Discovery of super-silicic and super-titanic garnets in garnet-pyroxenite in Zhaheba and its geological significance

Niu, He-Cai; Zhang, HaiXiang; Shan, Qiang; Yu, Xueyuan

doi:10.1007/s11434-008-0280-y

Cited by 10 publications

(4 citation statements)

References 26 publications

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“…Ophiolite, ultrahigh-pressure metamorphic rocks and the Nb-enriched basalts compose a tectonic mélange along the southern margin of the Iritish suture zone (Niu et al . 2008). Similar tectonic mélanges have been identified in other orogens (Furnes, Pedersen & Hertogen, 1991; Ota, Utsunomiya & Uchio, 2007; Xiao et al .…”

Section: Discussionmentioning

confidence: 99%

Age and geochemistry of the Zhaheba ophiolite complex in eastern Junggar of the Central Asian Orogenic Belt (CAOB): implications for the accretion process of the Junggar terrane

Zhang

Zou

et al. 2016

Geol. Mag.

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We report new field observations, zircon U–Pb ages and geochemical data for the discrete members of the Zhaheba ophiolite complex in northeastern Junggar of the Central Asian Orogenic Belt (CAOB) with the aim to understand the accretion process of the eastern Junggar terrane. The zircon age data reveal that the cumulates of the Zhaheba ophiolite crystallized at ~485 Ma while the volcanic sequences erupted at ~400 Ma. Thus, the volcanic sequences are not members of the Zhaheba ophiolite. Chromian spinels from the serpentinite have comparable elemental compositions to those of spinels from MORB-type ophiolites. Similarly, the rift affinity of clinopyroxene and positive zircon εHf(t) (13–20) and mantle δ18O (+5.37‰) values of the cumulates imply that the cumulates crystallized from primitive magmas derived from a depleted mantle source. Elemental and Nd isotopic compositions indicate that the basalts in the Zhaheba area were derived from partial melting of a mantle wedge metasomatized by adakitic melts and/or subduction-related fluids. The data presented in this contribution, together with previous studies, indicate that the Zhaheba–Almantai and Kelameili ophiolites were MORB-type, which implies that there were at least two mid-ocean ridges during Ordovician to early Devonian times in the Junggar Ocean. In the earlier stage, intra-oceanic subduction led to the formation of the intra-oceanic arc, and then the Kelameili ophiolite accreted to an intra-oceanic accretionary wedge. In the later stage, the Zhaheba–Almantai ophiolite accreted to the accretionary wedge along the southern margin of the Iritish suture zone during the roll-back of the subduction zone from north to south.

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Section: Discussionmentioning

confidence: 99%

Age and geochemistry of the Zhaheba ophiolite complex in eastern Junggar of the Central Asian Orogenic Belt (CAOB): implications for the accretion process of the Junggar terrane

Zhang

Zou

et al. 2016

Geol. Mag.

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“…In addition, in the ophiolitic mélange in the Zhaheba area, Nb-enriched basalts and ultra-high pressure (UHP) rocks typically associated with an intra-oceanic arc have been discovered [57]. The UHP rocks are lherzolites with olivines that contain oriented masses of melted magnetite, garnet pyroxenites that contain high-Si and high-Ti garnets, quartz magnesites, and garnet amphibolites [58][59][60]. The presence of these rocks suggests that this region was once characterised by the ultra-deep subduction of oceanic crust.…”

Section: Geological Background and Samplesmentioning

confidence: 99%

Discovery of ∼4.0 Ga detrital zircons in the Aermantai ophiolitic mélange, East Junggar, northwest China

Huang¹,

Niu²,

Zhang³

et al. 2013

Chin. Sci. Bull.

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The East Junggar is an important part of the Central Asian Orogenic Belt (CAOB). Using in situ zircon dating and Hf isotopic analysis by LA-ICP-MS and MC-ICP-MS, respectively, a detrital zircon of 4040 Ma age was found in sedimentary sequences from the Aermantai ophiolitic mélange, East Junggar. This is the oldest age record in the East Junggar terrane, and also marks the first zircon locality in the CAOB with an age older than 4.0 Ga, which is attributed to the Hadean crust. The 4040 Ma detrital zircon has an ε Hf (t) value of-5.2 and a two-stage Hf modal age of 4474 Ma, suggesting the presence of very old (Hadean) crustal material in the source area. Beside peak ages of 446 Ma, we found four age groups of 3.6-3.1 Ga, 2.53-2.37 Ga, 1.14-0.89 Ga and 0.47-0.42 Ga from 141 effective measuring points. The age of 426±4 Ma for the five youngest detrital zircons defines the lower limit of the deposition time of sedimentary sequencess in the Aermantai ophiolitic mélange. The 0.47-0.42 Ga zircons exhibit 176 Hf/ 177 Hf ratios of 0.282156 to 0.282850, corresponding to variable ε Hf (t) values from-9.3 to 12.0 and Hf model ages from 2011 to 646 Ma. These characteristics are similar to those of the early Paleozoic igneous and gneissic zircons from the Altai, but significantly different from those of the East Junggar. Based on the material structures of felspathic greywacke, the morphology, internal texture and age distributions of dated detrital zircons, in combination with a study of the regional geological data, it is suggested that the sedimentary sequences in the Aermantai ophiolitic mélange was deposited in the Late Silurian, with the main provenance from the Altai Orogen in the north. This indicates that the early Paleozoic ocean represented by the Aermantai ophiolitic mélange was readily closed during the Late Silurian, and the northern edge of the East Junggar terrane was accreted to the Altai Orogen. The joint of them then served as a marginal orogen in the southern edge of the Siberia Paleocontinent.

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“…Garnet dominated calcitic ijolite, which represents the most 'hybrid' carbonate-silicate suite of rocks at Oka, occurs solely proximal to the nature center (Fig. 1) and is the only rock type containing garnet within the complex.Titanium-rich garnets commonly consist of andradite melanite (Ca 3 Ti 2 [Al<Fe 3+ ] 2 SiO 12 ), and have been found within various extrusive and intrusive Si-undersaturated alkaline igneous rocks and related rock types (e.g., Niu et al, 2008;Chakhmouradian and McCammon, 2005;Vuorinen et al, 2005;Gwalani et al, 2000;Dingwell and Brearley, 1985;Manning and Harris, 1970). The garnets occurring in skarns and serpentinized peridotite bodies are interpreted to be of metamorphic or metasomatic origin (Russell et al, 1999;Dingwell and Brearley, 1985;Deer et al, 1982).…”

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Mineral chemistry of melanite from calcitic ijolite, the Oka carbonatite complex, Canada: Implications for multi-pulse magma mixing

et al. 2016

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Ti-rich garnet is found within calcitic ijolite from the Oka carbonatite complex in Canada, which is characterized by 58%-73% andradite component (2.12 wt.%-4.18 wt.% TiO 2 ) and classified as melanite. The garnet displays complex zoning and contains abundant high field strength elements (HFSEs) and rare earth elements (REEs). Three groups (I, II, III) have been identified based on their petrographic nature. Compared to groups II and III, Group I garnet cores contain higher TiO 2 , MgO, HFSE, and REE and lower SiO 2 abundances. The distinct chemical and petrographic signatures of the investigated garnets cannot be attributed to simple closed system crystallization, but they are consistent with the multi-pulse magma mixing. Combined with previously reported U-Pb ages for apatite from the calcitic ijolite, at least three stages of magma evolution and subsequent mixing have been involved in the generation of calcitic ijolite at Oka. The early-formed melt that generated Group I garnet core was later mixed with at least two small-volume, more evolved melts. The intermediate stage melt formed the remaining garnet along with some pyroxene, calcite, nepheline, and apatite at 127±3.6 Ma. The youngest, most evolved melt generated the majority of pyroxene, calcite, nepheline, and apatite within the calcitic ijolite at 115±3.1 Ma. KEY WORDS: melanite garnet, calcitic ijolite, Oka, magma mixing. INTRODUCTIONThe Oka intrusive carbonatite complex (Fig. 1) comprises a broad spectrum of rocks, including carbonatite, okaite, ijolite, calcitic ijolite, jacupirangite, and alnöite. Previous chemical, isotopic, and geochronological investigations of the carbonatite and associated silicate rocks from Oka indicate the involvement of periodic generation of small volume, partial melts from a heterogeneous mantle plume and subsequent magma mixing Simonetti, 2014, 2013;Zurevinski and Mitchell, 2004). In addition, liquid immiscibility has been proposed for the formation of the carbonatite and associated silicate rocks at Oka (Treiman and Essene, 1985;Eby, 1975). Garnet dominated calcitic ijolite, which represents the most 'hybrid' carbonate-silicate suite of rocks at Oka, occurs solely proximal to the nature center (Fig. 1) and is the only rock type containing garnet within the complex.Titanium-rich garnets commonly consist of andradite melanite (Ca 3 Ti 2 [Al

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Discovery of super-silicic and super-titanic garnets in garnet-pyroxenite in Zhaheba and its geological significance

Cited by 10 publications

References 26 publications

Age and geochemistry of the Zhaheba ophiolite complex in eastern Junggar of the Central Asian Orogenic Belt (CAOB): implications for the accretion process of the Junggar terrane

Age and geochemistry of the Zhaheba ophiolite complex in eastern Junggar of the Central Asian Orogenic Belt (CAOB): implications for the accretion process of the Junggar terrane

Discovery of ∼4.0 Ga detrital zircons in the Aermantai ophiolitic mélange, East Junggar, northwest China

Mineral chemistry of melanite from calcitic ijolite, the Oka carbonatite complex, Canada: Implications for multi-pulse magma mixing

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