TY - JOUR A1 - Rehman, Hafiz Ur A1 - Lee, Hao-Yang A1 - Chung, Sun-Lin A1 - Khan, Tahseenullah A1 - Yamamoto, Hiroshi O´Brien T1 - Source and mode of the Permian Panjal Trap magmatism: Evidence from zircon U-Pb and Hf isotopes and trace element data from the Himalayan ultrahigh-pressure rocks JF - Lithos : an international journal of mineralogy, petrology, and geochemistry N2 - We present an integrated study of LA-ICP-MS U-Pb age, Hf isotopes, and trace element geochemistry of zircons from the Himalayan eclogites (mafic rocks) and their host gneisses (felsic rocks) from the Kaghan Valley in Pakistan in order to understand the source and mode of their magmatic protoliths and the effect of metamorphism. Zircons from the so-called Group I (high-pressure) eclogites yielded U-Pb mean ages of 259 +/- 10 Ma (MSWD = 0.74), whereas those of Group II (ultrahigh-pressure) eclogites yielded 48 3 Ma (MSWD = 0.71). In felsic gneisses the central or core domains of zircons yielded ages similar to those from Group I edogites but zircon overgrowth domains yielded 47 +/- 1 Ma (MSWD = 1.9). Trace element data suggest a magmatic origin for Group I-derived (having Th/U ratios: >0.5) and metamorphic origin for Group II -derived (Th/U < 0.07) zircons, respectively. Zircon Hf isotope data, obtained from the same dated spots, show positive initial Hf-176/Hf-177 isotopic ratios referred to as "epsilon(Hf)(t)" of around +10 in Group I eclogites; +7 in Group II eclogites; and +8 in felsic gneisses zircons, respectively, thus indicate a juvenile mantle source for the protolith rocks (Panjal Traps) with almost no contribution from the ancient crustal material. The similar epsilon(Hf)(t) values, identical protolith ages and trace element compositions of zircons in felsic (granites or rhyolites) and mafic (basalt and dolerite) rocks attest to a bimodal magmatism accounting for the Panjal Traps during the Permian. Later, during India-Asia collision in Eocene times, both the felsic and mafic lithologies were subducted to mantle-depths (>90 km; coesite-stable) and experienced ultrahigh-pressure metamorphism before their final exhumation. (C) 2016 Elsevier B.V. All rights reserved. KW - Himalaya KW - Panjal Traps KW - UHP edogites and felsic gneisses KW - Zircon U-Pb age KW - Hf isotopes KW - Trace element geochemistry Y1 - 2016 U6 - https://doi.org/10.1016/j.lithos.2016.06.001 SN - 0024-4937 SN - 1872-6143 VL - 260 SP - 286 EP - 299 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Läger, Kathrin A1 - Halama, Ralf A1 - Hansteen, Thor A1 - Savov, Ivan P. A1 - Murcia, Hugo F. A1 - Cortes, Gloria P. A1 - Garbe-Schönberg, Dieter T1 - Crystallization conditions and petrogenesis of the lava dome from the similar to 900 years BP eruption of Cerro Machin Volcano, Colombia JF - Journal of South American earth sciences N2 - The last known eruption at Cerro Machin Volcano (CMV) in the Central Cordillera of Colombia occurred 900 years BP and ended with the formation of a dacitic lava dome. The dome rocks contain both normally and reversely zoned plagioclase (An(24-54)), unzoned and reversely zoned amphiboles of dominantly tschermakite and pargasite/magnesio-hastingsite composition and olivine xenocrysts (Fo = 85-88) with amphibole/clinopyroxene overgrowth, all suggesting interaction with mafic magma at depth. Plagioclase additionally exhibits complex oscillatory zoning patterns reflecting repeated replenishment, fractionation and changes in intrinsic conditions in the magma reservoir. Unzoned amphiboles and cores of the reversely zoned amphiboles give identical crystallization conditions of 910 +/- 30 degrees C and 360 +/- 70 MPa, corresponding to a depth of about 13 +/- 2 km, at moderately oxidized conditions (f(O2) = +0.5 +/- 0.2 Delta NNO). The water content in the melt, calculated based on amphibole chemistry, is 7.1 +/- 0.4 wt.%. Rims of the reversely zoned amphiboles are relatively enriched in MgO and yield higher crystallization temperatures (T = 970 +/- 25 degrees C), slightly lower melt H2O contents (6.1 +/- 0.7 wt.%) and overlapping pressures (410 +/- 100 MPa). We suggest that these rims crystallized following an influx of mafic melt into a resident magma reservoir at mid-crustal depths, further supported by the occurrence of xenocrystic olivine. Crystallization of biotite, albite-rich plagioclase and quartz occurred at comparatively low temperatures (probably <800 degrees C) during early stages of ascent or storage at shallower levels. Based on amphibole mineral chemistry, the felsic resident melt had a rhyolitic composition (71 +/- 2 wt.% SiO2), whereas the hybrid magma, from which the amphibole rims crystallized, was dacitic (64 +/- 3 wt.% SiO2). The bulk rock chemistry of the CMV lava dome dacites is homogenous. They have elevated (La/Nb)(N) ratios of 3.8-4.5, typical for convergent margin magmas, and display several geochemical characteristics, of adakites. Both Sr and Nd isotope compositions (Sr-87/Sr-86 similar to 0.70497, Nd-143/Nd-144 similar to 0.51267) are among the most radiogenic observed for the Northern Volcanic Zone of the Andes. They are distinct from oceanic crust that has been subducted in the region, pointing to a continental crustal control on the isotope composition and hence the adakitic signature, possibly in a crustal "hot zone". KW - Colombian Andes KW - Cerro Machin Volcano KW - Magma mixing KW - Amphibole geothermobarometry KW - Trace element geochemistry Y1 - 2013 U6 - https://doi.org/10.1016/j.jsames.2013.09.009 SN - 0895-9811 VL - 48 IS - 12 SP - 193 EP - 208 PB - Elsevier CY - Oxford ER -