Steven C. Bergman

Petrology of Lamproites

Petrology of Lamproites: Roger H. Mitchell, S.C. Bergman ... Geochemistry and petrology of the Early Miocene lamproites ... Petrology of lamproites (Book, 1991) [WorldCat.org] Petrology of Lamproites (030643556X) by Mitchell, Roger H ... CLASSIFICATION OF LAMPROPHYRES, LAMPROITES, KIMBERLITES ... Mineralogy of Lamproites | SpringerLink Lamproite Wikipedia Petrogenesis of Proterozoic Lamproites and Kimberlites ... Kimberlite Wikipedia Petrology of Lamproites from Smoky Butte, Montana ... Lamproite an overview | ScienceDirect Topics Petrology of Lamproites 1991, Roger H. Mitchell, S.C ...

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

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).

A Miocene collisional belt in north Borneo: uplift mechanism and isostatic adjustment quantified by thermochronology

Subduction followed by underthrusting of continental lithosphere, driven by Oligocene–Early Miocene spreading in the South China Sea marginal basin, account for the tectonic features of Sabah. Isostatic rebound then caused Late Miocene uplift of the Western Cordillera. The strata were buried under 4–8 km of overburden then rapidly exhumed and cooled at >10°C Ma−1. A rate of exhumation of 0.5–0.7 mm a−1 is deduced from thermochronology. The same order of uplift in the Labuk Highlands has exposed metamorphic rocks of the epidote-glaucophane facies. Rapid erosion of the Western Cordillera supplied abundant clastic sediments to the Miocene–Pliocene Baram Delta oil-bearing basin and to the Eastern Lowlands and Sulu Sea. The Eastern Lowlands were affected by Miocene rifting of the Sulu Sea marginal basin. In contrast to the Western Cordillera, the strata contain apatite crystals whose fission track ages pre-date the containing rocks, indicating burial by only about 2–3 km of overburden. The terrain has been isostatically stable. Some apatite and all zircon crystals, extracted from Tertiary strata, yield Cretaceous fission track provenance ages.

Pennsylvanian pluton stitching of Wrangellia and the Alexander terrane, Wrangell Mountains, Alaska

A quartz monzonite-syenite-alkali granite plutonic complex in eastern Alaska crosscuts the contact of the Alexander terrane and Wrangellia and intrudes the basement rocks of both terranes. Zircon U-Pb data indicate an intrusion age of 309 {plus minus} 5 Ma (Middle Pennsylvanian) for the pluton, and {sup 40}K-{sup 40}Ar age for hornblende separates indicate cooling to about 450 C during Middle Pennsylvanian-Early Permian time. The new field relations and age data demonstrate the Wrangellia and the Alexander terrane were contiguous during the Middle Pennsylvanian. This conclusion provides an important new constraint on paleogeographic reconstructions of the northwest Cordillera, and necessitates reassessment of stratigraphic and paleomagnetic data that were cited as evidence that the terranes evolved separately until the late Mesozoic.

Tertiary Tectonic and magmatic evolution of western Sulawesi and the Makassar Strait, Indonesia: evidence for a Miocene continent-continent collision

Abstract New field and laboratory data from western Sulawesi, Indonesia, integrated with available data establish its Late Cenozoic igneous framework and a new model for its tectonic evolution. Western Sulawesi contains three major Neogene N-S-trending tectonic domains (from W to E): (1) an active foldbelt, in which Pliocene and Miocene volcanogenic rocks are involved in W-vergent thrusting which extends into the Makassar Strait; (2) a central belt comprised of a deformed submarine Miocene volcanoplutonic arc built on an Oligocene-Eocene clastic and carbonate platform with Latimojong Mesozoic basement metamorphic and sedimentary rocks thrust over its eastern margin on W-vergent faults; and (3) an accreted Cretaceous-Palaeogene(?) ophiolite (Lamasi Complex) between the Latimojong basement block and Bone Bay. The Lamasi Complex ophiolite includes dioritic plutons, basaltic sheeted dykes, pillow lavas, greenstones, tuffs and volcanic agglomerates with depleted (MORB-like) Sr & Nd isotope and REE characteristics of probable normal oceanic crust with possible subduction-related or back-arc affinity. New K-Ar, 40Ar-39Ar, Rb-Sr, and Nd-Sm isotope data suggest Cretaceous to Eocene crystallization and Oligocene to Miocene obduction. Late Miocene to Poliocene extrusive and intrusive rocks form a cogenetic volcanoplutonic complex of calc-alkalic to mildly alkalic, potassic, and shoshonitic felsic and mafic magmatic rocks of bimodal composition which were erupted and intruded during a short episode of Middle Miocene to Pliocene (3–18 Ma) lithospheric melting. Based on new Rb-Sr, Nd-Sm, and U-Pb isotope, and major and trace element geochemical data, parental source rocks of the Miocene melts were Late Proterozoic to Early Palaeozoic crustal and mantle lithospheric assemblages which became heated and melted owing to a continent-continent collision in which west-vergent continental lithosphere derived from the Australian-New Guinea plate was subducted beneath eastern-most Sundaland. The timing of this magmatism and subsequent cooling and denudation history are constrained by 113 new K-Ar, 40Ar-39Ar, and fission track ages. The new tectonic model differs significantly from previous models: the Makassar Strait is now interpreted as a foreland basin bound on both sides by converging Neogene thrust belts, in contrast to previous models suggesting Late Tertiary oceanic spreading or continental rifting. West-vergent obduction of a pre-Eocene oceanic, primitive arc, or back-arc crust onto western Sulawesi occurred during late Oligocene to Miocene times. The Late Miocene western Sulawesi magmatic arc is envisioned as a continent-continent collision product, in contrast to previous models involving a normal ocean-continent or ocean-ocean subduction-related magmatic arc (west or east vergent) or post-subduction rifting. The east Sulawesi ophiolite extends into western Sulawesi, suggesting that Bone Bay resulted from collapse of the over-thickened Miocene orogen. The new tectonic model illustrates the central role western Sulawesi plays in unlocking the complex evolution of Indonesia as well as the temporal and magmatic details of a continent-continent collision zone.

Carbon Dioxide in igneous petrogenesis: I

AbstractA number of experimental CO2 solubility data for silicate and aluminosilicate melts at a variety of P- T conditions are consistent with solution of CO2 in the melt by polymer condensation reactions such as SiO4(m4−+CO2(v)+SinO3n+1(m)(2n+1)⇌Sin+1O3n+4(m)(2n+4)−+CO3(m)2−.For various metalsilicate systems the relative solubility of CO2 should depend markedly on the relative Gibbs free change of reaction. Experimental solubility data for the systems Li2O-SiO2, Na2O-SiO2, K2O-SiO2, CaO-SiO2, MgO-SiO2 and other aluminosilicate melts are in complete accord with predictions based on Gibbs Free energies of model polycondesation reactions.A rigorous thermodynamic treatment of published P- T-wt.% CO2 solubility data for a number of mineral and natural melts suggests that for the reaction CO2(m) ⇌ CO2(v)(1)CO2-melt mixing may be considered ideal (i.e., {

Proterozoic lithospheric mantle source for the Prairie Creek lamproites: Re-Os and Sm-Nd isotopic evidence

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Postorogenic denudation along the late Paleozoic Ouachita trend, south central United States of America: Magnitude and timing constraints from apatite fission track data

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