scholarly journals U - Pb zircon age of gabbro and plagiogranite in Hiep Duc, Quang Nam and their geological significances

2021 ◽  
Vol 62 (4) ◽  
pp. 21-28
Author(s):  
Thanh Xuan Ngo ◽  
Hau Vinh Bui ◽  
Hai Thanh Tran ◽  
Binh Van Phan ◽  
Hanh Hong Thi Nguyen ◽  
...  
Keyword(s):  
Island Arc ◽  
Age Dating ◽  
Ophiolite Complex ◽  
Zircon Age ◽  
Research Results ◽  
Northeastern Part ◽  
Late Cambrian ◽  
Arc Magma ◽  
Magma Series

The gabbro and plagiogranite magmas of the Ngoc Hoi and Dieng Bong complexes are mainly distributed in the northern part of the Kon Tum block. They were previously considered parts of the Tam Ky - Phuoc Son ophiolite complex. In this study, 02 samples of gabbro and plagiogranite were collected from the Hiep Duc area. Petrographic characteristics showed that the rocks were highly foliated and weakly metamorphosed; the schist formed after the crystallization of the rocks. U - Pb zircon age dating from the gabbro rocks as 497.7±1.4 Ma, similar to the plagiogranite age of 498.0±1.3 Ma. The available results in the northern Kon Tum block and Laos indicate the existence of magma series formed during the Late Cambrian period that is probably extended from the northern Kon Tum block to the northeastern part of Laos. The research results on the northern Kon Tum block also confirmed two types of magma in the area: island - arc magma complex and ophiolite type magma complex.

Geochronology of the Twillingate Granite and Herring Neck Group, Notre Dame Bay, Newfoundland

1976 ◽  
Vol 13 (11) ◽  
pp. 1591-1601 ◽  
Author(s):  
Harold Williams ◽  
R. D. Dallmeyer ◽  
R. K. Wanless
Keyword(s):  
New World ◽  
Linear Array ◽  
Volcanic Rocks ◽  
Ocean Basin ◽  
Late Ordovician ◽  
Island Arc ◽  
Zircon Age ◽  
Mafic Dike ◽  
Plate Convergence ◽  
Late Cambrian

Zircons from the Twillingate Granite form a linear array with a concordia intercept of 510 + 17 – 16 m.y. Mafic dikes that cut deformed granite along the southern contact of the pluton at New World Island record 40Ar/39Ar hornblende ages of 440 ± 10 and 473 ± 9 m.y. These ages indicate that the mafic dikes are Ordovician, and confirm their correlation with mafic volcanic rocks of the nearby Herring Neck Group. The dates also suggest that Herring Neck volcanism and mafic dike intrusion extended from Early to Late Ordovician. Together with the zircon age, they define a narrow chronologic bracket for intrusion, deformation, and metamorphism of the Twillingate Granite (`~510–475 m.y.).Within the central portion of the Twillingate pluton. a metamorphosed mafic dike cutting massive granite and an amphibolite inclusion within Foliated granite yield similar,40Ar/39Ar hornblende ages of 443 ± 11 and 438 ± 9 m.y. These ages are anomalously young compared with the 473 m.y. age of a mafic dike cutting deformed granite at New World Island. They are interpreted to indicate prolonged metamorphism and/or slower post-meta mo rphic cooling for central portions of the pluton compared to its southern margin.The isotopic ages support the view that the Twillingate Granite and nearby mafic volcanic rocks are collectively part of a single island-arc complex. The granite may have been generated during a period of subduction as sociated with plate convergence and closing of the proto-Atlantic ocean. A 510 m.y. (Late Cambrian) age for the granite suggests that convergence began rather early in the evolution of the Northern Appalachians. In addition, where dated Newfoundland ophiolite suites appear to be younger than, or contemporaneous with some granitic plutons (such as Twillingate), it is likely that they formed in a marginal ocean basin environment behind an older island-arc terrane.Les zircons du granite de Twillingate forment un réseau linéaire avec intercept à 510 + 17 – 16 Ma. Les dykes mafiques qui recoupent le granite déformé le long de la bordure sud du pluton à New World Island donnent des âges 40Ar/39Ar pour la hornblende de 440 ± 10 et de 473 ± 9 Ma. Ces âges indiquent que les dykes mafiques sont Ordoviciens et confirment leurs liens avec des roches mafiques volcaniques du groupe de Herring Neck dans le voisinage. Les dates suggèrent aussi que le volcanisme de Herring Neck et l'intrusion de dykes mafiques se sont produits du début à la fin de l'Ordovicien. Avec les âges des zircons, ils définissent un intervalle de temps assez court pour l'intrusion, la déformation et le métamorphisme du granite de Twillingate (~510–475 Ma).A l'intérieur de la portion centrale du pluton de Twillingate, un dyke mafique métamorphisé recoupant un granite massif et une inclusion d'amphibolite dans un granite foliacé donnent des âges 40Ar/39Ar semblables pour les hornblendes de 443 ± 11 et 438 ± 9 Ma. Ces âges sont anormalement faibles si on les compare avec l'âge de 473 Ma du dyke mafique qui recoupe le granite déformé de New World Island. On les interprète comme indiquant un métamorphisme prolongé et/ou un refroidissement post-métamorphique plus lent pour les portions centrales du pluton par comparaison à sa bordure sud.

scholarly journals Cr - spinel and clinopyroxene compositions from metagabbro of Nui Ngoc complex in Tam Ky area: evidence of island - arc magma

2021 ◽  
Vol 62 (5) ◽  
pp. 1-11
Author(s):  
Thanh Xuan Ngo ◽  
Du Khac Nguyen ◽  
Dao Anh Vu . ◽  
Chi Thi Pham ◽  
Hanh Hong Thi Nguyen ◽  
...  
Keyword(s):  
Suture Zone ◽  
Island Arc ◽  
Research Results ◽  
Continental Arc ◽  
Study Results ◽  
Ophiolitic Complex ◽  
Arc Magma

The hornblende and biotite - bearing metagabbro of the Nui Ngoc complex were exposed into a few small blocks in the southwest Tam Ky city and were viewed as parts of the Tam Ky - Phuoc Son ophiolitic complex (TPO). These rocks were undergone mylonitic deformation and metamorphism. The rocks consist mainly of orthopyroxene, clinopyroxene, plagioclase, olivine, hornblende, biotite and very few microscopic Cr - spinel. The clinopyroxene and Cr - spinel minerals were analyzed for their composition by EPMA, the results showed that: (1) The clinopyroxenes have low Al2O3 (3,2÷3,5 wt %), TiO2 (0,70÷0,82 wt %) contents and (2) the Cr - spinels have low TiO2 (0,23÷0,58 wt %) content and Mg#100* (Mg/ (Mg+Fe2+)) (32÷42) but has medium Cr# (Cr/ (Cr+Al)) (45÷52).These features are similar to those of rocks formed in anoceanic - oceanicsubduction zone that was reported for the plagiogranite of Dieng Bong complex nearby. This study results combined with previous research results in the Tam Ky - Phuoc Son suture zone show the existence of island arc, continental arc, and MOR - magmatic types.

scholarly journals Aleutian island arc magma production rates and mechanisms

2019 ◽  
Author(s):  
Yongliang Bai ◽  
Diya Zhang ◽  
Dongdong Dong ◽  
Shiguo Wu ◽  
Zhenjie Wang
Keyword(s):  
High Temperature ◽  
Production Rate ◽  
Island Arc ◽  
Mantle Melting ◽  
Fracture Zones ◽  
Seismic Profiles ◽  
Production Rates ◽  
Aleutian Arc ◽  
Slab Dehydration ◽  
Arc Magma

Abstract. The variation in island arc magma production rates and their influencing mechanisms are of great significance since island arc magma is considered a main source of continental crust growth. The island arc magma directly originates from the molten mantle wedge, and the mantle melting is driven by fluids or melts from the subducted slab. Slab dehydration flux mainly depends on the slab thermal structures, and subducted slab melting requires a sufficiently high temperature. For the Aleutian subduction system, the subducted Pacific Plate has diverse thermal structures due to the existing fracture zones, ridges and slab window, so it is an ideal region for arc magma production rate research. However, the previous estimations are based on seismic profiles that only provide magma production rates at specific regions of the Aleutian arc, and these results are controversial. Here, we design a magma production rate estimation method based on gravity inversion constrained by deep seismic profiles. The first overview map of magma production rates along the Aleutian arc strike demonstrates that the magma production rates have the same trend as the slab dips, and the peaks correspond to the subduction of the fracture zones and ridges. The potential mechanisms for these correlations are as follows: (1) Slab water flux at subarc depths increases with increasing slab dip. More fluid flux would induce more mantle melting, and so the arc magma production rates are increased. (2) Water-rich serpentine is formed by hydrothermal alteration on or near the surface of the subducted slab when there are fracture zones. Serpentine decomposition at a depth of 80–120 km releases fluids in addition to the fluids released during normal slab dehydration. Therefore, more fluids induce more mantle melting and correspond a larger magma production rate. (3) The slab located in the Emperor Seamounts has a relatively high temperature and is also weak, so its melting is easier. Similarly, more slab melt means more mantle melt and a higher island arc magma production rate.

The geochemistry of marine sediments, island arc magma genesis, and crust-mantle recycling

1989 ◽  
Vol 94 (1-2) ◽  
pp. 1-21 ◽  
Author(s):  
Dalila Ben Othman ◽  
William M. White ◽  
Jonathan Patchett
Keyword(s):  
Marine Sediments ◽  
Island Arc ◽  
Magma Genesis ◽  
Arc Magma

Slab melt as metasomatic agent in island arc magma mantle sources, Negros and Batan (Philippines)

Island Arc ◽  
2008 ◽  
Vol 9 (4) ◽  
pp. 472-486
Author(s):  
Fernando G. Sajona ◽  
Rene C. Maury ◽  
Gaëlle Prouteau ◽  
Joseph Cotten ◽  
Pieree Schiano ◽  
...  
Keyword(s):  
Island Arc ◽  
Metasomatic Agent ◽  
Mantle Sources ◽  
Slab Melt ◽  
Arc Magma

The Mings Bight Ophiolite Complex, Newfoundland: Appalachian oceanic crust and mantle

1978 ◽  
Vol 15 (5) ◽  
pp. 781-804 ◽  
Author(s):  
W. S. F. Kidd ◽  
John F. Dewey ◽  
John M. Bird
Keyword(s):  
Volcanic Rocks ◽  
Pillow Lava ◽  
High Temperature Deformation ◽  
Temperature Deformation ◽  
Ophiolite Complex ◽  
Pillow Lavas ◽  
Late Cambrian ◽  
Head Formation ◽  
Lava Sequence ◽  
Thrust Sheets

The Mings Bight Ophiolite Complex, of probable early Ordovician age, is disposed in four major thrust sheets with an eastward vergence at the northern end of the Baie Verte Lineament. This narrow ophiolitic belt, and (to the south) an adjacent zone of early Devonian volcanic rocks and sediments, were affected by a strong Acadian (Middle Devonian?) deformation between more resistant blocks consisting mainly of rocks that were deformed and regionally metamorphosed, prior to the development of the ophiolites and overlying mafic sediments and volcanic rocks, probably in Late Cambrian to earliest Ordovician. The ophiolite sequence and conformably overlying sedimentary and volcanic sequence define an overturned synclinal structure with an eastward vergence; the three western thrust sheets contain an inverted sequence, the eastern sheet is upright. The thick mafic volcaniclastic and pillow lava sequence overlying the ophiolite complex suggests that the ophiolite complex was generated as the the floor of a small rear-arc or intra-arc basin. The ophiolite complex, although dissected by faults, consists of an ordered sequence from non-cumulate tectonite harzburgite through cumulate ultramafic rocks, gabbro and sheeted dike complex to pillow lavas. The continuous, coastal exposures show the relationships between the lithologies of the ophiolite complex unusually clearly, and these are described in some detail. In particular, the relationships between the sheeted dikes and both the homogeneous upper gabbro and the pillow lavas, and the intrusive complexities and the high-temperature deformation in the layered gabbros and ultramafics, are very clearly displayed. An ocean floor fault containing diapiric serpentinite is preserved in one thrust sheet. Two new formations are proposed, for the mafic volcaniclastic sediments (Big Head Formation) and for the overlying pillow lavas (Barry–Cunningham Formation) above the ophiolite complex.

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