Goldschmidt 2012 Conference Abstracts Tracing crustal contamination along Multi-scale modeling of transverse the Java segment of Sunda Arc, reactive mixing in a coastal aquifer 1,3* 1 1,2 Indonesia H. M. NICK , A. RAOOF , M. THULLNER , P.A.G. REGNIER3 JOLIS, E. M.1*, TROLL, V. R.1, 4, DEEGAN, F. M. 2, 1Faculty of Geosciences, Utrecht University, Utrecht, The BLYTHE, L. S. 1, HARRIS, C.3, FREDA, C. 4, HILTON, D. 5, Netherlands (*correspondence: [email protected], [email protected]) 6 6 CHADWICK, J. , VAN HELDEN, M. 2Department of Environmental Microbiology, UFZ – Helmholtz Centre for Environmental Research, Leipzig, Germany 1 Dept. Earth Sciences, CEMPEG, Uppsala, Sweden ([email protected]) (*[email protected]) 3Department of Earth and Environmental Sciences, Université Libre 2 Lab. for Isotope Geology, SMNH, Stockhom, Sweden de Bruxelles, Brussels, Belgium ([email protected]) 3 Dept. of Geological Science, UCT, South Africa 4 Istituto Nazionale di Geofisica e Vulcanologia, Rome, Italy The transverse mixing between freshwater and seawater in 5 Scripps Oceanographic Institute, San Diego, USA 6 Dept. Petrology, Vrije, Universiteit Amsterdam, Netherlands coastal aquifers is a key process controlling the chemistry of submarine groundwater discharge (SGD). The quantification of such Arc magmas typically display chemical and petrographic mixing and its effects on the fate of reactive chemical compounds in characteristics indicative of crustal input. Crustal contamination can take place either in the mantle source region or as magma coastal waters are still the subject of debate. We developed reactive traverses the crust (e.g. [1]). While source contamination is transport model approaches to study the mechanisms responsible for generally considered the dominant process (e.g. [2, 3, 4]), crustal contamination in high level magma chambers has also controlling reactive mixing processes in coastal aquifers. These been recognised at volcanic arcs (e.g. [5, 6]). In light of this, we models employ hybrid numerical methods for solving flow and aim to test the extent of upper crustal versus source contamination along the Java segment of the Sunda arc, which, transport [1,2], and benefit from utilizing the biogeochemical because of its variable upper crustal structure, is ideal for the reaction network simulator (BRNS) [3]. task. We present a detailed geochemical study of 7 volcanoes Critical to advancing our understanding is the study of the along a traverse from Anak-Krakatau in the Sunda strait interplay between reaction and flow. We particularly investigated the through Java (Gede, Slamet, Merapi, Kelut, Kawah-Ijen) and Bali (Batur). Using rock and mineral elemental geochemistry impact of dispersion, heterogeneity induced velocity variations and and radiogenic (Sr, Nd and Pb) and, stable (O) isotopes, we show a correspondence between changes in composition of the biogeochemical reactivities on reactive transport for density driven upper crust and the apparent degree of upper crustal flow scenarios representing seawater-groundwater-interface in contamination. There is an increase in 87Sr/86Sr and δ18O, and a decrease in 143Nd/144Nd from Krakatau towards Merapi, coastal aquifers. Our numerical observation showed e.g., that for indicating substantial input from the thick quasi-continental highly reactive dissolved organic carbon (DOC) degradation basement beneath East and Central Java. Volcanoes to the east of Merapi, and the Progo-Muria fault zone, where the upper processes are limited by the porous media properties controlling crust is thinner and increasingly oceanic in nature have lower dispersion, whereas for relatively less reactive DOC degradation is 87Sr/86Sr and δ18O, and higher 143Nd/144Nd indicating a stronger influence of the mantle source [7]. Our new data represent a controlled by reaction kinetics. systematic and high-resolution arc-wide sampling effort that In general, we found three reactive flow regimes: reaction allows us to distinguish the effects of the upper crust on the compositional spectrum of individual volcanic systems along controlled, reaction-dispersion controlled and dispersion the Sunda arc. controlled transport. This is supported by further simulations utilizing pore-scale models to investigate these regimes at the [1] Davidson, J.P, Hora, J.M, Garrison, J.M & Dungan, M.A smaller scale. Our results suggest that the chemical reactivity as (2005), J. Geotherm. Res., 140, 157-170. well as dispersivity are important parameters governing the [2] Hilton, D.R., Fischer, T.P. & Marty, B. (2002), Rev. Mineral. Geochem., 47, 319-370. biogeochemical dynamics of SGD. Hence, an adequate [3] Gertisser, R. & Keller, J. (2003). J. Petrol., 44, 457-489 representenation of these processes in the macro-scale models is [4] Debaille, V., Doucelance, R., Weis, D., & Schiano, P. (2005), Geochim. Cosmochim. Acta, 70,723-741. essential. [5] Gasparon, M., Hilton, D.R., & Varne, R. (1994), Earth Planet. Sci. Lett., 126, 15-22. [1] S.K. Matthai, et al. (2009) Transport in Porous Media 83, 289- [6] Chadwick, J.P., Troll, V.R., Ginibre, C., Morgan, D., 318. Gertisser, R., Waight, T.E. & Davidson, J.P. (2007), J. Petrol., [2] A. Raoof, et al. (2010) Vadose Zone Journal 9, 624-636. 48, 1793-1812. [3] P. Regnier, et al. (2002) Applied Mathematical Modeling 26, [7] Whitford, D.J. (1975), Geochim. Cosmochim. Acta, 39, 913-927. 1287-1302. Mineralogical Magazine | www.minersoc.org 2045 Downloaded from http://pubs.geoscienceworld.org/minmag/article-pdf/76/6/2045/2920060/gsminmag.76.6.13-M.pdf by guest on 25 September 2021 Goldschmidt 2012 Conference Abstracts Mantle Evolution from Plate Heterogeneous mantle sources of the Subduction to Post-orogenic alkaline-tholeiitic intraplate basalts Extension: Evidence from Permo- from the Aleppo Plateau, NW Syria 1,2* 2 3 Triassic Mafic Dike Swarms in GEORGE S.-K. MA , JOHN MALPAS , KATSUHIKO SUZUKI , 4 1 1 Northern Tibet Plateau CHING-HUA LO , KUO-LUNG WANG , YOSHIYUKI IIZUKA 2 AND COSTAS XENOPHONTOS CHANGQIAN MA1,2*, JINYANG ZHANG2, FUHAO 1IES, Academia Sinica, Taipei 11529, Taiwan, 2 2 2 2 XIONG , BIN LIU , JIAN HUANG AND BAIHUA WANG [email protected] 1 State Key Lab. of Geological Processes and Mineral Resources, 2Department of Earth Sciences, The University of Hong Kong, Hong Wuhan, China, [email protected] (* presenting author) Kong 3IFREE, JAMSTEC, Japan 2 China University of Geosciences,Wuhan,China 4Department of Geosciences, National Taiwan University, Taiwan Five large mafic dike swarms have been discovered within the ~270 km-long Xiangride-Golmud segment of the East Kunlun belt, Mantle-derived magmas are characterised by considerable chemical and isotopic variability that is difficult to reconcile with Northern Tibet Plateau, which are named, from east to west, the partial melting of a peridotite mantle alone. This reflects the Balong, Binggou, Xiaomiao, Bairiqili and Nanshankou dyke swarms. presence of heterogeneities in the mantle, originated from, for The number of dikes in a given swarm can vary from 10 to 42, and instance, recycled oceanic crust or metasomatised lithosphere [1, 2, the width of individual dikes ranges from 0.1 to 5 m. Most of the 3]. Identification of such heterogeneities and thus the mineralogy of the mantle source becomes more ambiguous because both crustal dikes trend N-S. The widest dikes are clearly banded with coarser contamination and crystal fractionation may mask important source textures and more phenocrysts in the middle portions than in the characteristics. margins. Most of the dikes are porphyritic diabase with the coarser- We present age, chemical and isotopic data to constrain the grained varieties grading into diorites. All of the mafic dikes are source and the chemical evolution of the continental alkaline- composed chiefly of clinopyroxene, plagioclase and amphibole. tholeiitic intraplate magmas from the Aleppo Plateau and vicinity, NW Syria. With the aid of new 40Ar/ 39Ar ages, two phases of Based on the field relationships, hornblende Ar-Ar and zircon volcanism have been recognised in the Miocene, ~19-18 Ma (Phase U-Pb dating we consider that the dike swams were formed in three 1) and ~13.5-12 Ma (Phase 2), in the studied area. The chemical and 87 86 143 144 episodes; Early Permian, late Permian and Triassic to Late Triassic. isotopic compositions [ Sr/ Sr = 0.7036-0.7051, Nd/ Nd = 0.51269-0.51287 and (187Os/188Os) = 0.151-0.453] of the lavas The Xiaomiao (277 Ma) and Binggou (225 Ma) mafic dikes are t reflect the unequivocal influence of crustal assimilation and calc-alkaline in composition with low ∑REE (˘100 ppm) and fractional crystallisation. However, it is interpreted that the two relatively flat, chondrite-normalized REE patterns with no Eu phases of volcanism likely sampled a mineralogically heterogeneous anomalies. These rocks also have low Ni, Cr and V but are enriched source, as reflected by their compositional variations seen in the in Rb, K, Pb and P, and depleted in Nb and Ta. In contrast, the Balong most-primitive, least contaminated magmas. Such variations are: (1) relatively high Si, low Ti and trace-element contents in the Phase 1 dike swarms (253 Ma) have high ∑REE (~100 to >150 ppm˅and lavas, consistent with partial melting of a largely peridotitic mantle are enriched in HREE, with higher trace element contents than the source; (2) relatively low Si, high Ti, Fe, Ca, P, alkalis, and L- other dikes. The Xiaomiao and Binggou dike swarms have similar MREE/HREE, plus sub-chondritic Th-(U)/Nb, Pb/Ce and Zr/Sm in Sr-Nd isotopic characteristics with ISr = 0.707-0.711 and εNd(t) the Phase 2 lavas, approaching compositions of experimental melts ranges from -3.4 to 3.9, whereas the Bairiqili (251 Ma) and Balong of amphibole-rich metasomatic veins [3]. Thus, it is inferred that the Syrian lithosphere had been pervasively metasomatised and dikes have somewhat more enriched and variable compositions, with contained veins of amphibole-rich cumulates shortly before ISr = 0.709-0.719 and εNd(t) ranging from -7.8 to -3.6.