Origin of postcollisional magmas and formation of porphyry Cu deposits in southern Tibet

Wang, Rui; Weinberg, Roberto F.; Collins, William J.; Richards, Jeremy P.; Zhu, Di

doi:10.1016/j.earscirev.2018.02.019

Cited by 180 publications

(70 citation statements)

References 158 publications

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“…Adakite‐like potassic rocks from postcollisional setting usually exhibit high Sr/Y ratio and negative Nb, Ta, and Ti anomalies, but the absence of obvious Eu anomalies (Conticelli et al, ; Topuz et al, ; Wang et al, ). In these respects, they are similar to the adakites from arc settings that are thought to have derived from the subducted oceanic crust (Defant & Drummond, ).…”

Section: Discussionmentioning

confidence: 99%

Adakite‐Like Potassic Magmatism and Crust‐Mantle Interaction in a Postcollisional Setting: An Experimental Study of Melting Beneath the Tibetan Plateau

et al. 2019

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Adakite‐like potassic rocks are widespread in postcollisional settings where they provide potential insights into deep crustal processes that include partial melting, lower crustal flow and thickening, plateau uplift, and the creation of porphyry metal deposits. Although substantial progress has been made in characterizing the geochemical and geophysical features of postcollisional adakite‐like potassic rocks, their petrogenesis remains controversial. Here we report direct experimental evidence for the origins of these rocks with partial melting experiments on (1) garnet amphibolite and (2) the same garnet amphibolite mixed with 20 wt. % of a primitive Tibetan shoshonite. The experiments were conducted at 1.5–2.0 GPa and 800–1,000 °C. The partial melts of garnet amphibolite have typical adakitic signatures and are calc‐alkalic but lack the enrichment in potassium and other strongly incompatible elements (Rb, Ba, Th, U) that are characteristic of Tibetan adakite‐like rocks. In contrast, all characteristic features of the natural adakite‐like rocks are convincingly reproduced by the hybrid experiments. This includes negative inflections for Nb, Ta, and Ti on mantle‐normalized plots which are inherited from source materials rather than the effects of rutile in melting residues. The input of mantle‐derived shoshonitic mafic melts to a crustal source can be argued to provide not only the high concentrations of incompatible elements characteristic of adakite‐like potassic magmas but also the heat necessary for crustal melting. Our experimental results demonstrate that, in the case of the Tibetan Plateau at least, the production of adakite‐like potassic rocks in postcollisional settings can be best explained by such a model.

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Section: Discussionmentioning

confidence: 99%

Adakite‐Like Potassic Magmatism and Crust‐Mantle Interaction in a Postcollisional Setting: An Experimental Study of Melting Beneath the Tibetan Plateau

et al. 2019

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“…The Qulong porphyry Cu-Mo deposit, situated at the southwest margin of the Lhasa terrane, southern Tibet ( Fig. 2A), is a representative porphyry deposit from the Gangdese porphyry copper belt formed in a postcollisional setting Wang et al, 2018). This giant deposit contains >2,200 million tonnes of ore with an average grade of 0.5% and 0.03% for Cu and Mo, respectively (Li et al, 2017b).…”

Section: Deposit Geology and Samplesmentioning

confidence: 99%

Controlling Mechanisms for Molybdenum Isotope Fractionation in Porphyry Deposits: The Qulong Example

McCoy-West

Zhang

et al. 2019

Economic Geology

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Molybdenite-bearing porphyry deposits are the predominant supplier of molybdenum to industrialized society and one of the main hosts of Mo in the upper continental crust. The Mo isotope compositions (δ98/95Mo, normalized to NIST3134 equals 0‰) of molybdenite show considerable variation (–1.62 to +2.27‰), but the factors controlling this variability remain poorly constrained. This information is critical for underpinning genetic models of porphyry deposits, understanding elemental cycling, and utilizing the δ98/95Mo of marine sediments as a paleoredox proxy. Using the well-characterized Qulong porphyry Cu-Mo deposit (Tibet) as an example, here we discuss how rapid cooling, facilitated by mixing hot magmatic fluid with cold meteoric water, can be a controlling factor on efficient mineralization, and then tackle how fluid evolution regulates molybdenum isotope fractionation. Molybdenites, which preferentially partition isotopically light Mo (Rayleigh fractionation), precipitated from a single fluid will develop a heavier δ98/95Mo composition over time, and this also creates heterogeneous δ98/95Mo between molybdenite grains. Whereas a fluid undergoing multiple episodes of intensive boiling will gradually lose its isotopically heavy Mo to the vapor phase, molybdenites crystallizing successively from the residual liquid will then have lighter δ98/95Mo over time. However, when mineralization efficiency becomes too low, a negligible variation in δ98/95Mo of molybdenite is observed. Given that the mineralization efficiency (i.e., the amount of Mo crystallized as molybdenite from the fluid) rarely reaches 100% and molybdenite favors isotopically light Mo, the presence of a residual fluid with isotopically heavy Mo is inevitable. This residual fluid may then become trapped in alteration halos; hence, δ98/95Mo has the potential to aid in locating the mineralization center (e.g., lighter δ98/95Mo toward the orebody). The residual fluid may also feed surface hydrological systems and eventually impact Mo cycling. Our study highlights that understanding the controls of isotope fractionation is critical to bridge the gap between ore formation and elemental cycling, and that other transition metals (e.g., Cu, Fe, and Zn) may follow similar trajectories.

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“…In island arcs and continental arcs, where porphyry deposits form, it is generally thought that oxidized, sulphur-rich fluids released from subducting slabs migrate into the asthenospheric mantle wedge, where they cause partial melting and mobilization of metals (Richards, 2003), and ultimately transfer these metals into the crust. Recently, large porphyry copper deposits (PCDs) have been found in association with post-collisional (Miocene; 22-12 Ma), high-Sr/Y granitoid plutons emplaced in the eastern section of the Paleocene-Eocene Gangdese magmatic arc in the Himalayan-Tibetan orogenic belt (Hou et al, 2004(Hou et al, , 2015Yang et al, 2009;Wang et al, 2018). These discoveries raise questions about the nature of magmatic and metallogenic processes during continental collision.We review the literature and compile available data on whole rock and isotope geochemistry for Cenozoic igneous rocks from Tibet, with new zircon Ce 4+ /Ce 3+ and Ti-in-zircon thermometry data to better understand variations in oxidation state and thermal evolution of these suites, which are key controls on Cu mineralization.…”

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confidence: 99%

“…Porphyry copper mineralization is associated with a moderately oxidized (ΔFMQ = +0.8 to +2.9), water-rich (≥4.5 wt.%) high-Sr/Y granitoid suite with minor occurrences of transitional (hybrid) monzonitic and trachytic rocks (Wang et al, 2014ab). The Miocene high-Sr/Y granitoids have many compositional and isotopic similarities to the Paleocene-Eocene Gangdese arc rocks, and are interpreted to have been derived by melting of the hydrated arc root, with minor mantle input (Wang et al, 2015(Wang et al, , 2018.Although partial melting of subduction-modified lower crust has been proposed to generate such magmas, the main debate arises from the discussion that whether the lower crust can provide enough S for giant porphyry deposit formation. In addition, the porphyry system is common with several pulses of magmatism coeval with mineralization.…”

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confidence: 99%

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confidence: 99%

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Origin of giant post‐collisional porphyry Cu metallogenic belt in southern Tibet: constrains from magmatic H2O, fO2, and S

Wang

Hou

Richards

et al. 2019

Acta Geologica Sinica (Eng)

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Origin of postcollisional magmas and formation of porphyry Cu deposits in southern Tibet

Cited by 180 publications

References 158 publications

Adakite‐Like Potassic Magmatism and Crust‐Mantle Interaction in a Postcollisional Setting: An Experimental Study of Melting Beneath the Tibetan Plateau

Adakite‐Like Potassic Magmatism and Crust‐Mantle Interaction in a Postcollisional Setting: An Experimental Study of Melting Beneath the Tibetan Plateau

Controlling Mechanisms for Molybdenum Isotope Fractionation in Porphyry Deposits: The Qulong Example

Origin of giant post‐collisional porphyry Cu metallogenic belt in southern Tibet: constrains from magmatic H2O, fO2, and S

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