KAITAN TIPOLOGI PANTAI DENGAN KEBERADAAN PASIR BESI DI PANTAI MUKOMUKO, BENGKULU

Pasir besi merupakan salah satu potensi di sebagian kawasan pantai Indonesia yang erat kaitannya dengan keberadaan kondisi geologi batuan bersusunan andesitik-basaltik, oleh sebab itu salah satunya dipilih pantai Mukomuko sebagai objek penyelidikan. Pasir besi ini terakumulasi sebagai endapan alokhton dari hasil pelapukan dan erosi tanah yang diangkut oleh sungai dan diendapkan di pantai. Proses marin berupa abrasi dan akrasi terbentuk di sepanjang garis pantai oleh pemusatan gelombang dan arus sejajar pantai. Metode penyelidikan meliputi deskripsi kualitatif karakteristik pantai, penentuan posisi, pemercontohan sedimen, analisis megaskopis, dan pemisahan mineral bersifat magnetik dengan menggunakan magnet tangan disertai foto mikrograf. Tipologi pantai Mukomuko terdiri dari gisik berpasir (Sand beach) yang sebagian di atasnya ada bangunan dinding laut, dan gisik berkerikil (Gravel beach). Endapan pasir besi umumnya menempati gisik berpasir, baik pada muka pantai maupun pada tanggul gisiknya yang sebagian membentuk pematang pantai. Distribusi persentase magnetit (% Fe) sejajar pantai memiliki pola besaran relatif sama dengan kadar frekuensi yang berkisar antara 0 % - 10 %, anomali dijumpai secara setempat pada tanggul gisik dengan kisaran antara 30,07 % - 45,73 %. Berdasarkan klasifikasi cebakan plaser, genesa pasir besi terkonsentrasi oleh media cair yang bergerak sebagai jenis plaser pantai yang dipengaruhi oleh fluviatil. Keterdapatan pasir besi diduga berasal dari Formasi Hulusimpang yang dikorelasikan sebagai Andesit Tua, Batuan Gunungapi Kuarter dan lapisan konglomerat aneka bahan Formasi Bintunan yang bersusunan andesitik-basaltik. Kata Kunci : Karakteristik pantai, magnetit, plaser pantai, sumber batuan, pantai Mukomuko Bengkulu. Iron sand is one of the mineral potential in some coastal areas of Indonesia, which is related to the presence of andesitic-basaltic rocks, therefore Mukomuko coast is then selected as the object of investigation. The iron sand is accumulated as the alochton deposit as the product of the weathering and soil erosion transported by the river and it is accumulated on the beach. The abrasion and accretion processes are formed along the shoreline by waves and currents parallel to the coast. The methods of investigation include coastal characteristics mapping, positioning, sediment sampling, megascopic analysis, and magnetic separation of minerals by using a hand magnet with micrograph photo. The coastal characteristics of Mukomuko consist of gravel beach, and sand beach that some sea walls built on. Iron sand deposits generally occupy a sand beach, either on the beach face or on the berm which partially form the beach ridge. The distribution of magnetite parallel to the coast has the same relative magnitude patterns with the frequency content ranging from 0 % - 10 %, anomaly is found locally on the berm with the frequency content ranging between 30.07 % - 45, 73 %. Based on the classification of placer deposits, iron sand is concentrated in the formation of moving liquid media as placer beach types affected fluvial. The presence of iron sand supposed to be derived from the Hulusimpang Formation is correlated as Old Andesite, Quaternary Volcanic Rocks and conglomerate layers of different materials of andesitic-basaltic composition from Bintunan Formation. Keywords: Coastal Characteristics, magnetite, beach placer, source rocks; shore of Mukomuko, Bengkulu.

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KANDUNGAN MINERAL DI PERAIRAN BINUANGEUN, LEBAK-BANTEN

JURNAL GEOLOGI KELAUTAN ◽

10.32693/jgk.12.2.2014.248 ◽

2016 ◽

Vol 12 (2) ◽

pp. 79

Author(s):

Udaya Kamiludin ◽

Udaya Kamiludin

Keyword(s):

River Sediments ◽

Volcanic Rocks ◽

Mineral Resources ◽

Fine Sand ◽

Source Rocks ◽

Coarse Silt ◽

Sand Beach ◽

Offshore Area ◽

Rock Fragments ◽

Shell Fragments

Data dan informasi sumberdaya mineral terkait dengan batuan penyusunnya di daerah pantai dan lepas pantai masih terbatas. Untuk keberadaan sumberdaya mineral ini maka dilakukan identifikasi kandungan mineral dalam sedimen sebagai objek penelitian guna mengetahui jenis, persentase, distribusi dan perkiraan sumber batuannya. Metode penelitan meliputi pengambilan sampel sedimen, pemisahan konsentrat dulang, analisis mineragrafi butir, dan petrografi batuan. Ragam mineral di dalam endapan sedimennya terdiri dari kuarsa, magnetit, amfibol, ilmenit, felspar, glaukonit, apatit, piroksen, limonit, zirkon, fragmen batuan dan pecahan cangkang. Fraksi mineral yang dominan adalah fraksi pasir sangat halus dan lanau kasar. Secara lateral distribusi kuarsa, felspar dan piroksen relatif membesar ke arah endapan sedimen gisik pasir, tanggul gisik dan sedimen sungai dengan persentase tertinggi, masing-masing mencapai 49 %, 21 % dan 13 %. Sedangkan distribusi limonit dan zirkon membesar ke arah endapan sedimen gisik pasir dengan persentase tertinggi, masing-masing mencapai 5 % dan 2 %. Persentase tertinggi magnetit 17 %, ilmenit 23 %, apatit 3 %, fragmen batuan 51% dan pecahan cangkang 90 % umumnya terdapat dalam endapan sedimen permukaan dasar laut. Keterdapatan mineral utama dan tambahan ini diduga bersumber dari Batuan Gunungapi andesiti-basaltik, dan Formasi Batuan Sedimen berbahan volkanik. Sedangkan klastika biogeniknya bersumber dari batugamping terumbu. Hasil analisis petrogafi menunjukan bahwa fragmen batuannya memiliki kesesuaian dengan penyusun litologinya. Kata Kunci : Kandungan mineral, distribusi mineral, sumber batuan, Perairan Binuangeun. Data and information mineral resources related to rock forming mineral on shore and offshore area is still limited. For the existence of mineral resources is then to identify the content of the sediment as the object study in order to determine the type, percentage, distribution and estimation of rocks origin. The method includes sedimentary sampler, pan concentrates separation, grain mineragraphy analysis, and petrography rock. The mineral in the sediment consist of quartz, magnetite, amphibole, ilmenite, feldspar, glauconite, apatite, pyroxene, limonite, zircon, rock fragments and shell fragments. The minerals fractions are dominant in very fine sand and coarse silt. Laterally, the distribution of quartz, feldspar and pyroxene relatively increasing towards sand beach, berm and river sediments with the highest percentage, respectively reach 49 %, 21 % and 13 %. While, distribution of limonite and zircon are increasing toward sand beach with the highest percentage, respectively 5 % and 2 %. The highest percentage of magnetite (17 %), ilmenite (23 %), apatite (3 %), and rock fragments (51 %) and shell fragments of surfacially sediments (90 %). The occurrence of these main and accessory minerals is thought to be originated from andesitic-basaltic volcanic rocks and from volcanoclastic sediments whereas bioclastic sediments are from reefs limestone. The petrography analysis shows that their rock fragments are compatible with their rocks forming minerals. Keywords: The minerals content, mineral distribution, source rocks, and Binuangeun Waters.

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KETERDAPATAN PASIRBESI DI PANTAI BEO DAN SEKITARNYA, KEPULAUAN TALAUD PROVINSI SULAWESI UTARA

JURNAL GEOLOGI KELAUTAN ◽

10.32693/jgk.14.2.2016.353 ◽

2017 ◽

Vol 14 (2) ◽

Author(s):

Mohammad Akrom Mustafa ◽

Deny Setiady ◽

Udaya Kamiludin

Keyword(s):

Source Rocks ◽

Tectonic Activity ◽

Ultramafic Rocks ◽

Liquid Media ◽

Sediment Sampling ◽

Magnetite Content ◽

Waves And Currents ◽

Placer Deposits ◽

Tectonic Movements ◽

Moving Liquid

Pasirbesi (magnetit) merupakan salah satu hasil pelapukan batuan di daratan dan abrasi pantai oleh pemusatan gelombang dan arus sejajar pantai. Tujuan penelitian menentukan keterdapatan pasirbesi di sekitar Pantai, Kepulauan Talaud, Sulawesi Utara. Metode penelitian meliputi karakteristik pantai, pemercontohan sedimen, analisis megaskopis dan mineral butir disertai fotomikrograf. Tipologi Pantai Beo terdiri dari pantai berkantong pasir dan berbatuan. Endapan Magnetit umumnya menempati pantai berkantong pasir yang sebagian membentuk tanggul gisik. Kadar persentase magnetit (% Fe) antara 0.139 % - 38.11 %. Anomali magnetit dengan kadar kisaran antara 21,414 % dan 38,106 % dijumpai di Pantai Beo, Maririka dan Pantai Batumbalango. Lingkungan keterdapatan magnetit dipengaruhi oleh aktivitas pergerakan tektonik aktif Resen yaitu terangkatnya terumbu karang. Genesa magnetit terkonsentrasi oleh media cair bergerak sebagai endapan plaser pantai yang dipengaruhi oleh fluviatil. Keterdapatan Magnetit diduga berasal dari Batuan Gunungapi Pampini, batuan campuraduk Bancuh Karakelang dan Batuan Ultramafik Kabaruang.Kata Kunci : Magnetit, Karaktersitik pantai, aktivitas tektonik, endapan plaser, sumber batuan, Pantai Beo.Ironsand (magnetite) is one of the mineral potential in some coastal areas of Indonesia, which is related to the presence of andesitic-ultramafic rocks. Therefore Beo coast and its vicinity are then selected as the object of investigation. Magnetite is accumulated as the alochton deposit as the product of rocks weathering in land and coastal abrasion processes are formed by waves and currents parallel to the coast. The methods of investigation include coastal characteristics mapping, positioning, sediment sampling, megascopic and grain minerals analysis with photomicrograph. Coastal characteristics of Beo consist of pocket beach and rocks. Magnetite deposits are usually occupies a pocket beach which is partially formed Berm. The percentage of magnetite content ranging from 0.139% - 38.11%. Anomalies magnetite grading between 21,414 % dan 38,106 % found in Beo, Maririka and the Batumbalango Beach. Magnetite environment is impacted by tectonic movements active in Resen vertically namely the lifting of coral reefs. Magnetite is concentrated on the formation of moving liquid media as placer beach types affected fluvial. The presence of magnetite supposed to be derived from Pampini Volcanics, and mixture of heterogenous rocks Karakelang Melange and Kabaruang Ultramafics. Keywords: Magnetite, coastal characteristics, tectonic activity, placer deposits, source rocks, Beo Beachs

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The Peninsular Ranges Batholith: an insight into the evolution of the Cordilleran batholiths of southwestern North America

Earth and Environmental Science Transactions of the Royal Society of Edinburgh ◽

10.1017/s0263593300014152 ◽

1988 ◽

Vol 79 (2-3) ◽

pp. 105-121 ◽

Cited By ~ 151

Author(s):

L. T. Silver ◽

B. W. Chappell

Keyword(s):

Baja California ◽

Volcanic Rocks ◽

Oceanic Lithosphere ◽

Radiometric Dating ◽

Island Arcs ◽

Magmatic Arc ◽

Metasedimentary Rocks ◽

Basaltic Composition ◽

Peninsular Ranges ◽

General Aspects

ABSTRACTThe Peninsular Ranges Batholith of southern and Baja California is the largest segment of a Cretaceous magmatic arc that was once continuous from northern California to southern Baja California. In this batholith, the emplacement of igneous rocks took place during a single sequence of magmatic activity, unlike many of the other components of the Cordilleran batholiths which formed during successive separate magmatic episodes. Detailed radiometric dating has shown that it is a composite of two batholiths. A western batholith, which was more heterogeneous in composition, formed as a static magmatic arc between 140 and 105 Ma and was intrusive in part into related volcanic rocks. The eastern batholith formed as a laterally transgressing arc which moved away from those older rocks between 105 and 80 Ma, intruding metasedimentary rocks. Rocks of the batholith range from undersaturated gabbros through to felsic granites, but tonalite is the most abundant rock throughout. Perhaps better than elsewhere in the Cordillera, the batholith shows beautifully developed asymmetries in chemical and isotopic properties. The main gradients in chemical composition from W to E are found among the trace elements, with Ba, Sr, Nb and the light rare earth elements increasing by more than a factor of two, and P, Rb, Pb, Th, Zn and Ga showing smaller increases. Mg and the transition metals decrease strongly towards the E, with Sc, V and Cu falling to less than half of their value in the most westerly rocks. Oxygen becomes very systematically more enriched in18O from W to E and the Sr, Nd and Pb isotopic systems change progressively from mantle values in the W to a more evolved character on the eastern side of the batholith. In detail the petrogenesis of the Peninsular Ranges Batholith is not completely understood, but many general aspects of the origin are clear. The exposed rocks, particularly in the western batholith, closely resemble those of present day island arcs, although the most typical and average tonalitic composition is distinctly more felsic than the mean quartz diorite or mafic andesite composition of arcs. Chemical and isotopic properties of the western part of the batholith indicate that it formed as the root of a primitive island arc on oceanic lithosphere at a convergent plate margin. Further E, the plutonic rocks appear to have been derived by partial melting from deeper sources of broadly basaltic composition at subcrustal levels. The compositional systematics of the batholith do not reflect a simple mixing of various end-members but are a reflection of the differing character of the source regions laterally and vertically away from the pre-Cretaceous continental margin.

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Platinum-group minerals from alluvial placers of the Kitoy river (south-east part of East Sayan, Russia)

10.5194/egusphere-egu21-14020 ◽

2021 ◽

Author(s):

Olga Kiseleva ◽

Yuriy Ochirov ◽

Sergey Zhmodik ◽

Brian Nharara

Keyword(s):

Publishing House ◽

Primary Source ◽

Platinum Metal ◽

Mineral Chemistry ◽

Source Rocks ◽

Tectonic Deformation ◽

Platinum Group Minerals ◽

Placer Deposits ◽

Platinum Group ◽

Eastern Sayan

The studied area is in the southeastern region of Eastern Sayan. Several tectonically dissected ophiolite complexes were exposed along the margin of the Gargan block and tectonically thrust over this block. Placer nuggets of PGE alloys from the Kitoy river were examined using a scanning electron microscope. Platinum-group minerals (PGM's) in placer deposits provide vital information about the types of their primary source rocks and ores as well as the conditions of formation and alteration. The primary PGM's are Os-Ir-Ru alloys, (Os, Ru)S2, and (Os, Ir, Ru)AsS. (Os, Ru)S2 form overgrowth around the Os-Ir-Ru alloys. The secondary, remobilized PGM's are native osmium, (Ir-Ru) alloys, garutite (Ir, Ni, Fe), zaccarinite (RhNiAs), selenides, tellurides (Os, Ir, Ru), and non-stoichiometric (Pd, Pt, Fe, Te, Bi) phases (Fig.1). Secondary PGM's (garutite and RhNiAs) form rims around Os-Ir-Ru alloys, intergrowth with them, or form polyphase aggregates. Such PGM's (identical in composition and microstructure) are also found in chromitites from Neoproterozoic ophiolite massifs of Eastern Sayan (Kiseleva et al., 2014; 2020). Platinum-metal minerals, exotic for ophiolites, are found among secondary PGM's such as selenides and tellurides (Os, Ir, Ru), (Pt, Pd)3Fe, Pd3(Te, Bi), (Au, Ag), and non-stoichiometric (Pd, Pt, Fe, Te, Bi) phases. They occur as inclusions in the Os-Ir-Ru alloys or fill cracks in crushed grains of primary PGM's. PGM's in placer deposits of the Kitoy river are similar to the mineral composition of PGE in chromitites of the Ospa-Kitoy ophiolitic massif, which contain Pt-Pd minerals and Pt impurities in Os-Ir-Ru alloys (Kiseleva et al., 2014). Selenides (Os-Ir-Ru) are rare within PGM's from ophiolite chromitites (Barkov et al., 2017; Airiyants et al., 2020) and also occur in chromitites of the Dunzhugur ophiolite massif (Kiseleva et al., 2016). Features of selenides and tellurides (Os, Ir, Ru) indicate their late formation as a result of the influence of magmatic and metamorphic fluids on primary PGE alloys. The filling of cracks in crushed (Os-Ir-Ru) alloys indicates that selenides and tellurides formed during tectonic deformation processes. The source of platinum-group minerals from the Kitoy river placer is the Ospa-Kitoy ophiolite massif, and primarily chromitites.<img src="https://contentmanager.copernicus.org/fileStorageProxy.php?f=gepj.eb9553e3c70065361211161/sdaolpUECMynit/12UGE&app=m&a=0&c=f3ccc1c7cf7d06094d2afaa34fe9d9a1&ct=x&pn=gepj.elif&d=1" alt="">Figure 1. BSE microphotographs of PGM from from alluvial placers of the Kitoy riverMineral chemistry was determined at the Analytical Centre for multi-elemental and isotope research SB RAS. This work supported by RFBR grants: No. 16-05-00737a,&#160; 19-05-00764&#1072;, 19-05-00464a and the Russian Ministry of Education and ScienceReferencesAiriyants E.V., Belyanin D.K., Zhmodik S.M., Agafonov L.V., Romashkin P.A.&#160; // Ore Geology Reviews. 2020. V. 120. P.&#160; 103453Barkov A.Y., Nikiforov A.A., Tolstykh N.D., Shvedov G.I., Korolyuk V.N. // European J. Mineralogy. 2017. V.29(9). P.613-621.Kiseleva O.N., Zhmodik S.M., Damdinov B.B., Agafonov L.V., Belyanin D.K. // Russian Geology and Geophysics. 2014. V. 55. P. 259-272.Kiseleva O.N., Airiyants E.V., Belyanin D.K., Zhmodik S.M., Ashchepkov I.V., Kovalev S.A. // Minerals. 2020. V. 10. N 141. P. 1-30.Kiseleva O.N., Airiyants E.V., Zhmodik S.M., Belyanin D.K / Russian and international conference proceedings &#8220;The problems of geology and exploitation of platinum metal deposits&#8221; &#8211; St.Petersburg: Publishing house of St.Petersburg State University. 2016. 184 P.

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Contrasting fold styles in a volcano-sedimentary succession

Canadian Journal of Earth Sciences ◽

10.1139/e96-090 ◽

1996 ◽

Vol 33 (8) ◽

pp. 1193-1200

Author(s):

Pierre A. Cousineau ◽

Robert Marquis

Keyword(s):

Sedimentary Basin ◽

Volcanic Rocks ◽

Sedimentary Rocks ◽

Structural Models ◽

Sedimentary Basins ◽

Basaltic Rocks ◽

Field Evidence ◽

Sedimentary Succession

Structural analyses of folded volcano-sedimentary basins rely heavily on the identification and use of way-up structures. These structures are more numerous and widespread in sedimentary rocks than in volcanic rocks. Structural models for such basins can therefore be biased by this fact. The Caldwell Group of the Quebec Appalachians is a folded volcano-sedimentary basin bounded bay major faults. It contains locally abundant basalt-rich bands. Near Lac-Etchemin, way-up in basalt flows is determined by pillow shelves that reflect paleohorizontal planes. The strike and dip of these shelf structures were measured and plotted on stereographic projections. Field evidence and the interpretation of stereographic projections indicate that the basalt-rich bands form open folds that plunge gently to the southwest. However, sandstone-rich bands form tight folds with undulating hinge lines (sheath-like). During initial folding, the basalt formed competent bands with limited aerial extent that were fractured by synthetic and antithetic faults rather than folded. The basalt slivers maintained a near-horizontal attitude while adjacent sedimentary rocks were folded and faulted. Further shortening tightened folds in the sediment-rich bands while producing open folds in slivers of basaltic rocks.

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The Witwatersrand pyrites and metamorphism

Mineralogical Magazine ◽

10.1180/minmag.1983.047.345.08 ◽

1983 ◽

Vol 47 (345) ◽

pp. 473-479 ◽

Cited By ~ 17

Author(s):

D. K. Hallbauer ◽

K. von Gehlen

Keyword(s):

Trace Element ◽

Fluid Inclusions ◽

Depositional Environment ◽

Volcanic Rocks ◽

Source Rocks ◽

Fine Grained ◽

Mineral Inclusions ◽

Ore Minerals ◽

Hand Specimen

AbstractEvidence obtained from morphological and extensive trace element studies, and from the examination of mineral and fluid inclusions in Witwatersrand pyrites, shows three major types of pyrite: (i) detrital pyrite (rounded pyrite crystals transported into the depositional environment); (ii) synsedimentary pyrite (round and rounded aggregates of fine-grained pyrite formed within the depositional environmen); and (iii) authigenic pyrite (newly crystallized and/or recrystallized pyrite formed after deposition). The detrital grains contain mineral inclusions such as biotite, feldspar, apatite, zircon, sphene, and various ore minerals, and fluid inclusions with daughter minerals. Most of the inclusions are incompatible with an origin by sulphidization. Recrystallized authigenic pyrite occurs in large quantities but only in horizons or localities which have been subjected to higher temperatures during the intrusion or extrusion of younger volcanic rocks. Important additional findings are the often substantial amounts of pyrite and small amounts of particles of gold found in Archaean granites (Hallbauer, 1982) as possible source rocks for the Witwatersrand detritus. Large differences in Ag and Hg content between homogeneous single gold grains within a hand specimen indicate a lack of metamorphic homogenization. The influence of metamorphism on the Witwatersrand pyrites can therefore be described as only slight and generally negligible.

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Geochemistry and origin of Mesoproterozoic metavolcanic rocks from Fisher Massif, Prince Charles Mountains, East Antarctica

Antarctic Science ◽

10.1017/s0954102096000120 ◽

1996 ◽

Vol 8 (1) ◽

pp. 85-104 ◽

Cited By ~ 23

Author(s):

E. V. Mikhalsky ◽

J. W. Sheraton ◽

A. A. Laiba ◽

B. V. Beliatsky

Keyword(s):

Tectonic Setting ◽

Active Continental Margin ◽

Volcanic Rocks ◽

Granulite Facies ◽

Island Arc ◽

Crustal Component ◽

Basaltic Rocks ◽

Metavolcanic Rocks ◽

High K ◽

Low K

Fisher Massif consists of Mesoproterozoic (c. 1300 Ma) lower amphibolite-facies metavolcanic rocks and associated metasediments, intruded by a variety of subvolcanic and plutonic bodies (gabbro to granite). It differs in both composition and metamorphic grade from the rest of the northern Prince Charles Mountains, which were metamorphosed to granulite facies about 1000 m.y. ago. The metavolcanic rocks consist mainly of basalt, but basaltic andesite, andesite, and more felsic rocks (dacite, rhyodacite, and rhyolite) are also common. Most of the basaltic rocks have compositions similar to low-K island arc tholeiites, but some are relatively Nb-rich and more akin to P-MORB. Intermediate to felsic medium to high-K volcanic rocks, which appear to postdate the basaltic succession, have calc-alkaline affinities and probably include a significant crustal component. On the present data, an active continental margin with associated island arc was the most likely tectonic setting for generation of the Fisher Massif volcanic rocks.

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Density determinations of basic volcanic rocks of the Yellowknife supergroup by gravity measurements in mine shafts—Yellowknife, Northwest Territories

Geophysics ◽

10.1190/1.1441036 ◽

1980 ◽

Vol 45 (1) ◽

pp. 18-31 ◽

Cited By ~ 3

Author(s):

R. A. Gibb ◽

M. D. Thomas

Keyword(s):

Volcanic Rocks ◽

Volcanic Belt ◽

Mine Shaft ◽

Average Interval ◽

Basaltic Rocks ◽

Surface Samples ◽

Gravity Measurements ◽

Vertical Density ◽

Basic Volcanic

Gravity measurements were made in two gold mine shafts sunk in the Archean Yellowknife greenstone belt to determine the in‐situ densities of basic volcanic rocks of the Kam formation, Yellowknife supergroup. Thirteen stations were occupied between the surface and a depth of 608 m at an average interval of about 50 m in the C shaft of Giant Yellowknife Mines Limited, and 14 stations were occupied between the surface and a depth of 1598 m at an average interval of about 120 m in the Robertson shaft of Con mine, Cominco Limited. Densities were computed using the terminology of borehole gravimetry with appropriate corrections for surface terrain and underground voids such as shafts, drifts, and stopes. Weighted mean in‐situ densities of [Formula: see text] (36 to 608 m depth) and [Formula: see text] (surface to 1598 m depth) were obtained from the gravity measurements for the Giant and Robertson sections, respectively; these values compare with mean densities of 2.82 and [Formula: see text] obtained from rock samples collected at the underground gravity stations. Sheared specimens and massive specimens collected at both underground and surface gravity stations have mean densities of 2.80 and [Formula: see text], respectively. Unaltered surface samples collected at stratigraphic intervals of about 150 m throughout the entire volcanic sequence have a mean density of [Formula: see text]. Core samples obtained from holes drilled from the bottom of C shaft extend the vertical density profile for the Giant section from a depth of 608 to 1416 m; the mean density of these samples is [Formula: see text]. The lower bulk densities obtained from the mine shaft experiments reflect in part the high proportion of sheared rocks and in part the presence of lower‐density members of the Kam formation (andesite, dacite, tuff, breccia, and agglomerate) in the vicinity of the shafts, as opposed to purely massive basaltic rocks. A density of [Formula: see text] based on the proportion of low‐ and high‐density rocks in the volcanic belt is considered to be more representative of the Kam formation as a whole.

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Geochemistry of Siluro-Devonian Tobique volcanic belt in northern and central New Brunswick (Canada): tectonic implications

Canadian Journal of Earth Sciences ◽

10.1139/e89-108 ◽

1989 ◽

Vol 26 (6) ◽

pp. 1282-1296 ◽

Cited By ~ 23

Author(s):

J. Dostal ◽

R. A. Wilson ◽

J. D. Keppie

Keyword(s):

New Brunswick ◽

Mantle Source ◽

Upper Mantle ◽

Volcanic Rocks ◽

Volcanic Belt ◽

Continental Rift ◽

Basaltic Rocks ◽

Incompatible Elements ◽

Tectonic Implications

Siluro-Devonian volcanic rocks of the northwestern mainland Appalachians are found mainly in the Tobique belt of New Brunswick where they consist predominantly of bimodal mafic–felsic suites erupted in a continental-rift environment. The axis of the Tobique rift trends north-northeast – south-southwest, obliquely to the regional northeast–southwest trend of the Appalachians. These geometric relationships are interpreted as being the result of rifting in a sinistral shear regime produced during emplacement of the Avalon terrene. The basaltic rocks are continental tholeiites and transitional basalts derived from a heterogeneous upper-mantle source that was enriched in incompatible elements relative to the primordial mantle. The mantle source was probably affected by the subduction processes.

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Discerning asthenospheric, lithospheric, and crustal influences on the geochemistry of Quaternary basalts from the Iskut–Unuk rivers area, northwestern British Columbia

Canadian Journal of Earth Sciences ◽

10.1139/e95-117 ◽

1995 ◽

Vol 32 (9) ◽

pp. 1451-1461 ◽

Cited By ~ 5

Author(s):

Brian L. Cousens ◽

Mary Lou Bevier

Keyword(s):

Volcanic Rocks ◽

Volcanic Belt ◽

Volcanic Field ◽

Northwest Pacific ◽

Small Range ◽

Geochemical Composition ◽

Basaltic Rocks ◽

Depleted Mantle ◽

Mid Ocean Ridge ◽

Ocean Ridge

Pleistocene- to Holocene-age basaltic rocks of the Iskut–Unuk rivers volcanic field, at the southern terminus of the Stikine Volcanic Belt in the northern Canadian Cordillera, provide information on the geochemical composition of the underlying mantle and processes that have modified parental magmas. Basaltic rocks from four of the six eruptive centres are moderately evolved (MgO = 5.7–6.8%) alkaline basalts with chondrite-normalized La/Sm = 1.6–1.8, 87Sr/86Sr = 0.70336–0.70361, εNd = +4.4 to +5.9, and 206Pb/204Pb = 19.07–19.22. The small range of isotopic compositions and incompatible element ratios imply a common "depleted" mantle source for the basalts, similar to the sources of enriched mid-ocean ridge basalts from northwest Pacific spreading centres or alkali olivine basalts from the western Yukon. Positive Ba and negative Nb anomalies that increase in size with increasing SiO2 and 87Sr/86Sr indicate that the basalts are contaminated by Mesozoic-age, arc-related, Stikine Terrane crust or lithospheric mantle through which the magmas passed. Lavas from a fifth volcanic centre, Cinder Mountain, have undergone greater amounts of fractional crystallization and are relatively enriched in incompatible elements, but are isotopically identical to least-contaminated Iskut–Unuk rivers basalts. Iskut–Unuk rivers lavas share many of the geochemical characteristics of volcanic rocks from other Stikine Belt and Anahim Belt centres, as well as alkali olivine basalts from the Fort Selkirk volcanic centres of the western Yukon.

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