Pavel A. Balykin

The Khao Que-Tam Tao gabbro-granite massif, Northern Vietnam: A petrological indicator of the Emeishan plume

New data obtained on the Khao Que-Tam Tao gabbro-granite pluton (Northern Vietnam) are discussed. It was established that this pluton was formed at the Permian-Triassic boundary (250.5 ± 3.2 Ma, 40Ar/39Ar isotopic age). Morphologically, it represents a hypabyssal fracture intrusion. The first stage was marked by the intrusion of the picrobasaltic melt, the differentiation of which resulted in the formation of the layered peridotite-gabbro series and the quartz-bearing monzodiorites and granophyres in its endocontact at the final stage. At the second stage, the Khao Que peridotite-gabbro massif was broken in its central part by a fault, along which the Tam Tao granodiorite-granite massif was localized. Numerical simulation using the COMAGMAT program for the basic system and geochemical estimates for the granite system allow the statement that the mafic and granitic melts evolved independently, and their final products were quartz-bearing monzodiorite and granophyre, on the one hand, and aplites and pegmatites, on the other hand. The compositional correlation of the Permian-Triassic magmatic associations in Northern Vietnam (the Nui Chua gabbro pluton and the Khao Que-Tam Tao gabbro-granite and Pia Bioc granite plutons) and in Southeast China (flood basalts) allows these complexes to be regarded as a part of a single large igneous province produced by the Emeishan plume activity.

International Perspectives on the Effects of Climate Change on Inland Fisheries

A range of perspectives is presented from the International Fisheries Section of the American Fisheries Society on climate change effects on inland fisheries from standing and flowing waters in Africa, Asia, Australia, Europe, and Latin America.

Permian – Triassic Metallogeny

Three mineralization complexes were formed during the Permian – Triassic period in the following order: PGE-Cu-Ni and V-Ti – Fe of magmatic origin; Au – sulfide and Sn – sulfide. The first ore complex including magma-origin Cu-Ni-(Pt) mineralization is related to ultramafic - mafic magmatic differentiation in structures of Song Da, Song Hien rifts (such as Ban Phuc, Ban Khoa, Suoi Cun blocks, etc.) as well as being connected to layered gabbro – peridotite intrusions in folded structures surrounding the Song Chay anticlinoria (such as Nui Chua and Khao Que blocks). Cu-Ni-(PGE)-type mineralization is found in Ta Khoa – and Suoi Cun-type mafic – ultramafic, while Ti-Fe-(V) (mainly) ore type and Cu-Ni-(PGE) are characterized for Nui Chua-type ultramafic intrusion. Radiometric age determined for Ta Khoa ultramafic magmas is 257–270 Ma, for Suoi Cun is 260 Ma and for Nui Chua mafic magmas is 251 Ma; the ages are also applied for the related ore formation, implying that the mineralization of Cu-Ni-(PGE) and Ti-Fe-(V) in geological structures in northern Vietnam was associated with Permian – Triassic tectono-magmatic period. Besides, associated with Cu-Ni-(PGE) ore type is highly potential Ni-Co-As hydrothermal mineralization (discovered in inner contact zones in Ban Phuc block within the Song Da structure). Au-sulfur-type ore complex is widely developed in various structures in northern Vietnam; Representatives of Sn-sulfur-type ore complex are located to the southern margin of Song Hien rift and Lo Gam belt.

Permian – Triassic Pluton – Volcanic Magmatic Associations in the Song Hien Structure, Northeast Vietnam

The Song Hien Basin in northeast Vietnam is linear- shaped, running in the northwest – southeast direction from Vietnam-China border to the easternmost of Lang Son province; with a total length about 200 km the structure divides the Ha Lang belt to the northeast and Phu Ngu belt in the south and southwest. Permian – Triassic magmatism comprises pluton-volcanic felsic and mafic bimodal magmatic associations, including basalt, gabbrodolerite – dolerite (and lherzolite-gabbronorite); rhyodacite – rhyolite and granite. These magmatic associations are spatially, temporally and genetically related. Detailed mineralogical, geochemical and chemically mineralized studies have been conducted intensively on the Song Hien magmatism; among these, the mafic and ultramafic magmas have been described separately while gabbrodolerites were grouped to pluton-volcanic basaltoidic associations. Formation ages of lhrzolite and gabbro-dolerite are 260–262 Ma, while rhyolite – 246 Ma. Geochemical and isotopic data show genetic relationship between basalts and gabbro-dolerite and rhyolite and porphyric granite.

Metallogeny in the Cenozoic

The Cenozoic mineralization in structures associated with the Red River shear zone (RRSZ) in northern Viet Nam includes the following mineralized ore types TR- (U-Th)-Pb-Zn and TR- (U-Th) –Ba-F, Au-Cu in the Song Da rift zone. The origin of the mineralizations is spatially and (possibly) temporally related to the formation of Paleogene potassic mafic – ultramafic and silisic associations. Molybdenum –precious metals (Mo-W-Cu-Au) in the along with Cu-Au mineralization in the Phan Si Pan uplift are related to Paleogene granitoidic magmatism in the Ye Yen Sun complex. Beside, Cu-(Au – REE) mineralizationsin the Phan Si Pan Uplift are described.

An Overview on the Structures, Tectonics and Magmatic Activities in North Vietnam

Reconstruction of paleo-geodynamic framework of Vietnam in the relation to major tectonic events in southeast Asia reveals that Paleozoic structures in Northern Vietnam (from northeastern Song Ma suture zone northward) were developed in the southern and southeastern margins of the Yangtze Block. Northern Vietnam is divided into two major folding systems, based on their positions relative to the Song Hong fault zone.

Paleogene Potassic and Ultra-potassic Volcano-Plutonic Associations in the Song Da Rift

Paleogene potassic and ultra-potassic alkaline volcano-plutonic magmas in the northwestern Song Da structure and in the boundary between this structure and the Phan Si Pan uplift are compositionally diversified, ranging from alkaline mafic (lamproite, absarokite, minette) to alkaline felsic (trachyte and syenite). Geological, mineralogical, geochemical and isotpe characteristics of Ol-Cpx, Cpx-Phl lamproites, absarokite, minette and trachyte and syenite are presented. Lamproite in the northwest Vietnam are compared with low-Ti Mediterranean-type lamproite. Study on the inclusions in clinopyroxene from lamproite showed formation of the potassic and ultra-potassic magmas in the Song Da rift zone is a result of fractional crystallization of melts whose compositions were equivalent to lamproitic magmas, which were subsequently evolved by magma differentiation would lead to form diversified magmas. Mineralogical and geochemical studies of trachyte and syenite showed their genetic relationship. The formation ages of lamproite, trachyte and syenite (42–30 Ma; Ar-Ar and Rb-Sr methods) suggest they are late Paleogene intraplate extension activities in the northwest Vietnam.

Plutonic: Volcanic Associations in the Tu Le Basin and Phan Si Pan Uplift, Northwest Vietnam

Major and trace elements and whole rock Sr–Nd isotope data of Late Permian silicic plutonic and volcanic rocks from the Phan Si Pan–Tu Le region in NW Vietnam were studied in order to establish their petrogenetic relationship with the magmatic rocks of the Song Da zone (NW Vietnam) and the alkaline silicic rocks of the Panxi area of the Emeishan large igneous province (ELIP) in SW China. The granites and rhyolites have geochemical characteristics of anorogenic granites (e.g. high Fe# and high Ga/Al) and are further subdivided based on mineralogy. The Phu Sa Phin and Muong Hum granites contain sodic to sodic–calcic amphiboles and sodic pyroxene, while the Phan Si Pan granite does not. The Phu Sa Phin and Muong Hum granites occasionally show peralkaline to metaluminous compositions, while the Phan Si Pan granites and the Tu Le rhyolites have metaluminous to peraluminous compositions. The chondrite-normalized REE patterns and the primitive mantle-normalized spidergrams (enrichment in high field strength elements) are similar to those of the Song Da silicic rocks. The eNd(t) values range from weakly negative to moderately positive values (−2.2 to +2.2), suggesting the silicic rocks may be assimilated by basement rocks during magma emplacement. Permian magmatic rocks in the Phan Si Pan–Tu Le region are petrologically, geochemically and geochronologically comparable to those of the inner zone of ELIP.

Gabbro and Syenite Intrusions in the Lo Gam Structure, Northeast Vietnam

Lo Gam structure (including Phu Ngu) in northeast Vietnam comprises Permian – Triassic gabbro-peridotite, monzogabbro, high-Al granite and syenite intrusive blocks. The studies have also revealed that gabbro – syenite magmas in folded structures around southeastern margin of the Song Chay anticlinoria form three association types distinguished by their co-existing mineral assemblages, mineralogical compositions and geochemical indexes (titanium content and alkalinity): layered peridotite- gabbro (Nui Chua complex), biotite granite (Phia Bioc complex) and compositionally heterogeneous gabbro-syenite. The uniformity of their geochemical and isotopic compositions indicates, on the one hand, generic relationship of the gabbro and syenite, and geochemically common source origin of the magmas, on the other. Being enriched in large ionic lithophile elements (LILE), rare earth elements (REE) and strongly depleted in Nb, Ta and Zr the gabbroid and syenite magmas reflect typical geochemistry of an above-subduction-zone affiliation. This is the basic feature of Permian – Triassic pluton – volcanic and plutonic magmatic associations in various geological structures in northeastern Vietnam. The formation ages of lherzolite and monzogabbro (Nui Chua complex), gabbro, syenite and biotite granite (Cho Don area) are 251–246 Ma (U-Pb, zircon, SHRIMP, Ar-Ar).

Permian – Triassic Magmatic Activity in the Song Da Structure

Late Permian mafic-ultramafic volcanic and sub-volcanic rocks in the Song Đa Rift include four different associations in terms of low-Ti and high-Ti types. Low-Ti, high-Mg volcanic and sub-volcanic rocks are composed of komatiite, komatiitic basalt and basalt and are divided into three groups according to their petrological and geochemical features. Chemical composition of rocks of the komatiite-basalt association is alkali-low (but rather Na-high), very Ti-low, varying from Al-high komatiite to Al-low basalt. They are characterized by high content of Mg, Al, Ni, Co, Cu and Cr, and low of Ti, Fe, Na, K, P, Rb, Ba, Sr, Nb, Ta, Nd, Hf, Zr and REE. In general, based on geochemical and isotopic characteristics the Song Đa mafic-ultramafic rocks of the komatiite-basalt association may be products of a melt derived from depleted mantle suffering the impact of mantle plume. Digital modeling showed that the initial melt composition was correspondent to komatiitic basalt. Eruption ages of the magmas are 257 ± 24 Ma (by Rb/Sr age dating), and 270 ± 21 Ma (by Re/Os age dating).