Mineralogical evidence for fractionation processes in the Himalayan leucogranites of the Ramba Dome, southern Tibet

Liu, Zhichao; Wu, Fu‐Yuan; Liu, Xiaochi; Wang, Jiangang; Yin, Rong; Zhili, Qiu; Ji, Wei‐Qiang; Yang, Lei

doi:10.1016/j.lithos.2019.05.004

Cited by 73 publications

(32 citation statements)

References 81 publications

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“…From the typical compositions of plagioclase and K-feldspar in the Himalayan 1. leucogranites (Z.-C. Liu et al, 2019), the Ab% (in plagioclase) and Or% (in K-feldspar) were both assumed to be 90%, which indicates a Δ 56 Fe biotite-plagioclase of 0.77‰ and Δ 56 Fe biotite-K-feldspar of 0.89‰. Accordingly, biotite, tourmaline, muscovite, and garnet are all predicted to be Fe isotopically lighter, while feldspars are isotopically heavier than the co-existing leucogranitic melt (summarized in Table 1).…”

Section: Fe Isotopic Fractionation Factors Among Minerals and Meltmentioning

confidence: 99%

“…Here we consider the possible effect of FC for two-mica and tourmaline leucogranites. For the Rayleigh fractionation model (Equation 1) and mass balance (Equation 2 Liu et al, 2019;. The geochemical composition of endmembers for AFC modeling was from Ji et al (2020) and the Sr isotopic ratios were corrected at 20 Ma.…”

Section: Fe Isotope Evidence and A Simple Fractional Crystallization Modelmentioning

confidence: 99%

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Petrogenesis of Himalayan Leucogranites: Perspective From a Combined Elemental and Fe‐Sr‐Nd Isotope Study

et al. 2021

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The petrogenesis of Himalayan leucogranites remains crucial for understanding the thermal and tectonic evolution of the Himalayan orogen. To understand whether they are largely pristine melts of crustal anatexis or have experienced a high degree of fractional crystallization (FC), we present Fe isotopic data of 30 representative Himalayan leucogranites and 9 local metasedimentary rocks. Excepting three garnet leucogranites with low δ 56 Fe (−0.04‰-0.06‰) that are likely affected by garnet accumulation, tourmaline, and two-mica leucogranites have largely homogeneous δ 56 Fe from 0.13‰ to 0.24‰ irrespective of their highly variable SiO 2 , MgO, and FeOt contents. Combined with observed mineral assemblages and available fractionation factors, this does not support a high degree of FC (with or without assimilation) in their petrogenesis. The elevated δ 56 Fe relative to the supposed source rocks, represented by metasedimentary rocks and/or metabasite with a δ 56 Fe value of 0.10‰, by ∼0.07‰, may reflect Fe isotope fractionation during crustal anatexis. This study indicates most leucogranites can provide robust constraints on the conditions of crustal anatexis and thus the thermal and tectonic evolution of the Himalayan orogen.Plain Language Summary The Himalayas have been formed from the collision between two tectonic plates. During their formation, the rocks of the continental crust have melted to form leucogranites which potentially provide important information on how the collision process evolves. Several recent studies of rare-element mineralization associated with these granites have argued that the magmas result from extensive removal of early formed minerals during the cooling of the magma (fractional crystallization [FC]) which, if true, would undermine their usefulness as monitors of the collisional process. In this study, we address this issue through a geochemical approach that combines isotopic data from iron, strontium, and neodymium. Whereas Sr and Nd give information on the source of the magmas, the isotopes of Fe will remain largely unfractionated if the granites result simply from melting the crust but fractionate significantly during FC. Our results reveal very limited fractionation of Fe isotopic compositions for two types of leucogranites, which is inconsistent with the model requiring a high degree of FC but supports the interpretation that they represent largely unfractionated crustal melts. Our study therefore confirms that Himalayan leucogranites can provide reliable probes for the thermal and tectonic evolution of the Himalayan crust. SHI ET AL.

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Section: Fe Isotopic Fractionation Factors Among Minerals and Meltmentioning

confidence: 99%

Section: Fe Isotope Evidence and A Simple Fractional Crystallization Modelmentioning

confidence: 99%

Petrogenesis of Himalayan Leucogranites: Perspective From a Combined Elemental and Fe‐Sr‐Nd Isotope Study

et al. 2021

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“…Crawford and Windley, 1990;Searle and Godin, 2003;Annen et al, 2006;Godin et al, 2006b;Weinberg, 2016). Cenozoic Himalayan granites are subdivided into two roughly parallel, near E-W striking intrusive belts, the North Himalayan granites and the High Himalayan leucogranites (Debon et al, 1986;Crawford and Windley, 1990;Guo and Wilson, 2012;Liu et al, 2019). These different manifestations of crustal melts can all be found within the study area along the Chuwa Khola (River in Nepali), in northwest Nepal (Fig.…”

mentioning

confidence: 83%

“…Cenozoic Himalayan granites are subdivided into two roughly parallel, near E-W striking intrusive belts, the North Himalayan granites and the High Himalayan leucogranites (Fig. 2.4) (Debon et al, 1986;Deniel et al, 1987;Crawford and Windley, 1990;Harrison et al, 1997;Guo and Wilson, 2012;Liu et al, 2019). The North Himalayan granites are exposed along the trace of the North Himalayan antiform, intruding both gneiss domes and the overlying Tethyan sedimentary sequence (Fig.…”

Section: Himalayan Granitesmentioning

confidence: 99%

Timing and Source of Melting at the Eastern Edge of the Gurla Mandhata Core Complex, Nw Nepal Himalaya

Martin¹,

Provided²,

Godin³

et al. 2020

Geological Society of America Abstracts With Programs

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northwest sense of shear at ca. 15 Ma to 13 Ma, the Chuwa Khola exhibits dominant top-tothe southwest suggesting the existence of a strain partitioning boundary between the two areas.v ACKNOWLEDGEMENTS I would like to first and foremost thank my supervisor, Dr. Laurent Godin, for giving me the chance to work on such an exciting and challenging project, as well as for allowing me to travel to one of the most beautiful places on the planet. This has been a life changing opportunity and I am very grateful to have had his support and guidance through it all. I would also like to thank John Cottle for his expertise in guiding monazite petrochronology. I also thank Chris Yakymchuk for his invaluable help with interpreting my geochemical analyses.Thank you to the following people for their analytical and technical assistance: Agatha Dobosz for her help with thin section mapping and mineral characterization on the scanning electron microscope; Brian Joy for his help with X-ray chemical mapping of monazites on the electron microprobe; and Andrew Kylander-Clark (UCSB) for his help with guiding monazite petrochronology. I would also like to thank my thesis examination committee, Dr.

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“…Partition coefficients for micas were sourced from Icenhower and London (1995) and partition coefficients for feldspars were sourced from Michael (1984). The detailed calculating process can be found in Liu et al (2019).…”

Section: Supplementary Tablementioning

confidence: 99%

Carbon and nitrogen isotope evidence for widespread presence of anoxic intermediate waters before and during the Permian-Triassic mass extinction

Luo

Joachimski

et al. 2021

GSA Bulletin

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The largest mass extinction since the advent of animals occurred during the Permian-Triassic (P-Tr) transition, ca. 252 Ma, and is commonly attributed to the eruption of the Siberian Traps large igneous province. However, the direct killing mechanism is still debated. In this study, we investigated marine redox conditions of the intermediate water column that most organisms inhabit with special attention to the time interval before the onset of the mass extinction. The carbon isotope composition of carbonate and organic carbon (δ13Ccarb and δ13Corg) as well as the nitrogen isotope composition of bulk nitrogen (δ15N) were analyzed in four P-Tr boundary sequences (Zhongli, Jianshi, Ganxi, and Chaotian sections), which record a transect from a shallow water carbonate platform to a deep water, lower ramp slope in South China. δ13Ccarb shows a distinct negative shift in all sections and displays a clear, 2−4‰, decreasing gradient accompanying an increase in water depth both before and after the mass extinction. A distinct negative shift in δ15N is observed in the shallow water Zhongli section, whereas a minor negative shift is present in the three deeper water sections. Before the mass extinction, the δ15N values from shallow water sections are higher than those from deeper waters. The low δ15N values close to 0‰ in deeper water sections suggest that microbial nitrogen fixation was the predominant source of biologically available nitrogen before the onset of the mass extinction. Thus, the water depth- dependent gradient in δ13Ccarb and δ15N suggests that an oxygen-deficient intermediate water column was already present before the mass extinction. The uniform δ15N values around 0‰ accompanying the onset of the mass extinction reveal that anoxic intermediate waters expanded into shallow waters. Meanwhile, the distinct positive shift in δ13Corg observed in upper ramp slope sections, i.e., the Jianshi and Ganxi sections, suggests that a euxinic photic zone was at least episodically present in the earliest Triassic. The temporal coincidence between the expansion of intermediate water column anoxia and the onset of the P-Tr mass extinction supports the hypothesis that marine anoxia was a direct killing mechanism.

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Mineralogical evidence for fractionation processes in the Himalayan leucogranites of the Ramba Dome, southern Tibet

Cited by 73 publications

References 81 publications

Petrogenesis of Himalayan Leucogranites: Perspective From a Combined Elemental and Fe‐Sr‐Nd Isotope Study

Petrogenesis of Himalayan Leucogranites: Perspective From a Combined Elemental and Fe‐Sr‐Nd Isotope Study

Timing and Source of Melting at the Eastern Edge of the Gurla Mandhata Core Complex, Nw Nepal Himalaya

Carbon and nitrogen isotope evidence for widespread presence of anoxic intermediate waters before and during the Permian-Triassic mass extinction

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