Ailao Shan-Red River Fault Research Articles

Collision-induced basalt eruptions at Pleiku and Buôn Mê Thuột, south-central Viet Nam

Neogene-Quaternary basalts occur as dispersed volcanic clusters in the vicinity of the Tethyan tectonic belt, possibly representing ‘far-field’ effects of the Early Tertiary collisions of Gondwana fragments with the southern margin of Eurasia. In Indochina, such a ‘Diffuse Igneous Province’ post-dates the 45–42Ma ‘hard’ India-Asia collision and southeastward, collision induced (c. 30–17Ma.), extrusion of Indochina. Extrusion was accommodated by left-lateral strike-slip shearing on the Ailao Shan-Red River Fault, coeval with seafloor spreading in the East Viet Nam (South China) Sea. The Indochina basalts mostly comprise shield-building tholeiites capped by small-volume undersaturated types, the latter often bearing mantle xenoliths and ‘exotic’ xenocrysts such as sapphire, zircon. They appeared at c. 17Ma, more-or-less coinciding with the cessation of both continental extrusion and seafloor spreading. At this point extensional stress appears to have shifted westwards to continental Indochina, with magmatic activity appearing, characteristically, at ‘pull-apart’ basins. However, the relationship of mantle melting beneath this region to its geodynamic setting is controversial, being variously attributed to mantle plumes, extreme lithospheric stretching, and lateral asthenospheric displacement. There is little or no definitive evidence for regional mantle upwelling while lithosphere stretching alone appears to be insufficient to allow for melting, Here, we present geochemical and Sr, Nd, and Pb isotopic (and paleomagnetic data), for cored sections from the Pleiku and Buon Mê Thuột plateaus in south-central Viet Nam, representative in most respects of the Indochina province as a whole. In the Pleiku shield olivine tholeiite flows are intercalated with quartz tholeiites while, in contrast, alkali basalts predominate over olivine tholeiite in the Buon Mê Thuột (BMT) shield. The first of these features (in Pleiku) probably reflects crustal wall-rock reaction while the second (at BMT), suggests an atypical magma supply system, possibly reflecting a contemporaneous change in the regional stress field. In common with most Indochina shields, tholeiites at Pleiku and BMT show slightly higher Mg – for equivalent MgO contents than those of later-stage undersaturated magmas, suggesting the former may have interacted with lithospheric mantle, depleted by prior melting. On the other hand, because the xenolith- and xenocryst-bearing post-shield magmas show near-primitive, uncontaminated character, and probably tap the more fertile asthenosphere, realistic potential temperatures (Tp) may be interpolated, estimates ranging between c. 1440° and 1660°C, as compared to expected ‘normal’ values (1280–1300°C). The new data are used to re-examine earlier postulates that thermally anomalous asthenosphere was displaced laterally prior to and during the Early Tertiary India–Asia collision, serving as a potential driver of lithosphere extrusion while allowing for localized, transtensional mantle melting. New paleomagnetic data confirm indications of existing data that there has been little or no tectonic rotation, as predicted by the extrusion model. However, variable asthenospheric flow paths are suggested by the distribution of Pleiku, BMT, and other volcanic centers, matched by geodetic data, suggesting minimal traction between Indochina lithosphere and the underlying ductile mantle.

Tectonic deformation around the eastern Himalayan syntaxis: constraints from the Cretaceous palaeomagnetic data of the Shan-Thai Block

SUMMARY Lower to Middle Cretaceous red sandstones were sampled at four localities in the Lanpin-Simao fold belt of the Shan-Thai Block to describe its regional deformational features. Most of the samples revealed a characteristic remanent magnetization with unblocking temperatures around 680 °C. Primary natures of magnetization are ascertained through positive fold test. A tilt-corrected formation-mean direction for the Jingdong (24.5°N, 100.8°E) locality, which is located at a distance of 25 km from the Ailaoshan–Red River Fault, revealed northerly declination with steep inclination (Dec./Inc. = 8.3°/48.8°, α95= 7.7°, N= 13). However, mean directions obtained from the Zhengyuan (24.0°N, 101.1°E), West Zhengyuan (24.0°N, 101.1°E) and South Mengla (21.4°N, 101.6°E) localities indicate an easterly deflection in declination; such as Dec./Inc. = 61.8°/46.1°, α95= 8.1° (N= 7), Dec./Inc. = 324.2°/−49.4°, α95= 6.4° (N= 4) and Dec./Inc. = 51.2°/46.4°, α95= 5.6° (N= 13), respectively. The palaeomagnetic directions obtained from these four localities are incorporated into a palaeomagnetic database for the Shan-Thai Block. When combined with geological, geochronological and GPS data, the processes of deformation in the Shan-Thai Block is described as follows: Subsequent to its rigid block clockwise rotation of about 20° in the early stage of India–Asia collision, the Shan-Thai Block experienced a coherent but southward displacement along the Red River Fault prior to 32 Ma. This block was then subjected to a north–south compressive stresses during the 32–27 Ma period, which played a key role in shaping the structure of Chongshan-Lancang-Chiang Mai Belt. Following this some local clockwise rotational motion has occurred during the Pliocene-Quaternary time in central part of the Shan-Thai Block as a result of internal block movements along the reactivated network of faults.

Shear wave splitting across the Ailao Shan‐Red River fault zone, SW China

A broad band seismic array was set up across the Ailao Shan‐Red River (ASRR) fault zone, SW China. The shear wave splitting parameters on SKS and SKKS phases are calculated using the method of Silver and Chan (1991) and indicate the polarization direction of 105 ± 6° and the delay time of 1.68 ± 0.44 s beneath the ASRR fault zone. Combined with previous studies, the average polarization direction is 110 ± 19° and the delay time is 1.58 ± 0.44 s to the SW side of the fault, while the values are 83 ± 30° and 1.29 ± 0.29 s to the NE side. This result implies that the upper mantle anisotropy to two sides of the ASRR fault zone are different. Compared with the SE polarization direction observed in the P‐S phase and the N‐to‐S surface movement in GPS data, our results suggest decoupling of the crust and upper mantle beneath the study region.

Structural and geochronological constraints on the tectonic evolution of the Dulong-Song Chay tectonic dome in Yunnan province, SW China

The Dulong-Song Chay tectonic dome lies on the border of China (SE Yunnan Province) and northern Vietnam, and consists of two tectonic and lithologic units: a core complex and a cover sequence, separated by an extensional detachment fault. These two units are overlain unconformably by Late Triassic strata. The core complex is composed of gneiss, schist and amphibolite. SHRIMP zircon U–Pb dating results for the orthogneiss yield an age of 799±10 Ma, which is considered to be the crystallization age of its igneous protolith formed in an arc-related environment. A granitic intrusion within the core complex occurred with an age of 436–402 Ma, which probably formed during partial closure of Paleotethys. Within the core complex, metamorphic grades change sharply from upper greenschist-low amphibolite facies in the core to low greenschist facies in the cover sequence. There are two arrays of foliation within the core complex, detachment fault and the cover sequence: S 1 and S 2. The pervasive S 1 is the axial plane of intrafolial S 0 folds. D 1 deformation related to this foliation is characterized by extensional structures. The strata were structurally thinned or selectively removed along the detachment faults, indicating exhumation of the Dulong-Song Chay tectonic dome. The major extension occurred at 237 Ma, determined by SHRIMP zircon U–Pb and 39Ar/ 40Ar isotopic dating techniques. Regionally, simultaneous tectonic extension was associated with pre-Indosinian collision between the South China and Indochina Blocks. The S 2 foliation appears as the axial plane of NW-striking S 1 buckling folds formed during a compressional regime of D 2. D 2 is associated with collision between the South China and Indochina Blocks along the Jinshajiang-Ailao Shan suture zone, and represents the Indosinian deformation. The Dulong granites intruded the Dulong-Song Chay dome at 144±2, 140±2 and 116±10 Ma based on 39Ar/ 40Ar measurement on muscovite and biotite. The dome was later overprinted by a conjugate strike-slip fault and related thrust fault, which formed a vortex structure, contemporaneously with late Cenozoic sinistral movement on the Ailao Shan-Red River fault.

Crust and uppermost mantle structure of the Ailaoshan-Red River fault from receiver function analysis

S-wave velocity structure beneath the Ailaoshan-Red River fault was obtained from receiver functions by using teleseismic body wave records of broadband digital seismic stations. The average crustal thickness, Vp/Vs ratio and Poisson’s ratio were also estimated. The results indicate that the interface of crust and mantle beneath the Ailaoshan-Red River fault is not a sharp velocity discontinuity but a characteristic transition zone. The velocity increases relatively fast at the depth of Moho and then increases slowly in the uppermost mantle. The average crustal thickness across the fault is 36―37 km on the southwest side and 40―42 km on the northeast side, indicating that the fault cuts the crust. The relatively high Poisson’s ratio (0.26―0.28) of the crust implies a high content of mafic materials in the lower crust. Moreover, the lower crust with low velocity could be an ideal position for decoupling between the crust and upper mantle.

A Study on Crustal Anisotropy Using P to S Converted Phases of Receiver Functions: Application to Ailaoshan‐Red River Fault Zone

AbstractAlthough both dipping boundary and anisotropy can cause significant energy in transverse component of receiver functions, they are distinguishable in the arrival time and period. According to different periodicities of transverse components, characteristic anisotropy or dipping boundary can be enhanced by weighted stacking method, and splitting parameters can be inferred from related waveform analysis. As an example, we studied crustal anisotropy near the Red River Fault using P to S converted phases of receiver function. The receiver functions are derived from four broadband digital seismic stations near the Red River Fault. The fast polarization direction is 132° with a time delay of 0.24s. The fast polarization direction in crust is consistent with tectonic line of this region but nearly perpendicular to the fast polarization direction of upper mantle, indicating that the crust and upper mantle may be de‐coupled near the Red River Fault.

Crust and upper mantle structure of the Ailao Shan-Red River fault zone and adjacent regions

Using arrival data of the body waves recorded by seismic stations, we reconstructed the velocity structure of the crust and upper mantle beneath the southeastern edge of the Tibetan Plateau and the northwestern continental margin of the South China Sea through a travel time tomography technique. The result revealed the apparent tectonic variation along the Ailao Shan-Red River fault zone and its adjacent regions. High velocities are observed in the upper and middle crust beneath the Ailao Shan-Red River fault zone and they reflect the character of the fast uplifting and cooling of the metamorphic belt after the ductile shearing of the fault zone, while low velocities in the lower crust and near the Moho imply a relatively active crust-mantle boundary beneath the fault zone. On the west of the fault zone, the large-scale low velocities in the uppermost mantle beneath western Yunnan prove the influence of the mantle heat flow on volcano, hot spring and magma activities, however, the upper mantle on the east of the fault zone shows a relatively stable structure similar to the Yangtze block. The low velocities of the deep mantle beneath the southeastern extending segment of the fault zone are probably related to the mantle convection produced by the pull-apart of the South China Sea.

New paleomagnetic constraints on the extrusion of Indochina: Late Cretaceous results from the Song Da terrane, northern Vietnam

Samples were collected for paleomagnetic investigations from the Upper Cretaceous Yen Chau Formation in the Song Da terrane (21.7°N, 103.9°E) bounded by the Ailao Shan–Red River fault system and Song Ma fault, in an attempt to examine extrusion tectonics of East Asia. Primary nature of the high-temperature (600–690 °C) component of magnetization from 13 sites is supported by a positive fold test. The tectonic corrected data provides the characteristic Late Cretaceous paleomagnetic direction for the Song Da terrane ( D=6.4°, I=32.0° with α 95=8.5°, N=13 sites), corresponding to a paleopole lying at 82.9°N, 220.7°E ( A 95=6.9°). Comparison with coeval paleomagnetic poles for the neighboring tectonic blocks indicates no latitudinal translation of the Son Da terrane with respect to the South China Block, whereas the Shan-Thai Block and the southern part of the Indochina Block revealed a southward displacement of 10.5±9.5° in latitude with respect to the Song Da terrane. We conclude that the southeastern segment of the Ailao Shan–Red River fault system to the east of the Dien Bien Phu fault is not a demarcation of the extruded Indochina Peninsula. The Indochina Block extruded probably along some faults between the Song Da terrane and the Khorat Plateau.

Deglacial and Holocene evolution of the Vietnam shelf: stratigraphy, sediments and sea-level change

On the Vietnam Shelf more than 1000 miles of shallow high-resolution seismics were analyzed to unravel post-glacial evolution in a tropical, siliciclastic environment together with 25 sediment cores from water depths between 21 and 169 m to determine stratigraphy, distribution and style of sedimentation. Fourty-seven samples were dated with the AMS- 14C technique. The shelf was grouped into three regions: a southern part, a central part, and a northern part. On the broad Southern Shelf, sedimentation is influenced by the Mekong River, which drains into the SCS in this area. Here, incised valley fills are abundant that were cut into the late Pleistocene land surface by the Paleo-Mekong River during times of sea level lowstand. Those valleys are filled with transgressive deposits. The Holocene sedimentation rate in this low gradient accommodation-dominated depositional system is in the range of 5–10 and 25–40 cm/ky at locations sheltered from currents. The Central Shelf is narrow and the sedimentary strata are conformable. Here, numerous small mountainous rivers reach the SCS and transport large amounts of detrital sediment onto the shelf. Therefore, the Holocene sedimentation rate is high with values of 50–100 cm/ky in this supply-dominated depositional system. The broad Northern Shelf in the vicinity of the Red River Delta shows, as on the Southern Shelf, incised valleys cut into the Pleistocene land surface by paleo river channels. In this accommodation-dominated shelf area, the sedimentation rate is low with values of 5–10 cm/ky. Where applicable, we assigned the sampled deposits to different paleo-facies. The latter are related to certain intervals of water depths at their time of deposition. Comparison with the sea-level curve of [Hanebuth, T.J.J., Stattegger, K., Grootes, P., 2000. Rapid flooding of the Sunda Shelf; a lateglacial sea-level record. Science, 288: 1033–1035.] indicates subsidence on the Central Shelf, which is in agreement with the high sedimentation rates in this area. In contrast, data from the Northern Shelf suggest tectonic uplift that might be related to recent tectonic movements along the Ailao Shan–Red River Fault zone. Data from the Southern Shelf are generally in agreement with the sea-level curve mentioned above.

Chemostratigraphic Correlation of Upper Permian Lavas from Yunnan Province, China: Extent of the Emeishan Large Igneous Province

Although the mantle plume model has been increasingly adopted for generation of the Emeishan basalts, doubts have been cast on the viability of this model because of the relatively small dimensions of this large igneous province (LIP) compared with typical LIPs. The Emeishan LIP was traditionally thought to be bounded on the southwest by the Ailaoshan-Red River (ASRR) fault zone. However, pre-Cretaceous strata in the Jinping area, southwest of the ASRR fault zone, are comparable to those at Binchuan in the western margin of the Emeishan LIP. This correlation is reinforced by similar chemostratigraphic variation of Upper Permian basalts from these spatially separated regions. Therefore, the Jinping basalts, which crop out ∼500 km southeast of the Binchuan counterpart, are interpreted as a dismembered part of the Emeishan basalts that were displaced to the present location by mid-Tertiary sinistral movement along the ASRR fault. We suggest that the ASRR fault does not bound the Emeishan LIP. Thus, this LIP has a much larger extent, and its western sector may have extended toward the Paleo-Tethyan ocean, and may have been destroyed by closure in the Triassic.

Exotic lithosphere mantle beneath the western Yangtze craton: Petrogenetic links to Tibet using highly magnesian ultrapotassic rocks

Research Article| September 01, 2001 Exotic lithosphere mantle beneath the western Yangtze craton: Petrogenetic links to Tibet using highly magnesian ultrapotassic rocks Yi-Gang Xu; Yi-Gang Xu 1Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, 510640 Guangzhou, China Search for other works by this author on: GSW Google Scholar Martin A. Menzies; Martin A. Menzies 2Department of Geology, Royal Holloway University of London, Egham TW20 OEX, UK Search for other works by this author on: GSW Google Scholar Matthew F. Thirlwall; Matthew F. Thirlwall 2Department of Geology, Royal Holloway University of London, Egham TW20 OEX, UK Search for other works by this author on: GSW Google Scholar Guang-Hong Xie Guang-Hong Xie 3Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, 510640 Guangzhou, China Search for other works by this author on: GSW Google Scholar Geology (2001) 29 (9): 863–866. https://doi.org/10.1130/0091-7613(2001)029<0863:ELMBTW>2.0.CO;2 Article history received: 11 Dec 2000 rev-recd: 07 May 2001 accepted: 21 May 2001 first online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share MailTo Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation Yi-Gang Xu, Martin A. Menzies, Matthew F. Thirlwall, Guang-Hong Xie; Exotic lithosphere mantle beneath the western Yangtze craton: Petrogenetic links to Tibet using highly magnesian ultrapotassic rocks. Geology 2001;; 29 (9): 863–866. doi: https://doi.org/10.1130/0091-7613(2001)029<0863:ELMBTW>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Highly magnesian ultrapotassic rocks that erupted ca. 30–40 Ma on either side of the northern Ailao Shan–Red River fault (western Yunnan) have initial 87Sr/86Sr values of 0.7064–0.7094 and ϵNd values of −3.8 to −4.6. Such isotopic compositions are distinct from asthenospheric signatures and most likely probe the lower lithosphere. Sm-Nd model age and trace element data for the Yunnan lavas indicate that at the time of eruption the mantle source was an old (>1 Ga) mica-bearing spinel harzburgite. However, such Proterozoic enriched lithospheric mantle could not have survived the thermo-tectonic processes associated with continental flood volcanism that affected the same part of the western Yangtze craton 250 Ma. Emeishan flood basalt volcanism would have purged the shallow mantle of all its fusible constituents and any enrichments would be younger than 250 Ma. We propose that the lithosphere mantle beneath the western Yangtze craton is exotic and probably represents part of the Tibetan lithosphere extruded to the east 40– 50 Ma. The Indo-Asia collision provides a suitable mechanism and explains the link between the west Yangtze craton and northern Tibet in terms of provenance (Sr-Nd) and the similar two-dimensional seismic velocity structure. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Long and complex thermal history of the Song Chay metamorphic dome (Northern Vietnam) by multi-system geochronology

Multi-system geochronology was used to unravel the long and complex thermal history of the Song Chay range (Northern Vietnam), a high-grade granitic and metamorphic dome in the vicinity of the Cenozoic, Ailao Shan–Red River fault zone. It was considered to be Proterozoic South China basement, but its geological history was basically unknown. Scattered field observations suggest three episodes of high-temperature deformation: firstly at the time of granite emplacement, secondly a décollement with top to the north shear and thirdly anticlinal doming of the foliations formed during the two first stages. P– T estimates suggest that metamorphism coeval with the second deformation phase culminated at ∼580°C and ∼4.5 kbar (∼16 km depth). Multi-system geochronology is applied to a two-micas granite sample, slightly deformed within the décollement. U/Pb dating of zircon yields an age of 428±5 Ma (±2 σ) interpreted as the time of granite crystallization within the South China ‘Caledonian’ belt. Rb/Sr on white micas and biotite yields ages of 206±10 Ma and 176±5.3 Ma, respectively (2 σ), whereas 39Ar/ 40Ar ages of the same minerals are 210±9 and 190±8 Ma (2 σ). These ages suggest an Upper Triassic episode of rapid cooling interpreted as due to doming a few million years after the end of movement on the décollement. The K-feldspar irregular 39Ar/ 40Ar age spectrum can, to the first order, be explained by a cooling history with two episodes of rapid cooling: one at ∼140 Ma and a second around 41 to 25 Ma. Apatite fission tracks central age (33.6±3.6 Ma, 1 σ) confirms a Tertiary rapid cooling event interpreted as the final exhumation of the Song Chay dome.