TY  - JOUR
A1  - Scott, James M.
A1  - Konrad-Schmolke, Matthias
A1  - O'Brien, Patrick J.
A1  - Günter, Christina
T1  - High-T, low-P formation of rare olivine-bearing symplectites in variscan eclogite
JF  - Journal of petrology
N2  - Extremely rare veinlets and reaction textures composed of symplectites of olivine (similar to Fo(43-55)) + plagioclase +/- spinel +/- ilmenite, associated with more common pyroxene + plagioclase and amphibole + plagioclase varieties, are preserved within eclogites and garnet pyroxenites in the Moldanubian Zone of the Bohemian Massif. Thermodynamic modelling integrated with conventional geothermometry conducted on an eclogite reveals that the symplectite-forming stage occurred at high T (similar to 850 degrees C) and low P (< 6 and > 2 center dot 5 kbar). The development of the different symplectite types reflects reactions that took place in micro-scale domains. The breakdown of high-P garnet controlled the formation of olivine-bearing and amphibole + plagioclase symplectites, whereas breakdown of high-P omphacite led to formation of pyroxene + plagioclase symplectites. In addition, post-eclogite facies but pre-symplectite stage porphyroblastic amphibole and phlogopite were also replaced by olivine-bearing symplectites. Material transfer calculations and thermodynamic modelling indicate that the formation of different symplectite types was linked despite their different bulk compositions. For example, the olivine-bearing symplectites gained Fe +/- Mg, whereas adjacent amphibole + plagioclase and pyroxene + plagioclase symplectites show losses in Fe and Mg; Al, Si and Ca were also variably exchanged. The olivine-bearing symplectites were particularly sensitive to Na despite the small concentration of this element. In eclogites where Na was readily available, the plagioclase composition in the olivine-bearing symplectites shifted from pure anorthite to bytownite, with the less calcic feldspar partitioning Si and inhibiting the formation of orthopyroxene. This regional high-T, low-P granulite-facies symplectite overprint may have been caused by advective heat loss from rapidly exhumed high-T, high-P granulitic bodies (Gfohl Unit) that were emplaced into and over the middle crust (Monotonous and Varied Series) during Carboniferous continent-continent collision.
KW  - olivine
KW  - symplectite
KW  - eclogite
KW  - thermodynamics
KW  - Variscan
Y1  - 2013
U6  - https://doi.org/10.1093/petrology/egt015
SN  - 0022-3530
SN  - 1460-2415
VL  - 54
IS  - 7
SP  - 1375
EP  - 1398
PB  - Oxford Univ. Press
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Wilke, Franziska Daniela Helena
A1  - O'Brien, Patrick J.
A1  - Altenberger, Uwe
A1  - Konrad-Schmolke, Matthias
A1  - Khan, M. Ahmed
T1  - Multi-stage reaction history in different eclogite types from the Pakistan Himalaya and implications for exhumation processes
N2  - Metabasites were sampled from rock series of the subducted margin of the Indian Plate, the so-called Higher Himalayan Crystalline, in the Upper Kaghan Valley, Pakistan. These vary from corona dolerites, cropping out around Saif- ul-Muluk in the south, to coesite-eclogite close to the suture zone against rocks of the Kohistan arc in the north. Bulk rock major- and trace-element chemistry reveals essentially a single protolith as the source for five different eclogite types, which differ in fabric, modal mineralogy as well as in mineral chemistry. The study of newly-collected samples reveals coesite (confirmed by in situ Raman spectroscopy) in both garnet and omphacite. All eclogites show growth of amphiboles during exhumation. Within some coesite-bearing eclogites the presence of glaucophane cores to barroisite is noted whereas in most samples porphyroblastic sodic-calcic amphiboles are rimmed by more aluminous calcic amphibole (pargasite, tschermakite, and edenite). Eclogite facies rutile is replaced by ilmenite which itself is commonly surrounded by titanite. In addition, some eclogite bodies show leucocratic segregations containing phengite, quartz, zoisite and/or kyanite. The important implication is that the complex exhumation path shows stages of initial cooling during decompression (formation of glaucophane) followed by reheating: a very similar situation to that reported for the coesite-bearing eclogite series of the Tso Morari massif, India, 450 km to the south-east.
Y1  - 2010
UR  - http://www.sciencedirect.com/science/journal/00244937
U6  - https://doi.org/10.1016/j.lithos.2009.07.015
SN  - 0024-4937
ER  - 
TY  - JOUR
A1  - Zack, Thomas
A1  - Konrad-Schmolke, Matthias
T1  - Distinguishing trace element redistribution during mineral reactions from fluid-induced trace element mobility in blueschists
Y1  - 2009
UR  - http://www.sciencedirect.com/science/journal/00167037
U6  - https://doi.org/10.1016/j.gca.2009.05.019
SN  - 0016-7037
ER  -