Supplemental Material: Rifting of the Indian passive continental margin: Insights from the Langjiexue basalts in the central Tethyan Himalaya, southern Tibet

Text S1: Analytical methods. Figure S1: Zr versus selected element variation diagrams to highlight the effects of alteration and metamorphism for the basalts from Langjiexue area. Figure S2: (A) Ti/Y vs. TiO2, and (B) Ti/Y vs. MgO diagrams for the basalt samples from the Langjiexue in Tethyan Himalaya. Table S1: Representative Permian-Triassic magmatic events along the Tethyan Himalaya. Table S2: Zircon LA-ICP-MS U-Pb in-situ analyzing results for zircons from the Langjiexue basalts. Table S3: Whole-rock major, trace element and Sr-Nd isotope data of Langjiexue basalts.

Supplemental Material: Rifting of the Indian passive continental margin: Insights from the Langjiexue basalts in the central Tethyan Himalaya, southern Tibet

Text S1: Analytical methods. Figure S1: Zr versus selected element variation diagrams to highlight the effects of alteration and metamorphism for the basalts from Langjiexue area. Figure S2: (A) Ti/Y vs. TiO2, and (B) Ti/Y vs. MgO diagrams for the basalt samples from the Langjiexue in Tethyan Himalaya. Table S1: Representative Permian-Triassic magmatic events along the Tethyan Himalaya. Table S2: Zircon LA-ICP-MS U-Pb in-situ analyzing results for zircons from the Langjiexue basalts. Table S3: Whole-rock major, trace element and Sr-Nd isotope data of Langjiexue basalts.

The Tethyan Himalaya igneous province: Early melting products of the Kerguelen mantle plume

The Kerguelen large igneous province (LIP) has been related to mantle plume activity since at least 120 Ma. There are some older (147–130 Ma) magmatic provinces on circum-eastern Gondwana, but the relationship between these provinces and the Kerguelen mantle plume remains controversial. Here we present petrological, geochronological, geochemical, and Sr–Nd–Hf–Pb–Os isotopic data for high-Ti mafic rocks from two localities (Cuona and Jiangzi) in the eastern Tethyan Himalaya igneous province (147–130 Ma). Zircon grains from these two localities yielded concordant weighted mean 206Pb/238U ages of 137.25 ± 0.98 and 131.28 ± 0.78 Ma (2σ), respectively. The analyzed mafic rocks are enriched in high field strength elements and have positive Nb–Ta anomalies relative to Th and La, which have ocean island basalt-like characteristics. The Cuona basalts were generated by low degrees of melting (3–5%) of garnet lherzolites (3–5 vol.% garnet), and elsewhere the Jiangzi diabases were formed by relatively lower degrees of melting (1–3%) of garnet lherzolite (1–5 vol.% garnet). The highly radiogenic Os and Pb isotopic compositions of the Jiangzi diabases were produced by crustal contamination, but the Cuona basalts experienced the least crustal contamination given their relatively low γOs(t), 206Pb/204Pbi, 207Pb/204Pbi, and 208Pb/204Pbi values. Major and trace element geochemical and Sr–Nd–Hf–Pb–Os isotope data for the Cuona basalts are similar to products of the Kerguelen mantle plume head. Together with high mantle potential temperatures (>1500°C), this suggests that the eastern Tethyan Himalaya igneous province (147–130 Ma) was an early magmatic product of the Kerguelen plume. A mantle plume initiation model can explain the temporal and spatial evolution of the Kerguelen LIP, and pre-continental break-up played a role in the breakup of eastern Gondwana, given the >10 Myr between initial mantle plume activity (147–130 Ma) and continental break-up (132–130 Ma). Like studies of Re-Os isotopes in other LIPs, the increasing amount of crustal assimilation with distance from the plume stem can explain the variations in radiogenic Os.

Eocene thickening without extra heat in a collisional orogenic belt: A record from Eocene metamorphism in mafic dike swarms within the Tethyan Himalaya, southern Tibet

Knowledge of the nature of the earliest metamorphism experienced by collisional orogenic belts is essential for reconstruction of tectonic processes that build high mountain chains and their environmental consequences. Understanding the metamorphic nature of Eohimalayan-phase orogeny of the Himalayan orogen, one of the typical examples of orogenic belts worldwide, could provide some important constraints to test different tectonic models (shallow continental subduction vs. slab breakoff) for the early phases of the development of large-scale orogenic belts. As exhumed middle- to lower-crustal rocks in the Kangmar gneiss dome, the garnet amphibolites with a protolith age of 176.4 ± 3.6 Ma experienced a phase of metamorphism at 47.2 ± 1.8 Ma with an increase in pressure as well as temperature from 3−5 kbar and 550−600 °C to over ∼11 kbar and 650 °C. This suggests that the middle- to lower-crustal rocks experienced heating at least by ∼50 °C while they underwent compression and thickening. Heat-flow estimation further demonstrates that the self-produced heat was high enough to achieve the observed pressure-temperature conditions recorded by the garnet amphibolite. Therefore, an additional heat supply is not required during early Eocene metamorphism. A breakoff of the leading part of the subducting Indian continental slab, if it occurred, should be younger than ca. 47 Ma.

Supplemental Material: Eocene thickening without extra heat in a collisional orogenic belt: A record from Eocene metamorphism in mafic dike swarms within the Tethyan Himalaya, southern Tibet

Table S1: EPMA data of minerals compositions for garnet amphibolite; Table S2: Zircon U-Pb SHRIMP data for garnet amphibolite T0526; Table S3: Major and trace element compositions of garnet amphibolites.

Supplemental Material: Eocene thickening without extra heat in a collisional orogenic belt: A record from Eocene metamorphism in mafic dike swarms within the Tethyan Himalaya, southern Tibet

Table S1: EPMA data of minerals compositions for garnet amphibolite; Table S2: Zircon U-Pb SHRIMP data for garnet amphibolite T0526; Table S3: Major and trace element compositions of garnet amphibolites.