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Topic: Dacite

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	DACITE - LoveToKnow Article on DACITE (Site not responding. Last check: 2007-11-07)
		Their felspar ranges andom oligoclase to andesite and labradorite, and is often very zonal; sanidine occurs also in some dacites, and when abundant gives rise to rocks which form transitions to the rhyolites.
		In the hand specimen many of the hornblende and biotite dacites are grey or pale brown and yellow rocks with white felspars, and fl crystals of biotite and hornblende.
		Among continental petrographers the older dacites (Carboniferous, andc.) are often known as porphyrites.
	www.1911encyclopedia.org /D/DA/DACITE.htm (259 words)

	A Complex Magma Mixing Origin for Rocks Erupted in 1915, Lassen Peak, California
		The hybrid andesites and ubiquitous undercooled inclusions in dacites at LVC are evidence for interaction of regional basaltic to andesitic magma with silicic magma.
		The groundmass of the fl dacite, dark andesite, and light dacite is hyalopilitic, whereas the groundmass of the andesitic inclusions is hyalo-ophitic.
		In the fl dacite and light dacite, olivine phenocrysts are typically found in 1-5 mm fragments of disaggregated andesitic inclusion groundmass (Plate 4a).
	library.iem.ac.ru /j-petr/1-4099/html/egc001_gml.html (11431 words)

	Dacite - Wikipedia, the free encyclopedia
		In the hand specimen many of the hornblende and biotite dacites are grey or pale brown and yellow rocks with white feldspars, and fl crystals of biotite and hornblende.
		They are mostly associated with andesites and trachytes, and form lava flows, dikes, and in some cases form massive intrusions in the centers of volcanoes.
		The word dacite comes from Dacia, a Roman province found between the Danube River and Carpathian Mountains (nowadays modern Romania) where the rock was first described.
	en.wikipedia.org /wiki/Dacite (303 words)

	USGS Photo Glossary: Dacite
		Dacite generally erupts at temperatures between 800 and 1000°C. It is one of the most common rock types associated with enormous Plinian-style eruptions.
		When relatively gas-poor dacite erupts onto a volcano's surface, it typically forms thick rounded lava flow in the shape of a dome.
		Dacite was erupted from Mount St. Helens 1980-86, Mount Pinatubo in 1991, and Mount Unzen 1991-1996.
	volcanoes.usgs.gov /Products/Pglossary/dacite.html (185 words)

	dacite -- Encyclopædia Britannica
		Dacite is primarily associated with andesite and trachyte and forms lava flows, dikes, and sometimes massive intrusions in the centres of old volcanoes.
		Like andesite, dacite consists mostly of plagioclase feldspar with biotite, hornblende, augite, or enstatite and generally has a porphyritic...
		The rock types that form lava domes are generally andesites, dacites, or rhyolites.
	www.britannica.com /eb/article-9028490?tocId=9028490 (502 words)

	Pallister
		Dacitic pumice first appeared as a minor component of the vertical eruption on June 12 and increased in abundance in the subsequent 1991 eruptions.
		Phenocryst-rich and phenocryst-poor dacitic pumice are the primary (~85 percent) and secondary (~15 percent) juvenile components of the June 15 climactic eruption.
		The depletion of incompatible elements in the dacites relative to the basalts indicates that the basalts cannot be parental to the dacites by major phase crystal fractionation.
	pubs.usgs.gov /pinatubo/pallister (15114 words)

	CD013.1: K-Ar dating of Mt. St. Helens dacite
		The conventional K-Ar dating method was applied to the 1986 dacite flow from the new lava dome at Mount St. Helens, Washington.
		Excess argon within mineral concentrates from the New Dacite Lava Dome at Mount St. Helens volcano.
		Helens dacite: The failure of Austin and Swenson to recognize obviously ancient minerals.
	www.talkorigins.org /indexcc/CD/CD013_1.html (202 words)

	Bernard
		The dacite is extraordinarily enriched in sulfur (1,474 to 2,211 ppm sulfur), most of which is present as phenocrysts and microphenocrysts of anhydrite.
		Dacites from Pinatubo and Mount St. Helens, plotted in the normative albite-orthoclase-anorthite triangle and compared to compositions produced by melting basalts experimentally.
		The presence of olivine xenocrysts in dacite suggest that a small amount of mantle-derived basalt was mixed into the dacite; mixing of more substantial amounts of basalt with dacite resulted in the formation of andesite.
	pubs.usgs.gov /pinatubo/bernard (13190 words)

	19 May 1915 Eruption of Lassen Peak
		Although early investigators arrived at this conclusion, it was subsequently abandoned in favor of an interpretation that stressed the generation of the lahar by heat exchange between a dacite lava flow and the residual snow pack.
		The existence of a deposit with many of the characteristics of those formed by volcanic blasts, including charred organic material, and the planimetric distribution of the effects of the eruption are the strongest evidence for a volcanic blast on the night of 19 May. The cause of the blast is, however, problematic.
		The 19 May dacite lava grains are distinguished from the older Lassen dacite by fresh, glassy surfaces and lack of hydrothermal alteration.
	www.msss.com /earth/lassen/lassen2.html (5889 words)

	Excess argon within mineral concentrates from the new dacite lava dome at Mount St Helens volcano
		Most dacite flows extended as lobes away from the top-centre of the dome, generally crumbling to very blocky talus on the flanks of the dome before reaching the crater floor (see Figure 3).
		Experimental data from the assemblage of minerals in the dacite indicate that just prior to the 18 May 1980 eruption the upper part of the magma chamber was at a temperature of 930°C and at a depth of about 7.2 km.
		No information was given to the lab concerning where the dacite came from or that the rock has a historically known age (ten years old at the time of the argon analysis).
	www.answersingenesis.org /home/area/magazines/tj/docs/v10n3_argon.asp (5101 words)

	Excess argon within mineral concentrates from the new dacite lava dome at Mount St Helens volcano
		The first two dacite lava domes built within the crater (late June and early August 1980) were destroyed by subsequent explosive eruptions (22 July and 17 October).
		Lithic inclusions of gabbro, quartz diorite, hornfelsic basalt, dacite, andesite and vein quartz together compose 3.5 percent of the dome dacite.
		Ar* in the dacite is not from radiogenic accumulation, but must have been resident already within the different mineral assemblages when the rock cooled from the lava in the year 1986.
	www.answersingenesis.org /tj/v10/i3/argon.asp?vPrint=1 (5101 words)

	CVO Website - Pre-Eruption Vapor, Mount Pinatubo - Abstract
		Degassing of melt in non-erupted dacite as a source of the excess sulfur implies volumes of non-erupted dacite larger than the estimated volume of the magma reservoir beneath the Mount Pinatubo region.
		It is proposed that the dacite erupted on June 15 was vapor-saturated at depth prior to eruption, and that an accumulated vapor phase in the dacite provided the immediate source of excess sulfur for the 17-Mt SO2 cloud.
		The climactic eruption released the accumulated vapor in the estimated 5 km^3 of erupted dacite.
	vulcan.wr.usgs.gov /Projects/Emissions/Reports/Pinatubo/pinatubo_abs.html (803 words)

	CVO Website - Pre-Eruption Vapor, Mount Pinatubo
		The volume, V, of non-erupted dacite required can be calculated from equation (3) constrained by the amount of S needed to make up the difference between the remote sensing and petrologic emission estimate for SO2 (17 Mt) and by data for d(m), f(m), and S(m) (table 1 and table 2).
		The pre-eruption bulk density of the dacite can be estimated from the sum of the vapor mass (table 5) and the erupted mass of crystals and glass (from data in table 1) divided by the sum of the ideal mixing vapor volume, V(vapor), and the DRE volume of erupted dacite.
		We conclude that the dacite magma erupted in the climactic June 15, 1991, eruption of Mount Pinatubo was vapor-saturated and contained an accumulation of at least 5 volume percent, water-rich vapor (about 80 mole percent H2O) at depth prior to eruption.
	vulcan.wr.usgs.gov /Projects/Emissions/Reports/Pinatubo/pinatubo.html (12534 words)

	Mountain Meadows Dacite: Oligocene Intrusive Complex That Welds Together the Los Angeles Basin, Northwestern Peninsular ... (Site not responding. Last check: 2007-11-07)
		Dikes and irregular intrusive bodies of distinctive Oligocene biotite dacite and serially related hornblende latite and felsite occur widely in the central and eastern San Gabriel Mountains, southern California, and are related to the Telegraph Peak granodiorite pluton.
		Identical dacite is locally present beneath Middle Miocene Topanga Group Glendora Volcanics at the northeastern edge of the Los Angeles Basin, where it is termed Mountain Meadows Dacite.
		Transported and redeposited clasts of dacite-latite occur in deformed lower Miocene and lower middle Miocene sandy conglomerates (nonmarine, nearshore, and infrequent upper bathyal) close to the northern and northeastern margins of the Los Angeles Basin for a distance of nearly 60 km.
	geopubs.wr.usgs.gov /prof-paper/pp1649 (510 words)

	Laddered Grid 1
		Er, it's going to be a compositional difference, I couldn't give you the exact composition of the dacite, but er, I think they're of, they're of similar grainsizes.
		So erm, I said before the, what the dolerite compositionally is, and the term dolerite is basically a, a grainsize, of a standard grainsize, so er, I assume that there will be a, er, compositional difference between the two.
		Well, the andesite, the basalt, the dacite, dolerite, the dunite-peridotite, gabbro, granodiorite, granite, the microgranite, the peridotite, the rhyolite and the trachyte.
	www.cse.unsw.edu.au /~cs9416/sisyphus/Protocols/lg/laddered_grid_1.html (3008 words)

	Mount St. Helens in 1980, by the USGS
		These eruptions of dacite pumice were followed by many lithic pyroclastic flows, which are believed to have been derived from domes; at least one of these pyroclastic flows reached a point 21 km from the center of the present volcano.
		A pyroclastic-flow deposit of breadcrusted blocks, as well as prismatically jointed blocks of dacite of the same composition as the dome, was found on the north slope of Mount St. Helens down slope from Sugar Bowl; this pyroclastic flow may have occurred at the time of the lateral blast.
		The Kalama eruptive period was characterized by frequent volcanism of considerable variety; rock types being erupted alternated from dacite to andesite and back to dacite, and the volcano grew to its pre-1980 size and shape.
	www.creationism.org /sthelens/USGS1250/USGS1250e003-015.htm (4118 words)

	Gabriel Resources Ltd. - Rosia Montana Project - Tue Oct 18, 2005 (Site not responding. Last check: 2007-11-07)
		The main dacitic bodies appear to have been intruded vertically into the maar diatreme complex and have spread laterally within and along the breccias and tuffaceous units.
		The Cirnic Dacitic dome complex is "mushroom shaped" in cross section and at depth forms a sub vertical intrusive plug with an approximate circular cross - section.
		The dacite, volcanoclastics, and sediments are brecciated and intensely altered; this alteration includes silification, argillic, and disseminated sulfides.
	www.gabrielresources.com /s/RosiaMontanaProject.asp (1498 words)

	Young-Earth Creationist 'Dating' of a Mt. St. Helens Dacite: The Failure of Austin and Swenson to Recognize Obviously ... (Site not responding. Last check: 2007-11-07)
		Considering that the dacite probably erupted in 1986 AD, Austin should have known that at least some of the samples would have given dates that were younger than 2 million years old and that Geochron Laboratories could not have provided reliable answers.
		That is, the various minerals (phenocrysts) in the dacite may have grown in the parent melt at different times and the entire crystallization process may have taken as much as a few million years.
		Based on the statements in his essays, Swenson simply assumes that excess argon is present in all of the components of the dacite and that any statements on the lack of a relationship between excess argon and crystal size in Dalrymple (1969) automatically apply to Austin's dacite.
	home.austarnet.com.au /stear/mt_st_helens_dacite_kh.htm (6857 words)

	Gerlach
		It is proposed that the dacite erupted on June 15 was vapor-saturated at depth prior to eruption, and that an accumulated vapor phase in the dacite provided the immediate source of excess sulfur for the 17-Mt SO cloud.
		The subordinate lithology is a grayish-tan, phenocryst-poor dacite pumice with a similar whole-rock composition but a texture characterized by abundant micrometer-sized broken crystals suggesting mechanical fragmentation and shattering of former phenocrysts.
		We conclude that the dacite magma erupted in the climactic June 15, 1991, eruption of Mount Pinatubo was vapor-saturated and contained an accumulation of at least 5 volume percent, water-rich vapor (~80 mole percent H
	pubs.usgs.gov /pinatubo/gerlach (12390 words)

	ARCUS \| Student Awards
		Water contents from dacite phenocryst melt inclusions and phase equilibia experiments on the andesite show that the two magmas last resided at a water pressure of 90 MPa, and contained ~3.5 wt % H
		Unzoned pyroxene and sodic plagioclase in the dacite indicate that it likely underwent significant crystallization at this depth; highly resorbed anorthitic plagioclase from the andesite indicates that it originated at greater depths and underwent relatively rapid ascent until it reached 3 km, mixed with dacite, and erupted.
		Disaggregation of enclaves, phenocryst transfer from one magma to another, and direct mixing of compositionally distinct melt phases were the three mechanisms by which hybridization was accomplished.
	www.arcus.org /Award/4th_Annual/Coombs.html (354 words)

	Dacite (Site not responding. Last check: 2007-11-07)
		Dacite is typically a light gray rock with 63 to 68 percent silica (SiO2).
		Dacite is one of a suite of rocks formed above Benioff zones.
		These rocks commonly have distict chronologies that progress from early mafic to late siliceous rocks.
	www.gly.uga.edu /petrology/redoubt/Dacite.html (93 words)

	Experimental Constraints on the Origin of the 1991 Pinatubo Dacite -- PROUTEAU and SCAILLET 44 (12): 2203 -- Journal of ...
		Experimental Constraints on the Origin of the 1991 Pinatubo Dacite -- PROUTEAU and SCAILLET 44 (12): 2203 -- Journal of Petrology
		Experimental Constraints on the Origin of the 1991 Pinatubo Dacite
		: Pinatubo dacite; slab melt; experimental petrology; arc magmas
	petrology.oxfordjournals.org /cgi/content/abstract/44/12/2203 (298 words)

	What is dacite? (Site not responding. Last check: 2007-11-07)
		Dacite lava consists of about 63 to 68 percent silica (SiO
		The principle minerals that make up dacite are plagioclase, quartz, pyroxene, or hornblende.
		Dacite generally erupts at temperatures between 800 and 1000 degrees C., and is one of the most common rock types associated with enormous Plinian-style eruptions.
	interactive2.usgs.gov /faq/list_faq_by_category/get_answer.asp?id=505 (140 words)

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