Petrogenesis of Late Mesozoic Calc-Alkaline Lamprophyres from Sulu UHP Terrane, Eastern China: Implications to Paleo-Pacific Plate Subduction and Destruction of the North China Craton

Destruction of the North China Craton has caused extensive concern on its multiple potential mechanisms including thermal erosion,chemical erosion and delamination.It is widely accepted that thinning of the

Lamprophyre Rocks in the Nassara Gold Deposit, Southwest Burkina Faso: Characteristics and Implication for Mining Exploration

The lamprophyres are late dykes that cut the formations hosting the gold mineralization in the Nassara deposit. They are geographically and spatially related to most orogenic gold deposits. It is with the aim of characterizing them and seeing their implications for exploration that this work is carried out. To achieve our objective, petrographic studies and chemical analyses of minerals (pyroxenes, amphiboles, feldspars, chromite) and geochemical analyses of total rock were carried out. These studies have enabled us to classify the Nassara lamprophyres as calc-alkaline lamprophyres of the spessartite type. The Cr, Co, Ni and Mg enrichment of these rocks would indicate a depleted mantle source, with LILE enrichment by fluids probably related to metasomatic activity. The various diagrams show that they are depleted in HREE and enriched in LREE. The high Nb/Ta ratios in our data indicate metasomatic activity probably linked to amphibole and rutile in the mantle prior to melting. The geodynamic context of spessartite-type lamprophyres indicates a signature linked to late-orogenic to post-collisional subduction. They are late-orogenic to post-collisional lamprophyres enriched in compatible elements (Cr, Ni, Co) and display a negative Ta-Nb-Ti (TNT) anomaly. The frequent association of these lamprophyre dykes with the deposits does not indicate the source of the gold for these deposits, but rather zones of crustal permeability capable of draining hydrothermal fluids at the time of emplacement. Good mapping of lamprophyre dykes, especially in shear zones, could therefore guide prospecting and identify potential zones of hydrothermal fluid circulation.

First Evidence of Lamprophyric Magmatism from the Konya Region, Turkey:a Genetic Link to High-K Volcanism

In the vicinity of Konya （Turkey）,mafic,micro-porphyritic sub-volcanic rocks intrude into the Mesozoic units,which represents the only example of such a rock type in the region.40Ar/39Ar dating of two whole rock samples from the sub-volcanics gave ages of 13.72±0.13 and 12.40±0.11 Ma,suggesting temporal association to the Late Miocene-Pliocene high-K calc-alkaline volcanism in the region.The mineral chemistry and geochemical data permit us to classify the rocks as ＂minette＂ lamprophyres.They include diopside and phlogopite phenocrysts in a microcrystalline groundmass composed of sanidine,phlogopite,diopside and titano-magnetite.Segregation and ocelli-like globular structures occur commonly in the samples.In terms of major elements,the lamprophyres are calcalkaline,and potassic to ultrapotassic rocks.All the lamprophyres display strong enrichments in LILE （Rb,Ba,K,Sr）,radiogenic elements （Th,U） and LREE （La,Ce） and prominent negative Nb,Ta,and Ti anomalies on primordial mantle-normalized trace element diagrams.Geochemical data suggest that the lamprophyres and high-K calc-alkaline rocks in the region derived from a subduction-modified lithospheric mantle source affected by different metasomatic events.Lamprophyric magmatism sourced phlogopite-bearing veins generated by sediment-related metasomatism via subduction,but high-K calc-alkaline magmas are possibly derived from a mantle source affected by fluid-rich metasomatism.

湖南锡矿山超大型锑矿床煌斑岩脉地质地球化学特征

湖南锡矿山超大型锑矿床是世界上已知最大的锑矿床,本文对该矿床矿区内唯一的岩浆活动显示——煌斑岩脉进行了较系统研究,研究表明该岩脉为幔源成因,结晶分异程度较低,其微量元素、稀土元素特征均表明锑矿床所在壳体的上地幔部分曾发生过广泛地幔交代作用,存在锑元素的富集。

大别山燕子河云斜煌岩的地质背景和岩石学基本特征

根据野外地质特征,大别山燕子河云斜煌岩脉是与燕山期后造山中酸性岩浆活动有时空联系的。所以,云斜煌岩脉及与其有成因联系的以减压为标志的麻粒岩相变质也发生在燕山期。云斜煌岩在矿物构成、岩石结构、岩石化学(主元素、稀土模式和微量元素蜘蛛图解)的特点都归属钙碱性煌斑岩,但它可能不是金的矿源。其SiO2含量和镁质指数偏低、CaO含量较高、缺乏高压矿物捕虏晶以及黑云母成分富钛指示的低压结晶条件表明它与原生基性岩浆有直接成因联系的可能性不大;相反它可能代表后来中酸性岩的母岩浆。其黑云母成分富钛指示的高氧逸度条件、岩石化学准铝型、稀土模式强烈右倾、耦合的TNT负异常等特征指示成岩中有陆壳物质(泥质或泥灰质)掺入。云斜煌岩浆的形成可能与大别碰撞造山带后造山伸张时减薄地壳在挥发份作用下减压重熔有关。