Similar lamprophyres also occur in the southern Sulu area in the Jiaodong Peninsula (e.g., 120 Ma; Deng et al., 2017) and the villages of Xiaya and Jingziyu in the western Luxi area (e.g., 130 Ma; Yang et al., 2019). Outcrops of the lamprophyres, which can usually be traced for less than 500 feet, range in width from 2 to 25 Ieet. lamprophyre may and often does contain all four minerals but is named according to the two which predominate. They generally strike at 050 to 055 degrees and dip steep to vertical, but occasionally Is a melilitic lamprophyre that usually contain between 10-30% of feldspathoids (Nepheline and Hauyne) and it normally contains the same minerals as occur in alnöite. lamprophyre dyke swarms occur widely in the Jiaodong Peninsula and they are thus suitable for constraining the c ompositions, ori- gins, and mechanisms of mantle metasomatism (e.g., Deng et al., Lamprophyre rocks are melanocratic or mesotype rocks hypabyssal rocks. They typically occur as shallow dikes, sills, plugs, or stocks. The iamprophyres are of two types, sodic syenites and sodic diorites. magmas which have undergone varying but generally low degrees of polybaric fractionation, together perhaps with mixing of more primitive and fractionated batches, during their ascent through the crust. Gem sapphires also occur as xenocrysts in alkaline basic lamprophyre such as for the Yogo Gulch deposit in Montana (Brownlow and Komorowski, 1988; Renfro et al., 2018), as mafic dikes of biotite monchiquite called ouachitite, a lamprophyre characterized by an abundance of phlogopite and brown amphibole, olivine, clinopyroxene, and analcime. Any of a heterogeneous group of gray to black, mafic igneous rocks characterized by a distinctive panidiomorphic and porphyritic texture in which abundant euhedral, dark-colored ferromagnesian (femic) minerals (dark mica, amphibole, pyroxene, olivine) occur in two generations—both early as phenocrysts and later in the matrix or groundmass—while felsic minerals … Wideiy scattered dark gray lamprophyre dikes in the Mount Rosa area strike generally north-northlvest and dip steeply. There are many different rocks grouped under the heading lamprophyre. Alnoite; From Alno island, Sweden. Feldspar is restricted to the ground mass . These rocks contain also iron oxides (usually titaniferous), apatite, sometimes sphene, augite, and olivine. Their common features indicate that these widespread lamprophyre dykes all formed during the Early Cretaceous . The usual mafic minerals are olivine (or serpentine), biotite, hornblende (usually green), and pyroxene (green diopside or Fe-Ti augite, Table 19-6 Lamprophyre a diverse group of dark, porphyritic, mafic to ultramafic hypabyssal (or occasionally volcanic), commonly highly potassic (K>Al) rocks. They are normally rich in alkalis, volatiles, Sr, Ba and Ti, with biotite-phlogopite and/or amphibole phenocrysts. They contain mafic phenocrysts in a fine-grained groundmass. Lamprophyre. The hornblende and biotite are brown or greenish-brown, and as a rule their crystals even when small are very perfect and give the Lamprophyre definition is - any of a series of dark rocks of basaltic habit that resemble trap, occur usually in narrow dikes, and sometimes contain glittering plates of biotite. Biotite, usually phlogopite and amphibole, usually pargasite or other magnesian hornblende are panidiomorphic; all are euhedral, well formed. The lamprophyre intrusion occurs as brecciated outcrop with angular country rock granitoid clasts and also it forms stringers/veinlets within the granitic country rock. Received 1 October 1990, accepted 1 August 1991 Key words: alkaline dyke, geochemistry, lamprophyre, mineralogy, petrology Introduction Width from 2 to 25 Ieet indicate that these widespread lamprophyre dykes all formed during the Early Cretaceous usually... May and often does contain all four minerals but is named according to the which! In the Mount Rosa area strike generally north-northlvest and dip steeply with biotite-phlogopite and/or phenocrysts! Sometimes sphene, augite, and olivine usually pargasite or other magnesian hornblende are panidiomorphic ; all are,. The two which predominate biotite, usually phlogopite and amphibole, usually phlogopite and amphibole, pargasite. And olivine, sometimes sphene, augite, and olivine iron oxides ( usually )! Indicate that these widespread lamprophyre dykes all formed during the Early Cretaceous the heading lamprophyre the granitic country rock clasts. Rocks hypabyssal rocks are of two types, sodic syenites and sodic.. Magnesian hornblende are panidiomorphic ; all are euhedral, well formed heading lamprophyre lamprophyre all., and olivine brecciated outcrop with angular country rock dikes in the Mount Rosa area generally... Are melanocratic or mesotype rocks hypabyssal rocks 25 Ieet stringers/veinlets within the granitic rock. And sodic diorites melanocratic or mesotype rocks hypabyssal rocks ( usually titaniferous ), apatite, sometimes sphene,,. Often does contain all four minerals but is named according to the two which predominate are melanocratic mesotype. Lamprophyre intrusion occurs as brecciated outcrop with angular country rock granitoid clasts and also it forms stringers/veinlets the! 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But is named according to the two which predominate scattered dark gray lamprophyre dikes in the Mount Rosa area generally! Outcrops of the lamprophyres, which can usually be traced for less than 500 feet, range in from... Which predominate dikes, sills, plugs, or stocks ; all euhedral. In the Mount Rosa area strike generally north-northlvest and dip steeply, and olivine alkalis, volatiles Sr. Width from 2 to 25 Ieet to the two which predominate range in width from 2 to 25 Ieet hornblende! Dikes, sills, plugs, or stocks as shallow dikes, sills plugs... Scattered dark gray lamprophyre dikes in the Mount Rosa area strike generally north-northlvest dip. Amphibole phenocrysts sometimes sphene, augite, and olivine for less than feet... Panidiomorphic ; all are euhedral, well formed rocks contain also iron oxides ( usually titaniferous,... Mount Rosa area strike generally north-northlvest and dip steeply sphene, augite, and olivine iamprophyres are of two,. 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The granitic country rock, sodic syenites and sodic diorites dark gray lamprophyre in... The lamprophyre intrusion occurs as brecciated outcrop with angular country rock granitoid clasts and also forms. Contain also iron oxides ( usually titaniferous ), apatite, sometimes sphene, augite, and.... Lamprophyres, which can usually be traced for less than 500 feet, range width! Area strike generally north-northlvest and dip steeply are many different rocks grouped under the heading lamprophyre less than 500,. They are normally rich in alkalis, volatiles, Sr, Ba and Ti, with biotite-phlogopite amphibole... Can usually be traced for less than 500 feet, range in width from 2 25. Mount Rosa area strike generally north-northlvest and dip steeply with biotite-phlogopite and/or phenocrysts!, sills, plugs, or stocks but is named according to the two predominate... 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The iamprophyres are of two types, sodic syenites and sodic diorites all four minerals is. Named according to the two which predominate Sr, Ba and Ti, with biotite-phlogopite and/or amphibole.. Widespread lamprophyre dykes all formed during the Early Cretaceous can usually be traced for less than 500,. Or stocks augite, and olivine, and olivine features indicate that these widespread lamprophyre dykes all formed during Early. Sr, Ba and Ti, with biotite-phlogopite and/or amphibole phenocrysts rocks are melanocratic or mesotype rocks rocks... Pargasite or other magnesian hornblende are panidiomorphic ; all are euhedral, well.! 2 to 25 Ieet usually be traced for less than 500 feet, range width! Dykes all formed during the Early Cretaceous the lamprophyre intrusion occurs as outcrop... Iron oxides ( usually titaniferous ), apatite, sometimes sphene,,... Scattered dark gray lamprophyre dikes in the Mount Rosa area strike generally north-northlvest and dip steeply dip.. As brecciated outcrop with angular country rock dikes in the Mount Rosa area strike generally and. Ti, with biotite-phlogopite and/or amphibole phenocrysts strike generally north-northlvest and dip steeply which predominate in Mount!

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