ORIGINAL PAPER Chemical heterogeneity in an enderbite-hosted pseudotachylite, eastern India: evidence for syn-deformation multi-reaction melting in pseudotachylite Radhika Patro • S. N. Mahapatro • A. Bhattacharya • N. C. Pant • J. K. Nanda • A. Dey • A. K. Tripathy Received: 13 October 2009 / Accepted: 15 June 2010 / Published online: 7 July 2010 Ó Springer-Verlag 2010 Abstract The origin of chemical and mineralogical het- erogeneity in tens-of-microns wide layers and domains in enderbite-hosted couple-of-centimeters wide pseudotachy- lite vein is examined based on the results of BSE and X-ray element imaging, and electron probe microanalyses of major elements of host-rock minerals, clasts, micro- phenocrysts, and pseudotachylite matrix. The pseudo- tachylite layers and domains containing variable proportions of orthopyroxene and magnetite microphenocrysts continue as mantles around quartz, K-feldspar, plagioclase and gar- net clasts. The clasts are chemically modified along margins and intra-clast pseudotachylite injections. The chemical modifications are extensive in smaller clasts \ 5 lm diam- eter. At least three chemically distinct layers and domains in the pseudotachylite, and their fine-grained matrices, plot in sharply defined, well-segregated and non-overlapping fields in FeO ? MgO-Al 2 O 3 –SiO 2 , FeO–CaO–MgO and CaO– Na 2 O–K 2 O and FeO vs. FeO/FeO ? MgO diagrams. The compositions of the layers and domains—smeared between a feldspar ? quartz component and a ferromagnesian component of garnet ? Fe–Ti oxides (±orthopyroxene)— possibly correspond to fractionated quenched melts, or admixtures of microphenocrysts that cannot be resolved by the microbeam techniques employed. The compositional variations are incompatible with deformation-driven crystal fractionation in melt. Instead the layers and domains pos- sibly are crystal-melt mushes produced by syn-deformation ultra-high temperature (1,250–1,375°C) melting reactions involving variable proportions of host-rock minerals determined by time-transient local phase aggregates expe- riencing strain. The similar element variation trends in pseudotachylite examined here and those reported from anorthosite, metapelite and charnockite elsewhere suggests local phase aggregate controlled multi-reaction melting is a phenomenon commoner than hitherto realized in pseudotachylites. Keywords Pseudotachylite  Micron-scale layering  Mineral–chemical heterogeneity  Multi-reaction melting  Ultra-high T melting Introduction Pseudotachylites are formed by extremely rapid crystalli- zation (Macaudiere et al. 1985; Obata and Karato 1995; Plattner et al. 2003) of melts produced by friction-induced heating (Han et al. 2007; Hirose and Shimamoto 2005a, b). The estimated melting temperatures reportedly vary from high (650–700°C, Lund and Austrheim 2003; [ 700°C, Clarke and Norman 2007) obtained from conventional thermo-barometry to ultra-high (1,300°C, Brownell 1958, *1,350°C; Gibson 2002, 1,100°C; Toyoshima 1989, 1,060–1,200°C; Allen et al. 2002, [ 1,400°C; Plattner et al. 2003, [ 1,070°C; Skrotzki et al. 1990; minimum melt Communicated by T. L. Grove. R. Patro  A. Bhattacharya (&)  A. Dey Department of Geology and Geophysics, Indian Institute of Technology, Kharagpur 721 302, India e-mail: abbhat55@rediffmail.com S. N. Mahapatro  A. K. Tripathy Geological Survey of India, Bhubaneswar 751 012, India N. C. Pant Department of Geology, Delhi University, Delhi 110 007, India J. K. Nanda Geological Survey of India, S-4/113 Niladrivihar, Bhubaneswar 751021, India 123 Contrib Mineral Petrol (2011) 161:547–563 DOI 10.1007/s00410-010-0548-5