The Dabie-Sulu Triassic collisional orogen in eastern Asia was created by northward subduction of... more The Dabie-Sulu Triassic collisional orogen in eastern Asia was created by northward subduction of the Yangtze continental-crust capped plate beneath the Sino-Korean craton. Eclogites, garnet peridotites, and surrounding country rock gneisses and marbles were all subjected to in situ UHP metamorphism, as indicated by the presence of rare but widespread coesite inclusions in eclogitic minerals and in zircon crystals in the country rocks, as well as by virtually identical metamorphic ages of various UHP rock types. Metamorphic P-T estimates, combined with investigations of mineral exsolution textures and high-P polymorphs, indicate that recovered depths of continental subduction may have exceeded 200 km. Parageneses of mineral inclusions in zoned zircon domains combined with U-Pb ages delineate a well-constrained P-T-time path, suggesting exhumation rates of 5-10 km/Myr. A similar P-T-time trajectory has been established for the microdiamond-bearing Kokchetav Massif. Thus far, however, diamond inclusions have not been confirmed from coesite-bearing zircon domains of Dabie-Sulu UHP rocks despite numerous detailed studies. Oxygen isotopes of minerals from many outcrop samples and the Chinese Continental Scientific Drilling (CCSD) project main hole cores indicate that δ 18 O depletion took place in a volume of Proterozoic protoliths exceeding 100 000 km 3 along the northern edge of the Yangtze craton. Evidently, passive-margin sediments and bimodal igneous rocks that had formed during rifting and breakup of the supercontinent Rodinia were subjected to extensive meteoric waterrock interactions attending terminal Neoproterozoic Snowball Earth conditions. Such hydrothermal alteration volatilized and depleted C from the relatively oxidized protoliths, accounting for the rare occurrences of graphite and apparent lack of microdiamond in Dabie-Sulu UHP rocks.
ABSTRACT To examine the tectonic history of the Taiwan segment of the eastern margin of South Chi... more ABSTRACT To examine the tectonic history of the Taiwan segment of the eastern margin of South China, six rock samples from the Tailuko belt, the metamorphic basement of Taiwan, were selected for zircon SHRIMP dating. The aim was to identify evidence shedding light on the timing of the change from passive to active tectonics for this part of the continental margin since South China separated from the supercontinent of Rodinia. The results lead to two age groups, 190–200 and 88–90 Ma. These age groups, augmented by the previously published age data, suggest that they could have resulted from two Mesozoic accretion/subduction events. In addition, this mid‐late Mesozoic Tailuko belt might have also been reactivated and structurally complicated by the late Cenozoic collision/accretion of the Luzon arc with the Eurasian continent. Records of older tectonic events, such as those derived from the Japanese Islands, are absent in this metamorphic basement. An important finding of this study is the existence of the 191±10 Ma Talun metagranite, the oldest granitic intrusion ever reported in the Taiwan region and along the eastern coast area of South China. In spite of a large age uncertainty, the occurrence of this metagranite is not consistent with the apparent younging trend of Jurassic‐Cretaceous igneous activity toward the coastline in South China, and should be taken into consideration by future studies.
Recognized ultrahigh-pressure (UHP) minerals in exhumed, once-subducted oceanic-continental rocks... more Recognized ultrahigh-pressure (UHP) minerals in exhumed, once-subducted oceanic-continental rocks from mantle depths in collisional orogens (e.g. Gilotti, 2013, Liou and Tsujimori, 2013 and references therein) survive best as tiny crystals in rigid minerals such as Grt, kyanite and zircon. Two of the most recent findings of UHP minerals in ultrahigh-T (UHT) granulites and ophiolitic chromitites are highlighted below. These together with many other well-documented occurrences of global UHP orogens reveal that microdiamond, coesite, and other UHP phases are more common than previously thought in both Alpine-and Pacific-type orogens. UHP minerals in UHT granulites: New occurrences of UHP minerals in UHT felsic granulites from NW Africa (Ruz-Cruz and Galdeang 2012) and the northern Bohemia Massif (e.g. Kotková et al. 2011) together with earlier findings of microdiamond, coesite and nano-size α-PbO 2-structured TiO 2 polymorph in pelitic gneisses of the central Erzgebirge suggest that a big segment of crustal basement has been exhumed from mantle depths > 150 km and subjected to mid-crustal HT-UHT granulite-facies recrystallization. Inclusions of microdiamond and coesite occur in Grt, kyanite and zircon of felsic granulites; those in Africa are unusual as these rocks have much higher P¬-T estimates of P > 4.3 GPa and T > 1100°C, exhibit topotaxial overgrowths of diamond and coesite, lack palisade quartz around relict coesite, and have intergrowths of coesite and phengite possibly after Kcymrite. The close association of mantle-derived Grt peridotites with those UHP-UHT granulites suggests that these peridotite bodies became interdigitated with deeply subducted continental crust under UHP conditions rather than being tectonically emplaced at shallow crustal levels. UHP minerals in chromitites associated with ophiolites: UHP minerals have also been discovered in podiform chromitites associated with ophiolite. For example,
Hydroxyl-rich topaz was recognized in thick kyanite quartzites from both high-pressure (HP) and u... more Hydroxyl-rich topaz was recognized in thick kyanite quartzites from both high-pressure (HP) and ultrahigh-pressure (UHP) belts of the Sulu terrane, China. These quartzites contain variable proportions of quartz, kyanite, and topaz, with minor phengite, pyrite, and rutile. Some topaz grains ...
Talc was identified as an equilibrium associate of omphacite, kyanite, zoisite, and garnet in som... more Talc was identified as an equilibrium associate of omphacite, kyanite, zoisite, and garnet in some coesitebearing eclogites and as a retrograde phase in associated garnet peridotite from the Bixiling mafic-ultramafic complex in the Dabie ultrahigh-P metamorphic terrane, central China. Observed talc- and tremolite-bearing assemblages within the coexisting mafic and ultramafic rocks together with established phase relations for the simple system CaO-MgO-Al2O3-SiO2-H2O constrain the P-T path for retrograde metamorphism. This, together with reported talc occurrences from the Dora Maira massif, leads to the conclusion that UHP talc assemblages are confined to mafic and pelitic rocks of unusual chemistry, and are not stable at ultrahigh pressures in ultramafic rocks. Thus, talc cannot be an important H2O-bearing phase in deep mantle ultramafic rocks.
Several coesite grains along garnet-omphacite grain boundaries were discovered in eclogites from ... more Several coesite grains along garnet-omphacite grain boundaries were discovered in eclogites from Yangkou Beach of the Sulu region, eastern China. These grains exhibit variable extents of conversion of coesite to palisade-through mosaic-to granoblastic-quartz aggregates. The rare occurrence of intergranular and matrix coesite in ultrahigh-pressure (UHP) crustal rocks is related to the fast rate of exhumation and the low amount of fluid infiltration required during retrograde recrystallization. Sluggish reactions due to the lack of fluid in both UHP and retrograde metamorphism resulted in the occurrence of intergranular coesite in these eclogites, the preservation of gabbroic texture and relict igneous minerals, and the metastable persistence of low-P assemblages in the coesite-stability field.
Http Dx Doi Org 10 2747 0020 6814 49 5 454, Aug 6, 2010
The 5158 m deep main hole of the Chinese Continental Scientific Drilling Project (CCSD-MH) at Mao... more The 5158 m deep main hole of the Chinese Continental Scientific Drilling Project (CCSD-MH) at Maobei, southwestern Sulu Belt, penetrated five major lithologic units: eclogite, amphibolite ± retrograde eclogite, ultramafic rock, paragneiss, and orthogneiss. All analyzed samples are overprinted to various extents by amphibolite-facies retrograde metamorphism. Ultrahigh-pressure (UHP) index minerals are preserved as inclusions in zircons separated from 137 core
Zircons from one jadeitite sample, collected from north of the Motagua fault, Guatemala, were sep... more Zircons from one jadeitite sample, collected from north of the Motagua fault, Guatemala, were separated for SHRIMP U-Pb dating and trace element analyses. The sub- to anhedral crystal form, lack of typical magmatic oscillatory zone, the presence of fluid and albite/quartz/jadeite inclusions, and the low Th/U ratios (<0.005) indicate that these zircons are of hydrothermal origin. The U-Pb concordia intercept
Page 1. Coesite-bearing eclogite from the Dabie Mountains ¡n central China Xiaomin Wang, JG Liou ... more Page 1. Coesite-bearing eclogite from the Dabie Mountains ¡n central China Xiaomin Wang, JG Liou Department of Geology, Stanford University, Stanford, California 94305 H. К. Mao Geophysical Laboratory, Carnegie Institution ...
In-situ U-Pb geochronology and Hf isotopic studies of zircons from the Pre-Tertiary basement comp... more In-situ U-Pb geochronology and Hf isotopic studies of zircons from the Pre-Tertiary basement complex and Eocene rocks of the Central Range of Taiwan were carried out to elucidate the history of detrital zircons older than 2.3 Ga. Zircons from the eastern Backbone Range and Eastern Central Range show Paleoproterozoic to late Neoarchean ages (2.3-≥2.5 Ga), whereas those from the Hsuehshan Range yield Neoarchean to Mesoarchean ages (2.6-3.2 Ga). The ε Hf (T) for the Paleoproterozoic to late Neoarchean zircons varies from-7.4 to +5.1, implying both juvenile crustal growth and reworking of old crusts. This dual origin could extend back to Mesoarchean-Paleoarchean (3.0-3.4 Ga) based on Hf isotopic model ages. Consistent but narrower ε Hf (T) values and Hf crustal model ages for zircons from Taiwan compared to Cathaysia suggest a possible common origin for these zircons, although Taiwan has a generally younger crustal evolution history than SE China.
... Sulu Terrane, Eastern China RUIXUAN ZHAO,1 JUHN G. LIOU, RU Y. ZHANG, Department of Geologica... more ... Sulu Terrane, Eastern China RUIXUAN ZHAO,1 JUHN G. LIOU, RU Y. ZHANG, Department of Geological and Environmental Sciences, Stanford University, Stanford, California 94305-2115 AND JOSEPH L. WOODEN US Geological Survey, Menlo Park, California 94025-3591 ...
Recognition of several ultrahigh-pressure (UHP) metamorphic terranes in continental collision bel... more Recognition of several ultrahigh-pressure (UHP) metamorphic terranes in continental collision belts has revolutionized the concept of geodynamic processes. In order to facilitate better communication and focus among active investigators, the Task Group 111-6 of the International Lithosphere Program 'Ultrahigh-Pressure Metamorphism and Geodynamics in Collision-type Orogenic Belts' held the first two day workshop at Stanford University in December, 1994. Petrotectonic settings, mineral paragenesis, geochronology, and geochemical characteristics of UHP rocks from several recognized and suspected UHP terranes were addressed. This special issue presents 11 papers from the more than 50 contributions from the 88 participants representing 15 countries. Many challenging petrotectonic and petrochemical problems remain to be investigated. These include detailed P-T time paths for both the CHP unit and adjacent units, the role of fluids at mantle depths, deep seismic profiles and mechanisms and rate of exhumation of the UHP unit.
In order to understand the dehydration process related to phengite decomposition during subductio... more In order to understand the dehydration process related to phengite decomposition during subduction of crust into the deep mantle, we systematically investigated mineral inclusions in zircons from Kokchetav diamond-grade eclogites. In the eclogites, phengite is absent from the matrix but only occurs as inclusions in clinopyroxene. The clinopyroxene is zoned; the core augite contains K2O up to 0.24 wt%, whereas the rim omphacite contains secondary K-feldspar inclusions. Phengite may have been consumed during prograde reactions, and K was fixed in clinopyroxene or in a fluid/melt phase. Inclusions of clinopyroxene and garnet were identified in zircon cores, whereas garnet, rutile, quartz, and composite inclusions are present in the mantles and quartz occurs in the rims. Distribution of mineral inclusions in zoned zircons indicates that zircon cores grew at the peak UHP stage, whereas the rims grew in the quartz stability field during decompression. The composite inclusions have assemblages of albite + glass + epidote, rutile + ilmenite, quartz + rutile, and rutile + albite. The former three-phase composite inclusions have rounded outlines and triple-junction grain boundaries, suggesting crystallization from fluid or melt. During the growth of zircon from core to mantle, phengite was consumed, and new garnet, rutile and fluid/melt were formed.
The Dabie-Sulu Triassic collisional orogen in eastern Asia was created by northward subduction of... more The Dabie-Sulu Triassic collisional orogen in eastern Asia was created by northward subduction of the Yangtze continental-crust capped plate beneath the Sino-Korean craton. Eclogites, garnet peridotites, and surrounding country rock gneisses and marbles were all subjected to in situ UHP metamorphism, as indicated by the presence of rare but widespread coesite inclusions in eclogitic minerals and in zircon crystals in the country rocks, as well as by virtually identical metamorphic ages of various UHP rock types. Metamorphic P-T estimates, combined with investigations of mineral exsolution textures and high-P polymorphs, indicate that recovered depths of continental subduction may have exceeded 200 km. Parageneses of mineral inclusions in zoned zircon domains combined with U-Pb ages delineate a well-constrained P-T-time path, suggesting exhumation rates of 5-10 km/Myr. A similar P-T-time trajectory has been established for the microdiamond-bearing Kokchetav Massif. Thus far, however, diamond inclusions have not been confirmed from coesite-bearing zircon domains of Dabie-Sulu UHP rocks despite numerous detailed studies. Oxygen isotopes of minerals from many outcrop samples and the Chinese Continental Scientific Drilling (CCSD) project main hole cores indicate that δ 18 O depletion took place in a volume of Proterozoic protoliths exceeding 100 000 km 3 along the northern edge of the Yangtze craton. Evidently, passive-margin sediments and bimodal igneous rocks that had formed during rifting and breakup of the supercontinent Rodinia were subjected to extensive meteoric waterrock interactions attending terminal Neoproterozoic Snowball Earth conditions. Such hydrothermal alteration volatilized and depleted C from the relatively oxidized protoliths, accounting for the rare occurrences of graphite and apparent lack of microdiamond in Dabie-Sulu UHP rocks.
ABSTRACT To examine the tectonic history of the Taiwan segment of the eastern margin of South Chi... more ABSTRACT To examine the tectonic history of the Taiwan segment of the eastern margin of South China, six rock samples from the Tailuko belt, the metamorphic basement of Taiwan, were selected for zircon SHRIMP dating. The aim was to identify evidence shedding light on the timing of the change from passive to active tectonics for this part of the continental margin since South China separated from the supercontinent of Rodinia. The results lead to two age groups, 190–200 and 88–90 Ma. These age groups, augmented by the previously published age data, suggest that they could have resulted from two Mesozoic accretion/subduction events. In addition, this mid‐late Mesozoic Tailuko belt might have also been reactivated and structurally complicated by the late Cenozoic collision/accretion of the Luzon arc with the Eurasian continent. Records of older tectonic events, such as those derived from the Japanese Islands, are absent in this metamorphic basement. An important finding of this study is the existence of the 191±10 Ma Talun metagranite, the oldest granitic intrusion ever reported in the Taiwan region and along the eastern coast area of South China. In spite of a large age uncertainty, the occurrence of this metagranite is not consistent with the apparent younging trend of Jurassic‐Cretaceous igneous activity toward the coastline in South China, and should be taken into consideration by future studies.
Recognized ultrahigh-pressure (UHP) minerals in exhumed, once-subducted oceanic-continental rocks... more Recognized ultrahigh-pressure (UHP) minerals in exhumed, once-subducted oceanic-continental rocks from mantle depths in collisional orogens (e.g. Gilotti, 2013, Liou and Tsujimori, 2013 and references therein) survive best as tiny crystals in rigid minerals such as Grt, kyanite and zircon. Two of the most recent findings of UHP minerals in ultrahigh-T (UHT) granulites and ophiolitic chromitites are highlighted below. These together with many other well-documented occurrences of global UHP orogens reveal that microdiamond, coesite, and other UHP phases are more common than previously thought in both Alpine-and Pacific-type orogens. UHP minerals in UHT granulites: New occurrences of UHP minerals in UHT felsic granulites from NW Africa (Ruz-Cruz and Galdeang 2012) and the northern Bohemia Massif (e.g. Kotková et al. 2011) together with earlier findings of microdiamond, coesite and nano-size α-PbO 2-structured TiO 2 polymorph in pelitic gneisses of the central Erzgebirge suggest that a big segment of crustal basement has been exhumed from mantle depths > 150 km and subjected to mid-crustal HT-UHT granulite-facies recrystallization. Inclusions of microdiamond and coesite occur in Grt, kyanite and zircon of felsic granulites; those in Africa are unusual as these rocks have much higher P¬-T estimates of P > 4.3 GPa and T > 1100°C, exhibit topotaxial overgrowths of diamond and coesite, lack palisade quartz around relict coesite, and have intergrowths of coesite and phengite possibly after Kcymrite. The close association of mantle-derived Grt peridotites with those UHP-UHT granulites suggests that these peridotite bodies became interdigitated with deeply subducted continental crust under UHP conditions rather than being tectonically emplaced at shallow crustal levels. UHP minerals in chromitites associated with ophiolites: UHP minerals have also been discovered in podiform chromitites associated with ophiolite. For example,
Hydroxyl-rich topaz was recognized in thick kyanite quartzites from both high-pressure (HP) and u... more Hydroxyl-rich topaz was recognized in thick kyanite quartzites from both high-pressure (HP) and ultrahigh-pressure (UHP) belts of the Sulu terrane, China. These quartzites contain variable proportions of quartz, kyanite, and topaz, with minor phengite, pyrite, and rutile. Some topaz grains ...
Talc was identified as an equilibrium associate of omphacite, kyanite, zoisite, and garnet in som... more Talc was identified as an equilibrium associate of omphacite, kyanite, zoisite, and garnet in some coesitebearing eclogites and as a retrograde phase in associated garnet peridotite from the Bixiling mafic-ultramafic complex in the Dabie ultrahigh-P metamorphic terrane, central China. Observed talc- and tremolite-bearing assemblages within the coexisting mafic and ultramafic rocks together with established phase relations for the simple system CaO-MgO-Al2O3-SiO2-H2O constrain the P-T path for retrograde metamorphism. This, together with reported talc occurrences from the Dora Maira massif, leads to the conclusion that UHP talc assemblages are confined to mafic and pelitic rocks of unusual chemistry, and are not stable at ultrahigh pressures in ultramafic rocks. Thus, talc cannot be an important H2O-bearing phase in deep mantle ultramafic rocks.
Several coesite grains along garnet-omphacite grain boundaries were discovered in eclogites from ... more Several coesite grains along garnet-omphacite grain boundaries were discovered in eclogites from Yangkou Beach of the Sulu region, eastern China. These grains exhibit variable extents of conversion of coesite to palisade-through mosaic-to granoblastic-quartz aggregates. The rare occurrence of intergranular and matrix coesite in ultrahigh-pressure (UHP) crustal rocks is related to the fast rate of exhumation and the low amount of fluid infiltration required during retrograde recrystallization. Sluggish reactions due to the lack of fluid in both UHP and retrograde metamorphism resulted in the occurrence of intergranular coesite in these eclogites, the preservation of gabbroic texture and relict igneous minerals, and the metastable persistence of low-P assemblages in the coesite-stability field.
Http Dx Doi Org 10 2747 0020 6814 49 5 454, Aug 6, 2010
The 5158 m deep main hole of the Chinese Continental Scientific Drilling Project (CCSD-MH) at Mao... more The 5158 m deep main hole of the Chinese Continental Scientific Drilling Project (CCSD-MH) at Maobei, southwestern Sulu Belt, penetrated five major lithologic units: eclogite, amphibolite ± retrograde eclogite, ultramafic rock, paragneiss, and orthogneiss. All analyzed samples are overprinted to various extents by amphibolite-facies retrograde metamorphism. Ultrahigh-pressure (UHP) index minerals are preserved as inclusions in zircons separated from 137 core
Zircons from one jadeitite sample, collected from north of the Motagua fault, Guatemala, were sep... more Zircons from one jadeitite sample, collected from north of the Motagua fault, Guatemala, were separated for SHRIMP U-Pb dating and trace element analyses. The sub- to anhedral crystal form, lack of typical magmatic oscillatory zone, the presence of fluid and albite/quartz/jadeite inclusions, and the low Th/U ratios (<0.005) indicate that these zircons are of hydrothermal origin. The U-Pb concordia intercept
Page 1. Coesite-bearing eclogite from the Dabie Mountains ¡n central China Xiaomin Wang, JG Liou ... more Page 1. Coesite-bearing eclogite from the Dabie Mountains ¡n central China Xiaomin Wang, JG Liou Department of Geology, Stanford University, Stanford, California 94305 H. К. Mao Geophysical Laboratory, Carnegie Institution ...
In-situ U-Pb geochronology and Hf isotopic studies of zircons from the Pre-Tertiary basement comp... more In-situ U-Pb geochronology and Hf isotopic studies of zircons from the Pre-Tertiary basement complex and Eocene rocks of the Central Range of Taiwan were carried out to elucidate the history of detrital zircons older than 2.3 Ga. Zircons from the eastern Backbone Range and Eastern Central Range show Paleoproterozoic to late Neoarchean ages (2.3-≥2.5 Ga), whereas those from the Hsuehshan Range yield Neoarchean to Mesoarchean ages (2.6-3.2 Ga). The ε Hf (T) for the Paleoproterozoic to late Neoarchean zircons varies from-7.4 to +5.1, implying both juvenile crustal growth and reworking of old crusts. This dual origin could extend back to Mesoarchean-Paleoarchean (3.0-3.4 Ga) based on Hf isotopic model ages. Consistent but narrower ε Hf (T) values and Hf crustal model ages for zircons from Taiwan compared to Cathaysia suggest a possible common origin for these zircons, although Taiwan has a generally younger crustal evolution history than SE China.
... Sulu Terrane, Eastern China RUIXUAN ZHAO,1 JUHN G. LIOU, RU Y. ZHANG, Department of Geologica... more ... Sulu Terrane, Eastern China RUIXUAN ZHAO,1 JUHN G. LIOU, RU Y. ZHANG, Department of Geological and Environmental Sciences, Stanford University, Stanford, California 94305-2115 AND JOSEPH L. WOODEN US Geological Survey, Menlo Park, California 94025-3591 ...
Recognition of several ultrahigh-pressure (UHP) metamorphic terranes in continental collision bel... more Recognition of several ultrahigh-pressure (UHP) metamorphic terranes in continental collision belts has revolutionized the concept of geodynamic processes. In order to facilitate better communication and focus among active investigators, the Task Group 111-6 of the International Lithosphere Program 'Ultrahigh-Pressure Metamorphism and Geodynamics in Collision-type Orogenic Belts' held the first two day workshop at Stanford University in December, 1994. Petrotectonic settings, mineral paragenesis, geochronology, and geochemical characteristics of UHP rocks from several recognized and suspected UHP terranes were addressed. This special issue presents 11 papers from the more than 50 contributions from the 88 participants representing 15 countries. Many challenging petrotectonic and petrochemical problems remain to be investigated. These include detailed P-T time paths for both the CHP unit and adjacent units, the role of fluids at mantle depths, deep seismic profiles and mechanisms and rate of exhumation of the UHP unit.
In order to understand the dehydration process related to phengite decomposition during subductio... more In order to understand the dehydration process related to phengite decomposition during subduction of crust into the deep mantle, we systematically investigated mineral inclusions in zircons from Kokchetav diamond-grade eclogites. In the eclogites, phengite is absent from the matrix but only occurs as inclusions in clinopyroxene. The clinopyroxene is zoned; the core augite contains K2O up to 0.24 wt%, whereas the rim omphacite contains secondary K-feldspar inclusions. Phengite may have been consumed during prograde reactions, and K was fixed in clinopyroxene or in a fluid/melt phase. Inclusions of clinopyroxene and garnet were identified in zircon cores, whereas garnet, rutile, quartz, and composite inclusions are present in the mantles and quartz occurs in the rims. Distribution of mineral inclusions in zoned zircons indicates that zircon cores grew at the peak UHP stage, whereas the rims grew in the quartz stability field during decompression. The composite inclusions have assemblages of albite + glass + epidote, rutile + ilmenite, quartz + rutile, and rutile + albite. The former three-phase composite inclusions have rounded outlines and triple-junction grain boundaries, suggesting crystallization from fluid or melt. During the growth of zircon from core to mantle, phengite was consumed, and new garnet, rutile and fluid/melt were formed.
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Papers by Juhn Liou