An Overview of the Tectonic Evolution of the Indochina block and Granitoid Emplacement, particularly in the central and south Vietnam

Science & Technology Development Journal, 23(3):610-631
Open Access Full Text Article Research Article
1University of Science, Vietnam National
University Ho Chi Minh City
2University of Technology, Vietnam
National University Ho Chi Minh City
Correspondence
Nguyen Anh Tuan, University of Science,
Vietnam National University Ho Chi Minh
City
University of Technology, Vietnam
National University Ho Chi Minh City
Email: nanhtuan@hcmut.edu.vn
History
 Received: 2020-04-07
 Accepted: 2020-07-14
 Published: 2020-08-24
DOI : 10.32508/stdj.v23i3.2062
Copyright
© VNU-HCM Press. This is an open-
access article distributed under the
terms of the Creative Commons
Attribution 4.0 International license.
An Overview of the Tectonic Evolution of the Indochina block and
Granitoid Emplacement, particularly in the central and south
Vietnam
Nguyen Anh Tuan1,2,*, Ngo Tran Thien Quy1, Vu Thi Hao1, PhamMinh1
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ABSTRACT
Introduction: Vietnam is mainly located within the Indochina block in Southeast Asia. Asmall
northern part of Vietnam belongs to the South China block, the southwest part liesadjacent to the
Sibumasu block and opens to the East Sea on the east side. Tectonicactivities in Vietnamwere very
complicated they relate to intense interactions betweenmany geological blocks at different times.
Magmatic emplacement is the final and instantproduct of tectonic activities. Methods: Geochem-
ical data analysis from rock samples withinVietnam collected by other researchers has been reused
in the scope of this study to verifythe relation between tectonic evolutions and their granitic mag-
matism. GCD (GeochemicalData Toolkit), an R language program for handling and recalculation
of geochemical data. Results: Geochronology and geotectonic model derived from rock analysis
have beenascertained main tectonic evolutions of the Indochina. The current granitoidclassifica-
tion in Vietnammostly based on petrographical studies. The Nui Camgranitoid isbeing classified as
Deo Ca, Dinh Quan granitoid. However, based on trace elements, they aredifferent. They may be-
long to different granitoid system. Conclusion: Major tectonic eventswithin the Indochina block
are well supported by the nature of granitoid emplacements. Petrological studies of these mag-
matic rocks would bring out valuable information toconfirm and clearly understand the tectonic
evolutions of the region. Igneous rocksclassification must based on tectonic fundamental instead
of petrographical studies.
Key words: Vietnam, Indochina, tectonic, granitoid emplacement
INTRODUCTION
The tectonic activities of the Indochina block and sur-
rounded geological blocks are much more complex.
The geological boundaries, defined as the tectonic su-
tures, where two geological blocks welded together,
have been reported in many different places through-
out the Indochina block. At least three main sutures
have been found, and they are:
1. TheOrdo-Silurian TamKy – Phuoc Son resulted
from the assimilation of South China and In-
dochina blocks;
2. The Middle Triassic Sông Mã suture resulted
from the welding of the Indochina and South
China blocks; and
3. The Late Triassic suture resulted from the
amalgamation of the Indochina and Sibumasu
blocks.
Some of these sutures have been intensively studied,
such as Sông Mã suture, the other just begins with
primarily study while the Sibumasu and Indochina
block while much of studies have been reported in
Thai Land, Cambodia, Malaysia, Laos, but it’s almost
ignored in Viet Nam. In this paper, with the other re-
searchers’ authorization, granitoid rocks petrochem-
ical data collected in the central and south Vietnam
were used and reprocessed in tectonic purposes to
support the presence of these tectonic features in the
Indochina block.
A review of the tectono-magmatism
An oceanic plate sinks beneath a continental plate; it
gradually moves deeper to the hot dense mantle core.
Under the increased heat and pressure conditions, it
begins to melt itself and produce a magma fluid. But
the most significant mechanism in the process is the
release of water into the mantle by metamorphosing
of hydrated serpentinites of the oceanic crust. The
amount of H2O then reduces the melting point of the
surrounding mantle. A partial melt of the mantle oc-
curs and generates magma fluid1,2. That magma fluid
produced within the mantle is lighter compare to the
surrounding environment moves up into the conti-
nental crust where it resides in the magma chambers.
Cite this article : Tuan N A, Quy N T T, Hao V T, Minh P. An Overview of the Tectonic Evolution of the
Indochina block and Granitoid Emplacement, particularly in the central and south Vietnam. Sci.
Tech. Dev. J.; 23(3):610-631.
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Science & Technology Development Journal, 23(3):610-631
Inside themagma chamber hotmagma cooler and so-
lidifies and forms granitoid pluton within the crust,
also some amount of SiO2 rich magma differentiated
within the magma chamber could escape to the sur-
face and forms an acidic volcanic chain.
Granitoid rocks have beenwell studied for a long time;
their classification is varied and depends on the scope
of researchs. In general, a classification of granitoid
rocks based on tectonic setting can be seen as the stud-
ies of Pitcher (1983, 1993), Barbarin (1990) Figure 2.
In a basic and simple model of convergent tectonic
between India and Eurasia plates, different types of
granitoid forming through each stage of the evolution
Figure 3.
(A) Initial subduction of India oceanic plate beneath
Eurasia plate; VAG I type granitoid produced from the
partialmelt ofmaficmaterial of the oceanic crust itself
and from the surrounding mantle; also S type grani-
toid forming as mixing of mantle magma with conti-
nental crust material;
(B) Further subduction of India into the core of Eura-
sia, India continenta ... ademy
and re-used in this study Table 216.
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Figure 13: Plots of Dai Loc, and Chu Lai granites VA (Volcanic Arc granite), COL (Collision granite), WP
(Within Plate granite).
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Table 2: Rock samples collected in Ben Giang and Que Son by Hieu Pham (2015).
Samples Hai Van Hai Van Hai Van Hai Van Ben Giang Ben Giang
SiO2 70.4 70.32 74.53 72.04 74.05 72.35
TiO2 0.4 0.52 0.24 0.46 0.23 0.25
Al2O3 14.73 14.39 13.62 13.22 14.2 14.71
Fe2O3t 2.63 4.83 1.93 3.73 0.39 2.01
MnO 0.03 0.08 0.03 0.05 0.04 0.05
MgO 0.73 2.15 0.87 1.44 0.32 0.63
CaO 2.35 0.87 1.06 1.33 1.02 1.05
Na2O 2.8 1.2 1.91 1.71 3.24 3.25
K2O 4.25 3.93 4.97 4.17 4.45 4.84
P2O5 0.09 0.09 0.11 0.16 0.16 0.21
LOI 0.38 1.16 1.06 1.2 1.84 0.78
Total 98.79 99.54 100.33 99.51 99.94 100.13
K2O/Na2O 1.52 3.28 2.6 2.44 1.37 1.49
A/CNK 1.09 1.84 1.3 1.35 1.18 1.18
A/NK 1.6 2.31 1.6 1.8 1.4 1.39
Sc 7.93 10.6 4.63 9.21 2.09 3.98
V 14 73.7 29.5 52.4 615 17.8
Cr 11.9 65.3 25.7 45.9 624 15.8
Co 1.51 9.92 3.89 7.43 110 2.67
Ni 7.52 26.2 11.2 20.4 267 7.57
Cu 18.6 28.5 18.5 36.7 29.6 47.3
Zn 67.6 7.75 4.89 65.9 61.9 71.9
Ga 17.4 20 15.2 19 19.1 21.6
Rb 219 223 257 223 227 205
Sr 154 73.9 88.2 90.2 41.2 83.1
Zr 158 170 119 229 112 125
Nb 13.6 18.8 9.88 15.2 13.7 14
Cs 10.4 13.7 12 11.6 30 22.2
Continued on next page
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Table 2 continued
Ba 806 638 644 581 196 419
Hf 4.56 4.61 3.45 6.56 2.06 3.51
Ta 1.11 1.24 0.9 1.4 2.01 1.68
Pb 22 13.1 32 32.6 46 41.7
Th 19.6 26.8 14.6 24.7 8.71 19.4
U 4.29 5.93 6.49 5.98 7.5 3.35
La 38.9 52.7 27.2 42.7 13.6 30.3
Ce 80.2 107 55 84.9 30.4 65
Pr 8.91 11.7 5.95 9.23 3.27 6.84
Nd 34.1 43.9 21.9 34.4 12.1 25.3
Sm 7.27 8.38 4.62 6.95 3.15 5.26
Eu 1.76 0.98 1.15 1.09 0.49 0.74
Gd 7.01 7.13 4.31 6.14 2.92 4.44
Tb 1.11 0.97 0.7 0.91 0.45 0.6
Dy 6.8 5.39 4.25 5.26 2.18 3.11
Ho 1.47 1.05 0.9 1.04 0.35 0.57
Er 4.28 2.88 2.63 2.92 0.8 1.47
Tm 0.65 0.41 0.42 0.45 0.11 0.22
Yb 4.27 2.71 2.86 3.07 0.74 1.47
Lu 0.64 0.4 0.43 0.47 0.11 0.21
Y 45.4 31.4 28.3 31.3 11 17.9
(La/Yb)N 6.1 13 6.4 9.3 12.3 13.8
(Tb/Yb)N 1.15 1.58 1.08 1.31 2.69 1.8
Eu/Eu* 0.76 0.39 0.79 0.51 0.5 0.47
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In geotectonic diagrams, almost all of the samples fall
into the field of the active continental margin, and
some samples could be found in the collision zone
Figure 14.
The convergence between Indochina and SouthChina
blocks produces both VAG and COLG granitoid
rocks. It may not clearly demonstrate the full scope of
tectonic evolution in detail, but it may prove that the
tectonic activities composed of the first stage of sub-
duction continued with the next stage of the collision
of these two blocks. It is suggested that South China
was subducted beneath the Indochina block based on
most of BenGiang andHaiVan granitoids have stayed
in the southern part of Song Ma suture, the location
where two blocks amalgamated together Figure 1.
Indochina/Sibumasu amalgamation and
granitoid emplacement
At the same time in the west side of the Indochina
block, the Sibumasu block, after broken up from
Gondwanaland, came and subducted beneath the
Indochina block. Granitoid emplacements for this
tectonic evolution were found in a long time span
from the early Permian toward the end of Cretaceous
time from northernThailand toward the south to the
Malaysia peninsula. In Vietnam, a conductive study
by the HCM University of Science with the cooper-
ative of Academia Sinica, Taiwan, by Ching Yin Lan
(2009) to collect samples of the Nui Cam batholith in
the SWcornerVietnam. Rock analysiswas performed
at the Academia Sinica, EPMA laboratory. Research
study has been presented in theGoldschmithGeology
Conferences, Canada 2009.
In the geotectonic plots, these samples are falling
mostly in the field of VAG, Syn-COLG, and WPG.
The Sibumasu block came and subducted beneath the
Indochina block, the tectonic activities and granitoid
emplacement could be found at the first stage of sub-
duction with VAG and later on with Syn COLG and
WPG in the next phase of collision COLG between
two plates and finally induced a type of within plate
granitoid WPG in the last phase, Figure 15.
Yanshangnian orogeny and granitoid em-
placement
By the Cretaceous time, the Paleo-Pacific oceanic
plate subducted beneath the Asia continental plate,
this type of convergence produced a broad and long
granitoid belt from north China toward the south to
Vietnam as Truong Son belt. Rock samples collected
in Dalat zone by Bich Thuy N. T. and analysis per-
formed by Memorial University of St. John’s New-
foundland, U K.17, Table 3. However, the nature of
this tectonic event is not simple with just a merely
subduction of the Paleo-Pacific oceanic crust beneath
the Eurasia continental crust. It is more complex
as10 suggestion that there is a continental fragment
that possibly on the Paleo-Pacific plate, following the
course of subduction, this block came to collide with
Indochina block Figure 16.
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Figure 14: Geotectonic plots: Hai Van (S>I type/VGA); Ben Giang (I type/COLG)
Figure 15: Geotectonic plots: Dinh Quan (I type/VAG); Ca Na, Deo Ca (I type/COLG).
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Figure 16: DinhQuan fall mostly in the field of VAG, and Ca Na, Deo Ca belong to COLG the stage, seeing as
the result of collision between the Indochina and the referred Luconia block.
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Figure 17: Differences between DeoCa-Dinh Quan and Nui Cam trace elements plot.
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Figure 18: Differences of Tdm ages of Dalat and NuiCam granitoids, Lan (2009).
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Table 3: Rock samples collected in the Dalat zone by Bich Thuy N. T (2004).
Samples DQ 1 DQ 2 DQ 3 DQ 4 DQ 5 DC 1 DC 2 DC 3 DC 4 CN 1 CN 2 CN 3 CN4
SiO2 58.01 63.82 70.01 67.32 68.2 68.21 76.32 70.71 76.62 77.12 73.25 77.81 73.51
TiO2 1.02 0.61 0.22 0.5 0.31 0.4 0.12 0.5 0.11 0.13 0.21 0.12 0.22
Al2O3 17.34 15.13 15.06 14.81 15.14 15.42 12.71 14.35 12.42 12.65 13.62 12.51 13.74
Fe2O3 7.02 5.81 3.04 3.92 3.71 3.6 1.14 2.72 1.61 1.41 1.9 1.02 2.05
MnO 0.12 0.12 0.11 0.07 0.08 0.05 0.01 0.06 0.05 0.02 0.02 0.01 0.03
MgO 2.81 2.4 0.52 1.61 1.2 1.41 0.11 0.77 0.05 0.02 0.25 0.05 0.28
CaO 6.23 4.33 2.11 3.35 3.32 3.62 0.95 2.11 0.62 0.61 1.62 0.61 1.62
Na2O 3.11 2.81 4.05 2.95 3.25 3.06 3.32 3.61 3.8 3.52 3.24 3.15 3.71
K2O 2.61 3.52 3.84 4.34 3.42 3.64 4.83 4.52 4.51 4.9 4.71 5.31 3.91
P2O5 0.32 0.21 0.11 0.11 0.21 0.11 0.13 0.15 0.03 0.01 0.06 0.01 0.06
H2O 0.52 0.7 0.41 0.52 0.5 1.13 0.21 0.3 0.3 0.31 0.51 0.42 0.61
Total 99.11 99.46 99.68 99.18 99.34 100.6 99.85 99.92 100.1 100.7 99.89 100 99.73
ASI 0.9 0.92 1.02 0.96 1.01 0.99 1.03 0.97 1.02 1.04 1.03 1.05 1.04
Co 0 0.02 0.5 0.01 0.42 0.11 0.41 0.11 0.32 0.61 0.5 0.6 0.55
Cr 87 71 91 157 112 5 21 40 134 28 19 30 23
Ni 51 31 32 28 35 2 25 19 27 24 20 16 22
Sr 474 285 246 233 404 306 79 302 38 8 127 22 235
Ba 465 393 553 295 543 401 118 566 218 10 262 16 443
Zr 183 160 209 160 124 129 99 224 112 101 133 99 106
Rb 97 153 146 210 109 113 304 211 180 291 264 351 150
Hf 4.76 3.42 4.9 4.51 3.51 3.54 3.61 0.89 2.52 2.41 4.71 3.11 3.51
Nb 8 5.3 5.6 7.1 6.2 11.1 12.2 10.5 11.5 11.1 6.2 4.1 7.5
Ta 0.83 0.71 0.8 0.92 0.76 1.51 0.53 1.12 1.32 1.19 1.2 2.52 1.1
Th 10.3 12.6 15.6 29.2 10.6 14.4 41.3 30.5 16.4 25.7 29.6 46.4 14.3
U 2.25 1.87 2.36 5.41 3.12 3.91 20.32 4.45 3.69 7.66 8.82 14.7 8.83
Y 25 27 28 26 16 20 21 26 29 51 48 76 24
Zn 71 65 50 44 64 56 15 44 37 40 46 30 31
La 24.3 25.9 32.3 28.2 22.4 21.8 21.1 42.7 19.3 19.7 29.1 38.6 22.6
Continued on next page
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Table 3 continued
Ce 50.7 53.1 60.5 55.4 41.4 42.6 38.9 82.4 41.5 45.6 59.8 77.5 44
Pr 6.01 6.16 6.84 6.13 4.5 4.71 3.76 8.8 4.8 5.81 6.98 10.9 4.91
Nd 23.6 23.3 24.8 22.1 16.3 17 11.6 30.8 17.7 24 26.5 40 17.7
Sm 5.04 4.92 4.91 4.62 3.21 3.42 1.9 5.32 3.89 6.5 6.14 8.87 3.81
Eu 1.5 0.91 0.9 0.81 0.8 0.8 0.22 1.01 0.32 0.11 0.5 0.31 0.5
Gd 4.42 4.33 4.08 3.86 2.53 2.96 1.51 4.2 3.61 6.32 5.82 6.59 3.31
Tb 0.65 0.62 0.63 0.63 0.42 0.51 0.23 0.51 0.52 1.04 1.01 0.87 0.52
Dy 3.91 4.1 3.82 3.45 2.24 2.84 1.6 3.22 3.3 6.68 6.31 4.76 3.21
Ho 0.83 0.95 0.85 0.7 0.51 0.62 0.43 0.61 0.71 1.4 1.32 0.9 0.75
Er 2.52 2.76 2.61 2.35 1.4 1.9 1.41 1.8 2.02 4.41 4.25 2.5 2.1
Tm 0.36 0.43 0.44 0.32 0.21 0.32 0.22 0.35 0.31 0.64 0.61 0.41 0.31
Yb 2.12 2.45 2.41 2.01 1.35 1.81 1.75 1.71 2.19 3.9 3.72 2.51 1.95
Lu 0.34 0.41 0.4 0.32 0.23 0.33 0.31 0.31 0.41 0.59 0.5 0.42 0.32
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DISCUSSION
Geochemical data of magma samples collected in the
central and Granitoid emplacements in Thailand also
in the Malaysia peninsula have been viewed as prod-
ucts of tectonic evolution of the region Figure 5,
and they have been seen by different granitoid belts
e.g., Western, Main range, Eastern, and Western In-
dochina Figure 6 . Not many studies on Nui Cam
batholiths, located at the corner of southwest Viet-
nam, zone D Figure 1; however, Nui Cam granitoic
rocks were defined and classified as Deo Ca and Dinh
Quan complex based merely on geographical studies
also on geochronological studies. Rock with the sim-
ilarities mineral assemblage is classified as the same
group (Granitoids emplacementmap in southernViet
Nam, 2004. HCM University of Science).
Recent studies in the region, these granitoids may
have belonged to the Western Indochina Belt Fig-
ures 5 and 6 granitic rocks with ages vary from early
Permian to Early Cretaceous. It is clearly different
between two groups, on the geotectonic plot Deoca
and Dinhquan complex belong to VAG while Nui
Cam moves to the field of Syn-COLG or WPG Fig-
ure 17. More than that Tdm determination of these
two groups16,18 showing they are different between
Dalat (1.2 Ga) compare to Nuicam (0.8 Ga) Figure 18.
CONCLUSION
Tectonic evolutions in Vietnam are very complex and
complicated. It is not evolved to the intereaction be-
tween two single geological blocks butmore than two.
Many studies and research have been done in the re-
gion to bring out the whole picture of tectonic evolu-
tion of Vietnam It’s likely suitable for major tectonic
activities with theirs granitoid emplacement through
space and time. Granitoids ages and their geotectonic
features seem to be agreeable with the relative location
compare with the boundary between them. However
more works need to be conducted to clarify Nuicam
batholith, it may not belong to Deoca/Dinhquan suite
as previously classified, but it may belong to another
system, the Western Indochina granitoid belt.
COMPETING INTERESTS
The author declares that this paper has no competing
interests.
ACKNOWLEDGMENT
The authors would like to thank for the authorization
of Dr. Nguyen B Thuy and Dr. Pham T Hiếu for us-
ing their geochemical data and their great supports for
this paper.
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