中研院地球科學研究所 - 質譜儀實驗室
IES, Academia Sinica - Mass Spectrometer Lab


Projects

Related projects are as follows

 To unravel the crustal evolution of East Asia, using geochemical (concentration of major and trace elements of whole rocks) and radiogenic isotopic (Nd-Sr isotopic composition of whole rocks, U-Pb and Lu-Hf isotopic composition of zircons) methods to investigate the geochemical characteristics of different magmatic activity, the source provenance of material, the petrogenesis and the tectonic implications.(Ching-Ying Lan)

The main contributions for my study are

  1. Establishing the crustal evolution history of Taiwan and its relationship with Cathaysia,
  2. New finding of the early Jurassic granitic rocks in southern Taiwan (Talun granite) which is the oldest granitic intrusion ever reported in the coastal region of South China,
  3. New finding of the Mesoarchean (3.2 Ga) detrital zircon in Taiwan which is the oldest relict age ever found in Taiwan,
  4. Establishing the magmatic evolution history of Indosinian orogeny in the Truong Son belt of central Vietnam as calc-alkaline volcano-plutonic association of the subduction product (Late Permian to Early Triassic), syn-collision peraluminous granite (Early Triassic), and alkaline post-collision volcano-plutonic association (Middle Triassic) due to the subduction of Paleotethys oceanic crust underneath the Indochina continent during Permo-Triassic time,
  5. New finding of pre-Indosinian LP/HT metamorphic event (~450 Ma) in Central Vietnam, i.e. early Paleozoic event which is most likely related to the collisional orogeny between the South China and Indochina blocks, and
  6. Micro-structural analysis of the Day Nui Con Voi metamorphic gneiss complex along the Red River Shear Zone in northern Vietnam show that the gneisses were formed during the Triassic Indosinian orogeny. This new finding is different from the previous thought to be formed by the strike-slip shearing and continental escape tectonics, and further suggests the strike-slip fault of the Red River Shear Zone needs not root from the mantle.


 In situ (laser) determinations of dating, elemental concentrations and isotope compositions on single mineral grains (Kuo-Lung Wang)

The laser lab at IES is equipped with New Wave UP 213 Nd-YAG laser ablation system with magnetic sector-ICP-MS (magnetic sector-ICP-MS; ThermoFinnigan Element XR; Fig.) and MC-ICP-MS ( NuPLasma; Fig.), separately to in situ analyze elemental concentrations and isotope compositions of single mineral grain. (Fig.) The method set up include:

1. In situ Hf isotope analysis on zircons
The in situ Hf-isotope analytical method set up at IES was carried out in-situ using a New Wave UP213 laser-ablation microprobe, attached to a Nu Plasma multi-collector ICPMS. Zircons were mounted in epoxy discs and polished before being imaged by cathodoluminescence and back-scattered electron techniques to look for heterogeneities.

Results: The laser-ablation analyses were carried out using the time-resolved analysis software, in which the signal for each mass and each ratio is displayed as a function of time during the analysis. This allows the more stable portions of the ablation to be selected for analysis, before the data are processed to give the final results. Background was collected on peak for 30 seconds before ablation began. Following each analysis, the 180Hf signal was followed down to background before starting the next analysis; this typically took less than one minute. Typical within-run precision (2SE) on the analysis of 176Hf/177Hf is ±0.000020, equivalent to an uncertainty of less than one epsilon unit. The mean deviation of 176Hf/177Hf between replicate analyses of the same grain is ±0.000017.

The zircon standards used are two natural zircon crystals, one is Mud Tank zircon from Australia and the other is 91500 from Canada. The latter one has been widely used in different laboratories worldwide as described by Weidenbeck et al. (1995), but recently the long-term database derived from GEMOC, Macquarie University in Sydney showed that the 91500 zircon has somehow heterogeneous Hf isotope compositions as shown the bimodal distribution in terms of their 176Hf/177Hf ratios (Griffin et al., 2007). Our data show similar but a little higher average ratios on 176Hf/177Hf to the reported value with not so clear bimodal distribution. The result at IES for the other relatively homogeneous Mud Tank zircon standard which is mainly used and recommended by GEMOC, show consistent ratios with that reported by GEMOC on the long-term basis with similar precision. (Fig.)

2. In situ elemental analysis on silicate minerals
Results: An evaluation to the limit of detection (LOD) is summarized in Fig. Around 15 analyses on BCR-2g as unknown demonstrate the LOD for most trace elements in igneous rocks is generally in ppm level, basically not more than 10 ppm. For REEs which is useful in petrogenetic studies, their LOD is essentially below ppm level and mostly not more than 2 ppm.

The general precision and accuracy of the LA-ICPMS have been tested against known international standards including (1) NIST glass standards, i.e. NIST SRM 610 and 612 (2) USGS rock-glass standards, i.e. BCR-2g. More specifically, data of analyzed BCR-2g runs are as a secondary standard. Precision of the LA-ICPMS analyses is in opposite way with element abundance, from 4- 5 % in few hundreds ppm of elements in BCR-2g to 7-14 % in few ppm elements in BCR-2g (Fig.). No matter of the concentrations or matrix of materials, RSD values in Zn, Rb, Sn, Sb, Cs, and Pb (~10- 20 %) essentially higher than the other analysed elements. It is ascribed to the different chemical behaviors of these elements from the internal standard, Ca, and thus their fractionation which cannot be well corrected by IS gives rise to the low reproducibility (cf. Jackson, 2001). And siderophile elements, e.g., Pb and Sb, have an affinity for alloying with Pt crucibles during the process of making these glass standards and, therefore, show heterogeneity in reference glasses in the scale of LA-ICPMS spatial resolution (Eggins and Shelly, 2002). To compare our analytical results in trace element contents with the literature or compiled values of USGS glass standards, BCR-2g, they are consistent with each other, differences essentially < 5% (Fig.), demonstrating good accuracy of the LA-ICPMS analysis. Since the synthetic glass NIST SRM 610 is used as the external standard, this further implies the matrix effect is not apparent in the LA-ICPMS measurements. Accordingly, this method can be well applied to the trace element analyses on silicate minerals.

3. In situ U-Pb dating on zircons
Results: During the study period, 207Pb/206Pb ratios of 91500 have almost the same values as the reported ones. Their average 207Pb/206Pb age is 1069 Ma for the last 13 optimized values, which is similar with the reported age of 1068 Ma . Similar consistency can also be shown from the age result of two reference materials, GJ-1 and Mud Tank (MT) zircons.

The general precision and accuracy of the in situ U-Pb dating results has been shown in (Fig.) using standard zircon 91500 as an example. Precision of the analyses for all three ratios are lower than 5%, and the age precision is lower than 4%. To compare our analytical results with the literature values, differences essentially < 1% (Fig.), demonstrating very good accuracy of our LA-ICPMS U-Pb dating analysis. Accordingly, this method can be well applied to unknown zircon in the near future.


 Tracking lithospheric mantle: in situ Re-Os perspectives (Kuo-Lung Wang)

Researches include:

1. Evolution of Asian Lithospheric mantle
In the course of Earth's geological history, the continental crust has formed, then grown and evolved. Both the continental crust on Earth and its formation related to presence of water are unique within the entire solar system. Thus, the growth and evolution of the continental crust have always been important research subjects in Earth sciences. These issues have been widely studied in the rocks of the crust, but little is known about a fundamental aspect: the disruption of the continental roots that must accompany such processes. These continental roots consist of the sub-continental lithospheric mantle (SCLM); they contribute to the stability and longevity of continents, and affect the response of the crust to tectonic stresses. The evolution of the SCLM is of essential importance to understanding the growth and stability of continents and long-term mantle evolution.

This project seeks to understand the processes of continental growth and their effect on the upper mantle. It will investigate the geochemical signatures of these processes as recorded directly in fragments of lithospheric mantle entrained in ascending basaltic magmas. The Central Asia region will be used as a natural laboratory to provide information on these processes, and the results will be applicable to analogous tectonic settings globally and throughout geological time. The Centra Asian Orogenic Belt (CAOB) is the world's largest site of juvenile crustal formation in the Phanerozoic eon. It is characterized by the complex amalgamation of dominantly accretionary-prism and magmatic-arc material, interspersed with massifs of older continental crust and silvers of oceanic crust. Thus, it provides a crucial example for study of accretionary tectonics and growth of the continental crust in the late part of the Earth's history. Processes for both deriving juvenile material from the mantle and accreting vertically are expected to affect the SCLM beneath CAOB. However, the nature and evolution history of the SCLM beneath this huge (>1000 km wide) orogenic zone is still little known. Are processes recorded in the mantle compatible with the history of regional crustal evolution? Can the SCLM sections survive long-distance movement of continental lithospheric domains, orogenic events and subsequent continental extension and asthenospheric upwelling? (Fig.)

The project will investigate mantle-derived xenoliths from several key areas: Vitim in the east of Lake Baikal, Tariat in Central Mongolia and Dariganga lave plateau in SE Mongolia. The novel laser techniques applied to in situ Re-Os isotope analysis will be introduced in this project to distinguish, characterize and date both ancient lithospheric stabilization events (mantle depletion) and younger fluid processes (metasomatism). The petrology and geochemistry studies in this project can integrate with geophysical data to help define the connection between mantle terranes and the major crustal terranes identified by geology and geophysics. This will represent a major advance in our knowledge of crust-mantle relationships. (Fig.1) (Fig.2)

2. Sulfides in mantle peridotites from Penghu Islands, Taiwan: Melt percolation, PGE fractionation, and the lithospheric evolution of the South China block (Wang et al., 2009) (Fig.)

3. Petrogenesis of Paleogene basaltic rocks drilled from Western Taiwan: insight to the initial rifting at the Southeastern Asian continental margin


 Short-lived radionuclide systems and the early evolution history of planetary accretion and differentiation (Der-Chuen Lee)

Using the short-lived radionuclide systems, e.g., 182Hf-182W and 92Nb-92Zr, and the isotopic variations of Mo and Ca to study the early evolution history of planetary formation and differentiation. (Fig.)


 The evolution history of stable transitional metals in the oceans and their relationships to global environmental and climate changes (Der-Chuen Lee)

The isotopic compositions of stable transitional metals, e.g., Fe, Ni, Zn, Mo, and Cd, tend to vary on account of changes, such as pressure, temperature, oxidation state, ionic bonding, and biological effects, in the environment. By measuring the isotopic variations of these transitional metals in seawater, marine micro-organisms, sediments, and also the aerosols in the atmosphere, it is possible to decipher the evolution history of these transitional metals in the oceans, and subsequently their connections to environmental and climate changes. (Fig.)


 The evolution history of stable transitional metals in Lake Baikal and their relationships to environmental and climate changes (Der-Chuen Lee)

Through measuring the isotopic variations and differentiation of transitional metals e.g., Fe, Ni, Zn, Mo, and Cd, in the water of Lake Baikal, sediments, and Fe-Mn crusts, in order to study the evolution history of Lake Baikal, and the relationship with climate changes.


 The variations of stable and radiogenic isotopic compositions of Sr in the corals from Nanwan Bay and pore fluids in mud volcanoes (Der-Chuen Lee)

By analyzing the stable and radiogenic isotopic compositions of Sr in the modern corals from Nanwan of Southern Taiwan, as well as the pore water extracted from the mud volcanoes throughout southeastern and southwestern Taiwan, to study the probability of using stable Sr isotope as a temperature proxy. Furthermore, radiogenic and stable Sr isotopic compositions can also be used to study the current changes in Nanwan Bay, and also the sources for pore water of mud volcanoes. (Fig.)


 Stable Ag isotopic compositions and the application to the formation, source, and differentiation of ore deposits (Der-Chuen Lee)

Through analyzing and quantifying the stable isotopic composition of Ag in various different sulfide minerals, it is possible to study the mineralization, source, and differentiation of ore deposits.


 The processes and rates of magma formation, ascent, storage, and differentiation, how these are influenced by tectonism, and how they control the style and frequency of volcanic eruptions. (Georg Zellmer)

Constraints on absolute rates are provided through uranium-series isotope studies, while geospeedometric work, which employs the diffusion of elements within and between crystals, yields crystal residence times relative to magmatic temperatures that can be determined independently. Recently, Georg has also become involved in studies of emissions of gases and aerosols from volcanic fumaroles.


 The natural laboratory of research (Georg Zellmer)

A wide range of local and international field areas, which include subduction zones (Aegean, Lesser Antilles, Mexico, Chile, Japan, and New Zealand), large igneous provinces (Iceland, Deccan), and mid-ocean ridges (East-Pacific Rise, Gorda Ridge, Juan-de-Fuca Ridge, Gakkel Ridge).


 The origin of evolved magmas in bimodal suites (Georg Zellmer)

Porphyritic alkali basaltic enclaves in trachytic host lavas formed during late-stage Deccan magmatism. (Fig.) Field-emission EPMA image (Na-map) of a large, complexly zoned plagioclase crystal from the 1998 central caldera flow of the Juan-de-Fuca axial seamount, used for geospeedometric studies. Field of view 4mm across. Most of these crystals have formed rapidly, within weeks to months prior to eruption. (Fig.)