ISLAND ARC NATURE OF THE LAYERED INTRUSIONS
OF NÚI CHÚA COMPLEX IN FOLD BELTS OF NORTH
VIỆT NAM: EVIDENCES FROM THEIR GEOCHEMISTRY

HOÀNG HỮU THÀNH¹, GLEB V. POLYAKOV²,
PAVEL A. BALYKIN ², TRẦN QUỐC HÙNG¹, NGÔ THỊ PHƯỢNG²

¹Institute of Geological Sciences, Hà Nội, Việt Nam;
²United Institute of Geology, Geophysics and Mineralogy, Novosibirsk, Russia

Abstract: The layered intrusions of the Núi Chúa Complex situated in a distinct fold belt of North Việt Nam consist of a mineralization potential formation in titanomagnetite, Cu-Ni and PGE. They have been considered as mafic intrusions of Late Triassic orogenic stage. New geochemical data show that this magma has transitional features of low-potassium calc-alkaline series (IAB) of slightly tholeiitic trend (MORB). The concentration of REE of various rock-types of layered Núi Chúa intrusions is low and appears to belong to a depleted mantle source.  The REE pattern is similar to that of N-MORB and has a strong positive anomaly of Eu. The N-MORB normalized spidergram of trace elements shows a typical pattern of island arc magmatism with negative anomaly of Nb and Ta. This was also supported by low Nb/Yb ratio (0.20-0.80), Nb/Ta ratio (10-15), Th/Nb ratio (0.30-1.5), Ba/Th ratio (37.1-717), Nb/Y ratio (0.02-0.07), Ta/Nd ratio (0.009-0.02), Th/Yb ratio (0.06-0.8) as well. Thus, the layered intrusions of Núi Chúa Complex in North Việt Nam should be considered as island arc magmatism of subduction-related formations.

 

I.   INTRODUCTION

The layered intrusions situated in a distinct fold belt of North Việt Nam have been grouped into one intrusive ultramafic-mafic association named as Núi Chúa Complex of Late Triassic age [4, 5]. Some massifs of big size of this complex are: Núi Chúa, Khao Quế, Yên Chu and Tri Năng (Fig. 1). Because of their specific composition and ore mineralization (titanomagnetite, ilmenite, Cu-Ni sulphides, PGE), these intrusions have been being a major subject of research of geologists.

Lacroix [15], a French geologist, was the first to give informations on the gabbro composition of above mentioned intrusions. Further studies include regional geological mapping and ore prospecting. Some placer deposits of titanomagnetite and ilmenite have been found in Núi Chúa and Khao Quế massifs [4]. The layering and potential mineralization of Cu-Ni sulphides and PGE of these massifs were established in past years through the collaboration between Russian and Vietnamese geologists [1, 8, 12, 21, 26]. Intrusions of the Núi Chúa Complex are composed of layered dunite, pyroxenite, plagioclase-bearing peridotite, olivine gabbro, olivine gabbronorite, troctolite, anorthosite and others, which are similar to those of worldwide layered intrusions. However, there are questions on the petrogenesis of Núi Chúa Complex, e.g. according to mineralogical features, the intrusions of this complex reflect two associations of rock types: dunite-lherzolite-gabbronorite (Núi Chúa massif) and wehrlite-troctolite-gabbro (the other massifs) [12, 22] and in fact they may be divided into two diferent complexes, if their dating data have been recorded. On the other hand the age of these intrusions is not quite clear also, because the gabbro yields a Rb-Sr WR age ranging from 176 Ma for Tri Năng Massif to 195 Ma for Núi Chúa one [2], whereas the younger, spatially related and intruding them granite of the Phia Bioc Complex yields a K-Ar biotite age of 240 to 270 Ma [4] or even a long time believed Tertiary granosyenite of the Chợ Đồn Complex is considered now as much older by new dating data (231 Ma by Rb-Sr and Nd-Sm, pers. comm. of Nguyễn Trung Chí, 2003). In geological literature, both complexes (Núi Chúa and Phia Bioc) have been considered as magmatism of Late Triassic orogeny [4, 5, 26]. Some other workers considered them as magmatism related to Mesozoic continental rifting (e.g., [14]).

In order to understand the regional evolution of these magmatic complexes, a number of representative samples have been re-examined. Based on these new data, the tectonic setting in genesis of layered intrusions of the Núi Chúa Complex was newly defined as island arc. Such new point of view required a number of sutures which probably took place at Middle Paleozoic within South China block in Northeast Việt Nam. This scenario is similar to the suture along Sông Mã ophiolite belt. However, this paper touches only upon some aspects of petrogenetic questions on the layered intrusions and the implication of geochemical characteristics for identifying their tectonic setting.

II. GEOLOGICAL BACKGROUND

Layered intrusions of the Núi Chúa Complex are generally exposed in two different blocks - Indochina and South China - separated by the Sông Mã ophiolite belt. However, the forming age of the suture was different and varied from Paleozoic [20, 26] to Mesozoic [3, 13, 16]. The Núi Chúa and Khao Quế massifs are located in the South China block, near Thái Nguyên City, whereas the Tri Năng and Yên Chu massif are located in the Indochina block near Thanh Hoá and Vinh cities, respectively.     

Common features of all layered intrusions of the Núi Chúa Complex are that they intruded Middle Paleozoic sediments and were penetrated by Late Triassic granitic rocks (Phia Bioc Complex). In some places they are covered by Late Triassic molassic formations (western part of Núi Chúa massif). The association of these mafic and granitic intrusions in space and time has been leading many workers to group them to an unique magmatic formation characterizing the Mesozoic orogeny (i.e collision) in North Việt Nam [4, 5, 26].    

Being the biggest layered intrusion in Việt Nam, the Núi Chúa massif is exposed near Thái Nguyên City in an ellipsoid form of west-east direction with a surface of up to 60 km². The massif was cut by a lot of faults and a better complete section through all layers is exposed in eastern block of the massif. Some small placer deposits of titanomagnetite and ilmenite are found in the southern and eastern parts of the massif. Surrounding rocks consist of fine-grained sandstone, sericitic and cherty schists, dipping monoclinally northwestward with an angle of 50-70⁰. This feature makes the Núi Chúa massif similar to a sill or concordant lopolith. Hornfels and especial graphite are widespread in surrounding rocks of the contact zone that are also found as xenoliths within the intrusion. The above mentioned rocks were assigned to the Ordovician-Silurian flyschoid Phú Ngữ Formation of 2-2.5 km in thickness. In the middle part of this formation, 20 km north of Núi Chúa Massif, a sequence of ophiolite is exposed. The serpentinite member of this ophiolite is known as Paleozoic ultramafic Bản Rịn.

Complex [4, 26]. The presence of metabasalt, diabase and chert in the outcrops with serpentinite were found by us in 1999, but they are not studied yet. Thus, the Phú Ngữ Formation must be of oceanic crust. In the eastern side, a tectonic contact was observed between gabbro and Ordovician sandstone and schist of  the Nà Mọ Formation [26]

However, in the western side, the gabbro of the massif is unconformably covered by Norian-Rhaetian (T₃) coal-bearing beds of the Văn Lãng Formation and red beds of the Hà Cối Formation (J _1-2) [26].

 The Khao Quế layered intrusion is located at about 40 km north of the Núi Chúa massif. There, the massif has a subsymmetrical shape of smaller size, about 30 km². Similar to Núi Chúa, it intruded O-S sediments of the Phú Ngữ Formation. A lot of xenoliths of the latter occur in gabbro. The southern part of the masssif was cut by biotite granite of the Linh Đam massif, which belongs to Late Triassic Phia Bioc Complex. A lot of xenoliths of gabbro are found in granite near the contact zone between them. Beside the veins of granite-aplite, there are many veins of syenite in gabbro. This syenite probably belongs to the Chợ Đồn  Complex, which is present with some small bodies in this area. Some veins of fine-grained diabase, cutting the layering of gabbro, are also found.

The Yên Chu layered intrusion is located at about 10 km south of Vinh City of Northwest Trưòng Sơn fold belt. In fact, two small bodies of gabbro are exposed here at the boundary of a large granitic intrusion, among them the northern one is called as Yên Chu massif and the southern one as Rào Nậy massif. The former is much bigger in size (9 km²) and most investigations were concentrated on it. Based on the positive magnetic anomaly, the size of the massif might be much bigger in the depth. The gabbro of this massif intruded O-S sandstone and limestone of the Sông Cả Formation [5] and was cut by Late Triassic granite of Núi Ông massif which belongs to the Phia Bioc Complex. On the surface the layered intrusion occupies the northwestern part, whereas the border series occupy all other parts.

The Tri Năng layered intrusion is located at about 100 km northwest of Thanh Hóa City. The intrusion has the shape of a long lens (3 x 20 km) of NW-SE direction. In the northern and eastern sides, gabbro of the massif shows a tectonic contact with S₂-D₁ sandstone, schist and limestone of the Huổi Nhị Formation. Along the southern and southwestern boundaries, this gabbro intruded Middle Triassic volcano-sedimentary beds of the Đồng Trầu Formation and was cut by Tertiary granite of the Bù Rinh massif of the Bản Chiềng Complex [5].

III. LAYERING AND PETROGRAPHIC FEATURES

As other layered igneous intrusions in the world, the rocks of Núi Chúa Complex show a macroscopic and cryptic layering. The layers of rock types vary in composition and texture. They are alternated in the strata sequence and form different layering rhythms. Usually, a full rhythm is composed of melanocratic rocks at the bottom (dunite, peridotite), mesocratic rocks in the middle (olivine gabbro, gabbro-norite) and leucocratic rocks on the top (gabbro, anorthosite, pegmatite). However, such arrangement is not always stable and different rock types occur without any rhythm. Thickness of the layers varies from millimetres to several metres. Peridotite and dunite were found in thin, but stable long layers. Gabbro and troctolite usually form thick layers. Pyroxenite is found in layers, but mostly in lenses or veins, so they were grouped into late differentiation as pegmatite. Anorthosite is found only in very thin layers (some millimetres). The ratio of rock types of different melanocratic features is greatly variable in each intrusion. In the Yên Chu and Tri Năng massifs, dunite and peridotite are more frequently exposed than two other ones. Cryptic layering of the intrusions was established by decreasing anorthositic components (An %) in plagioclase or increasing forsteritic components in olivine from the bottom to the top. Characteristic and most frequent rock types of each massif are as follows.

    In the Núi Chúa Massif thick layers of medium- and coarse-grained olivine and olivine-bearing gabbronorite are exposed. They are composed of labrador (An: 64-68 %), hyalosiderite (Fo: 69-71 %), subcalcic diopside (Fs: 18-22 %) and bronzite (Fs: 26-30 %). The Khao Quế Massif is composed of medium-grained olivine gabbro, in which plagioclase varies its composition from An 75 to An 85 %, olivine: Fo 79-82% and pyroxene (mainly diopside): Fs 17-20%. The Tri Năng massif is similar to the Khao Quế one in main outcrops of olivine gabbro, but some layers of dunite and plagioclase-bearing peridotite were found. Gabbro is composed of labradorite (An: 65-70% or 75-85 % in dunite), subcalcic diopside (Fs: 13-15%) and olivine (Fo: 78-80%). The Yên Chu massif is a specific one of the Núi Chúa Complex. The presence of orthopyroxene in all rock types (olivine gabbro-norite, gabbro, peridotite, dolerite) makes it more similar to the Núi Chúa massif. On the other hand, the concentration of ore metals and the presence of peridotite and olivine melanocratic gabbro-norite in the outcrops and in drill cores make the Yên Chu massif similar to the Khao Quế and Tri Năng ones [12, 22]. Contrarily to other massifs, here chromspinel was found and the concentration of Cr reaches 25,200 ppm in peridotite [12].

Ore minerals (oxides, sulphides) are disseminated in layers of all massifs. However, the character of their  distribution is different and the reason of this difference is not quite clear. Usually ore minerals are concentrated in coarse-grained gabbro, gabbronorite, especial pegmatoidal pyroxenite and gabbro with quantity of 3-5% in most cases, rarely up to 8-10% or more. Average concentration of ore metals in layered series of studied intrusions are shown in Table 1. It is to note that the high concentration of nickel and copper in ultramafic and subultramafic series do not yield the relative high content of sulphide phases in many cases. This may be explained by the entering of ore metals, especially nickel into olivine during the crystallization as shown by results of microprobe analysis of rock-forming minerals from rock types of the layered intrusions [12, 22].  

Textures of different rock types in the intrusions vary from even medium-, coarse-grained in layered series to taxitic border series. The trachytoidal texture has been found also in layered series, but poikilitic one is characteristic only for border series. Usually olivine, pyroxene and plagioclase are cumulus minerals. The forming mechanism of  layering of studied intrusions is crystallization fractionation of  basic magma in situ with the replacement step by step  of  earlier and higher-temperature fractionated cumulates by  later and  lower-temperature ones which was described in detail in Hoµng H÷u Thµnh et al. [11].

Based on composition and petrographic features, the rock types in each massif are grouped into three series: layered, pegmatoidal and border related (B). The pegmatoidal type may be considered as a special for late formation of layered series. It is further subdivided into melanocratic (PgM: coarse-grained, giant-grained pyroxenites) and leucocratic (PgL: gabbroic pegmatites) types. The layered series are subdivided into ultramafic (U: dunite, peridotite), subultramafic (SU: melanocratic gabbro, gabbronorite, pyroxenite), mafic (M: troctolite, olivine-bearing gabbro, gabbronorite) and submafic (SM: leucocratic gabbro, gabbronorite, anorthosite) types [12, 22] as shown in Table 1.

The internal structure of layered intrusions has been mapped and shown [12, 22]. The dip of layers is generally great in all studied massifs, except Núi Chúa. Thus, all mafic massifs of the Núi Chúa Complex are well layered and may be compared with worldwide layered intrusions, such as Bushveld, Stillwater, Skaergaard and others. However, the Bushveld intrusion and other intrusions have been considered as rift-related magmatism (e. g. [18]).

Table 1. The average chemical composition of ptrographic groups of layered intrusions of the  Núi Chúa Complex (%)
with their base metals (ppm) and the amount of analytical samples shown in the brackets resprectively.

IV. GEOCHEMISTRY

1. Whole-rock chemistry

Although a great number of rock types from studied massifs were analyzed for investigation on major and selected ore elements (Table 1), nevertheless the necessary data on REE concentration and accurate isotope dating for them are still absent. So, many problems on petrogenesis of these layered intrusions are not able to be decided finally. In this work, new data of representative rock types from layered intrusions of the Núi Chúa Complex in North Việt Nam are reported (Table 2). Major element concentration of four samples: T180, T138b, N1266 and N1271 were determined in the Department of Geosciences, Franklin and Marshall College, USA, using X-ray Fluorescence (XRF) techniques on fused glass disks and pressed powder briquettes, respectively. Other 8 samples with notation “T" were analyzed in Taiwan. Major elements were determined in the Department of Geological Sciences, National Taiwan University, Taipei, using XRF method and trace element concentration was determined by ICP-MS techniques in the same Department. The composition of samples (B6115, Kp6404a, 1/119 and B7204) listed in Table 2 were analyzed in the United Institute of Geology, Geophysics and Mineralogy, Siberian Branch of Russian Academia of Sciences, Novosibirsk: major elements by XRF, trace elements (Rb, Sr, Y, Zr, Nb, Cu, Ni, V, Cr and Co) by atomic absorption spectrometer (AAS) and REE by Radiochemical or Instrumental Neutron Activation Analysis (RNAA, INAA).

Rocks of all studied massifs commonly are high in Al₂O₃, MgO and low in TiO₂, K₂O (see Tables 1 and 2). However, the value of composition is different in each intrusion that was resulted by complex differentiation and crystal fractionation of basic melt in situ during its cooling according to a sequence in which the higher temperature cumulates were formed in lower parts and then were replaced by lower temperature cumulates upwards [11]. Simultaneously, the variations in mineralogical composition are parallel with their chemical composition. Usually magnesium plays important role in the formation of layered intrusions [27]. The relationship of major elements of layers in the layered intrusions of Núi Chúa Complex and magnesium show that only iron has a positive correlation with the latter, whereas other elements (Si, Al, Ti, Ca, K) have a negative relation [11, 12, 22]. Such variations were established in different layered intrusions [6, 17, 18, 27].  Although the layered intrusions of Núi Chúa Complex have variation trends similar to those of Bushveld intrusion or Skaergaard one, the composition of individual layers is different. For instance, ultramafic layers of the Núi Chúa massif (Table 1) in comparing with the harzburgite of the Upper Critical Zone of Bushveld intrusion [6] have similar concentration of TiO₂ (0.20 against 0.15 %), Al₂O₃ (4.71 against 4.08%), CaO (4.15 against 3.27%), Na₂O (0.33 against 0.38%), K₂O (0.10 against 0.13%) and higher concentration of FeO (21.65 against 14.18%) and lower concentration of MgO (26.56 against 33.45%). Similarly, the dominant gabbronorite of Main Zone of the Núi Chúa massif may be compared with the dominant norite of the Upper Critical Zone of the same massif. They have similar concentration of MgO, CaO, Na₂O, K₂O and much different concentrations of SiO₂, TiO₂, Al₂O₃, Fe₂O₃ and P₂O₅. Some specific variations in the concentration may be found in comparison of each to other of the Núi Chúa Complex (Table 1).

Another character of layered intrusions is that the gabbro of border series and pegmatoidal groups of layered series tend to increase the concentration of TiO₂ and total alkali (e. g., [18]) and this has been established in the Núi Chúa Complex too. Thus, the concentration of TiO₂ increases from 0.28-0.30% in gabbro, gabbro-norite of Main Zone to 0.47-0.99% in coarse-grained gabbro and

Table 2. Chemistry of representative rocks types of the layered intrusions
of Núi Chúa Complex (% and ppm).

Note:

      + 1-4: Núi Chúa massif; 5: Khao Quế massif; 6-7:  Tri Năng massif; 8-11: Yên Chu massif.

      + Samples (B6115, Rp6404a, 1/119, B7204) were analyzed in the United Institute of Geology, Geophysics and Mineralogy (Russian), the others - in the Dept of Geosciences, Franklin and Marshall Coll (USA) and Dept of Geol. Sciences, NTU (Taiwan).

pegmatites of the grouped pegmatite and Border Series (Table 1, Núi Chúa massif). Such tendency has been observed in other massifs of the Núi Chúa Complex (Table 1). The concentration of total alkali of rocks of the layered intrusions of Núi Chúa Complex is low with Na₂O > K₂O (Table 1 and 2) and belongs to subalkaline series. The tendency of increase of alkali in series is generally similar to that of TiO₂.

Totally, according to above mentioned features of major element concentration of layered rocks in the  studied massifs the magma of Núi Chúa Complex is close to  potassium-low calc-alkaline series, although some features of tholeiitic trend has been found [12, 22]. This transitional character of magma of the layered intrusions of Núi Chúa Complex may be interpreted as subduction-related magmatism with very low rate or in a local extent condition (Coleman, 1977). In order to determine the tectonic setting of the Núi Chúa Complex, a discrimination diagram of Mullen (1983) was used (Fig.1). The used elements are relatively immobile and insensitive to hydrothermal processes even in the temperature range of the greeenschist facies [24, pp. 198-199]. Samples of the Núi Chúa Complex were plotted in the field of the island arc magmatism (Fig.1). However, this result is contradictory to current geological idea relatively to North Việt Nam. The petrotectonic nature of the layered intrusions of Núi Chúa Complex can be explained further by trace element concentration.

2. Trace elements

Trace element concentration in layered intrusions of the Núi Chúa Complex is presented in Tables 1 and 2. Concentration of ore metals varies in layers and in each massif. The Núi Chúa massif has the highest concentration of Ni and Cu than others and is similar to those of the Bushveld massif. The concentration of Ni in ultramafic rocks of the Núi Chúa massif is 901-1444 ppm in comparison with the harzburgite of the Bushveld massif of 1500 ppm. The pyroxenite of Núi Chúa massif contains Ni of 773 ppm in comparison with the similar value of 400-1200 ppm for pyroxenite of Bushveld massif. In gabbronorite, the similar value of Ni has been observed in both intrusions: 649-667 ppm and 50-500 ppm respectively [6]. The concentration of Ni is higher than Cu in the studied massif and Ni/ (Ni + Cu) ratios vary from 0.55 to 0.90. However the Tri Năng massif shows lower ratio and varies from 0.1 to 0.58. Usually, the higher values of this ratio are related to melanocratic layers. However, the high abundance of sulphides as well as oxide minerals has been seen in the pegmatite series (pyroxenite, gabbro-pegmatite). This discrepancy may be explained by the entering of nickel into olivine during its crystallization. The concentration of vanadium varies and is different in different layers and at a large range. Its higher concentration has been seen in pegmatite series (Table 1) and anomalous high concentration has been observed in the Yên Chu massif. These variations in concentration of vanadium act as a measurement for oxygen activity of magma and the crystal fractionation processes took place in the layered intrusions of Núi Chúa Complex. On the other hand, vanadium and titanium are immobile elements under conditions of hydrothermal alteration and intermediate- to high-grade metamorphism and they were used for determination of tectonic setting. Plots of representative samples of the layered intrusions in this discrimination diagram show that the layered intrusions of the Núi Chúa Complex belong to island arc magmatism as shown in Fig. 2.

The total concentration of REE of various rock types of layered intrusions of Núi Chúa Complex is low and appears to belong to a depleted mantle source. The pattern is similar to that of N-MORB and has a strong positive anomaly of Eu (Fig. 3). This anomaly was resulted from dominant fractionation of cumulus of plagioclase during the formation of layered intrusions. It also indicates that the melt of magmatic chambers, differentiation and crystallization of which gave origin of layers in the intrusions, and moved upward into chambers directly from a plagioclase peridotitic layer. This implies that the island arc magma of Núi Chúa Complex has the REE concentration similar to that of primitive mantle and pattern similar to MORB. On the other side, the N-MORB normalized spider of trace elements shows a typical curve of island arc magmatism with negative anomaly of Nb and Ta (Fig. 4). In the spidergram the immobile elements (from Nb to Yb) are plotted below the N-MORB level (value = 1). This is supported by low Nb/Yb ratio (0.20-0.80), Nb/Ta ratio (10-15) and Th/Nb ratio (0.3 - 1.5) also [9, 19, see Table 2].

Usually, the concentration of mobile elements, such as Sr, Rb, Ba and K of island arc basalts, is higher than those of N-MORB as shown in Fig. 4. In addition, according to the relationship of Ba/Th ratio (from lowest - 37.1 for Khao Quế to highest - 717 for Tri Năng)  and Th/Nb ratio (0.3-1.5), Th/Yb ratio (0.06-0.8) as well as Ta/Nd ratio (0.009-0.02), the intrusions of this study belong to island arc magmatism (after [7]). The low Zr concentration (4.40-18.62 ppm) and the low Nb/Y ratio (mainly 0.02-0.07 and 0.55 for a sample N1266 from Yªn Chu) also supports the island arc nature of these intrusions. All these features once more indicate the island arc magmatism of the Núi Chúa Complex. Thus, the magma of the layered intrusions of Núi Chúa Complex in North Việt Nam has a transitional feature between island arc and MORB. However, the use of trace element concentration for reconstructing paleo-tectonics of layered intrusions must be careful, because of very complex behaviours of incompatible elements shown by McBirney [18, 19] and as well as of initial ⁸⁷Sr/⁸⁶Sr ratios shown by Eales & Cawthorn [6].

CONCLUSION

In brief, the magma of  layered intrusions of the Núi Chúa Complex in North Việt Nam belongs to a  potassium-low calc-alkaline series of island arc magmatism which is contrary to the long believed as the collision-related magmatism of Late Triassic age in the geological evolution of South China Block (e.g. [5, 26]). The new analytical data of representative samples from the layered intrusions, the REE pattern and N-MORB normalized spidergram, as well as different ratios of trace and rare earth elements, such as Nb/Yb, Nb/Ta, Nb/Y, Ta/Nd Th/Nb, Th/Yb, Ba/Th support also the island arc nature of these intrusions. However, each layered massif of the Núi Chúa Complex should be studied in different aspects due to their specific features in compositional characteristics, as mentioned above.

ACKNOWLEDGEMENT

This study represents a part of the Hoàng Hữu Thành´s PhD thesis in Russia, which has been gratefully granted by the fund of long-term co-operative scientific research between Institute of Geosciences (Việt Nam) and United Institute of Geology, Geophysics and Mineralogy (Russia). The authors gratefully acknowledge the support of Lan Ching-Ying, Lo Ching-Hua and Chung Sun-Lin (Taiwan) for analytical data and Phạm Thị Dung (Việt Nam) for technical construction of tables and figures. The original manuscript benefitted from the thorough reviews of Lan Ching-Ying.

REFERENCES

1.  Balykin P. A., Polyakov G.V. et al. 1995. Petrological types of gabbro-peridotite massifs and their appearance in northern structures of Việt Nam. J. of Geology,  Spec. issue: Proc. of the Intern. Symp.”Geology of SE Asia and adjacent Areas”. Hà Nội, 429-430.

2.  Bùi Quang Luận, Nguyễn Xuân Hãn, Trần Quốc Hùng and Hoàng Hữu Thành. 1985. Tuổi phóng xạ và nguồn gốc các đá gabroit miền Bắc Việt Nam. (Isotope age and origin of gabbroic rocks in North Việt Nam). TC Khoa học Trái đất. 7/1: 19-22. Hà Nội.

3.       Chung S. L., Lo C. H., Lan C. Y., Wang P. L., Lee T. Y., Hoà T.T., Thành H. H. and Anh T.T. 1999. Collision between the Indochina and South China blocks in the Early Triassic: Implications for the Indosinian Orogeny and closure of eastern Paleo-Tethys. Eos (Transactions, Ameri. Geoph. Union),  80 : F 1043.

4.  Dovzhikov A. E. (ed). 1965. Geology of   North Việt Nam. Gen. Dept. Geol., Hà Nội. 665 pp. (in Russian)..

5.  Đào Đình Thục, Huỳnh Trung (Coeditors), 1995. Địa chất Việt Nam. Tập II. Các thành tạo magma. (Geology of North Việt Nam. Vol. 2. Magmatic formations). Geol. Dept. of  Việt Nam, 359 pp.

6.  Eales H. V. and Cawthorn R. G., 1996. The Bushveld Complex. In: Cawthorn, R. G. (ed). 1996. Layered Intrusions. Amsterdam: Elsevier Science B.V., 181-229.

7.       Fretzdorff S., Livermore R. A., Devey C. W., Leat P. T. and Stoffers P. 2002. Petrogenesis of the Back-arc East Scotia Ridge, South Atlantic Ocean. J. of  Petrology 43/ 8 : 1435-1467.

8. Glotov A. I., Polyakov G. V., Balykin P. A. et al. 1991. Geochemistry and ore-bearing capacities of Mesozoic ultrabasite-basite associations of north Việt Nam. Proc. of Second Conf. on Geol. of Indochina, 1 : 301-311. Hà Nội.

9.       Green T. H. 1995. Significance of Nb/Ta as an indicator of geochemical processes in the crust-mantle system. Chemical Geology, 120 :  347-359.

10.   Hada S., Bunopas S., Ishii K. and Yoshikuka S. 1999. Rift- drift history and the amalgamation of Shan- Thai and Indochina/East Malaysia Blocks. In “Gondwana Dispersion and Asian Accretion, IGCP 321 Final Results Volume”, Metcalfe I. (Ed. in Chief), Ren Ji-Shun, Charvet J. & Hada S. (Assoc. Eds.), A.A. Balkema, Rotterdam/Brookfield, 67-87.

11.          Hoàng Hữu Thành, Ngô Thị Phượng, Bùi Ấn Niên. 1991. Một số vấn đề về điều kiện thành tạo tổ hợp gabro-periđotit phân lớp kiểu Núi Chúa. (Some problems on forming mechanism of layered peridotite-gabbroic association of Núi Chúa type.) In: Geology, Mineral resources, Sci. & Tech. Hà Nội, 58-63 ( with English abstract).

12.          Hoàng Hữu Thành. 1994. The layered peridotite-gabbroic intrusions in North Việt Nam. Ph. Dr. thesis., United Institute of Geol., Geophys. and Mineral., Novosibirsk (in Russian).

13.          Hutchison C.S., 1989. Geological evolution of South-East Asia. Oxford Sci. Publ. 13, Clarendon Press, Oxford, 368 pp.

14.          Kotchetkov A.Ya., Gatinsky Yu. G., Thái Quý Lâm, Trần Văn Trị, Vũ Xuân Định, 1993. Ore formations and regional metallogenic division of central part northeastern Việt Nam. J. of Geology of abroad,  7-11. Moskva (in Russian).

15.          Lacroix A., 1933. Contribution à la connaissance de la composition chimique et mineralogique des roches eruptives de L’indochine. Bull. Geol. de l’Indochine, 20 : 17-57.

16.          Lepvrier C., Maluski H.,  Nguyễn Văn Vượng, Roques D., Axente V., Rangin C., 1997. Indosinian NW-trending shear zones within the Trường Sơn Belt, Vieetj Nam 40Ar-⁴⁰Ar Triassic age and Cretaceous to Cenozoic overprints. Tectonophysics, 283 : 105-127. London.

17.   McBirney A. R., 1989. The Skaergaard Layered Series:I. Structure and average compositions. J. of Petrology, 30 : 363-397.

18.           McBirney A. R., 1996. The Skaergaard Intrusion. In: Cawthorn, R. G. (ed). 1996. Layered Intrusions. Amsterdam: Elsevier Science B. V., 147-180.

19.   McBirney A. 2002. The Skaergaard Layered Series. Part VI. Excluded Trace Elements. J. Petrol., 43/3 : 535-556.

20.          Metcalfe I., 1995. Gondwana dispersion and Asian accretion. J. Geology, B/5-6: 223-266. Hà Nội.

21.          Münker C., 1998. Nb/Ta fractionation in a Cambrian arc/back arc system, New Zealand: Source, constraints and application of refined ICPMS techniques. Chem. Geol., 144: 23-45.

22.          Polyakov G.V. and Nguyễn Trọng Yêm (eds)., 1996. Các thành tạo mafic-siêu mafic Permi-Trias miền Bắc Việt Nam. (Permian-Triassic mafic-ultramafic associations of North Việt Nam). Sci. & Tech.  Publ. House, Hà Nội, 172 pp. (with English and Russian summaries).

23.          Polyakov G. V., Trần Quốc Hùng and Hoàng Hữu Thành. 1984. New data on ore mineralization of the Núi Chúa basic complex. J. of Geol. & Geophys., 11 : 14-22 (in Russian).

24.          Rollinson H. R. 1998. Using geochemical data: Evolution, presentation, interpretation. Longman Singapore, 352.

25.          Trần Quốc Hùng. 1992. The Ultramafic-Mafic Complexes in North Việt Nam. Dr. Sci. thesis., United Institute of Geol., Geophys. and Min., Novosibirsk (in Russian).

26.          Trần Văn Trị (ed), 1977. Địa chất Việt Nam. Phần miền Bắc. (Geology of Việt Nam, the North part). Sci. & Techn. Publ. House, Hà Nội. 354 pp.

27.   Wager L. R. and Brown G. M. 1968. Layered Igneous Rocks. Edingburgh: Olier & Boyd, 588 p.