Carbonatites of Tarim (NW China): First evidence of crustal contribution in carbonatites from a large igneous province
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Keywords:
Carbonatite
Mantle plume
Large igneous province
Flood basalt
Ultramafic rock
Peridotite
Petrogenesis
Flood basalt
Mantle plume
Large igneous province
Platinum group
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This review paper starts with outlining some key research topics and methods in the field of Large Igneous Provinces(LIP) and mantle plumes.It is followed by an overview of the recent achievements and debates in the late Permian Emeishan continental flood basalt province in southwest China and early Permian Tarim traps in SW China.Data of various disciplines are evaluated by comparing observation against prediction of the plume hypothesis.It is shown that 7 out of 9 most convincing arguments in support of mantle plumes are met in the Emeishan LIP.In particular,sedimentologic data show unequivocal evidence for a lithospheric doming event prior to the Emeishan volcanism.These observations,the presence of high temperature magmas,emplacement of immense volume of magmas over a short time span and the spatial variation in basalt geochemistry,are all consistent with predictions of plume modeling,thus providing strong support for the validity of the mantle plume hypothesis.In the Tarim case,a two-stage dynamic model is proposed to account for the geochemical trend displayed by Tarim basalts.Finally some perspectives are made for the future studies in this field.
Mantle plume
Large igneous province
Flood basalt
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This paper discusses the tail of Emeishan mantle plume and suggests that it locates in Miyi—Yongren area, southern Sichuan—northern Yunnan. On the basis of the classic mantle plume theory, the estimated diameter of Emeishan plume tail was 65~105km when it reached the upper mantle. Picrite distributions and sedimentary responses showed that the center zone of the Emeishan plume was ca. 260~300km wide. Eruption and outcropping of flood basalts were constrained by deep-seated faults and paleogeomorphology, which resulted in the concentration of picrite in the west of the Emeishan large igneous province.
Mantle plume
Flood basalt
Large igneous province
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Flood basalt
Large igneous province
Mantle plume
Radiogenic nuclide
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The geochemical characteristics of the picritic rocks that we discovered recently and their associated basalts show that except the picrites, all the associated basaltic rocks belong to the high-Ti type. Like many other continental flood basaltic provinces, they are characterized by high Fe8 and (CaO/Al2O3)8 and low Na8, indicating high pressure. Their chondrite-normalized REE patterns and primitive mantle-normalized trace element patterns are similar, all of which display an enrichment of LREE and relative depletion of high field strength elements (HFSE) associated with an absence of Nb and Ta negative anomalies but a presence of P and K negative anomalies, as characterized by most flood basalts. Some trace element ratios characterizing the source regions, such as La/Ta, La/Sm, (La/Nb)pM, (Th/Ta)PM, Ta/Hf and Nb/Zr are within a narrow range. All these observations suggest the origin of mantle plume, and no or little crustal or lithospheric mantle contamination. They are generated by about 7% of partial melting of garnet Iherzolite at more than 75 km. Thus, the axis of the Emeishan mantle plume should be located beneath the Lijiang County Town, Yunnan Province.
Flood basalt
Large igneous province
Mantle plume
Trace element
Hotspot (geology)
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The Emeishan large igneous province in the western Yangtze Block was resulted from a mantle plume at end of the Middle Permian. Four super-large V-Ti-magnetite deposits and 10 large-medium Ni-Cu-(PGE) sulfide deposits have been explored in the Emeishan large igneous province. Precise age data indicated that these ore-bearing mafic-ultramafic intrusions were produced by the same mantle plume that caused the Emeishan flood basalts at 260 Ma±.The mafic-ultramafic intrusion hosting V-Ti-magnetite deposits and Ni-Cu-(PGE) sulfide deposits are distinguished in localization, scale, rock-assemblages, components of rock-forming minerals. The Emeishan large province can be divided to Inner- and Outer-Zones. The Inner-Zone is marked by large thickness of the Emeishan flood basalts, large layered intrusions, mafic-ultrmafic intrusive bodies, low-Ti basalts, alkaline intrusions, and various mineralizations related to the mantle plume. The basalts become thinner and consist of high-Ti basalts in the Outer-Zone where fewer mafic-ultramafic bodies are exposed. Special and geochemical relationship between the two type of magmatic deposits and high- and low-Ti basalts,the study on petrogenetic links between the Ni-Cu-(PGE) sulfide deposits and the Emeishan flood basalts in the Yangliuping area indicate that the magmatic deposits formed in different dynamic stages of the mantle plume. The V-Ti-magnetite deposits are associated with the high-Ti basaltic magmas and related to fractional crystallization. In contrast, the Ni-Cu-(PGE) sulfide mineralization may be related to either the high- or low-Ti basaltic magmas and controlled by three factors: high degree partial melting of upper mantle, contamination of the lower crust, and fractional crystallization. The Ni-Cu-(PGE) sulfide deposits were formed earlier than the V-Ti-magnetite deposits.
Flood basalt
Large igneous province
Mantle plume
Layered intrusion
Ultramafic rock
Fractional crystallization (geology)
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The Late Permian Emeishan large igneous province (ELIP) is considered to be one of the best examples of a mantle plume derived large igneous province. One of the primary observations that favour a mantle plume regime is the presence of ultramafic volcanic rocks. The picrites suggest primary mantle melts erupted and that mantle potential temperatures (TP) of the ELIP were > 200oC above ambient mantle conditions. However, they may represent a mixture of liquid and cumulus olivine and pyroxene rather than primary liquids. Consequently, temperature estimates based on the picrite compositions may not be accurate. Here we calculate mantle potential temperature (TP) estimates and primary liquids compositions using PRIMELT3 for the low-Ti (Ti/Y < 500) Emeishan basalt as they represent definite liquid compositions. The calculated TP yield a range from ~1400oC to ~1550oC, which is consistent with variability across a mantle plume axis. The primary melt compositions of the basalts are mostly picritic. The results of this study indicate that the Emeishan basalt was produced by a high temperature regime and that a few of the ultramafic volcanic rocks may be indicative of primary liquids.
Large igneous province
Flood basalt
Mantle plume
Ultramafic rock
Pyroxene
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