General Description of the Program
The proposed research project "Asian Orogenesis and Environmental Changes: A Multi-Disciplinary Approach" is aimed to tackle some of the most important geological problems, particularly, those concerning the growth, deformation history and tectonic evolution of Asia in the Phanerozoic era, and influence of tectonic uplift to the Cenozoic and recent environmental and climatic changes. The project assembles the currently most active and dynamic researchers at NTU and IES-Academia Sinica to work together. Their diverse disciplines will be coordinated to produce the most significant results. The project calls for a multi-disciplinary approach, including field and structural analyses, geochronological, petrological, geochemical and geophysical (particularly, paleomagnetic) studies. The field and structural analyses and geophysical study could only be achieved through cooperation with other specialists. Consequently, we emphasize the importance of international cooperation.
The present proposal comprises two seemingly unequal but tightly connected parts: the major part is composed of problem-oriented sub-projects and the minor part, but critical to all the others, is a technique-oriented project. The problem-oriented sub-projects represent a comparative and coherent study of accretionary and collisional orogens in East Asia, as well as the causal effect of the uplift of the Tibetan/Himalayan orogen on climatic change. The minor technique-oriented project would be focused on the development and enhancement of our analytical capabilities, particularly on state-of-the-art techniques of magnetic sector MC-ICPMS (Multi-Collector Inductively Coupled Plasma Mass Spectrometry). In summary, we present three interlocked sub-projects as follows:
- Growth and evolution of the Asian continent, as evidenced from contrasting orogens: accretionary (Central & East Asia, and Taiwan) and collisional (the Tibetan Plateau and Himalayas). In accretionary orogenic belts of Central and East Asia (e.g., the Altai and Xing'an Mountians in China), we intend to study an interesting style of orogeny in which abundant juvenile crust formed and the size of continent enlarged. This study is intimately connected to a new project of the International Lithosphere Program (ILP). In collisional orogenic belts, as represented by the Tibetan plateau and Himalayas, our goal is to study the processes of mountain building as well as thickening and recycling of the continental crust.
- Tectonic impacts on the environmental changes in East Asia. We will undertake some of most fashionable research topics and use the world-class geochemical facilities to be established at NTU. Our studies aim to understand the probable link between tectonic processes (mountain building) and paleoenvironmental/paleoclimatic changes, such as modification of atmospheric circulation or monsoon patterns, changes in the seawater composition, interactions between tectonic uplift, river erosion and alluvial deposition, provenance of loess deposits, as well as desertification in Central Asia.
- Establishment of a world-class laboratory of isotope geochemistry at the Department of Geosciences, National Taiwan University. This is very crucial to the success of the above research projects.
Breakthrough and Achievements
1. Application of geochronological, petrologic, geochemical and isotopic techniques to the planned systematic study of pre- to post-collisional magmatism in the southeastern part of the Tibetan plateau, and surrounding regions, to explore the petrogenesis as well as the orogenic evolution. Major outcomes include: (i) having conducted precise and the most comprehensive data set that includes Zircon SHRIMP U-Pb and whole-rock 40Ar/39Ar ages, major-trace element and Sr-Nd-Hf isotope data for the Gangdese batholith and Linzizong volcanic successions (pre-collisional), and (ii) obtained new SHRIMP U-Pb and 40Ar/39Ar ages and geochemical data for the collision-type ¡§adakites¡¨ and potassic to ultrapotassic lavas (post-collisional).
2. We have, for the first time, established the effectiveness of using new advanced scientific technology (zircon¡¦s in situ U-Pb dating by SHRMIP combined with Hf isotope analysis by MC-LA-ICPMS) to study the Tibetan-Himalayan orogenesis. The data allow us to (i) identify a major phase of crustal thickening in southern Tibet between ca. 40 and 30 Ma, (ii) suggest intense basaltic magma underplating and remelting during the Neo-Tethyan subduction that later served as a key control to the thickening, and (iii) better explain how and when the Earth¡¦s thickest continental crust was created, and the world¡¦s most spectacular topography or ¡§the roof of the world¡¨ formed.
3. Applying the above data base that we have just established to study the ¡§source to sink¡¨ relation in the Himalayan-Tibetan orogenic belt, which allows us to start exploring the complex interaction among tectonic uplift, drainage evolution, river erosion and alluvial deposition in the region, as well as the development/reorganization of principal Asian river system around the eastern Himalayan Syntaxis, by determining U-Pb ages and Hf isotope compositions of detrital zircons, as well as 40Ar/39Ar ages for detrital minerals, from the downstream sedimentary deposits.
- Combination of 40Ar/39Ar dating and structural analyses of major shear zones in Indochina and Eastern Himalayan Syntaxis allows us to better understand the response of crustal deformation during the India-Asian continental collision. The results provide constraints for revealing the tectonic controls on the drainage evolution in the region.
- Applying zircon U-Pb (by SHRIMP and/or LA-ICPMS), Rb-Sr, Sm-Nd and 40Ar/39Ar chronometers along with isotopic tracers, significant results of crustal growth in certain areas of the Central Asian Orogenic Belt have been successfully acquired, which are sufficient for a quantitative modelling of juvenile crustal growth in the Phanerozoic.
- The accretion of the Coastal Range or northern Luzon arc complex onto the Asian continental margin represents the initial stage of continental growth. With applying isotopic tracers, the project aims to unravel the erosion-sedimentation history during the formation of the Coastal Range, and to quantify or estimate the proportion of juvenile to recycled components. This will further help improving our understanding of accretionary orogens, and eventually make better sense to the assembly of Asia, as well as of the continents worldwide.
- The orogenic complex "Nipponides" in the Japanese Islands represents a segment of a 450 Ma old subduction-related orogen developed along the western Pacific convergent margin, and most tectonic units are composed of late Paleozoic to Cenozoic accretionary complexes. Our isotopic data on Cretaceous granites from the Sanyo Belt, suggest that a large proportion of Mesozoic and Cenozoic granitoids from SW Japan have Proterozoic Sm-Nd model ages, high initial 87Sr/86Sr ratios and negative eNd(T) values, which are in strong contrast with those observed in the Central Asian Orogenic Belt. This raises questions about the types of material accreted in accretionary complexes, and the validity of the hypothesis that the Nipponides contains very few fragments of older continental crust.
1. Determination of U-Th ages for sample Ho, S14-4, S14BR, and YHS-1 and a millennial-scale mid-Holocene dry event in Vietnam.
2. Analyses of d18O, d13C, Sr/Ca, Mg/Ca, Mg/Sr, Ba/Ca, and U/Ca of speleothem sample Ho. Reconstruction of the environmental changes from LGM to B/A.
3. Development of coral U-Th dating techniques with precision of better than 1 year
4. Demonstration of using coral thermal proxies of both Sr/Ca and d18O in the Son Tra Island, central Vietnam as Asian Winter Monsoon index.
5. U-Th dating of Mw 7.7 earthquake of 1935 A.D in the Sumatran Islands with a precision of ¡Ó 0.9 year.
6. A 250-yr recurrence of giant earthquakes in the Sumatran Islands by dating corals from South Pagai
7. Reconstruction sea-surface temperatures and salinities of the past 10,000 years in the Southern Okinawa Trough
8. Estimation of the contraction/expansion history of the Western Pacific Warm Pool during the last 800,000 years.
9. Re-evaluated and overthrown previous interpretations of the late Holocene Pulleniatina Minimum Event in the western Pacific marginal seas.
10. Participated in IMAGES 2006 Marco-Polo II Cruise and obtained two long, giant cores from the Benham Rise off Luzon Island, Philippines.
1. Set up Finnigan MAT 253 and Kiel IV device for measuring d18O and d13C of carbonate micro-samples.
2. Set up Thermo Electron Neptune MC-ICPMS for determining isotopic compositions of Sr, Nd, Hf, Pb and U.
3. Establishment of LA-QICPMS system for zircon U/Pb dating and in situ trace element analysis.
4. Development of high-precision carbonate trace metal analyses on Thermo Electron Element II.
5.Installation of Nu Noblesse for 40Ar/39Ar probe dating.
6. Set up a micro-sampling clean room for subsampling of diverse carbonate and rock samples.