Karsten Secher

Bio: Karsten Secher is an academic researcher from Geological Survey of Denmark and Greenland. The author has contributed to research in topics: Ultramafic rock & Kimberlite. The author has an hindex of 7, co-authored 23 publications receiving 317 citations.

Kimberlites and other ultramafic alkaline rocks in the Sisimiut–Kangerlussuaq region, southern West Greenland

Abstract: The alkaline province of southern West Greenland includes swarms of dykes described as kimberlites and lamproites (Larsen 1991), and these rock types are widely distributed in the Sisimiut‐Sarfartoq‐Kangerlussuaq region (Figs 1, 2). Kimberlites and lamproites are potential carriers of diamond, and since the description of the Sarfartoq carbonatite complex and the kimberlitic dykes related to this complex (Larsen 1980; Secher & Larsen 1980), the Sisimiut‐Sarfartoq‐Kangerlussuaq region has seen several campaigns of commercial diamond exploration. The latest and most persistent stage of exploration began in the mid-1990s and has continued to date, with varying intensity. Numerous reports of diamond-favourable indicator minerals from till sampling, finds of kimberlitic dykes, and recovery of actual diamonds from kimberlitic rocks have emerged since 1995 (Olsen et al. 1999). A drilling programme in late 2001 confirmed the unusually great length and width of a magnetic kimberlitic dyke (Ferguson 2001). The alkaline ultramafic dykes within the Sisimiut‐ Kangerlussuaq and Sarfartoq regions intrude the border zone between the Archaean craton and the Palaeoproterozoic Nagssugtoqidian orogen (van Gool et al. 2002, this volume). This border is defined as the southern boundary of Palaeoproterozoic reworking of the Archaean basement gneisses. The reworking has affected the Palaeoproterozoic Kangâmiut dolerite dykes, which

The Continuum of Primary Carbonatitic-Kimberlitic Melt Compositions in Equilibrium with Lherzolite: Data from the System CaO-MgO-Al2O3-SiO2-CO2 at 6 GPa

Abstract: -free CMAS solidus. The aimof this study was to trace the compositional path of thisline and determine the compositions of coexisting phases.The advantage of this approach is that bulk compositionscan be constructed that maximize the amount of liquidto facilitate analysis. As long as all five phases are present,the system remains invariant at constant temperatureand pressure; and adjustments of the starting composition

Lamproites and other potassium-rich igneous rocks: a review of their occurrence, mineralogy and geochemistry

Abstract: Summary In this paper the geological occurrence, geochemistry and mineralogy of ultrapotassic (K2O/Na2O > 3 (molar ratio)) and perpotassic (K2O/Al2O3 > 1 (molar ratio)) igneous rocks, especially lamproites, are reviewed and discussed in the context of compositionally-similar mantle-derived melts. Lamproites are K- and Mg-rich igneous rocks (typically K2O > 5 wt.%, MgO > 5 wt.%) which possess an exotic and diagnostic mineralogy and geochemistry. Known lamproites occur in 21 major suites or localities in continental regions with a variety of geological and tectonic environments; they range in age from the early Proterozoic dykes at Holsteinsborg, W Greenland, and Chelima, India, and Precambrian pipe at Argyle, W Australia, to the Middle Pleistocene flows and the Recent volcanics of the Leucite Hills, Wyoming, and Gaussberg, Antarctica, respectively. Intrusive and extrusive forms of lamproites include flows, a variety of pyroclastics (welded tuffs, piperno, air-fall tuffs, volcanic breccias etc.), cinder cones, dykes, sills and diatremes. Whereas kimberlite diatremes tend to be carrot shaped, the shape of olivine lamproite diatremes approximates a sherbet-glass. The recent discovery of diamondiferous lamproties of large volumetric proportion in the E and W Kimberleys, NW Australia, and the reclassification of the diamondiferous micaceous peridotite at Prairie Creek, Arkansas, as a lamproite substantiate their economic importance. The 21 lamproite suites considered here tend to be localized marginal to continental craton cores in areas that overlie fossil Benioff zones, in contrast with the general occurrence of kimberlites more interior to continental cratons. The petrographic diversity of lamproites has historically hindered the development of a concise and universal classification and nomenclature. Lamproites are distinguished from kimberlites and alkali basalts (and lamprophyres) in terms of mineralogy, mineral chemistry, geochemistry and volcanic extrusive character. Relative to kimberlites, lamproites are enriched in K, Si, Ti, Al, Rb, Sr, Zr and Ba and depleted in CO2, Ca, Mg, Fe, Ni, Co and Cr. Lamproites are characterized by the general presence of phlogopite, diopside, leucite and K-richterite, occasional glass, olivine, sanidine, priderite, perovskite, wadeite, apatite and chrome spinel, and very rare ilmenite. Lamproite amphiboles, diopsides and phlogopites are distinctly depleted in Al2O3 relative to those of nearly all other igneous rocks. Lamproite magmas are produced by the partial melting of old refractory mantle peridotite (approaching a dunite or harzburgite in mineralogy) that was enriched in K-bearing and other incompatible-element-enriched phases, such as phlogopite and apatite, most probably as a result of some metasomatic event which occurred prior to melting. In contrast with alkali basalt and kimberlite melts which are apparently produced from the partial melting of a CO2-enriched mantle periodtite (i.e. a source with a relatively high CO2/H2O ratio), water is the key volatile species involved with lamproite petrogenesis (source with a low CO2/H2O ratio).