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All Abstracts of Session SE11-10

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Oral Presentations

SE11-10 - Effects of India-Asia collision on evolution of Southeast Asia
Wednesday, August 05, 2015 | 311 | 16:00-18:00
1.
SE11-10-D3-PM2-311-002 (SE11-10-A011)
 
3D Discrete Element Simulation of Large-Scale Faulting and Crustal Thickening in the India-Asia Collision Zone
Liqing JIAO1+, Paul TAPPONNIER1#, Frederic Victor DONZE2, Luc SCHOLTES3, Yves GAUDEMER4, Zhenhua HUANG5
1 Nanyang Technological University, Singapore, 2 Université Joseph Fourier - Grenoble, France, 3 National School of Geology, University of Lorraine, France, 4 Institut de Physique du Globe de Paris, France, 5 University of Hawaii at Manoa, United States
#Corresponding author: tappon@ntu.edu.sg +Presenter

Modeling the discontinuous nucleation, growth and interaction of large faults within continents remains a challenge. Previous analog experiments simulating the India-Asia collision successfully modeled the large strike-slip faults developed in the Eurasian plate. However, these experiments were 2D, isotropic, dynamically unscaled with gravity, and did not allow the development of topographic relief. To address these problems, we use the YADE discrete element method (DEM) code to produce a suite of 3D models. Our models generate two large strike-slip faults that allow for the rotation and extrusion of two sub-blocks. At the same time, we observe incremental formation of a plateau in three distinct steps. The location and size of the two large strike-slip faults are consistent with the Red River and Altyn Tagh faults. Moreover, the generation of the plateau is in keeping with a model in which the Tibetan plateau is progressively raised from South to North by large crustal thrust faults. While using very simplified boundary conditions, such modeling results seem consistent with topographic, tectonic and geological observations.

3.
SE11-10-D3-PM2-311-004 (SE11-10-A003)
 
Geochemical and Sr-Nd-Pb Isotopic Characteristics of Volcanic Rocks in the Tram Tau District, Tu Le Basin, NW Vietnam: Implications for Mantle Source and Regional Geodynamics
Huong TRAN1#+, Nguyen HOANG1,2, Dao THAI BAC3
1 Institute of Geological Sciences, Vietnam Academy of Sciences and Technology, Viet Nam, 2 Geological Survey of Japan, Japan, 3 Center for Geological Information and Archives, General Department Geology and Minerals of Vietnam, Viet Nam
#Corresponding author: tranhuong.humg@gmail.com +Presenter

Volcanic rocks in the Tram Tau District, Yen Bai Province (Tu Le Basin) are consisted of rhyolite-trachyte, trachyte and a minor amount of basalt. They are rich in alkali (Na2O+K2O  6-9 wt% in trachyte), Rb, Th, Nb, Ta and the rare earth (except Eu). The measured 87Sr/86Sr ratios are high, from 0.72575 to 0.8414 and low 143Nd/144Nd, between 0.51227 and 0.51263. Age of the volcanics is 258-255 Ma based on U-Pb isotopic dating on zircons. However, the 87Sr/86Sr and 87Rb/86Sr values of samples from Ban Hat Liu village yielded an isochron of 154 ±1.14 Ma and an initial 87Sr/86Sr ratio at 0.7105. This age is in good agreement with a number of reported data. The initial Sr, Nd and Pb isotopic compositions of Tram Tau volcanic rocks (and Tu Le Basin, in general) are highly enriched and plotted outside the fields of Permian Emeishan and Song Da magmas. The isotopic enrichment is interpreted to reflects mixing between mantle and crustal sources. Nd model ages of the volcanic rocks are 1.1 ±0.2 Ga correspondent to Proterozoic. Given a Proterozoic granitic crust having 87Sr/86Sr isotopic ratios at 0.715, 0.720, and 0.730, a mantle source having 87Sr/86Sr isotopic ratio of 0.70315 would need to mix, respectively, 15%, 7% and 4% of the crustal rock to form the Tram Tau melts. The isotopic compositions are vastly different from A-type granite (T(DM))= 0.6 to 1.1 Ga) from southwest China (Gilder et al., 1996). The isotopic difference and lack of paleomagnetic evidence, the J3– K1 volcanic rocks in the Tu Le Basin (and elsewhere in northwestern Vietnam) may not be formed in western Yunnan by intraplate extension being transported southeastward along the Ailao- Shan- Red River Fault zone to the current location, following India – Eurasian collision since at least 30 million years.

4.
SE11-10-D3-PM2-311-005 (SE11-10-A009)
 
Petrology and Geochemistry of Mantle Xenoliths from Southern Vietnam
Christoph HAUZENBERGER1#+, Jürgen KONZETT2, Nguyen HOANG3,4, Khoi Ngoc NGUYEN5
1 University of Graz, Austria, 2 University of Innsbruck, Austria, 3 Institute of Geological Sciences, Vietnam Academy of Sciences and Technology, Viet Nam, 4 Geological Survey of Japan, Japan, 5 Hanoi University of Science, Viet Nam
#Corresponding author: christoph.hauzenberger@uni-graz.at +Presenter

Alkali basalts from south-central Vietnam contain frequently clinopyroxene, zircon and sapphire xenocrysts as well as mantle xenoliths. The mantle fragments comprise refractory spinel lherzolites and subordinate amounts of spinel harzburgites and pyroxenites. The basalts are part of widespread Neogene volcanism found in southern China and Indochina regions. Samples from different localities between the cities of Ban Me Thuot and Saigon were recovered. The mineral assemblage in most samples consists of the simple lherzolitic mineral assemblage Ol–Opx–Cpx-Sp. The Ol, Cpx and Opx crystals are equigranular while Sp occurs usually as smaller sized intersertal phase or as partly oriented inclusions in Cpx. Cpx II occurs in some samples as recrystallized “spongy rim” around Cpx I. The use of the Cpx-Opx thermometer (BREY & KOEHLER, 1990) and the Al and Cr in Ol thermometer (DE HOOG et al., 2010) allowed to constrain the temperature with 800 to 1100 °C. Pressure is thought to be in the range of 1.5 to 2.0 Gpa based an calculated temperature and an average geothermal gradient for this region. Trace and rare earth element composition of Cpx, Opx, and Ol was determined by LA-ICPMS. While most Cpx compositions are slightly depleted in LREE, typical for average depleted mantle compositions, some samples are strongly enriched in LREE indicating heterogeneous mantle metasomatic processes. The sample displaying the highest level of LREE enrichment in Cpx has the lowest calculated temperature (T = c. 800°C) and the highest Ni content in olivine. In addition elongated apatites are found in this sample indicating metasomatic influence from a possible carboantitic melts

Financial support from the Austrian Academy of Sciences and ASEA-Uninet is gratefully acknowledged. This is a contribution to IGCP557.

BREY, G.P., KOEHLER, T.P. (1990): J. Petrology, 31:1353–1378.

DE HOOG, J.C.M, GALL, L., CORNELL, D.H. (2010): Chem. Geol., 270, 196–215.

Poster Presentations

  SE11-10-D5-PM2-P-007 (SE11-10-A002)
 
Post-Opening of South China (East Viet Nam) Sea Geodynamic and Magmatic Evolution in Southern Viet Nam
Le DUC ANH1#+, Phung VAN PHACH1, Nguyen HOANG2,3, Nguyen NHU TRUNG1
1 Institute for Marine Geology and Geophysics, Vietnam Academy of Science and Technology (VAST), Viet Nam, 2 Institute of Geological Sciences, Vietnam Academy of Sciences and Technology, Viet Nam, 3 Geological Survey of Japan, Japan
#Corresponding author: leducanh010282@gmail.com +Presenter

New geophysical and structural analyses show that the SW tip of SW Sub-basin of East Vietnam Sea (EVS) has attenuated continental crust, not oceanic. The oceanic crust of EVS (South China Sea) does not spread to the west over the 112ºE longitude. The NW-SE Red River Fault, East Vietnam Fault Scarp and NW-SE striking Tuy Hoa Fault Zone were probably connected and acted jointly during the period of oceanic crust spreading (~ 32-17 Ma). This system may have controlled the oceanic spreading of the SW arm of the EVS to the SW. The NW-SE striking Tuy Hoa Shear zone may have played a role of transform fault and acted as SW boundary that has limited the spreading of oceanic crust further to the SW. The change from left- to right-lateral motion of NW-SE fault system may have led to the cessation of oceanic spreading in EVS and stimulated strong subsidence of Tertiary basins. Post- EVS opening, subsidence (extension) -related volcanism occurred in the oceanic crust and in the vicinity of the Hoang Sa (Paracels) Islands at two main episodes ca. 9 and <1 Ma, producing SiO2-poor and FeO-rich alkali basalt and nephelinite. Whereas, the contemporaneous subsidence-related volcanism appeared along extension faults running parallel to eastern Vietnam coastline from latitude 15°N to 10°N (underwater eruption of Iles Des Cendres in 1921) at two main episodes of 12 Ma and 1.5-0 Ma. The eruptions appear both on Ly Son (15°N) and Phu Quy (10°29’N) islands. The early comprises of high-SiO2, low-FeO tholeiite and the later, of low-SiO2, high-FeO olivine and alkaline basalt, implying melting sources were deepened with time. Although post-opening magmas occurred sporadically in the EVS and showed spatio-temporal differences, the volcanism was controlled mainly by subsidence (extension) tectonics, the activities are believed to govern the entire post-opening geodynamics.

  SE11-10-D5-PM2-P-008 (SE11-10-A006)
 
Young Basaltic Volcanism in Northern Palawan: OIB-Like Characteristics?
James Cesar REFRAN1#+, Carlo ARCILLA2
1 University of the Philippines, Philippines, 2 University of the Philippines Diliman, Philippines
#Corresponding author: jamesrefran@gmail.com +Presenter

The Philippines is dominated by SSZ-influenced magmatism. Very young lava flows in Northern Palawan form a large field with gentle topography suggesting  extensive, low viscosity flows. There are no active subduction zones beneath northern Palawan to cause typical arc volcanism. The rocks are basalts to basaltic andesites and straddle tholeiitic/calc-alkaline compositions but are not K-enriched. MORB-normalized spidergrams show enriched concentrations of Nb and other high field strength elements, further confirming the non-subduction zone origin. The lavas could be similar to OIBs found in the seamounts found in the South China Sea. The Nb-enriched Palawan lavas are the non-SSZ equivalents of Nb-rich lavas also encountered in the Sulu arc and Sulu seas, suggesting a fertile mantle source independent of SSZ contributions. This lava field, one of the largest in the Philippines, is to date the only  lavas in the Philippine archipelago with OIB characteristics.

  SE11-10-D5-PM2-P-009 (SE11-10-A010)
 
Petrology and Geochemistry of Apatite ± Whitlockite-Bearing Mantle Xenoliths from Southern Laos
Jürgen KONZETT1, Christoph HAUZENBERGER2#+, Katharina GROEBNER1, Anna-Katharina SIEBERER1, Nguyen HOANG3,4, Khoi Ngoc NGUYEN5
1 University of Innsbruck, Austria, 2 University of Graz, Austria, 3 Institute of Geological Sciences, Vietnam Academy of Sciences and Technology, Viet Nam, 4 Geological Survey of Japan, Japan, 5 Hanoi University of Science, Viet Nam
#Corresponding author: christoph.hauzenberger@uni-graz.at +Presenter

Cenozoic basalts are widespread throughout Southeast Asia and form what is called a “diffuse igneous province” consisting of tholeiites and late-stage, small-volume alkali basalts. We report the results of a petrological and geochemical study of a suite of spinel-lherzolites and ortho/clino-pyroxenites sampled by nepheline±leucite-bearing alkali basalts of the Bolaven Plateau/southern Laos. Lherzolites (ol+opx+cpx+sp+FeNi-sulfide) and pyroxenites (opx+cpx+FeNi-sulfide) show evidence for cryptic or modal metasomatism characterized by a strong enrichment of Li in cpx and opx with respect to ol (cryptic) and by the appearance of apatite rarely associated with minor phlogopite ± calcic amphibole. Two compositional types of apatite are present: (1) apatite characterized by low P2O5 (37.9-41.0 wt%) and low analytical totals (93.8-97.4 wt%) combined with high Na2O (0.9-1.6 wt%) indicative of a significant type-A carbonate-apatite component and (2) apatite with high P2O5 (40.5-42.4 wt%) and high analytical totals (97.7-100.9 wt%) combined with low Na2O (0.3-0.7 wt%). Low-P2O5 apatites show a restricted range in F and Cl (0.2-0.9 wt% F, 0.6-1.6 wt% Cl) compared to high-P2O5 apatites (0.3-3.1 wt% F, 0.3-4.1 wt% Cl). One apatite-bearing sp-lherzolite sample contains trace amounts of whitlockite-merrillite solid solution [Ca18Mg2(PO4)12[PO3(OH)]2-Ca18Na2Mg2(PO4)14] in addition to apatite+phlogopite+calcic amphibole. Whitlockite-merrillite is extremely rare in mantle rocks and has been known so far from only one locality in Siberia where its formation was ascribed to a distinct type of ±anhydrous REE-metasomatism (IONOV et al., 2006). In the sample from Laos, whitlockite-merrillite is always intergrown with apatite and was unambiguously identified using EMPA and micro-Raman spectroscopy. It contains 3.5-3.9 wt% MgO and 2.4-3.1 wt% Na2O, respectively. Thermometry of this sample yields 900-950°C for a pressure of 1.5 GPa.