Vestiges of Saxothuringian crust in the Central Sudetes, Bohemian Massif: Zircon evidence of a recycled subducted slab provenance
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Massif
Felsic
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The Saxby and Mt. Angelay Igneous Complexes represent the volatile rich, post ~1530
Ma granitoids of the Williams Batholith, and have been considered to be a possible
source of magmatic-hydrothermal fluids that produced IOCG deposits in Cloncurry
district. The evolution of these igneous complexes is studied in this thesis with the
ultimate aim to understand the chemistry of magmatic fluids and their involvement in ore
genesis. These igneous complexes contain a variety of intrusions including mafic,
intermediate and felsic members and their fluid evolution was examined by several bulk
and micro-analytical techniques.
The distribution of rock units and their contact relations were obtained from field
observations and regional and detailed mapping. The Saxby (SIC) and Mt. Angelay
(MAIC) Igneous Complexes are dominated by metaluminous, potassic, magnetite bearing
intrusive rocks, which intruded into the calc-silicate rocks of the Mary Kathleen
Group and psammo-pelitic rocks of the Soldiers Cap Group between 1530 and 1500 Ma.
The major rock types in the SIC include granites and a large number of mafic intrusions,
with limited pulses of intermediate magmas, typically observed at the magma
mixing/mingling locations. The MAIC apparently represents a more evolved pluton,
which has limited mafic intrusions with more intermediate rock types and abundant
felsic rocks. Other major rock types and structures include magmatic-hydrothermal
transition veins and ‘brain rocks’ of Mt. Angelay, mixed/mingled rocks and explosive
breccias of the SIC, and late igneous phases of pegmatites and aplites. Intense sodic/
sodic-calcic alteration is abundant in both complexes, complicating geochemical
interpretation.
Petrographic and geochemical studies were used as tools to distinguish various rock
types and magmatic crystallization processes from sub-solidus hydrothermal processes.
The major and trace element studies together with rare earth element (REE) patterns and
field observations suggest different magma sources for the mafic and felsic rocks. The
REE patterns, depletion in Eu, Sr, P and Ti, and Y-undepleted nature of K-rich, abundant
felsic intrusions suggest a crustal source which is more likely depleted in garnet, titanite,
apatite, pyroxenes and/or amphiboles and enriched in plagioclases. In mafic and
intermediate intrusions, the decrease in CaO, Nb, Sr, Sc, V and TiO2 with increasing
SiO2, together with negative Eu anomalies, suggested that fractional crystallisation of
plagioclase and amphibole were prominent processes involved in the formation of the
more silicic phases from mafic magmas. REE patterns also suggest that this mafic source
region was enriched in pyroxenes, amphiboles, apatite and titanite and depleted in
garnet.
The volatile evolution of the SIC and MAIC intrusions was particularly estimated from
halogen (F/Cl) abundances and ratios of hydrous minerals including biotite, hornblende
and apatite, and from calculated halogen activities of magmatic fluid in equilibrium with
biotite. The F and Cl concentrations of ferromagnesian minerals highly depend on Fe and
Mg contents; however, they show variable rates of compatibility with fractionation that
may have influenced the halogen concentration of the final magmatic-hydrothermal
fluid. The halogen contents of both whole rocks and minerals show high F and Cl
contents in mafic rocks and gradual loss in Cl with crystallization. The majority of F
analyses in the whole rocks are below detection, but the minerals show major increase in
F contents from mafic to intermediate rocks. The halogen variability in intrusions depends on a number of factors including bulk rock chemistry, wall rock alteration and
Fe-Mg avoidance.
Fluid inclusions were used as a tool to understand the magmatic-hydrothermal evolution
of the SIC and MAIC and the intrusions contain a variety of primary and secondary fluid
inclusions. The primary magmatic fluids of the SIC and MAIC include a common,
abundant CO2 rich fluid phase, which may have been sourced from mafic magma. High
salinity, primary, multisolid inclusions of Mt. Angelay brain rocks represent magmatichydrothermal
fluids; in which their magmatic origin is also confirmed by PIXE halogen
ratios. The multisolid inclusions show very high salinities (38-60wt% NaCl equivalent)
and high homogenization temperatures ranging from 450-600°C and more. Secondary
inclusions of L+V+S (16-46wt% NaCl equivalent) and L+V (1-30wt% NaCl equivalent)
are present in all the SIC and MAIC rocks including granites, brain rocks and breccias,
and they homogenize in between 140-300°C and 100-250°C respectively.
The field and analytical studies suggest that the Saxby breccia pipes and Mt. Angelay
brain rocks represent the release of magmatic fluids at the final stages of magma
evolution (Chapter 2 & 6). It is suggested that the process of magma mingling and the
variable CO2 input from mafic intrusions have played major role in the formation of
breccias and brain rocks. The fluid inclusion P-T estimations from these magmatic hydrothermal
locations together with geochemical and mineral chemical observations
also provide clues to the overall volatile evolution of the mafic and felsic magma, and
their possible role in IOCG genesis.
The metal and element budget of some Cloncurry ore deposits and SIC and MAIC
intrusions are compared as the fluid inclusions provide a direct correlation. The primary
fluid inclusions assemblage in Mt. Angelay brain rocks (CO2 inclusions + multisolid
inclusions) is similar to that found in the most obviously granite-related IOCG deposits
(especially Ernest Henry), and is verified in detail by PIXE and LA-ICP-MS analysis.
The element concentrations, ratios and Fe, Cu, Mn and Zn contents of multisolid
inclusions from these two settings show similarities, which suggest a magmatic
involvement in the IOCG ore genesis of Cloncurry. However, fluid mixing is also
suggested as a major process for the formation of ore deposits.
Although many previous studies supposed that granites were crucial in the magmatic-to-
IOCG connection, the data collected during this study suggest that mafic intrusions
played major roles in the evolution of Saxby and Mt. Angelay Igneous Complexes and in
the formation of some of the Cloncurry ore deposits.
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Based on the great thickness crustal struture and complex geophysical character,this paper points out the principle for dividing terranes in Qinghai─Xizang Plateau according to earthquake activities and wave field sign,lithospheric structure and velocity character,palemagnetic mark,potential field sign ,temperature sign, geological and tectonics character. From north to south of the Qinghai─Xizang Plateau and its neighbouring regions can be devided in seven terranes, ie, Qaidam terrane, Kunlun terrane, Hon Xil-Bayan Har terrane, Qangtang terrane, Lhasa-Gangdise terrane, Himalayan terrane and Ganges Plain terrane. The distribution and character of these terranes have important rools for the studies of the formation and evolution.of the plateau and plate movement and dynamic mechanism.
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Abstract The opening of the Japan Sea led to the separation of southwest Japan from the Eurasian continent. Subsequent to this event, a diverse range of igneous activities occurred in southwest Japan. On the back‐arc side of the region, igneous activity commenced at approximately 22 Ma and persisted for an extended period. In the trench‐proximal region of southwest Japan, magmatism initiated around 15.6 Ma, immediately following the cessation of the Japan Sea opening, in correlation with the subduction of the Philippine Sea plate beneath southwest Japan. The Amakusa Islands in western Kyushu host felsic to intermediate igneous rocks with Miocene radiometric ages. There has been a debate regarding the attribution of the igneous rocks in Amakusa Island among the Miocene igneous rocks in southwest Japan. To address this issue, we conducted zircon U–Pb dating and analyzed the major‐ and trace‐element compositions of felsic igneous rocks in the Amakusa Islands to elucidate their characteristics. The obtained U–Pb ages range from 14.5 to 14.8 Ma, suggesting contemporaneity between magmatism in the Amakusa Islands and the Setouchi Volcanic Rocks in the trench‐proximal region of southwest Japan. The major and trace element compositions of the felsic igneous rocks exhibit similarities to the dacites of the Setouchi Volcanic Rocks. These findings support previous suggestions that the magmatism in the Amakusa Islands can be correlated with the Setouchi Volcanic Rocks, based on the discovery of a high‐Mg andesite dike and paleo‐stress analysis utilizing the direction of dikes and sills. Therefore, the Setouchi Volcanic Belt is proposed to extend further west than the previously identified Ohno volcanic rocks in eastern Kyushu. The subduction of the Shikoku Basin of the Philippine Sea plate toward western Kyushu supports the hypothesis that the Kyushu‐Palau Ridge was positioned west of Kyushu at ~15 Ma.
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Table S1: Zircon U-Pb analytical results for samples from the felsic igneous rocks in Xilinhot, Inner Mongolia. Table S2: Major (wt%) and trace-element (ppm) concentrations of the felsic igneous rocks in Xilinhot, Inner Mongolia. Table S3: Whole-rock Sr-Nd isotopic compositions of the felsic igneous rocks in Xilinhot, Inner Mongolia. Table S4: Zircon Hf isotopic compositions of the felsic igneous rocks in Xilinhot, Inner Mongolia. Table S5: Summary of zircon U-Pb age data of granitic rocks in XIMOB. Table S6: Summary of whole-rock Nd isotope data of granitic rocks in XIMOB. Table S7: Summary of zircons Hf isotopic data of granitic rocks in XMOB.
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Table S1: Zircon U-Pb analytical results for samples from the felsic igneous rocks in Xilinhot, Inner Mongolia. Table S2: Major (wt%) and trace-element (ppm) concentrations of the felsic igneous rocks in Xilinhot, Inner Mongolia. Table S3: Whole-rock Sr-Nd isotopic compositions of the felsic igneous rocks in Xilinhot, Inner Mongolia. Table S4: Zircon Hf isotopic compositions of the felsic igneous rocks in Xilinhot, Inner Mongolia. Table S5: Summary of zircon U-Pb age data of granitic rocks in XIMOB. Table S6: Summary of whole-rock Nd isotope data of granitic rocks in XIMOB. Table S7: Summary of zircons Hf isotopic data of granitic rocks in XMOB.
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In southern Alaska, multiple terranes—slabs that have broken off from larger tectonic plates and shuffed around—create a complex patchwork that makes it challenging for scientists to untangle the tectonic history and structure of the region. One of these, the Yakutat terrane, which lies just offshore southern Alaska in the Gulf of Alaska, is converging with the North American plate and driving the growth of the Chugach–St. Elias mountains. The structure of this terrane has not been well studied until now. Worthington et al. conducted seismic studies to create a two‐ dimensional seismic velocity model of the Yakutat terrane. The model allows them to constrain the crustal thickness and composition of the terrane.
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