margin and modern example of a flat-slab subduction. Initial subduction of the CR has been previously investigated by examining upper plate deformation that was inferred to have resulted from the initial CR subduction. However, little attention has been paid to the extensive sedimentary archives on the CR that could hold important clues to the initial CR subduction. Drilling on the CR during IODP Expedition 344 discovered a pronounced sedimentary hiatus at Site U1381. Here we present paleomagnetic and rock magnetic results of the Cenozoic sedimentary sequences at this site that bracket the hiatus between ca. 9.61 and 1.52 Ma. We also examine the areal extent, timing, and geologic significance of the hiatus by analyzing sedimentary records from five other ODP/IODP sites on CR and Cocos plate. The analyses show that the hiatus appears to be regional and the presence/absence of the sedimentary hiatus at different locations on CR implies a link to the onset of CR shallow subduction, as a result of either bottom current erosion or CR buckling upon its initial collision at the MAT. Records directly from CR thus provide a new window to unraveling the geodynamic evolution of the central American margin.

Combined analyses of deep tow magnetic anomalies and International Ocean Discovery Program Expedition 349 cores show that initial seafloor spreading started around 33 Ma in the northeastern South China Sea (SCS), but varied slightly by 1-2 Myr along the northern continent-ocean boundary (COB). A southward ridge jump of approximate to 20 km occurred around 23.6 Ma in the East Subbasin; this timing also slightly varied along the ridge and was coeval to the onset of seafloor spreading in the Southwest Subbasin, which propagated for about 400 km southwestward from approximate to 23.6 to approximate to 21.5 Ma. The terminal age of seafloor spreading is approximate to 15 Ma in the East Subbasin and approximate to 16 Ma in the Southwest Subbasin. The full spreading rate in the East Subbasin varied largely from approximate to 20 to approximate to 80 km/Myr, but mostly decreased with time except for the period between approximate to 26.0 Ma and the ridge jump (approximate to 23.6 Ma), within which the rate was the fastest at approximate to 70 km/Myr on average. The spreading rates are not correlated, in most cases, to magnetic anomaly amplitudes that reflect basement magnetization contrasts. Shipboard magnetic measurements reveal at least one magnetic reversal in the top 100 m of basaltic layers, in addition to large vertical intensity variations. These complexities are caused by late-stage lava flows that are magnetized in a different polarity from the primary basaltic layer emplaced during the main phase of crustal accretion. Deep tow magnetic modeling also reveals this smearing in basement magnetizations by incorporating a contamination coefficient of 0.5, which partly alleviates the problem of assuming a magnetic blocking model of constant thickness and uniform magnetization. The primary contribution to magnetic anomalies of the SCS is not in the top 100 m of the igneous basement.

Eighty-nine basaltic lava flows from the northwest wall of Haleakala caldera preserve a concatenated paleomagnetic record of portions of the Matuyama–Brunhes (M–B) reversal and the preceding Kamikatsura event as well as secular variation of the full-polarity reversed and normal geomagnetic field. They provide the most detailed volcanic record to date of the M–B transition. The 24 flows in the transition zone show for the first time transitional virtual geomagnetic poles (VGPs) that move from reverse to normal along the Americas, concluding with an oscillation in the Pacific Ocean to a cluster of VGPs east of New Zealand and back finally to stable polarity in the north polar region. All but one of the 16 Kamikatsura VGPs cluster in central South America. The full-polarity flows, with 40Ar/39Ar ages spanning a total of 680 kyr, pass a reversal test and give an average VGP insignificantly different from the rotation axis, with standard deviation consistent with that for other 0–5 Ma lava flows of similar latitude. Precise 40Ar/39Ar dating consisting of 31 incremental heating experiments on 12 transitional flows yields weighted mean ages of 775.6±1.9 and 900.3±4.7 ka for the M–B and Kamikatsura transitional flows, respectively. This Matuyama–Brunhes age is ∼16 kyr younger than ages for M–B flows from the Canary Islands, Tahiti and Chile that were dated using exactly the same techniques and standards, suggesting that this polarity transition may have taken considerably longer to complete and been more complex than is generally believed for reversals.

We present new palaeomagnetic data from Ocean Drilling Program Site 1184 on the eastern salient of the Ontong Java Plateau (OJP) where 337.7 m of Early Cretaceous (c. 120 Ma) volcaniclastic rocks were drilled. Alternating field and thermal demagnetizations were equally effective in removing secondary components, allowing the characteristic remanent magnetization directions from a total of 173 samples (out of 183) to be defined. All samples have negative inclinations (normal polarity), and by treating each sample as an independent reading of the palaeomagnetic field a site-mean inclination of -53.9 ~ (N = 173; e~95 = 1.0 ~ k -109) was obtained. The corresponding palaeo-colatitude is in excellent accordance with previously published time-averaged palaeo-colatitudes from contemporaneous basalts drilled at OJP and the Nauru Basin. Based on the intersection of the seven palaeo-colatitudes a new Early Cretaceous (c. 120 Ma) Pacific palaeomagnetic pole was obtained with co-ordinates 63.0~ 10.1~ (95% confidence ellipse with a minor semi-axis of 2.9 ~ with an azimuth of 32 ~ and a major semi-axis of 47.7 ~ with an azimuth of 122~ This pole is far more easterly than previously published Early Cretaceous Pacific palaeomagnetic poles. Based on published Pacific palaeogeographic reconstructions in the fixed hotspot reference frame we were able to calculate different Pacific true polar wander (TPW) poles. All Pacific TPW poles are found to be statistically different from contemporaneous TPW poles obtained in the Indo-Atlantic realm, illustrating motion between the two groups of hot spots. During the Ocean Drilling Program (ODP) Leg 192, to the Ontong Java Plateau, approximately 120 Ma old basement rocks (Chambers et al. 2002) were retrieved at five sites (Fig.l). Timeaveraged site-mean palaeomagnetic inclination estimates have been obtained from the subaqueous basaltic lava flows and pillow units recovered at Sites 1183, 1185, 1186 and 1187 (Riisager et al. 2003b). In the present study we present new palaeomagnet ic data from the 337.7 m of volcaniclastic rocks drilled at Site 1184. These new data, together with previously published ODP and Deep Sea Drilling Project (DSDP) data, allow us to derive a new Early Cretaceous palaeomagnetic pole for the Pacific. In the following we will compare this new approximately 120 Ma palaeomagnet ic pole with the Pacific apparent polar wander path (APWP), and discuss its significance in relation to the true polar wander, hot-spot fixity and Pacific plate reconstructions. Geological setting The Ontong Java Plateau The Ontong Java Plateau (OJP; Fig. 1) is the world's largest volcanic oceanic plateau, with a surface area of 2.0 • 106 km 2 and an estimated volume of 4 • 107-5 • 107 km 3 (e.g. Eldholm & Coffin 2000). Existing age constraints point to the formation of mostly all of the OJP in a single geologically brief period around 120 Ma (e.g. Tarduno et al. 1991; Parkinson et al. 2001; Chambers et al. 2002), making it the largest magmatic event on Earth during the last 200 Ma. The enormous total partial melt volume (Coffin & Eldholm 1994), as well as the composition of lavas (Tejada et al. 2002), is best explained by the plume-head or plume-impact model, in which widespread basaltic flood eruptions occur as the inflated head of a rising new mantle plume approaches the base of the lithosphere (Richards From: FI~'ON, J. G., MAHONEY, J. J., WALLACE, P. J. & SAUNDERS, A. D. (eds) 2004. Origin and Evolution of the Ontong Java Plateau. Geological Society, London, Special Publications, 229, 31-44. 0305-8719/$15.00 9 The Geological Society of London 2004. at Copenhagen University Library on July 23, 2013 http://sp.lyellcollection.org/ Downloaded from

SUMMARY We conducted an integrated palaeomagnetic and stratigraphic study on a 5452.8 m thick sedimentary sequence of the Hoh Xil Basin in northern Qinghai-Tibet Plateau to obtain a chronostratigraphic framework for these sediments. A total of 966 individual oriented palaeomagnetic samples (spaced at stratigraphic intervals) were collected from six measured sections in the Hoh Xil Basin. Magnetic directions in these samples were obtained by progressive thermal (mainly) and alternating-field demagnetization experiments. Most samples exhibit two components of magnetization. The lower unblocking temperature component is an overprint resembling the present-day geocentric axial dipole field direction at the sampling locality. The most stable, characteristic remanence (ChRM) appears to be an early chemical remanent magnetization residing mainly in haematite. The positive results of fold and reversal tests indicate that the ChRM is a record of the palaeomagnetic field close to the time of formation of these sediments. Further evidence for the magnetization of these sediments acquired close to their time of deposition is the fact that patterns of magnetic reversals can be matched with the established polarity timescale. On the basis of the distinct interval of magnetic reversal zones and biostratigraphic datums, 13 magnetozones can be recognized at the Hoh Xil Basin that range from chrons C11 to C23 (30.1‐51.0 Ma). The age of the Fenghuoshan Group is palaeomagnetically dated as 51‐31 Ma (Early Eocene‐Middle Early Oligocene), and the age of the Yaxicuo Group is between 31 and 30 Ma (Middle Early Oligocene‐Late Early Oligocene). The new palaeomagnetic data from the Fenghuoshan Group suggest that it has undergone no significant rotation since the Oligocene. In contrast, declination data from the Yaxicuo Group in Wudaoliang area imply a vertical-axis clockwise rotation (29.1 ◦ ± 8.5 ◦ ) since the Late Oligocene. The Tertiary palaeomagnetic pole position of the Hoh Xil Basin implies a significant northward convergence of the Hoh Xil Basin (∼1600 km) with respect to Eurasia (Siberia) since Early Eocene‐Late Oligocene time. Our results are consistent with the pattern of disturbingly low palaeolatitudes derived from a large number of high-quality palaeomagnetic studies of Tertiary rocks from sites that reach all the way from eastern China to Kyrgyzstan. Future work is needed to separate the influences of sedimentary inclination shallowing and tectonic shortening.

The Hoh Xil Basin is the largest Cenozoic sedimentary basin in the hinterland of the Tibetan Plateau. Tertiary sedimentary strata 5.8 km thick, comprising the Fenghuoshan, Yaxicuo and Wudaoliang groups, provide compelling evidence concerning the crustal shortening, erosion and peneplanation of the northern Tibetan Plateau. The basal Fenghuoshan and overlying Yaxicuo groups span the Eocene-Early Oligocene stratigraphically, and have been dated by magnetostratigraphy as 56–30 Ma old. Both groups are composed of terrigenous rocks. Provenance analysis of sandstones and conglomerates demonstrates that Permian and Triassic strata in the Tanggula Orogenic Zone in the south were the source for the Fenghuoshan Group. In contrast, the Carboniferous–Triassic strata in the Tanggula, Bairizhajia, and Heishishan-Gaoshan orogenic zones in the north, were the source for the Yaxicuo Group. During the Late Oligocene, northern Tibet underwent strong north–south crustal shortening (∼43%) and thickening. Extensive erosion, which occurred over the entire plateau surface near the end of the Oligocene, resulted in development of a peneplain surface. The latter is overlain by the Early Miocene Wudaoliang Group, composed of fresh water limestones. These are exposed both on summit surfaces, as well as on the valley floors, showing that a phase of differential uplift occurred after the deposition of the Wudaoliang Group. This post-Miocene differential uplift was due to regional extension, in a region of overall shortening. Even though we have not succeeded in obtaining conclusive data about the exact timing of phases of rapid uplift of the Tibetan Plateau, it is most likely that the major phase of uplift occurred during the Late Oligocene.

Recent interest has focused on whether South Korea may have undergone variable tectonic rotations since the Cretaceous. In an effort to contribute to the answer to this question, we have completed a palaeomagnetic reconnaissance study of Early Cretaceous sedimentary and igneous rocks from the Kyongsang basin in southeast Korea. Stepwise thermal demagnetization isolated well-defined characteristic magnetization in all samples. The palaeomagnetic directions reveal patterns of increasing amounts of clockwise (CW) rotation with increasing age for Aptian rock units. Palaeomagnetic declinations indicate clockwise vertical-axis rotations of R = 34.3° ± 6.9° for the early Aptian rock unit, R = 24.9° ± 10.6° for the middle Aptian, and R = −0.9° ± 11.8° for the late Aptian relative to eastern Asia. The new Cretaceous palaeomagnetic data from this study are consistent with the hypothesis that Korea and other major parts of eastern Asia occupied the same relative positions in terms of palaeolatitudes in the Cretaceous. An analysis of and comparison with previously reported palaeomagnetic data corroborates this hypothesis and suggests that much of Korea may have been connected to the North China Block since the early Palaeozoic. A plausible cause of the rotation is the westward subduction of the Kula plate underneath the Asian continent, which is inferred to have occurred during the Cretaceous according to several geological and tectonic analyses.

The north-striking Tancheng-Lujiang (Tan-Lu) fault is a conspicuous and controversial feature of the eastern Asian landscape. Near the southeast extremity of the fault in Anhui Province, we collected paleomagnetic samples at 17 Middle Triassic (T2) and 10 Upper Cretaceous (K2) to lower Cenozoic (E1) sites. T2 remanent magnetizations are interpreted as primary in two of three areas. The three areas are rotated 37° to 137° counterclockwise with respect to the South China Block (SCB) reference direction. K2-E1 remanent magnetization directions pass regional fold and reversals tests and are not rotated with respect to surrounding areas. Counterclockwise rotation of T2 strata therefore ended before K2 and is attributed to left lateral shear acting along Tan-Lu during the North China Block (NCB)-SCB collision. In Shandong Province, 700 km north of the Anhui sites, four areas containing 33 Upper Jurassic (J3) and Cretaceous sites have negligible declination differences, except for one which has dispersed directions. The fold test is inconclusive for this latter area and positive for the other three. Regional concordance of the J3-E1 paleomagnetic data (including paleolatitudes) together with observed deformation patterns suggest that an extensional regime prevailed in the Late Cretaceous and Cenozoic. Euler pole positions that constrain the North-South China collision and account for Tan-Lu motion suggest at least 500 km of sinistral shear took place along the fault, and either (1) subduction and related ultrahigh pressure (UHP) metamorphism occurred near the present location of the Qinling-Dabieshan and Sulu UHP belts while Tan-Lu acted as a transform fault that connected the two subduction zones, or (2) Tan-Lu and Sulu were parts of the same transform fault system and no UHP rocks formed in situ at Sulu. In either case, UHP rocks originally exhumed near Dabieshan could have been transported by plate capture toward Sulu along Tan-Lu. After North and South China impacted near Dabieshan, the Tan-Lu fault grew within the SCB as the Dabieshan corner indented the SCB, causing folds in SCB cover rocks to conform to the NCB margin. Late Cretaceous to Cenozoic reactivation of Tan-Lu, with both right lateral strike-slip and normal fault motion, occurred as the SCB extruded east relative to the NCB under the influence of the India-Asia collision.

Three loess sequences located east of the Liupan mountain region, China, were studied to obtain records of the Blake polarity event. Palaeomagnetic records from the appropriate stratigraphic interval of these three sequences, however, record the Blake event poorly in one case and not at all in the other two cases. It is important to understand why these loess sequences miss the Blake event, whereas others record it quite well. We conclude that regional variations in the sedimentary environment over the Chinese loess plateau are responsible for the inconsistent recording of the Blake event. The palaeomagnetic records suggest a threefold subdivision of the Chinese loess plateau into (1) the central and southern portions of the part of the plateau that lies east of the Liupan Mountains, where the primary record of the Blake event has been severely smoothed or wiped out by pedogenic processes during palaeosol (S1) formation; (2) the northern margin of the loess plateau to the east of the Liupan Mountains, where frequent, severe dust storms have resulted in discontinuous records with a high probability of missing the Blake event; and (3) the region west of the Liupan Mountains, where loess sequences are deposited rapidly and nearly continuously with only minor pedogenesis, and are thus capable of recording short events like the Blake.

Published palaeomagnetic results for China unequivocally show that the three major blocks of China—North and South China Blocks and Tarim—were at or near equatorial latitudes in the Early and Middle Palaeozoic, although they certainly did not have their present relative configuration during that time. These Chinese blocks may have been an ancient equatorial archipelago lying between a northerly Siberia continent and a southerly Gondwanaland continent throughout the Palaeozoic. Palaeomagnetic evidence from Chinese blocks appear not to be consistent in detail with various speculations on rapid true polar wander during Early and Middle Palaeozoic. Late Palaeozoic palaeomagnetic data suggest that the various blocks of China were too far north to have attached to Gondwanaland and suggest that they rifted from Gondwanaland during the Late Devonian and Carboniferous. Studies of Late Permian palaeomagnetic data for the major blocks of China demonstrate major diachronous closures between the Chinese blocks themsel...

We report Late Carboniferous, Permian, and early Tertiary paleomagnetic data from the southern Tarim basin. Prefolding magnetizations were isolated in each case. The Late Carboniferous–Permian and early Tertiary poles lie at 64.6°N, 166.5°E, A95 = 6.3° and 58.1°N, 202.0°E, A95 = 12.7°, respectively. The Late Jurassic to early Tertiary (J3–E1) paleolatitudes of Tarim and several basins throughout central Asia are similar, yet significantly (10° to 20°) shallower than those predicted by the Eurasian apparent polar wander path. Resolving this discrepancy remains a major problem in Asian paleomagnetism. Discordance of the late Paleozoic poles from Tarim and Siberia suggest that Tarim has rotated about 30° counterclockwise with respect to Siberia since the Permian. Where paleomagnetic samples of both Late Carboniferous to Early Triassic (C3–T1) and J3–E1 ages were collected from the same area of Tarim, a great circle passes through the means of the poles and the sampling locality. This suggests that (1) only a difference in inclination (and not declination) distinguishes the two data sets, and (2) vertical axis block rotations of the C3–E1 strata occurred after E1. Although based on data of lesser quality, the mean Early to Middle Jurassic (J1–2) pole from Tarim differs significantly from the Eurasian reference pole, requiring radical tectonic solutions to resolve them. The Tarim J1–2 pole is indistinguishable from both the mean J3–E1 and C3–T1 poles. The similarity of all the poles and the analogous tectonic setting of present-day central Asia to that of the late Paleozoic in eastern North America raises the question whether all the data from Tarim are overprinted.

In order to better constrain the paleogeographic evolution of south China we measured Sm-Nd and Rb-Sr isotopic compositions for 23 Mesozoic granites that crop out throughout the area. Tightly grouped neodymium depleted mantle model ages (1.4 ± 0.3 Ga) suggest the region is underlain by relatively homogeneous Proterozoic crust and fail to define crustal provinces. Neither the isotopic nor geologic data suggest that a Mesozoic suture exists. However, granites possessing anomalously high Sm (>8 ppm) and Nd (>45 ppm) concentrations, relatively high initial epsilon neodymium (−4 to −8), and high but variable initial 87Sr/86Sr (0.759 to 0.713) form a northeast trending zone that coincides with two prominent Mesozoic basins. Southeast of the zone lie the majority of Mesozoic intrusives and Upper Triassic to Lower Cretaceous extensional basins found in south China. Mesozoic paleomagnetic poles are well clustered northwest of the zone. Pre-Cretaceous poles southeast of it are discordant with respect to those from the northwest. The only recognized tectonostratigraphic terrane in south China lies southeast of the zone. The terrane is bordered by a northeast trending sinistral fault that was active in the Mesozoic. Other faults in south China have similar attitudes, ages, and sense of shear. Together, the observations suggest that the Mesozoic tectonic regime in south China consisted of strike-slip activity plus concomitant rifting as terranes or fragments of similar crust were transported north along sinistral faults. The zone, defined by the granites enriched in Nd and Sm, demarcates displaced terranes to the southeast from relatively stable land to the northwest.

We report Early and Middle Triassic paleomagnetic data from the south Chinese provinces of Fujian and Guangxi. The characteristic magnetization of the rocks in each case is concluded to be a primary remanence that passes the fold test. The Triassic pole from western Guangxi and four other Triassic and Late Permian poles from three provinces that lie on undisputed parts of the Yangtze craton are well clustered. This suggests that Guangxi (except the southeast part) was also a part of the Yangtze craton, at least since the Triassic and probably since the Late Permian. With respect to the Yangtze craton, between the Early Triassic and the Late Cretaceous, Fujian may have been rotated 121 ± 9° counterclockwise and displaced 22 ± 9° north, or rotated 59 ± 9° clockwise and displaced 3 ± 9° south, depending on the hemisphere in which the magnetization was acquired. Based on consistency with other paleomagnetic results, and in accordance with the geologic data from the area, the former interpretation is preferred. A remarkable coincidence of Mesozoic poles for south China and south Korea is observed which, if true, implies that the South China Block (except for the displaced terranes in the coastal provinces) and Korea may have been part of the same continental landmass from the Triassic onwards. This is consistent with some geologic observations suggesting affinities between the two places. It also implies that the major fault zones in north China (e.g., the Tan-Lu fault) are unrelated to major fault zones in southeast China (e.g., the Changle-Nanao fault), with the former probably associated with the suturing of north and south China and the latter influenced by proto-Pacific plate motion.

How and when India collided with Asia is crucial for global climate and continental dynamics. We present new palaeomagnetic data showing that the Xigaze forearc basin of southern Tibet was located at 24.2 ± 5.9°N during 54-57 Ma, providing a direct constraint on the position of the southernmost margin of Asia at this crucial stage. Our study suggests 1) the age and locus of the initial India-Asia collision are at ~50 Ma and ~24°N, respectively; 2) Tibet resisted India's northward push during the first ~16 Ma of initial impact from the collision and experienced little latitudinal displacement; and 3) Sometime a little after 34 Ma, Greater India was consumed and thicker Indian Craton subsequently made contact with Asia, resulting in ~6° northward drift of Asia. Our model has implications for the process by which the high proto-Tibetan plateau formed and for the two slowdowns of India's convergence rate with Asia.

Presentamos un estudio paleomagnético, de magnetismo de rocas geocronológico y de paleointensidad conjunto, en rocas volcánicas Miocénicas del sector de la Faja Volcánica Transmexicana (FVTM). En el cual se emplearon 58 sitios compuestos por 7 a 21 unidades volcánicas de enfriamiento consecutivas de 4 secciones estratigráficas separadas. Nuestros nuevos fechamientos radiométricos sugieren que los flujos de lava de la secuencia Jesús Maria fueron emitidos durante un corto lapso de 11.1±0.8 a 10±0.8 Ma durante el cron de polaridad normal C5n.2n. La cercana sección de Atotonilco presenta características litológicas similares a la secuencia de Jesús Maria, con los 3 flujos de lava de la cima probablemente perteneciendo al cron C5n.1r. Nuestros resultados geocronológicos de la sección Funicular indican que estas lavas fueron emitidas durante un lapso más amplio, de 5.2±0.7 a 2.8±0.5 Ma. Con base en las observaciones de mineralogía magnética y de magnetismo de rocas de todas las muestras se determina que la mineralogía magnética es primaria e inalterada. Las titanomagnetitas de bajo-Ti, son resultado de la oxi-exosolución de las titanomagnetitas originales durante el enfriamiento inicial de los flujos. Los componente estables de la magnetización se determinaron después de experimentos detallados de desmagnetización térmica y de campos alternos. Nuestros resultados combinados con los datos paleomagnéticos regionales existentes indican que las áreas de muestreo no han sufrido desplazamientos N-S, ni rotaciones de bloque significativos desde hace al menos 11 Ma. Las determinaciones de paleointensidad aceptadas son de buena calidad técnica con chequeos estándares positivos de magnetización parcial termoremanente (pTRM). Los datos de paleointensidad obtenidos van de 17.5 a 34.3 mT, sugiriendo la existencia tanto de una alta intensidad del campo geomagnético como de fluctuaciones bajas durante el Mioceno. Nuestros resultados sugieren que las rocas preservan una memoria magnética del campo geomagnético del Mioceno tardío y delimitan las reconstrucciones paleogeográficas. Los nuevos resultados paleomagnéticos contribuyen potencialmente a la reconstrucción de los modelos de evolución tectónica de la FVMT.

We have collected oriented cores in Jurassic redbeds from two areas in southern Guangxi Province. Stepwise thermal demagnetization of the samples and subsequent statistical analysis show that the stable magnetization from both areas is a near-primary chemical remanence that passes the fold test. Area 1 lies in a shear zone and is rotated 24° ± 12° counterclockwise and insignificantly displaced 4° ± 12° northward with respect to Area 2, which lies outside the shear zone, 80 km to the northwest of Area 1. After adjusting for a post-Jurassic tectonic rotation identified in a previous paleomagnetic study, the pole for Area 2 is indistinguishable from an averaged Early to Middle Jurassic reference pole for the Yangtze craton, suggesting that this area was joined to the Yangtze craton by that time, and confirming that considerable clockwise rotation of south China relative to north China remained to be accomplished before the present configuration of the two blocks was attained. In combination with geological observations, these data support a terrane model based on sinistral shear acting parallel to recognized structural trends in this part of southeast China during post-Triassic time.

We report Cretaceous and Tertiary paleomagnetic data from Fujian, Guangxi and Guangdong provinces in south China. In Guangxi Province we sampled Early Cretaceous redbeds of the Xinlong Formation at eight localities separated by up to 100 km. The high-temperature component obtained by thermal demagnetization is of dual polarity and passes the fold test, and implies 18° ± 8° counterclockwise rotation and insignificant poleward displacement with respect to cratonic localities in Sichuan Province. A Tertiary basin lying in a southeast-trending fault zone is also rotated counterclockwise by 40° ± 8°. Both results can be explained very well by a simple block rotation model for the Cenozoic tectonic evolution of western Guangxi Province that is driven by left-lateral shear on southeast-trending faults. The timing and sense of shear are the same as for India-Asia collision models involving the extrusion of Indochina along the Red River fault zone, which lies several hundred kilometers to the southwest, but the magnitude of fault displacement in Guangxi is much less. In the coastal provinces of Fujian and Guangdong we find Late Cretaceous directions that are rotated clockwise with respect to Sichuan Province. Combined with similar clockwise rotations found by two other studies of coeval rocks from the same region, the mean rotation for the coastal provinces is 12° ± 8°; this could indicate a coherent block rotation of the region driven by extrusion tectonics. However, the limited number of sampling localities also allows the possibility that the directions reflect local rotations due to dextral shearing driven by circum-Pacific tectonics.

We have obtained paleomagnetic results from Silurian and Devonian rocks on the western margin of the North China Block (NCB), ages which previously were thought to be unrepresented throughout North China. High unblocking temperature components of magnetization isolated from both the Silurian and Devonian strata pass fold and reversal tests, suggesting that they are primary remanence. The corresponding paleopoles, at 228.4°E, 26.2°N (Silurian) and 228.7°E, 34.2°N (Devonian), imply low paleolatitude positions of North China during the middle Paleozoic, probably adjacent to east Gondwana.