scholarly journals Geochronology and Geochemistry of Late Paleozoic Volcanic Rocks and Their Relationship With Iron and Molybdenum Deposits in Xilekuduk Area, Northern Margin of Junggar

2021 ◽  
Vol 9 ◽  
Author(s):  
Xiaofeng Wei ◽  
Hao Wei ◽  
Zhen Liao ◽  
Zhiwei Wang ◽  
Dong Li ◽  
...  
Keyword(s):  
Volcanic Eruption ◽  
Mineral Exploration ◽  
Volcanic Rocks ◽  
Island Arc ◽  
Element Geochemistry ◽  
Northern Margin ◽  
Two Phases ◽  
Basic Volcanic ◽  
Two Stages ◽  
Volcanic Activities

A large number of intermediate basic volcanic rocks and porphyry Cu-Mo deposits as well as volcanic-hosted magnetite deposit have been recently discovered in the Xilekuduk area. However, no reports concerning petrogenesis and age or their relationship with mineralization have been published to date. The purpose of this study was to make up for the absence of previous studies on Devonian volcanic activities in the area and to confirm the relationship between two stages of volcanic activities and mineralization so as to provide important theoretical basis for mineral exploration. Based on research results of zircon U-Pb geochronology and element geochemistry of volcanic rocks in the area, the ages of dacite, andesite, and stomatal andesite are considered as 375.2 ± 2.9 Ma, 386.5 ± 3.0 Ma, and 317.9 ± 2.9 Ma, respectively, corresponding to the Middle Devonian and Late Carboniferous Period. The Devonian volcanic rocks belong to the high-K calc-alkaline series and island arc volcanic rocks, which are enriched in LREE, strongly enriched in large ion lithophile elements Th, Rb, Ba, and K and relatively depleted in high-field strength elements (HFSEs) Nb, Ta, and Ti. The Carboniferous volcanic rocks are enriched in LREE, as well as the large ion lithophile elements Th, Rb, Ba, and K are strongly enriched, while depleted in the HFSEs Nb, Ta, and Ti; moreover, the contents of TiO2 and V are 0.94–0.97% and 178–183×10–6, which are higher than those of island arc basalts. According to mineralogical typomorphic characteristics and geochemical analysis, magnetite mineralization is divided into two phases. The early stratiform magnetite ore MT1 has magmatic characteristics, forming a volcanic rock type magnetite deposit related to Devonian volcanic eruption and sedimentation (375–386 Ma). The magnetite MT2 in the magnetite-quartz vein is considered as hydrothermal genesis, which is a metal mineral in the early metallogenic stage of Carboniferous (317.1 ± 2.9 Ma) volcanic eruption and subvolcanism, and may be related to porphyry molybdenum mineralization. Therefore, the volcanism and Fe-Cu-Mo mineralization in this area is characterized by multistage superimposed mineralization.

Composition, structure and tectonic analysis of the Shangrimuce arc-continent collision zone on the northern margin of the Central Qilian, NW China

2021 ◽  
Author(s):  
Hongyuan Zhang ◽  
Zhibin Lei ◽  
Bo Yang ◽  
Qing Liu ◽  
Haijun Zhang ◽  
...  
Keyword(s):  
Shear Zones ◽  
Oceanic Lithosphere ◽  
Late Ordovician ◽  
Island Arc ◽  
Qilian Mountain ◽  
Northern Margin ◽  
Early Ordovician ◽  
Collision Zone ◽  
Two Stages ◽  
Back Arc

<p>A 1:50000 regional survey, covering an area of about 2000 km<sup>2</sup>, was carried out in the Shangrimuce area of Qilian Mountain in Northwest China. The results show that during Caledonian, the northern margin of the Central Qilian block experienced collision with mature island arcs and subsequently northward expansion. In the Shangrimuce study area, five geological units have been identified; they are, form south to north, back-arc basin, early Ordovician island arc, inter arc basin, middle Late Ordovician island arc, and fore-arc and oceanic lithosphere amalgamation zone. </p><p>(1) back-arc basin. In the Yangyuchi- Shule River- Cuorigang- Wawusi area, there may be a back-arc spreading basin, and there should be spreading basins in this area. It is speculated that there was a northward reverse subduction in the late Ordovician, accompanied by a syenite body, a broad spectrum dyke swarms and an accretionary wedge zone in the whole area.</p><p>(2) early Ordovician island arc. In the Shangrimuce-Dander area, the Proterozoic basement granitic gneiss, the early Ordovician island arc block and the high-pressure geological body all occur in the form of thrust horses, forming a double metamorphic belt, which reveals the existence of ocean subduction to south in the early Ordovician. </p><p>(3) inter arc basin. On both banks of Tuolai River to the east of Yanglong Township, there are early Middle Ordovician inter-arc basins with oceanic crust. </p><p>(4) middle Late Ordovician island arc. To the north of Tuolai River, there is a middle Late Ordovician island arc belt. Both sides of the island arc zone experienced strong ductile shear deformation, which recorded a complex arc-continent collision. </p><p>(5) fore-arc and oceanic lithosphere amalgamation zone (Fig.1). The Yushigou area has developed a fore-arc and oceanic lithospheric amalgamation zone, with weakly deformed fore-arc flysch basin, strongly deformed siliceous rocks, pillow Basalt, diabase, gabbro, peridotite and other rock assemblages.</p><p>Combined with the characteristics of arc-continent collision zone in the Western Pacific, there are two stages of shear zone series (Fig.2). One is ductile shear zones formed by the South dipping gneissic belt, revealing the existence of oceanic subduction accretion wedge and emplacement of high-pressure rocks. Another superimposed one is north dipping. This indicates that the arc-continent collision caused by back-arc reverse subduction, which ultimately controls the overall geometric and kinematic characteristics of the shear zones in the region.</p><p><img src="https://contentmanager.copernicus.org/fileStorageProxy.php?f=gepj.8219836ca50067454890161/sdaolpUECMynit/12UGE&app=m&a=0&c=40b3389c641f2d0ca723e1527c32927e&ct=x&pn=gepj.elif&d=1" alt=""></p><p>Figure 1 United sections showing a Caledonian trench-arc system in the Qilian Mountain, NW China.</p><p><img src="https://contentmanager.copernicus.org/fileStorageProxy.php?f=gepj.8def566da50066084890161/sdaolpUECMynit/12UGE&app=m&a=0&c=e82258ecc235c4e618abd6c035b58232&ct=x&pn=gepj.elif&d=1" alt=""></p><p>Figure 2 Structural analysis at Hongyahuo, indicating two stages of deformation.</p><p>The research has been supported by projects from the Ministry of Land and Resources (No.201211024-04; 1212011121188) and the 2020 undergraduate class construction project from China University of Geosciences (Beijing) (No. HHSKE202003).</p><p> </p>

A Cambrian island arc in Iapetus: geochronology and geochemistry of the Lake Ambrose volcanic belt, Newfoundland Appalachians

1991 ◽  
Vol 128 (1) ◽  
pp. 1-17 ◽  
Author(s):  
G. R. Dunning ◽  
H. S. Swinden ◽  
B. F. Kean ◽  
D. T. W. Evans ◽  
G. A. Jenner
Keyword(s):  
Volcanic Rocks ◽  
Volcanic Belt ◽  
Detailed Examination ◽  
Island Arc ◽  
Trace Element Geochemistry ◽  
Geochemical Type ◽  
Element Geochemistry ◽  
South Central ◽  
Iapetus Ocean ◽  
Felsic Volcanic

AbstractThe Lake Ambrose volcanic belt (LAVB) outcrops as a 45 km long northeast-trending belt of mafic and felsic volcanic rocks along the eastern side of the Victoria Lake Group in south-central Newfoundland. It comprises roughly equal proportions of mafic pillow basalt and high silica rhyolite, locally interbedded with epiclastic turbidites. Volcanic rocks have been metamorphosed in the greenschist facies and are extensively carbonatized.U-Pb (zircon) dates from rhyolite at two, widely separated localities give identical ages of 513 ± 2 Ma (Upper Cambrian), and this is interpreted as the eruptive age of the volcanic sequence. Primitive arc and low-K tholeiites can be recognized on the basis of major and trace element geochemistry, ranging from LREE-depleted to LREE-enriched. Geochemical variation between mafic volcanic types is interpreted predominantly to reflect contrasts in source characteristics and degree of partial melting; some variation within each geochemical type attributable to fractional crystallization can be recognized. Detailed examination of some samples indicates that the heavy REE and related elements have locally been mobile, probably as a result of carbonate complexing.The LAVB is the oldest well-dated island arc sequence in Newfoundland, and perhaps in the Appalachian–Caledonian Orogen. Its age requires modification of widely held models for the tectonic history of central Newfoundland. It is older than the oldest known ophiolite, demonstrating that arc volcanism was extant before the generation of the oldest known oceanic crust in this part of Iapetus. It further demonstrates that there was a maximum of approximately 30 Ma between the rift-drift transition which initiated Iapetus, and the initiation of subduction. This suggests that the oceanic sequences preserved in Newfoundland represent a series of arcs and back arc basins marginal to the main Iapetus Ocean, and brings into question whether the Appalachian accreted terranes contain any remnants of normal mid-ocean ridge type Iapetan crust.

Platinum-group element geochemistry of the Panjal Traps: constraints on mantle melting and implications for mineral exploration

2021 ◽  
pp. SP518-2020-241
Author(s):  
J. Gregory Shellnutt ◽  
Kwan-Nang Pang ◽  
Liang Qi ◽  
Ghulam M. Bhat
Keyword(s):  
Mineral Exploration ◽  
Volcanic Rocks ◽  
Temperature Behaviour ◽  
Element Geochemistry ◽  
Tiny Amount ◽  
Sulfide Melt ◽  
Platinum Group ◽  
Group 2 ◽  
Different Origins ◽  
Group 1

AbstractForty-two volcanic rocks of the Panjal Traps were analyzed for platinum-group elements (PGE) to investigate magma genesis, high-temperature behaviour, and exploration potential of these elements. The PGE data exhibit substantial variability and show no systematic relation to their low-Ti or high-Ti affinity. Instead, the basalts can be subdivided into PGE-undepleted (group 1) that has ∑PGE > 10 ppb and Cu/Pd < 30000, and PGE-depleted, that consists of a subgroup showing limited (group 2A) or substantial depletion in IPGE relative to Ni (group 2B). The group 1 samples indicate a S-undersaturated history whereas the group 2 samples might have different origins in terms of S-saturation. Fractionation of a tiny amount of sulfide melts (0.075 to 0.1%) from a representative group 1 sample accounts for the chalcophile element patterns observed in the group 2B samples. The relatively high Cu/Pd, unfractionated Ni/Ir, and low PGE abundances observed in the group 2A samples cannot be explained by equilibration of an immiscible sulfide melt alone, and probably requires decomposition of residual sulfides into sulfide melt and a mss in the mantle restite. Our results question the notion that the coexistence of PGE-undepleted and PGE-depleted magmas are prospective in the exploration of magmatic Ni-Cu-(PGE) sulfide mineralization.

Early Devonian volcanism in the eastern Klamath Mountains, California: evidence for an immature island arc

1985 ◽  
Vol 22 (2) ◽  
pp. 214-226 ◽  
Author(s):  
H. Lapierre ◽  
F. Albarede ◽  
J. Albers ◽  
B. Cabanis ◽  
C. Coulon
Keyword(s):  
Volcanic Rocks ◽  
Island Arc ◽  
Magmatic Differentiation ◽  
Klamath Mountains ◽  
Early Devonian ◽  
Volcanic Sequence ◽  
Volcanic Succession ◽  
Basic Volcanic ◽  
Almost All ◽  
Low K

The Early Devonian volcanic sequence of the eastern Klamath Mountains (northern California) consists of the Copley Greenstone, a basalt–andesite series, overlain by the Balaklala Rhyolite. All the rocks are metamorphosed to the greenschist facies.The Copley Greenstone consists of massive flows and pyroclastic deposits in the lower part that are overlain by pillow lavas. No sediments are interlayered in the volcanic pile except in the easternmost outcrop area, where sandstones with granitic debris and shaly tuffs are interbedded in the uppermost flows. High-Mg andesites occur only near the top of the basic volcanic succession. The Balaklala Rhyolite is formed of massive flows, breccias, and tuffs.The Copley volcanic rocks, poor in titanium, belong to a low-K tholeiitic suite formed in an island-arc geodynamic environment. The occurrence of olivine with chromium spinels in almost all the lava types, the enrichment in magnesium, chromium, and nickel, and the depletion in hygromagmaphile elements suggest that magmatic differentiation was a marginal process. The Balaklala Rhyolite shows very homogeneous petrographic and geochemical features, characteristic of tholeittic products.From its characteristics here described (pillowed flows, lack of sedimentation, presence of high-Mg andesites and low-K rhyolites, bimodality of the volcanism) the Early Devonian volcanic sequence represents an immature island arc related to a back-arc basin, similar to the present-day Mariana island arc.

The petrochemistry of the basic volcanic rocks of the South Connemara Group (Ordovician), western Ireland

1983 ◽  
Vol 120 (2) ◽  
pp. 141-152 ◽  
Author(s):  
P. D. Ryan ◽  
M. D. Max ◽  
T. Kelly
Keyword(s):  
Regional Metamorphism ◽  
Volcanic Rocks ◽  
Major And Trace Elements ◽  
Metamorphic Rocks ◽  
Low Grade ◽  
The South ◽  
Northern Margin ◽  
Southern Side ◽  
Western Ireland ◽  
Basic Volcanic

Summary16 samples of Ordovician basic volcanic rocks of the South Connemara Group, which abut the southern side of the metamorphic rocks of the Connemara massif in western Ireland, have been analysed for both major and trace elements. Although subject to low grade regional metamorphism and subsequently hornfelsed by the Galway Granite (400 Ma), their immobile element contents do not appear to be significantly disturbed. These elements characterise the metabasites of the South Connemara Group as ocean floor basalts having their origins in a marginal basin. The Skird Rocks Fault, separating the South Connemara Group from high grade metamorphic rocks of the Connemara massif, is consequently regarded as the northern margin of the vestiges of the lapetus Ocean which can be traced into, and along, the Southern Uplands Fault.

Stratigraphy, structure and evolution of the Tibetan–Tethys zone in Zanskar and the Indus suture zone in the Ladakh Himalaya

1983 ◽  
Vol 73 (4) ◽  
pp. 205-219 ◽  
Author(s):  
M. P. Searle
Keyword(s):  
Subduction Zone ◽  
Late Cretaceous ◽  
Volcanic Rocks ◽  
Ocean Basin ◽  
Suture Zone ◽  
Island Arc ◽  
Indian Plate ◽  
Northern Margin ◽  
Ladakh Himalaya ◽  
Late Tertiary

ABSTRACTThe Tibetan–Tethys zone of the Zanskar Himalaya shows a complete Mesozoic shelf carbonate sequence overlying metamorphic basement of the Central crystalline complex and Palaeozoic sedimentary rocks. Continental rifting in the Permian produced the alkaline and basaltic Panjal volcanic rocks and by Triassic time a small ocean basin was developed in the Indus-Tsangpo zone. Stable sedimentation continued until the Middle-Late Cretaceous when a thick sequence of tholeiitic to andesitic island arc lavas (Dras arc) were erupted in the basin above a N-dipping subduction zone. The Spontang ophiolite was emplaced southwards onto the Zanskar shelf edge during latest Cretaceous or earliest Tertiary times.Following emplacement of the Spontang ophiolite, deep-sea sedimentation ended abruptly with initial collision between the Indian plate and the Dras island arc. Emplacement of the massive Ladakh (Trans-Himalayan) batholith along the southern margin of Tibet in late Cretaceous-Eocene time occurred by crustal melting as a result of northward subduction of Mesozoic oceanic crust along the Indus subduction zone. Southward-directed thrusting in both Zanskar and Indus zones accompanied ocean closure during the late Cretaceous–Eocene. Late Tertiary compression caused intense folding, overturning and a phase of northward-directed thrusting along the Indus suture zone and the northern margin of the Tibetan–Tethys zone, resulting in a large amount of crustal shortening.

Mafic igneous rocks and mineralisation in the Palaeoproterozoic Ketilidian orogen, South-East Greenland: project SUPRASYD 1996

1997 ◽  
pp. 66-74
Author(s):  
Henrik Stendal ◽  
Wulf Mueller ◽  
Nicolai Birkedal ◽  
Esben I. Hansen ◽  
Claus Østergaard
Keyword(s):  
Mineral Exploration ◽  
Volcanic Rocks ◽  
Shear Zones ◽  
Field Work ◽  
Igneous Rocks ◽  
Border Zone ◽  
The South ◽  
East Greenland ◽  
North West ◽  
Arc Setting

NOTE: This article was published in a former series of GEUS Bulletin. Please use the original series name when citing this article, for example: Stendal, H., Mueller, W., Birkedal, N., Hansen, E. I., & Østergaard, C. (1997). Mafic igneous rocks and mineralisation in the Palaeoproterozoic Ketilidian orogen, South-East Greenland: project SUPRASYD 1996. Geology of Greenland Survey Bulletin, 176, 66-74. https://doi.org/10.34194/ggub.v176.5064 _______________ The multidisciplinary SUPRASYD project (1992–96) focused on a regional investigation of the Palaeoproterozoic Ketilidian orogenic belt which crosses the southern tip of Greenland. Apart from a broad range of geological and structural studies (Nielsen et al., 1993; Garde & Schønwandt, 1994, 1995; Garde et al., 1997), the project included a mineral resource evaluation of the supracrustal sequences associated with the Ketilidian orogen (e.g. Mosher, 1995). The Ketilidian orogen of southern Greenland can be divided from north-west to south-east into: (1) a border zone in which the crystalline rocks of the Archaean craton are unconformably overlain by Ketilidian supracrustal rocks; (2) a major polyphase pluton, referred to as the Julianehåb batholith; and (3) extensive areas of Ketilidian supracrustal rocks, divided into psammitic and pelitic rocks with subordinate interstratified mafic volcanic rocks (Fig. 1). The Julianehåb batholith is viewed as emplaced in a magmatic arc setting; the supracrustal sequences south of the batholith have been interpreted as either (1) deposited in an intra-arc and fore-arc basin (Chadwick & Garde, 1996), or (2) deposited in a back-arc or intra-arc setting (Stendal & Swager, 1995; Swager, 1995). Both possibilities are plausible and infer subduction-related processes. Regional compilations of geological, geochemical and geophysical data for southern Greenland have been presented by Thorning et al. (1994). Mosher (1995) has recently reviewed the mineral exploration potential of the region. The commercial company Nunaoil A/S has been engaged in gold prospecting in South Greenland since 1990 (e.g. Gowen et al., 1993). A principal goal of the SUPRASYD project was to test the mineral potential of the Ketilidian supracrustal sequences and define the gold potential in the shear zones in the Julianehåb batholith. Previous work has substantiated a gold potential in amphibolitic rocks in the south-west coastal areas (Gowen et al., 1993.), and in the amphibolitic rocks of the Kutseq area (Swager et al., 1995). Field work in 1996 was focused on prospective gold-bearing sites in mafic rocks in South-East Greenland. Three M.Sc. students mapped showings under the supervision of the H. S., while an area on the south side of Kangerluluk fjord was mapped by H. S. and W. M. (Fig. 4).

scholarly journals Morphotectonic Analysis along the Northern Margin of Samos Island, Related to the Seismic Activity of October 2020, Aegean Sea, Greece

Geosciences ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 102
Author(s):  
Paraskevi Nomikou ◽  
Dimitris Evangelidis ◽  
Dimitrios Papanikolaou ◽  
Danai Lampridou ◽  
Dimitris Litsas ◽  
...  
Keyword(s):  
Fault Zone ◽  
Seismic Activity ◽  
Volcanic Rocks ◽  
Active Tectonics ◽  
Normal Fault ◽  
Aegean Sea ◽  
Northern Margin ◽  
The North ◽  
Eastern Aegean ◽  
Half Graben

On 30 October 2020, a strong earthquake of magnitude 7.0 occurred north of Samos Island at the Eastern Aegean Sea, whose earthquake mechanism corresponds to an E-W normal fault dipping to the north. During the aftershock period in December 2020, a hydrographic survey off the northern coastal margin of Samos Island was conducted onboard R/V NAFTILOS. The result was a detailed bathymetric map with 15 m grid interval and 50 m isobaths and a morphological slope map. The morphotectonic analysis showed the E-W fault zone running along the coastal zone with 30–50° of slope, forming a half-graben structure. Numerous landslides and canyons trending N-S, transversal to the main direction of the Samos coastline, are observed between 600 and 100 m water depth. The ENE-WSW oriented western Samos coastline forms the SE margin of the neighboring deeper Ikaria Basin. A hummocky relief was detected at the eastern margin of Samos Basin probably representing volcanic rocks. The active tectonics characterized by N-S extension is very different from the Neogene tectonics of Samos Island characterized by NE-SW compression. The mainshock and most of the aftershocks of the October 2020 seismic activity occur on the prolongation of the north dipping E-W fault zone at about 12 km depth.

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