high-Al Basalts Research Articles

The Colima volcanic complex, Mexico: Part II. Late-quaternary cinder cones

Since the late Pleistocene, eleven cinder and lava cones have erupted on the floor of the southern Colima graben, NE and NW of the large, active, andesitic volcano Colima. Scoria and lava samples from nine of the cones form a completely transitional basic alkalic series including basanites (9), leucite-basanites (3), and minettes (15), the commonest variety of mica lamprophyre. These samples represent primitive, high temperature magmas with 47.6–50.3% SiO2, 7.4–15.3% MgO, 2.5–4.4% K2O, and 2.2–9.9% normative nepheline. All members of this basic alkalic suite contain Mg-olivine (Fo75–94), chromite, augite, and late plagioclase and titanomagnetite. The petrographic transition from basanite to minette is marked by the appearance of sanidine and the volatile-bearing phases phlogopite, apatite, and analcime during late stages of crystallization. As these phases increase in abundance, presumably reflecting a rise in magmatic volatile content, there are corresponding increases in the whole rock concentrations of 16 incompatible elements. Although these incompatible elements are relatively abundant even in the basanites, many are highly concentrated in the minettes: Ba≦ 4,200 ppm, Sr≦3,100 ppm, Zr≦ 550 ppm, Ce≦190 ppm, Hf ≦18 ppm. Among the incompatible elements, the degrees of enrichment in the minettes relative to the basanites decrease in the order: H, Th, Ce, La, Nd, Zr, Hf, U, Ba, Sm, Eu, Pb, P, Nb, Sr, Ti. These enrichments may reflect the increasing importance of minor, incompatible element rich mantle phases during partial melting. The concentrations of alkali metals K, Na, Rb, and Cs do not correlate with these other elemental enrichments. The leucite-basanties have similar incompatible element contents to many minettes, differing from them only in the presence of leucite rather than analcime, and Ti-F-rich groundmass phlogopite rather than hydrous phlogopite phenocrysts; thus the leucite-basanites represent relatively dry equivalents of minettes. Two of the eleven cinder cones are calc-alkaline in nature and do not belong to the basanite-minette group; the easternmost cone is constructed of high-Al basalt, and the northernmost of basaltic andesite. The high-Al basalt (49.5% SiO2, 9.3% MgO, 221 ppm Ni) closely approximates a parental magma to the post-caldera andesitic suite of V. Colima (56.5–61.6% SiO2). The basaltic-andesite is relatively enriched in incompatible elements compared to the high-Al basalt — V. Colima trend. The ne-normative basanite-minette samples are highly enriched in incompatible elements, while the contemporaneous hy — qz-normative calc-alkaline suite, encompassing the high-Al basalt and V. Colima's andesites, is characterized by relatively low abundances of these elements. No likely mineral assemblage can relate the alkaline and calc-alkaline suites through crystal fractionation; they probably represent fundamentally different melting events. During the Quaternary, the main focus of andesitic volcanism in the southern Colima graben has migrated southward with time. Volcan Colima marks its present position, 5 km south of the Pleistocene volcano Nevado de Colima, and another 15 km from the still older Volcan Cantaro. The eruptions of basic alkalic magma probably occurred during the late stages of Nevado's life and through the life of V. Colima. They generally migrated from west to east with time, towards V. Cantaro. The most recent cone, V. Apaxtepec, is the only one east of the andesitic Colima-Cantaro axis. The oldest and the two youngest cones produced basanites, while minettes dominated at cones of intermediate ages. The cinder cone eruptions may have coincided with a phase of lamprophyre dike injection into plutons solidifying beneath the extinct volcanoes north of V. Colima. The southern end of the Colima graben can be viewed, then, as the volcanic analog of many classical, post-plutonic, hypabyssal lamprophyre localities.

Geology and Petrology of Volcan Ceboruco, Nayarit, Mexico

Volcan Ceboruco is a moderately sized stratovolcanc located in the northwestern part of the Mexican Volcanic Belt. The bulk of the volcano consists of relatively alkali and incompatible element—poor hypersthene andesites erupted prior to the formation of two concentric calderas. These precaldera andesites were followed in the eruptive sequence by the eruption 1,000 yr ago of a white rhyodacite pumice, termed the Jala pumice. The eruption apparently caused the formation of Ceboruco9s outer caldera. A low-silica dacite dome and lava flow were then erupted and partially filled this caldera. These dacites contain xenoliths of high-Al basalt that were apparently partially molten at the time of their inclusion, suggesting that the dacite magma formed as a result of magma mixing involving Jala pumice and basaltic magmas. The dacite dome later collapsed to form the inner caldera, and Ceboruco again erupted andesites. These postcaldera andesites contain both augite and hypersthene and are enriched in alkalis and incompatible elements relative to the precaldera andesites. Finally, between 1870 and 1875, rhyodacite lava flows were erupted during Ceboruco9s only historic activity. Crystal fractionation models using both major and trace elements suggest that the 1870 dacites and the Jala pumice could have been derived from magma with postcaldera andesite composition. To determine the origin of the Ceboruco andesites, trace-element partial-melting models tested three possible sources: subducted oceanic crust in the eclogite facies and the amphibolite facies and mantle peridotite. All models were found unreliable because of the many assumptions involved. It is concluded that a complex process involving partial melting, fractional crystalization, magma mixing, and, perhaps, crustal assimilation was responsible for the generation of the andesites. Such a model cannot be tested, however, because there are at present no viable constraints that can be placed on this complex sequence of events.

Oxygen isotopic determinations of sequentially erupted plagioclases in the 1974 magma of Fuego Volcano, Guatemala

Plagioclases in the 1974 high-Al basalt from Fuego Volcano have δO18 values of +6.0 to +8.5 per mil. Meteoric water cannot have played a significant role in Fuego’s magma. Large, weakly zone clear phenocrysts had δO18 values in the accepted mantle range, while patchyzoned and oscillatory-zoned plagioclases inferred to have formed later and shallower levels have slightly heavier oxygen isotopic ratios.

Geochemistry of calc-alkaline volcanic rocks from southeastern Iran (kouh-e-shahsavaran)

The Upper Tertiary to Quaternary volcanic complex of Kouh-e-Shahsavaran in southeastern Iran is composed of calc-alkaline rocks of island are type (high-alumina basalts, basic andesites, andesites and dacites) even though it was emplaced on the continental basement. The volcanic rocks of the complex are genetically related and were probably derived by low-pressure fractional crystallization of high-Al basalts. The anomalously high content of Sr in some rocks probably reflects an accumulation of plagioclase. The trace element data are consistent with the origin of the parental magma by partial melting of an “enriched” upper mantle peridotite.

Search for chemical effect on partitioning of rare-earth elements in the crystallization process of basaltic systems at 20kb, with some applications.

Employing two kinds of basalts, i.e., alkali olivine basalt and high-alumina basalt, the partitioning of REE was investigated for partial crystallization at 20kb. Even with the same alkali olivine basalt, the peak-shaped and the terrace-shaped partition coefficient functions were obtained, although both of them belong to a major “rectilinear” partition coefficient group. This difference in the shape appears to be associated with the relative content of Ca to Mg and Fe in crystal phase. Meanwhile, use of a high-Al basalt yielded a new partition coefficient function (schanze-shaped) quite distinct from rectilinear functions and their varieties. Intriguingly, addition of MgO (5%) to the high-Al basalt powder (95%) brought about a drastic change of partition coefficient function, resulting in the terrace-shaped one. It is evinced that the higher values of atomic ratios, Al/(Mg+Fe+Ca) and Si/(Mg+Fe+Ca), in the starting material are favorable to the appearance of schanze-shaped partition coefficient function. Besides, REE in island arc tholeiite from New Britain were accurately determined. REE abundances in this sample have demonstrated to imply that this basalt has a history of temporary separation from melt with 6-8 times chondritic REE abundances through the regulation of the terrace-shaped partition coefficient function. It was also attempted to use the schanze-shaped partition coefficient function in order to explain the genesis of felsic potassic basalt (KAY and GAST, 1973) based on two-stage fractional crystallization model. The REE pattern of the material removed during the second stage was calculated together with the “liquid-type” pattern corresponding to the switching point between two stages in question.

High-K2O island-arc volcanic rocks from the Finisterre and Adelbert Ranges, northern Papua New Guinea

Research Article| June 01, 1976 High-K2O island-arc volcanic rocks from the Finisterre and Adelbert Ranges, northern Papua New Guinea A. L. JAQUES A. L. JAQUES 1Geological Survey of Papua New Guinea, Box 778, Port Moresby, Papua New Guinea Search for other works by this author on: GSW Google Scholar Author and Article Information A. L. JAQUES 1Geological Survey of Papua New Guinea, Box 778, Port Moresby, Papua New Guinea Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1976) 87 (6): 861–867. https://doi.org/10.1130/0016-7606(1976)87<861:HIVRFT>2.0.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation A. L. JAQUES; High-K2O island-arc volcanic rocks from the Finisterre and Adelbert Ranges, northern Papua New Guinea. GSA Bulletin 1976;; 87 (6): 861–867. doi: https://doi.org/10.1130/0016-7606(1976)87<861:HIVRFT>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract A thick, extensive volcanic formation of Oligocene to early Miocene age, the Finisterre Volcanics, forms part of a Cenozoic sequence comprising the Finisterre and Adelbert Ranges of northern Papua New Guinea. The formation contains a high proportion of diverse volcaniclastic rocks and is lithologically similar to volcanic sequences described from island-arc assemblages elsewhere. The volcanic rocks are dominantly potassic basalt and low-silica andesite (48 to 56 percent SiO2) containing 1.5 to 6.5 percent K2O and having low TiO2 content typical of circumoceanic volcanic rocks. Two main groups can be recognized: abundant shoshonite and related rocks (absarokite, rare leucite trachyte) and high-K, high-Al basalt (with some high-K, low-Si andesite).The Finisterre Volcanics are chemically similar to high-K rocks described from island arcs elsewhere in the southwest Pacific and in the Mediterranean. However, unlike some other island arcs, there is no evidence of a three-stage evolution from arc tholeiite to calc-alkalic andesite to shoshonite. The volcanic rocks probably formed in a volcanic arc that developed north of a northeastward-dipping subduction zone in response to early Tertiary plate interactions. The Finisterre volcanic magmas may have originated by partial melting of mantle material modified by slab-derived silicic melts. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

The Petrology of Lunar Breccia 15445 and Petrogenetic Implications

Lunar breccia 15445, collected near the rim of Spur Crater, contains iron-rich olivine and ortho-pyroxene mineral clasts and two types of white lithic clasts. The dominant type (Type A) is composed principally of anorthite - magnesian orthopyroxene and appears to be a low-pressure cumulate from a magnesian, high-Al basalt. A minor type (Type B) is composed of olivine + chrome pleonaste + aluminous orthopyroxene + minor plagioclase. Type B clasts have affinities to terrestrial spinel peridotites and have a REE pattern unique for the moon. Considerations of the observed mineralogy and the trace element geochemistry suggest that garnet was originally a phase in this peridotite but was subsequently lost during subsolidus reequilibration. Hence, Type B clasts provide indirect evidence for the existence of garnet in the lunar interior.

IV. Regional studies. Hudson Geotraverse: geology of the Mid-Atlantic Ridge at 45° N/ Petrology of submarine volcanics from the NE Pacific

A strip across the Crest Mountains and High-Fractured Plateau of the Mid-Atlantic Ridge has been surveyed systematically between latitudes 45 and 46° N. Continuous bathymetric, magnetic and gravimetric data have been obtained. Seismic refraction experiments have revealed a complex structure lineated parallel to the axis of the Ridge. Seismic reflexion studies have revealed a picture of the sediment cover, and have shown the possible existence of block faulting of the underlying rocks, with faults alined both parallel and at right angles to the axis of the Ridge. The major rock types found in 46 dredge stations can be grouped as follows: (1) Ubiquitous basalts and tuffs (ranging from theoleiites to alkali basalts, with a few ferro-basalts and high-Al basalts). Basalts rich in resorbed high-calcic plagioclase xenocrysts are common; these occur both on the slopes of shield volcanoes and in the deepest hole of the Median Valley. A nearby fault scarp yielded coarse-grained gabbros. (2) Serpentinized mafic and ultramafic rocks are not restricted to elongated, presumably blockfaulted seamounts, but are also common on the slopes of what had been interpreted on morphological grounds as shield volcanoes; they are absent, however, on the Median alley floor and its immediate scarp slopes. The pre-serpentinization rock types include dunites, harzburgites, gabbros, troctolitic gabbros and amphibolitic peridotites showing crude cumulate textures. (3) The lower parts of the steep inner walls of the Median Valley have yielded metabasalts and metadiabases showing alteration within the greenschist facies of etamorphism, whilst still retaining original igneous characteristics. (4) Restricted to the fault scarps of elongated seamounts further removed from the Median Valley are higher grade metamorphic rocks of the almandine amphibolite facies of metamorphism. These rocks have lost all igneous textures and exhibit a strong gneissic fabric. (5) Three localities yielded dioritic rocks in association with serpentinized ultramafics. The diorites vary in character from hornblende-rich quartz diorites to more siliceous, almost hornblende-free trondhjemites. The latter show considerable albitization. The whole suite of rocks shows great affinities with similar suites found as late stage intrusives in alpine-type ultramafic complexes. About 23% of the specimens collected included gneissic, granitic and sedimentary rock types of erratic origin, ice rafted into the area in the Pleistocene. A study of their distribution indicates that there are no erratics in the Median Valley, that they are scarce on the mountain ranges immediately flanking the Valley, but beyond these areas they are abundant and are randomly distributed over the whole area. Such a distribution may be a result of ocean-floor spreading, indicating that the Median Valley is younger than the last ice age, or that extrusions subsequent to the last ice age have engulfed any erratics present in the Median Valley. The thickness of manganese coating on extrusive rocks and their K/Ar and fission track ages increase systematically with distance on either side of the axis of the M.A.R., strongly supporting the ocean-floor spreading hypothesis. The ages and coatings both show a marked change in their rate of increase beyond a distance of 50 to 60 km on either side of the axis. The position at which this occurs coincides with the thickening in these areas of sediments found in the inter-volcanic valleys, and the morphological changes between the Crest Mountains and the High-Fractured Plateau. The combined data strongly suggest that there was either a quiescent period sometime in the Pliocene during which ocean-floor spreading was inactive, or that the rate of spreading had accelerated during the Pliocene from less than 1 cm a -1 to a computed 2.5 cm a -1 in Pleistocene times.

High potassium calc-alkaline rocks from Cape Nelson, eastern Papua

High-K calc-alkaline rocks from Cape Nelson, eastern Papua are dominated by andesites containing numerous basic inclusions. High-Al basalts and dacites are subordinate. The slight iron enrichment and a systematic variation in K2O/SiO2 correlation observed in these rocks suggests a relationship to nearby rocks of a shoshonite association. The chemical composition of the inclusions illustrates the trends of major and minor element evolution which contradict the idea of complimentariness of high-K calc-alkaline rocks and alpine ultramafic rocks. The chemical character of the lavas (high K, Rb and Ba as well as high Cr and Ni) can be explained by fractional melting involving a mica phase.

Genetic significance of V and Ni content of andesites: Comments on a paper by Taylor, Kaye, White, Duncan and Ewart

The inference of Taylor etal. (1969) that andesite cannot have formed by fractional crystallization of high Al-basalt is based on a method of calculation which is questioned. When the calculation relative to vanadium content is made assuming a reasonable fraction of residual andesite liquid, it seems feasible to derive andesite from high Al-basalt.