Development of zircon and other Zr phases in hydrothermal deposits indicates that Zr can be highly mobile in these systems. Mobility is most common in, but not restricted to, F-rich hydrothermal systems related to alkalic, F-rich igneous suites; these suites can range from peralkaline through metaluminous to peraluminous. A few examples are neither alkalic nor F rich. Three locations in the Trans-Pecos Magmatic Province, Texas, U.S.A., demonstrate this hydrothermal Zr mobility. All three igneous systems are alkalic and F rich but vary in alkali/Al ratios. Peralkaline rhyolites and trachytes in the Christmas Mountains contain as much as 2100 ppm Zr, mostly in aegirine or arfvedsonite; zircon is rare or absent

The mobility of zirconium and other immobile' elements during hydrothermal alteration

Apatites from the major types of mainly magmatic-hydrothermal mineral deposits (30 localities, mostly in British Columbia, Canada) together with apatites from carbonatites (29 intrusive complexes) and unmineralized rocks (11 localities) have been analyzed by electron microprobe and laser ablation-inductively coupled plasma mass spectrometry. Discriminant analysis using Mg, V, Mn, Sr, Y, La, Ce, Eu, Dy, Yb, Pb, Th, and U reveals that apatites from mineral deposits can be distinguished from apatites in carbonatites and unmineralized rocks. Apatites from mineral deposits are characterized by higher Ca and correspondingly lower total contents of trace elements that partition onto the Ca sites (rare earth elements (REEs), Y, Mn, Sr, Pb, Th, and U) than apatites from unmineralized rocks and carbonatites. Apatites from the different deposit types also have distinct trace element compositions that are readily discriminated by the discriminant functions. Apatites from worldwide carbonatites have the most fractionated REE distributions with light REE enrichment (Ce/Yb CN = 35–872), high V (1.6–1,466 ppm), Sr (1,840–22,498 ppm), Ba (1.8–275 ppm), and Nb (0.4–19 ppm) contents, the lowest W contents (0.05–0.55 ppm), and no significant Eu anomalies (Eu/Eu* = 0.9–1.2). Apatites from alkalic porphyry Cu-Au deposits in the North American Cordillera possess high V contents (2.5–337 ppm), whereas apatites from calc-alkaline porphyry Cu-Au and Cu-Mo deposits have high Mn contents (334–10,934 ppm) and typically large negative Eu anomalies (Eu/Eu* = 0.2–1.1). Apatites from iron oxide Cu-Au (IOCG) and related Kiruna-type iron oxide-apatite (IOA) deposits in Canada, China, and Mexico typically have large negative Eu anomalies (Eu/Eu* = 0.2–1.5) and low Mn contents (40–5,753 ppm). Apatites from orogenic Ni-Cu, porphyryrelated Cu-Au breccia, Au-Co skarn, Pb-Zn skarn, and Cu skarn deposits have relatively low abundances of impurity cations. This study demonstrates that detrital apatite grains collected during regional geochemical surveys are effective in identifying specific types of buried mineral deposits in glaciated terranes.

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Apatite Trace Element Compositions: A Robust New Tool for Mineral Exploration

Permian-Triassic boundary microbialites (PTBMs) are thin (0.05-15 m) carbonates formed after the end-Permian mass extinction. They comprise Renalcis-group calcimicrobes, microbially mediated micrite, presumed inorganic micrite, calcite cement (some may be microbially influenced) and shelly faunas. PTBMs are abundant in low-latitude shallow-marine carbonate shelves in central Tethyan continents but are rare in higher latitudes, likely inhibited by clastic supply on Pangaea margins. PTBMs occupied broadly similar environments to Late Permian reefs in Tethys, but extended into deeper waters. Late Permian reefs are also rich in microbes (and cements), so post-extinction seawater carbonate saturation was likely similar to the Late Permian. However, PTBMs lack widespread abundant inorganic carbonate cement fans, so a previous interpretation that anoxic bicarbonate-rich water upwelled to rapidly increase carbonate saturation of shallow seawater, post-extinction, is problematic. Preliminary pyrite framboid evidence shows anoxia in PTBM facies, but interbedded shelly faunas indicate oxygenated water, perhaps there was short-term pulsing of normally saturated anoxic water from the oxygen-minimum zone to surface waters. In Tethys, PTBMs show geographic variations: (i) in south China, PTBMs are mostly thrombolites in open shelf settings, largely recrystallised, with remnant structure of Renalcis-group calcimicrobes; (ii) in south Turkey, in shallow waters, stromatolites and thrombolites, lacking calcimicrobes, are interbedded, likely depth-controlled; and (iii) in the Middle East, especially Iran, stromatolites and thrombolites (calcimicrobes uncommon) occur in different sites on open shelves, where controls are unclear. Thus, PTBMs were under more complex control than previously portrayed, with local facies control playing a significant role in their structure and composition.

Microbialites and global environmental change across the Permian-Triassic boundary: a synthesis.

The Zagros fold-and-thrust belt of SW Iran is a young continental convergence zone, extending NW–SE from eastern Turkey through northern Iraq and the length of Iran to the Strait of Hormuz and into northern Oman. This belt reflects the shortening and off-scraping of thick sediments from the northern margin of the Arabian platform, essentially behaving as the accretionary prism for the Iranian convergent margin. Distribution of Upper Cretaceous ophiolites in the Zagros orogenic belt defines the northern limit of the evolving suture between Arabia and Eurasia and comprises two parallel belts: (1) Outer Zagros Ophiolitic Belt (OB) and (2) Inner Zagros Ophiolitic Belt (IB). These belts contain complete (if disrupted) ophiolites with well-preserved mantle and crustal sequences. Mantle sequences include tectonized harzburgite and rare ultramafic–mafic cumulates as well as isotropic gabbro lenses and isolated dykes within the harzburgite. Crustal sequences include rare gabbros (mostly in IB ophiolites), sheeted dyke complexes, pillowed lavas and felsic rocks. All Zagros ophiolites are overlain by Upper Cretaceous pelagic limestone. Limited radiometric dating indicates that the OB and IB formed at the same time during Late Cretaceous time. IB and OB components show strong suprasubduction zone affinities, from mantle harzburgite to lavas. This is shown by low whole-rock Al2O3 and CaO contents and spinel and orthopyroxene compositions of mantle peridotites as well as by the abundance of felsic rocks and the trace element characteristics of the lavas. Similarly ages, suprasubduction zone affinities and fore-arc setting suggest that the IB and OB once defined a single tract of fore-arc lithosphere that was disrupted by exhumation of subducted Sanandaj–Sirjan Zone metamorphic rocks. Our data for the OB and IB along with better-studied ophiolites in Cyprus, Turkey and Oman compel the conclusion that a broad and continuous tract of fore-arc lithosphere was created during Late Cretaceous time as the magmatic expression of a newly formed subduction zone developed along the SW margin of Eurasia.

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Geodynamic evolution of Upper Cretaceous Zagros ophiolites: formation of oceanic lithosphere above a nascent subduction zone

Carboniferous mantle-derived felsic intrusion in the Chinese Altai, NW China: Implications for geodynamic change of the accretionary orogenic belt

The behaviour of trace and rare earth elements (REE) during hydrothermal alteration in the Rangan area (Central Iran)

A-type granite of the Hasan Robat area (NW of Isfahan, Iran) and its tectonic significance

The Nain ophiolite is a highly dismembered ophiolite complex cropping out at the north of the Nain town to the west of central Iran. The igneous rocks of this complex consist of both mantle and crustal suites and include serpentinized peridotites, peridotites, harzburgites associated with dunite and lherzolite, pegmatitic and isotropic gabbros, plagiogranites, sheeted dikes and pillow lavas. Several pyroxenite, wehrlite and rodingite dikes are present in the ultrabasic rocks. The sheeted dikes include subalkaline basalts, basaltic andesites and andesites. Their magma was of sub-alkaline (low potassium tholeiite) type and they are chemically similar to island arc tholeiitic basalts. The N-MORB-normalized incompatible elements for the sheeted dike samples indicate depletion in most of the high field strength elements (HFSE). The concentrations of the large ion lithophile elements (LILE) in these rocks are all greater than those in the N-MORB. Significant chemical characteristics of the these rocks are the positive anomaly for Th and negative anomaly of Nb that are considered to represent a subduction zone component. The chondrite-normalized rare earth element (REE) patterns of these rocks show HREE enrichment and LREE depletion [(LaN/SmN)ave = 0.63]. Their geochmistry also shows that the primary melt derived from high degrees of partial melting of a mantle source previously depleted with respect to the source of mid-ocean ridge basalts, and were subsequently enriched by aqueous fluids driven off subducted oceanic lithosphere in an arcbasin setting. We conclude that the Nain ophiolite is a supra-subduction zone type ophiolite.

Geochemistry of sheeted dikes in the nain ophiolite (central iran)

The significance of mafic microgranular enclaves in the petrogenesis of the Dehno Complex, Sanandaj–Sirjan belt, Iran

The nature of hydrothermal fluids in the Kahang porphyry copper deposit (Northeast of Isfahan) based on mineralography, fluid inclusion and stable isotopic data

Mahmoud Khalili

Papers

The behaviour of trace and rare earth elements (REE) during hydrothermal alteration in the Rangan area (Central Iran)

A-type granite of the Hasan Robat area (NW of Isfahan, Iran) and its tectonic significance

Geochemistry of sheeted dikes in the nain ophiolite (central iran)

The significance of mafic microgranular enclaves in the petrogenesis of the Dehno Complex, Sanandaj–Sirjan belt, Iran

The nature of hydrothermal fluids in the Kahang porphyry copper deposit (Northeast of Isfahan) based on mineralography, fluid inclusion and stable isotopic data