Analysis of abstracts 青年論壇 2012

1. Analysis of abstracts青年論壇 2012

2. The variation of the thermocline structure in the southern marginal West Pacific Warm Pool during 2.4 -3.3 million years ago Matteo Ternelli, Kuo Yen Wei Department of Geoscience, National Taiwan University (298 words) Late Pliocene has been recognized as a good analog to the possible future global warming condition since it is warm than today, but already in a glacial-interglacial fluctuation period.For this reason is widely used to create patterns for the climatic changes in the future, since we are going to face a global climate warming. (The) Pacific Ocean and in particular the West Pacific Warm Pool are areas of great interest for determine the climate evolution in this geological period. We therefore determine the temperature evolution of the West Pacific Warm Pool using (the) oxygen isotopic (δ18O) and trace elements (Mg/Ca) methods on a species of planktonic foraminifera which lives in the thermocline: Neogloboquadrinadutertrei, and its ancestor form: Neogloboquadrinahumerosa. Known the similarity between the two species a new distinction method has been developed. The specimens have been collected from the deep-oceanic core ODP 1115 retrieved on the southern margin of the West Pacific Warm Pool out of the east coast of the Papua New Guinea. An overview of the Pacific Ocean’s climate in that period has already been made by other researchers, the results from our analyzes can give further data to confirm or deny previous works, in order to create new conclusions on what has been the climatic evolution in the thermocline and what have been the mechanisms that permit these changes to happen. From the count of the number of specimens of the two species per level, we can understand already that there’s a slow process through the time of improving of the climatic conditions, the number of specimens rise up from the bottom to the top of the core. Coupling these data with the curves of temperature and salinity may reveal interesting conclusion about the environmental conditions and the ability of get acclimatized of these two species.

3. A Test of Earthquake Early Warning System for simulating the past large earthquakes in Taiwan (299 words) Da-Yi Chen 陳達毅 Department of Geosciences National Taiwan University The earthquake early warning (EEW) system is a practical tool for providing earthquake information before strong ground-shaking coming. In the past twenty years, Taiwan had suffered many large earthquakes resulted in great damage of property and life. Therefore, to build up a reliable and robust EEW system is quite important. Using the Earthworm module named pick_ew, the developing EEW system is able to automatically detect the P wave arrival. Furthermore, by modifying the module, the peak value of displacement (Pd), velocity (Pv) and acceleration (Pa) of the seismic waveform were calculated in the time window of 3 seconds after the P wave arrival. Meanwhile, the new module named tcpd was created for using the P wave arrivals to determine the earthquake location and taking advantage of the Pd, Pv and Pa to determine the magnitude. As the seismic wave propagating away from the epicenter, more seismometers recorded seismic waveforms. The EEW system can update the EEW report with time. The rapid report system in Central Weather Bureau Taiwan adopted strong motion seismometers with 16-bit dynamic range and 50 Hz sampling rate. All the large earthquakes were well recorded by this system. This is a great opportunity to test the developing EEWS. We selected 23 earthquakes occurred around Taiwan with magnitude greater than 6 and depth shallower than 40 km. The first EEW report was obtained in about 12.1 seconds after the earthquake occurred, the epicenter error is about 12.94 km, the magnitude error is about 0.3, 0.2 and 0.4 by the parameter of the Pa, Pv and pd, respectively. The parameter of the Pa is more correlated to the magnitude lager than 6.

4. Gas composition and soil CO2 fluxin active volcanic areas, China (354 words) 溫心怡Hsin-Yi Wen1, Tsanyao Frank Yang1, Zhengfu Guo2, Ching-Chou Fu1, Ai-Ti Chen1, Maoliang Zhang2 Changbaishan intra-plate volcano and Tengchong hydrothermal area are two of the active volcanic areas in China. Changbaishanis located on the border of China and North Korea. This volcano violently erupted 1000 years ago and produced massive magma and widespread volcanic ash, resulting in one of the largest explosive eruptions during the last 2000 years.Tengchong hydrothermal area is located in western Yunnan Province.Tengchong is near the Indo-Eurasian collision margin sothe tectonic setting here is very complicate. The hydrothermal eruptions were occurred recently at Rehai during 1993-2003. In order to better understand current status of the Changbaishan intra-plate volcano and Tengchong hydrothermal area, we have conducted the soil gas survey aroundtheTianchicrater lake and Rehai geothermal area, respectively. Bubbling gas from hot springs were also collected and analyzed. In Changbaishan volcano, the results show that CO2 is the major component gas for most samples. The maximum value of helium isotopic ratio 5.8 RA (where RA = 3He/4He in air) implies more than 60% of helium is contributed by mantle component, while carbon isotope values fall in the range of -5.8 to -2.0‰ (vs. PDB), indicating magmatic source signatures as well. Nitrogen dominated samples, 18Dawgo, have helium isotopic ratio 0.7 RA and carbon isotope value of -11.4‰, implying the gas source might be associated with regional crustal components in 18Dawgo. The first-time systematic soil CO2 flux measurements indicate the flux is 22.8 g m-2 day-1 at the western flank of Changbaishan, which is at the same level as the background value in the Tatun Volcano Group (24.6 g m-2 day-1), implying that Changbaishan may not be as active as TVG. In Tengchong hydrothermal area, the preliminary results show that CO2 is the major component gas for most samples. The helium isotope ratio fall in the range of 0.5 RA to 3.2 RA (where RA = 3He/4He in air).Dagungguo, have the highest value of helium isotopic ratio 3.2 RA implies 40% of helium is mantle-derived. Nevertheless, samples from Banglazhang and Shihchiang hydrothermal areas showmuch lower helium isotopic ratio0.8 RA and 0.5 RA, respectively.It suggeststhat the local tectonic setting plays an important role for the gas degassing in this area.

5. Multi-proxies from lacustrine sediments revealing human activities in northeastern Taiwan during the past two centuries 黃致展Jyh-Jaan Huang1, Kuo-Yen Wei1, Chih-An Huh2, Sheng-Rong Song1, Wen-Hsuan Liao2, Tien-Nan Yang2, Shu-Fen Lin3,Meng-Yang Lee4, Chih-Chieh Su5 and Teh-Quei Lee2 1.Department of Geosciences, National Taiwan University, Taiwan 2.Institute of Earth Sciences, Academia Sinica, Taiwan 3.Institute of History and Philology, Academia Sinica, Taiwan 4.Department of Earth and Life Science, Taipei Municipal University of Education, Taiwan 5.Institute of Oceanography, National Taiwan University, Taiwan Abstract (284 words) Deforestation and land-use changes affect the intensity of geomorphic processes more than small climatic fluctuations during late Holocene. The ITRAX-XRF core scanner offers a fast, non-destructive technique capable of detecting elemental variations directly from sediment cores at sub-millimeter resolution. It has become an increasingly common practice to use this technique to obtain paleo-proxy data from lacustrine and marine cores. According to Guyard et al. (2007) and our experiences, besides elemental signals, variation of organic materials content can also be derived from the ratio of incoherent to coherent scattering (inc/coh). In order to assess the importance of human affect nature environment in Lan-Yang Plain, here we present an ultra high resolution (1 mm & 200 um) records of inc/coh ratio from lacustrine cores, named MHL-09-01 and MHL-11-02, recovered from the center of Lake Meihwa (Ilan County, northeastern Taiwan, 121° 43.57', 24° 38.35'). These cores have been analyzed for 137Cs, 210Pb and 239,240Pu, providing an excellent age model for the reconstruction of natural processes and human activities in the past century. We believe that this area has been impacted by agronomical activities around 100 years ago based on the trend of the inc/coh ratio in two cores and that of the palynological data (Alnus, Mallotus, Trema and herbs) in a nearby core (MHL-5A) from the same lake. Besides, the presence of a yellow and earthy layers between 11-17 cm in MHL-09-01 and 12-20 cm in MHL-11-02 are in all likelihood attributable to the land development associated with the construction of a temple complex on the hillslope to the south of the lake from AD 1970 to AD 1982. Lower inc/coh ratios in the earthy layer also reflect deep excavation of the hillslope during the construction period.

6. Carbon and hydrogen isotope and related biogeochemistryfrom Gas Hydrate Potential Area Offshore SW Taiwan 陳乃禎Naichen Chen, Tsanyao Frank Yang Department of Geosciences, National Taiwan University (321 words) In previous studies, high methane flux in offshore SW Taiwan was considered related to the dissociation from gas hydrate. However, dynamic microbial activities have been observed in the shallow sediments indicating mixture of methane from these shallow reactions. In this study, piston cored samples were collected from the studied area during several surveys since 2007 ( r/v ORI, Leg 828, 835, 860 and r/v Marion Dufresne 178 cruise). The 13C of dissolved inorganic carbon (DIC) and methane and the D of methane and interstitial water of cored samples were measuredin order to identify the source of methane gas and biogeochemistry processes. We can have following conclusions based on the results of this study. (1) methane gas of samples collected from lower slope of active continental margin are mainly generated by microbial activities (13C = -60 ~ -112‰); on the other hand, methane gas from upper slope of active continental margin is mainly from thermogenic source (13C = -45 ~ -63.8‰). (2) The lightest 13C value of methane and DIC usually occur at the sulfate methane transition zone (SMTZ) of depth profile, indicating that carbon cycling within this transition zone indeed exists. Thus, we can conclude that the 13C-depleted methane could be generated at the top of methanogenic zone when the 13C-depleted CO2 produced by the microbially-mediated process of anaerobic oxidation of methane (AOM), and it may be recycled back to methane pool by the process of CO2 reduction. (3) TheD of methane and interstitial water infer that CO2 reduction could occur at SMTZ.(4) 13C values of DIC become heavier with increasing depth in many sites, indicating that CO2 reduction process became more important at the depth of the profiles. All these evidences indicate that significant microbial activities in the studied area. Therefore, methane from microbial activities should not be overlooked in high methane flux area, even at gas hydrate potential area.

7. Tracing Miocene Event in Yuli belt, Tananao Metamorphic Complex – Chronological Aspect 羅允杰Yun-Chieh Lo1, Ching-Hua Lo1, Yuan-His Lee2 1Department of Geosciences, National Taiwan University 2Department of Earth and Environmental Sciences, National Chung Cheng University Abstract (207 words) Yuli belt of Tananao metamorphic complex located at the eastern boundary of Eurasian plate had experienced high degree of metamorphism, once thought to be the oldest stratum in Taiwan which uplift rapidly in the last 6 Ma (Penglai Orogeny). In a few kilometers away, arc-volcanism of the coastal range started approximately 15 Ma and ended at about 8.6-5.6 Ma as arc-continental collision began. Some previous studies reported samples with metamorphic age of 8-14Ma in Yuli belt. However, the chronology and tectonic history of Yuli belt have not been systematically studied. In order to study the Miocene metamorphic history of Yuli belt, rocks of meta basites and meta sediments were sampled from Juisui and Wanjung. Minerals separated from these samples were selected for U-Pb and Ar-Ar dating. Igneous or metamorphic zircon U-Pb age of meta basites might imply the source of rock or metamorphic time. Detrital zircon age distribution and youngest age of meta sediments could be use for stratigraphic correlation and Ar-Ar age of minerals for understanding the metamorphic/Thermal history. Preliminary zircon U-Pb dating suggested zircon metamorphic age of 15 Ma at Wanjung and Miocene materials exist in Juisui block. Chronological studies on these materials will be helpful for reconstructing the pre-orogeny tectonic history of eastern Taiwan.

8. Constraints on crustal deformation of the Taiwan plate boundary from CGPS strain rate field and stress inversions 陳冠翔Sean K. Chen1, 2Yih-Min Wu1Yu-Chang Chan2 Ya-Ju Hsu2 1Institute of Geosciences, National Taiwan University, Taipei, Taiwan 2Institute of Earth Science, Academia Sinica, Taipei, Taiwan Abstract (348 words) Many studies used the continuous global positioning system(CGPS) observations and modeling results representing the crustal deformation around the global plate boundaries. However, the relation between the surface geodetic data and crustal deformation is still a major debate since there were few available deeper data for constraints. We use both updated CGPS and earthquake focal mechanism data from 1994 to 2010 and 1991 to 2010 to re-evaluate 3D spatial variations of surface strain rate and crustal stress state in the Taiwan mountain belt. We estimate strain rate with a simple approach that solves for surface velocity on a 0.1°x0.1°grid while weighting the distance between observations and each grid node, after removing the co-seismic and post-seismic effects from main shocks in the period. We implemented the genetic algorithm in a nonlinear global search for the focal mechanism solutions with magnitude ranging from ML 1.6 to 7.3 by first motion polarities of P waves recorded, also eliminating the aftershock sequences produced by main shocks which lead to perturbations in the estimation of background stress pattern, then performing a stress tensor inversion from more than 7000 determined events around Taiwan. In the comparison of orientations of strain rate and stress axes, we find the regional variation of stress orientations from surface to the base of crust is significant and not homogenous in Taiwan during the present-day mountain building process. Our results show the CGPS data reveal deeper deformation at least down to 20 km depth in most of Taiwan regimes; 25 km in WS foothills and southern Central Range; more than 30 km in Chi-Chi rupture zone and southern Coastal Range. We suggest that the common decoupling depth starts form 20 km indicating a brittle-ductile transition boundarybeneath Taiwan, and the mechanism of stress accumulation for the 1999 Mw 7.6 Chi-Chi and 2003 Mw 6.8 Cheng-Kung larger events is an interpretation for the deeper depth of consistent orientations from strain rate and stress field. The regimes without consistency of strain rate and stress axes may cause by the worse data distribution and coverage, or the complex of regional structures.

9. Trace metal flux from shallow hydrothermal vents in Kueishantao islet, Taiwan and their effect on ambient seawater 余采倫Tsai-Luen Yu, Bo-Shian Wang, Yue-Gau Chen (236 words) Increases in trace nutrients, in particular iron, can enhance oceanic primary production and may be an important control on draw-down of atmospheric CO2 and influence global climate cycles. Hydrothermal fluids have potentially important supplement role on Fe sources and may affect phytoplankton growth through upwelling from deep waters. Because the residence time of iron is short (70-200 years), it is difficult to identify iron pathways and estimate its impact on oceanic primary production. The possibility that shallow hydrothermal fluids can directly release Fe to surface waters has not been systematically assessed. Compared to deep hydrothermal system, shallow hydrothermal system is more easily accessible, and their contribution of global budgets may be larger than expected. Kueishantao islet, Taiwan, is an appropriate place to study this issue. There are a cluster of more than 30 hydrothermal vents at depths of about 10-30m. However, there is just one report focusing on the chemistry of hydrothermal fluids in Kueishantao islet. This data has shown the roughly emission of trace nutrients and metals in the Kueishantao hydrothermal fluid, but the ultimate flux to the ocean of trace nutrients and metals is still unknown. The purpose of this project would be to quantify trace nutrients and metals from hydrothermal fluids to surface waters and employ isotopic chemistry for tracing the marine biogeochemical cycle. Through these data allows better assessment of the impact of oceanic primary production and understand of isotopic fractionation process.

10. A feasibility study on the application of luminescence dating for quartz from different rock types as a thermochronometer 巫姿萱 Tzu-Shuan Wua, Alexander Kunza, Manoj K. Jaiswalb, Yue-Gau Chena Department of Geosciences, National Taiwan University, Taiwan. Department of Earth Sciences, Indian Institute of Science Education and Research-Kolkata, India. (219 words) Thermal ages (e.g. fission track, 39Ar/40Ar and U-Th/He ages) are important to understand mountain building activities within the upper crust. In order to understand the exhumation history of Taiwan, researchers are looking for the applicability of thermal ages from fairly low cooling temperatures by using luminescence dating methods. The low-temperature-involved recent past is a point of great interest. Since the reliability of the luminescence dating method is sample dependent, this ongoing study starts with checking relevant characteristics of the luminescence properties from appropriate minerals (e.g. quartz). The samples for this study were collected from the Central Range in Taiwan from two different rock types: 1) cherty-marble and 2) meta-sandstone. This sampling strategy is intended to decipher rock dependent variation because cherty-marble has not undergone as much stress as meta-sandstone. We compare luminescence behaviors of quartz between samples from cherty-marble and meta-sandstone. The equivalent doses were determined by conventional single aliquot regenerative-dose (SAR) protocol and SAR isothermal thermoluminescence (ITL) protocol. Results suggest that the preheat process may not be applicable for quartz from both cherty-marble and meta-sandstone of Taiwan. The SAR ITL protocol without preheat processes was applied successfully on the sample for such an approach. Although our current results of ITL seem promising, further and detailed luminescence characteristics of ITL should be examined before the feasibility is finally proposed.

11. Carbon and hydrogen isotope and related biogeochemistryfrom Gas Hydrate Potential Area Offshore SW Taiwan 陳乃禎Naichen Chen, Tsanyao Frank Yang Department of Geosciences, National Taiwan University (321 words) In previous studies, high methane flux in offshore SW Taiwan was considered related to the dissociation from gas hydrate. However, dynamic microbial activities have been observed in the shallow sediments indicating mixture of methane from these shallow reactions. In this study, piston cored samples were collected from the studied area during several surveys since 2007 ( r/v ORI, Leg 828, 835, 860 and r/v Marion Dufresne 178 cruise). The 13C of dissolved inorganic carbon (DIC) and methane and the D of methane and interstitial water of cored samples were measuredin order to identify the source of methane gas and biogeochemistry processes. We can have following conclusions based on the results of this study. (1) methane gas of samples collected from lower slope of active continental margin are mainly generated by microbial activities (13C = -60 ~ -112‰); on the other hand, methane gas from upper slope of active continental margin is mainly from thermogenic source (13C = -45 ~ -63.8‰). (2) The lightest 13C value of methane and DIC usually occur at the sulfate methane transition zone (SMTZ) of depth profile, indicating that carbon cycling within this transition zone indeed exists. Thus, we can conclude that the 13C-depleted methane could be generated at the top of methanogenic zone when the 13C-depleted CO2 produced by the microbially-mediated process of anaerobic oxidation of methane (AOM), and it may be recycled back to methane pool by the process of CO2 reduction. (3) TheD of methane and interstitial water infer that CO2 reduction could occur at SMTZ.(4) 13C values of DIC become heavier with increasing depth in many sites, indicating that CO2 reduction process became more important at the depth of the profiles. All these evidences indicate that significant microbial activities in the studied area. Therefore, methane from microbial activities should not be overlooked in high methane flux area, even at gas hydrate potential area.

12. Rapid and precise determination of natural carbonate rare earth elements in femtogram quantities by ICP-SF-MS 吳忠哲Chung-Che Wu,* Yi Liu, †,* Jain-Ru Jhou,* Chuan-Chou Shen* *High-precision Mass Spectrometry and Environment Change Laboratory (HISPEC), Department of Geosciences, National Taiwan University, Taipei, Taiwan 106, R.O.C. † CAS Key Laboratory of Crust-Mantle Material and Environment, School of Earth and Space Science, University of Science and Technology of China, Hefei, 230026, China Abstract (169 words) A rapid and precise technique for measuring of femtogram quantity rare earth elements (REE) levels in natural carbonate samples by ICP-SF-MS, has been developed, at the Department of Geosciences, National Taiwan University. REE/Ca ratios are calculated directly from the intensities of the ion beams of 46Ca, 139La, 140Ce, 141Pr, 146Nd, 147Sm, 153Eu, 160Gd, 159Tb, 163Dy, 165Ho, 166Er, 169Tm, 172Yb, and 175Lu using external matrix-matched synthetic standards to correct for instrumental ratio drifting and mass discrimination. A routine measurement time of 3 minutes is typical for one sample containing 20-40-ppm [Ca]. Replicate measurements made on natural coral and foraminiferal samples with REE/Ca ratios of 2-242 nmol/mol show external precisions of 1.9-6.5% (2RSD) can be achieved with only 10-1000 femtogram REEs in 10-20 μg carbonate consumed. The key advantages of this established technique are to (1) provide a possibility of directly analyzing REE isotopic composition in femtogram quantities without chemical separation steps (2) and to offer high precision, high temporal resolution REE records in carbonates, such as sclerosponges, tufa, and speleothems.

13. Toward a seismic tomography of Taiwan orogeny from joint inversion of local andteleseismic data Huang, Hsin-Hua1, Yih-Min Wu1, Xiaodong Song2, Zhen James Xu2, and Chien-Hsin Chang3 1Department of Geosciences, National Taiwan University 2Department of Geology, University of Illinois, Urbana, IL 3Central Weather Bureau, Taipei, Taiwan (242 words) Taiwan orogenic belt is created by the oblique collision between the Eurasian continental margin and Luzon volcanic arc riding on the Philippine Sea Plate. It is one of the youngest and most active orogenies in the world, accompanied by numerous faults and high seismicity. Many previous studies have been conducted and provided abundant measurements and observationsin various fields, including geophysics, geodesy, geology, geomorphology, and so on. However, the mechanism of mountain building is still being under debate (e.g., Suppe, 1980, 1981; Wu et al., 1997; Shyu et al., 2005a). Among the proposed models, a key controversy is the different interpretations of deeper structures such as South China Sea Plate, Fore-arc basement, and the geometry of subducting slabs. Seismic tomography is one of the important techniques to uncover the subsurface structures. Yet numerous local seismic tomographic studiesthat have been carried out since 1990s (Rau and Wu, 1995; Ma et al., 1996; Kim et al., 2005; Wu et al., 2007) have been limited by the irregular distribution of local seismicity. The resolution of most of them can only reach to 40-50 km except the subduction zones because of no earthquakes occurring deeper. Therefore, integrating additional data, e.g. teleseismic data, to extend the resolution to the deeper part is truly needed. In this study, we jointly invert the local and teleseismic data simultaneously to gain the insight into the upper mantle. Byexposing the deeper structures, weare enabled to inspect the different models of Taiwan orogeny.