The Greater Himalayan Sequence – Tectonic, Petrographic and Kinematic Evolution of the Metamorphic Core Zone of the Himalayan Orogeny

Robyr, Martin; Carosi, Rodolfo; Iaccarino, Salvatore; Montomoli, Chiara

doi:10.1002/9781394228621.ch5

Cited by 1 publication

(1 citation statement)

References 35 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The metamorphic core of the orogen, represented by the Greater Himalayan Sequence (GHS) is lithologically dominated by metapelites that generally record a medium-pressure, medium-temperature history (e.g. Robyr et al, 2023). In the central and eastern Himalaya (Ama Drime, Sikkim and Bhutan) isolated metabasaltic rocks exposed at the highest structural levels of the GHS instead record a higher pressure (plagioclaseabsent) to higher temperature (orthopyroxene-present) evolution (Corrie et al, 2010;Cottle et al, 2009;Groppo et al, 2007;Grujic et al, 2011;Kali et al, 2010;Kellett et al, 2014;Liu et al, 2007;Lombardo & Rolfo, 2000;Regis et al, 2014;Rolfo et al, 2008;Wang et al, 2017;Warren et al, 2011).…”

Section: Introductionmentioning

confidence: 99%

Allanite U–Pb dating places new constraints on the high‐pressure to high‐temperature evolution of the deep Himalayan crust

Wood,

Warren,

Kunz

et al. 2024

Journal Metamorphic Geology

View full text Add to dashboard Cite

During continental collision, crustal rocks are buried, deformed, transformed and exhumed. The rates, timescales and tectonic implications of these processes are constrained through the sequence and conditions of metamorphic reactions in major and accessory phases. Petrographic, isotopic and elemental data from metabasite samples in NW Bhutan, eastern Himalaya, suggest initial equilibration under high‐pressure (plagioclase‐absent and rutile‐present) conditions, followed by decompression to lower pressure conditions at high‐temperatures that stabilized plagioclase, orthopyroxene and ilmenite. Field observations and chemical indicators suggest equilibration under the lower pressure conditions is likely linked to the infiltration of melt from the host metasedimentary rocks. The metabasites preserve two metamorphic growth stages of chemically‐and petrographically distinct allanite that temporally overlap two stages of zircon growth. Allanite cores and zircon mantles grew at c. 19 ± 2 and 17–15.5 Ma respectively, linked texturally and chemically to the high‐pressure evolution. Symplectitic rims on embayed allanite cores, wholly symplectized Aln–Ilm and Aln–Cpx grains, and high U zircon rims grew at c. 15.5–14.5 Ma, linked chemically to the presence of melt and lower pressure, high‐temperature conditions. A single garnet Lu–Hf date is interpreted as geologically meaningless, with the bulk rock composition modified by melt infiltration after garnet formation. The open system evolution of these rocks precludes precise determination of the reactive bulk composition during metamorphic evolution and thus absolute conditions, especially during the early high‐pressure evolution. Despite these limitations, we show that combined geochemical and petrographic datasets are still able to provide insights into the rates and timescales of deep orogenic processes. The data suggest a younger and shallower evolution for the NW Bhutan metabasites compared to similar rocks in the central and eastern Himalayas.

show abstract