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Late Neogene structural inversion around the northern
Gulf of Tonkin, Vietnam: Effects from right-lateral
displacement across the Red River fault zone
Michael B. W. Fyhn1 and Phung V. Phach2
1Geological Survey of Denmark and Greenland, Copenhagen, Denmark, 2 Institute of Marine Geology and Geophysics,
Hanoi, Vietnam
AbstractContinental extrusion may take up much of the deformation involved in continental collisions.Major strike-slip zones accommodate the relative extrusion displacement and transfer deformation away
from the collision front. The Red River fault zone (RRFZ) accommodated left- and right-lateral displacements
when Indochina and South China were extruded during the Indian-Eurasian collision. The northern Song
Hong basin onshore and offshore in the Gulf of Tonkin delineates the direct extension of the RRFZ and thus
records detailed information on the collision-induced continental extrusion. We assess the rapidly evolving
kinematics of the fault zone buried within the basin based on seismic analysis. Contrary to previous
studies, we do not identify indications for latest Miocene left-lateral motion across the RRFZ. We tentatively
consider the shift from left- to right-lateral motion to have occurred already during the middle Late
Miocene as indicatedby inversionof NE-SW-striking faults in theBach Long Vi area. Right-lateral displacemen
terminated around the end of the Miocene in the Song Hong basin. However, continued inversion in the Bach
Long Vi area and NNW-SSE-striking normal faulting suggests a stress regime compatible with right-lateral
motion across the onshore part of the RRFZ continuing to the present. Inversion around the Bach Long Vi
Island may have accommodated up to a few kilometers of right-lateral displacement between the Indochina
and South China blocks. Comparable NE-SW-striking fault zones onshore may have accommodated a larger
fraction of theright-lateralslip across theRRFZ, thusaccountingfor therestrictedtransfer of lateraldisplacemen
to the offshore basins.
1. Introduction
Escape tectonics may take up much of the deformation associated with continental collisions [ Burke and
Sengr, 1984;Tapponnier et al., 1986]. During the process, major crustal blocks are squeezed away from the
collision zones across major strike-slip faults, thus transferring collision-related deformation away from the
suture zone [Sengr et al., 1985;Tapponnier et al., 1986;Leloup et al., 2001]. Escape tectonics may evolve
rapidly during the progress of continental collisions. This is recorded in changing deformation styles along
the transform edges of the extruded crustal blocks. Resolving of exact timing and extent of these processes
tends to be highly intricate.
Although controversial, much of the deformation linked with the collision of India and Eurasia is proposed to
have been taken up by lateral escape of the Indochina, South China andNorth China blocks [e.g.,Tapponnier et al.
1982, 1986;Leloup et al., 2001]. The RRFZ constitutes one of the primary strike-slip fault zones that accommodate
the extrusion of the Indochina and South China blocks away from the Himalayan collision front (Figure 1).The RRFZ stretches from eastern Tibet to the extensional basins underlying the Gulf of Tonkin offshore
northern Vietnam (Figure 1). Signicant mid-Cenozoic to Recent lateral extrusion of Indochina and South
China is recorded within the fault zone [Leloup et al., 1995, 2001]. The RRFZ initially took up left-lateral
displacement between the Indochina and South China blocks [e.g., Leloup et al., 1995]. During the latter half
of the Neogene, the RRFZ reversed and became right-lateral due to the progression of the India-Eurasia
collision [Allen et al., 1984;Replumaz et al., 2001;Schoenbohm et al., 2006;Trinh et al., 2012;Zuchiewicz et al.
2013]; however, the timing and nature of this change in deformation is not well-constrained by the outcropping
part of the fault zone.
The Red River delta and the Gulf of Tonkin are underlain by Cainozoic extensional basins outlining the direc
continuation of the RRFZ(Figure 1) [Tapponnier et al., 1986; Rangin et al., 1995]. The changing phases of latera
FYHN AND PHACH 2015. American Geophysical Union. All Rights Reserved. 290
PUBLICATIONS
Tectonics
RESEARCH ARTICLE10.1002/2014TC003674
Key Points:
Right-lateral slip across the Red River
fault zonelikelybeganin theL Miocene
Right-lateral slip drove structural
inversion of the Gulf of Tonkin
rift systems
Lateral shearing is taken up by
shortening across existing
NE-SW-striking faults
Correspondence to:
M. B. W. Fyhn,
Citation:
Fyhn, M. B. W., and P. V. Phach (2015),
Late Neogene structural inversion around
the northern Gulf of Tonkin, Vietnam:
Effects from right-lateral displacement
across the Red River fault zone, Tectonics,
33, 290312, doi:10.1002/2014TC003674.
Received 8 JUL 2014
Accepted 10 JAN 2015
Accepted article online 14 JAN 2015
Published online 21 FEB 2015
http://publications.agu.org/journals/http://onlinelibrary.wiley.com/journal/10.1002/(ISSN)1944-9194http://dx.doi.org/10.1002/2014TC003674http://dx.doi.org/10.1002/2014TC003674http://dx.doi.org/10.1002/2014TC003674http://onlinelibrary.wiley.com/journal/10.1002/(ISSN)1944-9194http://publications.agu.org/journals/7/23/2019 Fyhn and Phac, 2015
2/23
deformation in the RRFZ are therefore recorded by the complex buried structures and stratigraphy in these
basins [Rangin et al., 1995], and the rapid Cainozoic deposition allows for a detailed chronologic resolution of
the tectonic development.
This study documents Late Neogene tectonic inversion and uplift taking place in the northern central part of
the Song Hong basin (Chinese name: Yinggehai basin) and in a corridor connecting the Beibuwan and
the Song Hong basins. Thendings are based on roughly 20,000 km 2-D seismic data tied to exploration wells
andcomplemented by sparker seismic data, as well as outcrop information and core data from the Bach Long
Vi Island (Figure 2). The spatial and temporal variation in deformation are discussed in a regional context, and
a Late Neogene tectonic model is proposed in which Late Miocene
Recent extrusion-related right-lateralmotion between South China and Indochina is taken up by compression across NESW-trending structural
lineaments like the Bach Long Vi inversion zone and comparable fault zones onshore northern Vietnam.
2. Geological Setting
2.1. Late Neogene Activity in the Red River Fault Zone
The RRFZ outlines a conspicuous topographic lineament traceable for roughly 900 km between the Eastern
Himalaya and the Hanoi trough in Vietnam (northern onshore part of the Song Hong basin) (Figure 1).
The fault zone continues for another ~1000 km within the offshore basins anking the Vietnamese margin
(Figure 1) [Fyhn et al., 2009a, 2009b]. The fault zone accommodated substantial left-lateral displacement
between the Indochina and South China blocks especially during Oligocene time [Leloup et al., 1995]. Based
Figure 1.Simplied structural outline of Cenozoic basins and selected fault zones onshore and offshore Indochina and
southernmost China adapted afterSchoenbohm et al. [2004] andFyhn et al. [2009a, and references therein]. Small insert
map illustrates the main structural framework in greater East Asia. Box indicates the position of study area and Figure 2.
AS = Ailao Shan metamorphic core complex, BLV = Bach Long Vi Island, DNCV= Dai Nui Con Voi metamorphic core
complex, EVBFZ= East Vietnam Boundary fault zone, MPSZ= Mai Ping shear zone, TPSZ = Three Pagodas shear zone, and
XXFS = Xianshuihe-Xiaojiang fault systems.
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on extrusion tectonic models, Tapponnier et al. [1982] predicted a Neogene slip reversal across the fault zone
dueto thenorthwardprogression of the Indian indenter into Eurasia. The expected reversal has subsequently
been veried by right-lateral river offsets observed across the fault zone taken to imply Pliocenesub-Recen
right-lateral motion across the fault zone [Allen et al., 1984;Replumaz et al., 2001;Schoenbohm et al., 2006;Trinh et al., 2012;Zuchiewicz et al., 2013].
Total right-lateral offset estimates range from approximately 5 km to more than 50 km, with more recent
estimates of ~25 and ~40 km [Replumaz et al., 2001 andSchoenbohm et al., 2006, respectively] (Table 1).
Displacement assessments are based on the reconstruction of fault-offset geomorphology as well as of
laterally displaced lithologic units. These methods are not without complications since (1) the right-lateral
offset followed a left-lateral offset an order of magnitude larger potentially rendering assessment of offset
lithologic units difcult and (2) matching offset tributaries may be difcult in the continuously and rapidly
developing drainage network associated with the humid tropical climate and the developing topography
along the RRFZ.
The onset of right-lateral motion along the RRFZ is poorly constrained. Left-lateral motion throughout the
Miocene as suggested byRangin et al. [1995] would restrict right-lateral motion to the PliocenePleistocene
On the other hand,Schoenbohm et al. [2006] tentatively suggested a Late Miocene onset.Replumaz et al.[2001] argued for an onset no later than the earliest Pliocene. BothSchoenbohm et al. [2006] andReplumaz
et al. [2001] proposed a long-term slip-rate of ~5 mm/yr or greater, whereas Allen et al. [1984] suggested a
smaller offset and thus a lower long-term slip-rate of ~23 mm/yr (but possibly up to 5 mm/yr) (Table 1).
The present relief along the RRFZ decreases toward the southeast. This complicates assessment of the
right-lateral offset based on offset geomorphological markers in northern Vietnam northwest of Hanoi
where the RRFZ becomes buried underneath modern sediments in the Red River delta (Song Hong delta).
Zuchiewicz et al. [2013] based on geomorphic analysis of the north Vietnamese part of the RRFZ, recently
estimated the Quaternary offset to be ~14 km with a long-term slip-rate of ~5.57.8 mm/yr across the RRFZ
Similarly,Trinh et al. [2012] suggested a slip-rate of 8 5 mm/yr for the past 150 Kyr based on offset of Late
Pleistocene alluvial fans, tributaries, and river valleys along the north Vietnamese part of the RRFZ.
Figure 2.Structural outline of the northern Song Hong basin emphasizing the main fault system conning Paleogene
syn-rift depressions and structural highs. The two doted areas denote Late Neogene inversion zones discussed in the
text. Blue lines delineate the available 2-D seismic database with red stippled lines indicating the position of documented
seismic examples. CFZ= Chay fault zone, SLFZ = Song Lo fault zone, and VNFZ = Vinh Ninh fault zone.
Tectonics 10.1002/2014TC003674
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GPS measurements document a distinct
modern east-southeast-ward displacement
of South China and Indochina. The signal
is less clear on the extent of differential
motion between the South China andIndochina blocks and, by inference, the
present right-lateral displacement taking
place across the RRFZ [Zhao et al., 1993;Zhao
1995;Cong and Feigl, 1999; Michel et al., 2001
Iwakuni et al., 2004;Simons et al., 2007;
To et al., 2013]. Some studies suggest
~13 mm/yr right-lateral motion across the
fault zone based on super-regional Asian GPS
networks [Simons et al., 2007;Zhang et al.,
2013] (Table 1), while others consider the
RRFZ as a now passive lineament [Chen et al.
2000; Shen etal., 2005]. Across the Vietnamese
portion of the RRFZ, To et al. [2013] was not
able to pick outan offset signicantly different
from 0 at a 95% condence level based on a
denser local GPS network, but a consistent
sense of right-lateral displacement across the
RRFZ was suggested by their data with a
possible yearly slip-rate compatible to that
proposed bySimons et al. [2007] (~2 mm/yr).
The long-term slip-rates generally tend to be
higher compared to the calculated short
term slip-rates across the RRFZ. This has been
ascribed to either a fairly recent decrease
in slip-rates or the build-up of strain andinstantaneous fault ruptures accompanied by
substantial earthquakes recurring in hundreds
or even thousands years intervals [Allen et al.
1984;Cong and Feigl, 1999;Replumaz et al.,
2001;Schoenbohm et al., 2006].
Large earthquakes have not been documented
directly along the trace of the RRFZ in recen
history [Allen et al., 1984;Lap, 1988; Cong
and Feigl, 1999; Nguyen et al., 2012;H.-H.
Huang et al., 2013]. The largest shocks are
mainly associated with left-lateral slip along
the NESW to NS-striking fault systemsnorth and south of the RRFZ (Dien Bien Phu
fault system in Vietnam and Laos and the
Xianshuihe-Xiaojiang fault system in China)
(Figure 1). Minor earthquakes along the
anks of the RRFZ in Vietnam have been
recorded. Their focal mechanisms suggest
strike-slip faulting and general northsouth
compression compatible with right-lateral
offset across the NWSE-striking fault zone
[Cong and Feigl, 1999].Table
1.
CompilationofExistingRight-LateralDisplacementEstimatesAcrosstheRedRiverFaultZone
Reference
Total
Offset(RightLateral)
Duration
SlipRate
StudyArea
Metho
d
Schoenbohm
etal.[2005]
>40km
LateMioceneRecent
(~8My)
5mm/yr
Yunnan
Displacedgeologic
almarkersand
offsetgeomo
rphology
ZuchiewiczandCuong[2009]
N.A.
LatePleistocene
(mayhaveinitiatedearlier)
5.5
7.8mm/yr
No
rthernVietnam
Offsetgeomo
rphology
Allenetal.[1984]
56km
Pleistocene
(mayhaveinitiatedearlier)
2
3mm/yr
(possiblyupto5mm/yr)
Yunnan
Offsetgeomo
rphology
Replumazetal.[2001]
25km
PlioceneRecent
5mm/yr
YunnanandNorthernVietnam
Offsetgeomo
rphology
Trinhetal.[2012]
(1.2
km
since150KA)
N.A.
85mm
No
rthernVietnam
Offsetgeomo
rphology
Zuchiewiczetal.[2013]
(~14km
during
thePleistocene)
N.A.
5.57.8mm/yr
No
rthernVietnam
Offsetgeomo
rphology
CongandFeigl[1999]
N.A.
N.A.
15mm/yr
No
rthernVietnam
Geodeticmeasureme
ntincludingGPS
Simonsetal.[2007]
N.A.
N.A.
2mm/yr
SEAsia
Geodeticmeasureme
ntincludingGPS
Iwakunietal.[2004]
N.A.
N.A.
Insignicant
(below
GPSdetectionlimit)
Indochina/SEAsia
Geodeticmeasureme
ntincludingGPS
Micheletal.[2001]
N.A.
N.A.
Below
GPSdetection
limit(2km) thickness of the Upper Neogene along the south-eastern ank of the Bach Long
Vi inversion zone documents fairly rapid subsidence and deposition in this area (Figure 5). Comparable to
that along the anks of the central northern Song Hong basin, subsidence may have been enhanced by the
loading and exural bending associated with the adjacent Bach Long Vi inversion uplift.
Inversion-related deformation and internal thickness variations of the Upper Neogene succession document
that inversion starting during the Late Miocene and continued into the PliocenePleistocene (Figures 6, 12
Figure 14.Gross-depositional facies map based on seismic interpretation from part of the Upper Miocene in the area west
of the Bach Long Vi Island. Depositionwas governed by contemporaneous inversion as well as the structural style inherite
after Paleogene rifting.
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and 15). Inversional deformation of
Upper Pleistocene and Holocene strata
indicated by shallow seismic data
suggests that inversion continues to the
present (Figure 16).
Analysis of the Upper Neogene seismic
facies indicates that deposition along
theanks of the Bach Long Vi area was
strongly inuenced by the inversion.
Along the south-eastern ank of the
inversion zone, the south-eastward
prograding clinoforms are interpreted
as marine deltaic units building out from
the inversion uplift (Figure 13). The
unconformities capping the clinoform
topsets are in places interlayered by
sets of stacked channels several tens
of milliseconds (TWT) deep which is
interpreted to reect periods of
relative uplift followed by uvial/alluvia
deposition signifying periods of
regression. This pattern suggest a highly
dynamic Late Miocene depositional
environment characterized by pulsed
uplift along the inversion trend and
rapid subsidence and sedimentation in
the east with deposition guided by
uplift and erosion along the Bach Long
Vi inversion trend. The aerially restricted
occurrence of the unconformities
favours local tectonic uplifts rather than
glacio-eustatic sea-level uctuations,
for example, as forcing mechanism of
these Late Miocene regressions.
Along the south-western inversion
strand, the Upper Miocene prograding
clinoforms are similarly interpreted as
deltaic foresets (Figure 14). Basinward
from the foresets, the bottomsets cut
by incisions are interpreted as fairly
deep-marine strata cut by turbidite
channels. In turn, the amalgamation
of the topsets into a single strong
soft-kick reector is interpreted as a thin
coal-dominated succession deposited on
a Late Miocene delta plain. The platform
buildup capping a basement high is
interpreted as a carbonate platform.
Clinoforms prograded basinward during
the Miocene and were guided by the
Bach Long Vi inversion zone, supporting
Late Miocene inversion activity. Along
the southern inversion strand, the
0
0.5
1.0
1.5
2.5
2.0
TWT(sec.)
Thickness variation due to inversion
Acoustic basement
Palaeogene syn-rift
Plio. Pleistocene
M. U. Miocene
U. Miocene
2 km
0
2 km
0
0.5
1.0
1.5
TWT(
sec.)
0.5
1.0
1.5
TWT(sec.)
2 km
0
0.5
1.0
1.5
TWT(sec.)
2 km
0
0.5
1.0
1.5
TWT(sec.)
2 km
0NW SE
0.5
1.0
1.5
2.5
2.0
TWT(sec.)
Figure 15.(a) Seismic transect and (b) redrawnstratigraphic section from
the the southwestern ank of the Bach Long Vi inversion zone. (cf)
Thickness variations a cross inversion zones document inversion taking
place since the Late Miocene, which is emphasized by back-stripping
(disregarding burial compaction).
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Seafloor
m
ultiple
10
BachLo
ngViIsland
BachLongViIsland
~3kmW E
30
50TWTmsec
70
10
U. Pleistocene Holocene Fault
30
50TWTmsec
70
2 km
Eocene OligoceneWater
Figure 16.Sparker seismic lines from conjugated sides of the Bach Long Vi Island resolving the upper few tens of meters of section. The shallow seismic data
document inversion-related deformation of latest PleistoceneHolocene sediments around the island and thus document the inversion continuing to the presen
along the Bach Long Vi trend.
0
0.5
1.0
1.5
2.5
2.0
TWT(sec.)
0
SW NE
NNW-trending normal faults
Near-basePliocene
Periodoflocalmax.inversion
0.5
1.0
1.5
2.5
2.0
TWT(sec.)
2 km
Acoustic basement
Palaeogene syn-rift
U. Miocene
Plio. Pleistocene
Figure 17. In the southern part of the Bach Long Vi inversion trend, Late Neogene inversion seems to have peaked
already during the Late Miocene. During the PliocenePleistocene minor NNWSSE-striking normal faulting affected this
area as well.
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PliocenePleistocene decrease in inversion-related thickness variations and deformation suggest a decrease in
inversion during the latter Neogene in this area.
At the same time, the formation of NNWSSE-striking subtle extensional faults in the south-eastern part of
the Bach Long Vi trend may indicate a slight change in the regional stress regime (Figure 8). The prevailing
position of the NNWSSE-striking subtle extensional faults above the fairly at crest of inversion structurestogether with their deep rooting suggests a regional tectonic rather than a local gravity induced origin for
the extension.
The subtle increase in maturity from top to bottom in the core well from Bach Long Vi Island suggests a
normal to low geothermal gradient at the time of maximum maturation (~maximum burial), in which case
a maturity ofRo0.39% andTmax of 431C may correspond to an approximate burial depth in the order of
~12 km. This is compatible with the level of sandstone diagenisis of the cored Paleogene succession.
This suggests that apart from the observed ~1.5 km of Late Neogene relative inversion uplift, as much
as 12 km of additional uplift and erosion may have occurred across the central part of the inversion zone.
However, the regional stratigraphic outline suggests that the maximum burial in the Bach Long Vi area
occurred already before the end of the Oligocene, and that part of the uplift and denudation took place
immediately thereafter, thus preceding the Late Neogene. It is not possible to assess how much of the
additional roughly 1
2 km uplift occurred during the Late Neogene.
5. Discussion
5.1. Evolving Late Neogene Stress Pattern and Strike-Slip Deformation
Lying at the direct continuation of the RRFZ, the highly dynamic Late Neogene development of the northern
Gulf of Tonkin testies to the rapidly shifting nature of continental extrusion. Intense deformation and high
depositional rates make the northern Gulf of Tonkin excellently suited for studying South China and Indochinas
escape away from the Indian-Eurasian suture zone and makes the region well-suited for investigating the
dynamic extrusion tectonic mechanisms in general.
Since Late Neogene deformation in the region is virtually restricted to reactivation of older rift structures,
hints of the approximate stress pattern affecting the region at a given period of time cannot be deduced
solely from deformation across single faults but is rather provided by (1) the combination of fault trendsactive at the given period of time, (2) the combination of inactive fault trends, (3) the nature of deformation
(compressive or dilative), (4) the relative magnitude of deformation taking place across individual fault
trends, and (5) potential indicators of strike-slip motions, e.g., the presence ofower structures.
The inferred stress patterns indicated in Figure 8 are average stress patterns covering the roughly 30,000 km2
study area throughout longer periods of time corresponding to the analyzed stratigraphic intervals. The
stress regimes may therefore have deviated from this average more locally andduring more restricted stages
During Middle and early Late Miocene time in the central northern Song Hong basin, the roughly EW-striking
extensional faults together with the NWSE-striking compressional faults delineating prominent ower
structures suggest a left-lateral deformation pattern associated with roughly NS extensional and EW
compressional stresses (Figure 8a).
During the second half of Late Miocene time, the compression affecting the NW-trending lineaments within
the central part of the northern Song Hong basin, together with the coeval compression across the centralNE-verging Bach Long Vi inversion zone, suggests a stress regime dominated by both roughly NESW
and NWSE compression (Figure 8b). This is in accordance with the halt of normal faulting across the centra
Song Hong basin prior to this period.
This stress regime does not provide unequivocal information as to the overall displacement sense across the
offshore continuation of the RRFZ. Lateral displacement is not revealed by consistent releasing/restraining bend
geometries or other deformation features. This could be taken to indicate the absence of strike-slip across
the RRFZ and a prevalence of pure thrusting taking place across the offshore part of the RRFZ. However, the
geometric outline of the two inversion zones could be explained by right-lateral motion across the RRFZ in
a pure shear model (and a left-lateral component across the Bach Long Vi inversion zone). This would be
comparable to the modern relationships between the right-lateral onshore RRFZ and left-lateral Dien Bien Phu
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and the Xianshulhe-Xiaojiang fault systems. Furthermore, this would be in accordance with the timing
considerations from the onshore part of the fault zone [Schoenbohm et al., 2006].
A Late Miocene strike-slip inversion is thus tentatively proposed in this study, with right-lateral displacement
prevailing from around middle Late Miocene time. This pushes back the strike-slip inversion in the
offshore realm by a few million years as compared to previous estimates [Rangin et al., 1995]. The availablebiostratigraphic data in the area from exploration wells do not allow a detailed subdivision of the Upper
Miocene and thus assignment of the precise age of inversion (Vietnam Petroleum Institute in house reports)
A rough estimate of the onset age of inversion may be deduced if more or less uniform long-term subsidence
and depositional rates are assumed since the start of inversion for the depocenter south of the Bach Long Vi
inversion trend and further assuming a paleobathymetry/-topography at the start of inversion and at the
earliest Pliocene comparable to the present. The age of the PliocenePleistocene succession is fairly well
constrained. Based on the above assumptions, the thickness of the Upper Miocene succession deposited
during the inversion may be compatible to a roughly 34 My long depositional period. Inversion may thus
have commenced around roughly 810 Ma. Concurrent estimates are reached for the Upper Miocene
depocenters along the eastern ank of the central northern Song Hong basin. However, the mechanism
inuencing subsidence across these depocenters seems to have changed after the Late Miocene, and the
later estimate could be more coincidental.
The lack of faulting since the end of the Miocene in the central northern Song Hong basin precludes
PliocenePleistocene right-lateral motion across the basin. On the other hand, inversion continued in the Bach
Long Vi area during the the PliocenePleistocene, although apparently in the west at a more moderate scale
than during the Late Miocene. Together with the NNWSSE-striking normal faulting in the southern part of the
Bach Long Vi inversion zone, this suggest a prevailing PliocenePleistocene stress pattern dominated by
roughly NNWSSE-compression and more subtle WSWENE extension. This is compatible with right-lateral
motion across NWSE-striking faults like the RRFZ and is consistent with the modern stress regime indicated by
fault plane solutions and GPS analysis (Figure 8c) [Cong and Feigl, 1999;Simons et al., 2007].
The gradually evolving Neogene inversions in the area around the northern Song Hong basin seem to reect
the increasing compressional extrusion forces coming to dominate the latter Neogene in the area. We
speculate that the compression is related to the increasing effects of the South China block extrusion and the
northward indentation of the Indian continent. During Miocene time, the extrusion of the South China block
accelerated and the escape of the Indochina block diminished, causing convergent forces between the
two blocks to dominate, in contrast to the former strike-slip dominance [ Replumaz and Tapponnier, 2003]. As
theescape rate of the South China block eventually exceeded theIndochinese rate during the latest Miocene
the relative motion across the RRFZ changed to right-lateral [Tapponnier et al., 1982].
5.2. Lateral Offset and the Take-up of Right-Lateral Displacement
The disconnected nature of faults within the middle and upper Upper Miocene does not indicate a Late
Miocene right-lateral offset greater than a few kilometers in the Song Hong basin (Figures 5 and 6). Furthermore
the lack of PliocenePleistocene faulting in the central northern Song Hong basin precludes any direct
right-lateral displacement across the basin in the latter period (Figure 7). Extrusion-related lateral displacement
must therefore have been taken up withinand/or northwest of thestudy area. The Bach Long Vi zone may have
acted to accommodate lateral shearing and a fraction of the differential motion between the South China
and Indochina blocks during the Late Neogene inversion. Inversion across the Bach Long Vi zone continuedduring the PliocenePleistocene when right-lateral shearing had ceased in the Song Hong basin. This suggests
that part of the PliocenePleistocene extrusion of the South China block observed onshore may have been
accommodated within the Bach Long Vi inversion. However, the extent of Late Neogene shortening taking
place across the inversion zone may only have accommodated a relative displacement in the order of 25 km
Onshore deformation zones must therefore have accommodated most of the relative motion between the
South China and the Indochina blocks when considering onshore RRFZ-displacement estimates around 25 to
40 km [e.g.,Replumaz et al., 2001;Schoenbohm et al., 2006].
There is no hard-link between the Bach Long Vi inversion zone and the RRFZ being active during the Late
Neogene. Consequently, the offshore right-lateral displacement of the South China block relative to the
Indochina block is considered to have been modest.
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Compatible with the orientation of the Bach Long Vi inversion zone, a broad belt of NE SW-striking faults
exist onshore in northern Vietnam and extend into China (Figure 5). Shortening may have taken place across
the onshore belt by analogy to the Late Neogene shortening across the parallel Bach Long Vi inversion
zone. The onshore fault belt may thus have accommodated relative displacement between the Indochina
and the South China blocks since the Late Miocene. This could explain the absence of lateral offset across the
Song Hong basin during a period of well documented right-lateral motion across the RRFZ immediately to
the northwest.
Similar to in the Beibuwan basin, Pubellier et al. [2003] interpreted the onshore NESW-striking fault system to
have accommodated left-lateral extrusion-related motion during the Paleogene by extension. This suggests
that the onshore fault system behaved as a crustal weakness zone prone to being reactivated by Late
Neogene extrusion tectonics.
5.3. Exhumation of the RRFZ and Displacement Rates
Based on geomorphological offsets across the onshore RRFZ, cumulative right-lateral displacement estimate
~25 km have been proposed [Allen et al., 1984;Replumaz et al., 2001;Schoenbohm et al., 2006;Trinh et al.
2012;Zuchiewicz et al., 2013]. Major incision along the Red River and its tributaries has been interpreted as
PliocenePleistocene in age, occurring in response to thesuper-regional Tibetanplateau uplift [e.g., Replumaz
et al., 2001;Schoenbohm et al., 2004, 2005, 2006].
However, our data suggest an earlier onset of uplift and denudation along a narrow belt at least including the
southern part of the RRFZ. The domed Middle to Late Miocene inversion zone in the central northern Song
Hong basin lies in direct continuation of the Dai Nui Con Voi metamorphic core complex outlining the
southern part of the RRFZ (Figure 5). In the northern, data covered part of the Song Hong basin (Figure 2);
several hundred meters of exhumation occurred regionally during the Middle to Late Miocene. We speculate
that the style and trend of the basinal inversion makes a similar contemporary uplift event plausible
across the Dai Nui Con Voi metamorphic core complex. Onset of uplift and denudation along part of the RRFZ
may thus precede the PliocenePleistocene plateau growth.
Apatite Fission Track (AFT) analyses of the Dai Nui Con Voi metamorphic core complex yield fully reset
ages between 18 and 30 Myr [Maluski et al., 2001;Viola and Anczkiewicz, 2008], which suggest a Late
OligoceneEarly Miocene cooling event and most likely in the range of 23 km of Neogene exhumation to
the present surface level without specifying potential periods of pulsed uplift. AFT analysis from the Aliao
Shan metamorphic core complex on the other hand yield ages around 1014 Myr [Bergman et al., 1997]
which suggest a MiddleLate Miocene cooling event and further may indicate uplift and exhumation in the
range of 23 km to the present surface level. This is overlapping with the timing and style of inversion in
the northern central Song Hong basin. However, a potential genetic link between the Miocene inversion in
the northern Song Hong basin and the coeval exhumation of the Aliao Shan metamorphic core complex
remains speculative.
If uplift along part of the RRFZ took place already during the Middle to Late Miocene, the present
geomorphological pattern along the Red River may have initiated before the Pliocene. This calls for caution in
the assessment of the long-term right-lateral slip rates across the fault zone. A PliocenePleistocene lateral
offsetof ~25 km would require an average slip rate around 5 mm/yr. If the uplift commencedalready during the
Middle to Late Miocene time, average slip rates may in fact be less than half. We note that this seems more
compatible with measured modern slip-rates [e.g. ,Simons et al., 2007] (Table 1).
Furthermore, if uplift started already during Middleearly Late Miocene time, the RRFZ would have been in a
left-lateral slip regime during the initial exhumation phase. This may further complicate quanti cation of the
total offset based on geomorphology.
6. Conclusion
1. Extrusion of both Indochina and South China controlled basin development in the northern Gulf of
Tonkin, making the area ideal for studying the mechanisms behind continental escape tectonics. The Late
Neogene progression of the continental escape tectonics caused basin inversion and reversals of the
RRFZ strike-slip regime.
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2. There is no indication of left-lateral motion during the latest Miocene in the Song Hong basin. In contrast
inversion in the Bach Long Vi area is tentatively interpreted to reect Late Miocene onset of right-latera
displacement across the RRFZ.
3. In the central northern Song Hong basin, the termination of faulting after the Miocene preclude
PliocenePleistocene strike-slip movement across the basin. In contrast, continued inversion across the
NESW-trending Bach Long Vi inversion zone together with moderate NWSE-striking extensional faulting
suggests a stress regime compatible with continued right-lateral shearing across the onshore RRFZ.
4. Late Neogene deposition was strongly inuenced by the ongoing inversion. The proto-Red River was
diverted by uplift to a prevailing path along the northeastern ank of the Song Hong basin. Similarly,
the depositional pattern along the Bach Long Vi inversion zone was inuenced by alternating periods of
uplift and subsidence and progradation away from or along the uplifted inversion zone guided by the
overall structural trend.
5. Inversion within the Bach Long Vi zone may have accommodated up to a few kilometers of right-latera
displacement between the Indochina and South China blocks. The amount of compression and the lack
of a Late Neogene hard-link to the onshore RRFZ preclude accommodation of a larger offset within the
inversion zone. However, comparable fault zones located immediately onshore may have accommodated a
larger fraction of the right-lateral motion across the RRFZ, thus accounting for the restricted transfer of
motion to offshore.6. The Middle to Late Miocene inversion uplift zone within the central northern part of the Song Hong basin
lies in direct continuation of the Dai Nui Con Voi and Ailao Shan metamorphic core complexes, and a
related Middle Neogene uplift of the core complexes is speculated. This predates other suggestions for
their late-stage uplift and consequently calls for caution in the evaluation of right-lateral slip-rates and
total displacement based on geomorphological analysis.
ReferencesAllen, C. R., A. R. Gillespie, H. Yuan, K. E. Sieh, Z. Buchun, and Z. Chengnan (1984), Red River and associated faults, Yunnan Province, China:
Quarternary geology, slip rates, and seismic hazard, Geol. Soc. Am. Bull.,95, 686700.
Bergman, S. C., P. H. Leloup, P. Tapponnier, U. Schrer, and P. O Sullivan (1997), Apatite ssion track thermal history of the Ailao Shan-Red
River shear zone, China, (Abs.): Strasbourg, France, paper presented at European Union of Geoscience meeting 2327 March 1997.
Burke, K., and C. Sengr (1984), Tectonic escape in the evolution of the continental crust, inReection Seismology: The Continental Crust,
Geodyn. Ser., vol. 14, pp. 4153, AGU, Washington, D. C.
Chen, Z., B. C. Burchel, Y. Liu, R. W. King, L. H. Royden, W. Tang, E. Wang, J. Zhao, and X. Zhang (2000), Global Positioning Systemmeasurements from eastern Tibet and their implications for India/Eurasia intercontinental deformation, J. Geophys. Res.,105,
16,21516,227, doi:10.1029/2000JB900092 .
Cong, D. C., and K. L. Feigl (1999), Geodetic measurement of horisontal strain across the Red River fault near Thac Ba, Vietnam, 19631994
J. Geod. ,73, 298310.
Fyhn, M. B. W., L. O. Boldreel, and L. H. Nielsen (2009a), Geological development of the Central and South Vietnamese margin: Implications
for the establishment of the South China Sea, Indochinese escape tectonics and Cenozoic volcanism, Tectonophysics,478, 184222,
doi:10.1016/j.tecto.2009.08.002.
Fyhn, M. B. W., et al. (2009b), Geological evolution, regional perspectives and hydrocarbon potential of the northwest Phu Khanh Basin,
offshore Central Vietnam,Mar. Pet. Geol.,26, 124, doi:10.1016/j.marpetgeo.2007.07.014.
Fyhn, M. B. W., H. I. Petersen, L. H. Nielsen, T. C. Giang, L. H. Nga, N. T. M. Hong, N. D. Nguyen, and I. Abatzis (2012), The Cenozoic Song Hong
and Beibuwan Basins, Vietnam, Geol. Surv. Den. Greenl. Bull.,26, 8184.
Huang, B., H. Tian, R. W. T. Wilkins, X. Xiao, and L. Li (2013), Geochemical characteristics, palaeoenvironment and formation model of Eocene
organic-rich shales in the Beibuwan Basin, South China Sea, Mar. Pet. Geol.,48, 7789, doi:10.1016/j.marpetgeo.2013.07.012.
Huang, H.-H., Z. J. Xu, Y.-M. Wu, X. Song, B.-S. Huang, and L. M. Nguyen (2013), First local seismic tomography for Red River shear
Zone, Northern Vietnam: Stepwise inversion employing crustal P and Pn waves, Tectonophysics, 584 , 230239, doi:10.1016/
j.tecto.2012.03.030.
Iwakuni, M., T. Kato, H. Takiguchi, T. Nakaegawa, and M. Satomura (2004), Crustal deformation in Thailand and tectonics of Indochinapeninsula as seen from GPS observations, Geophys. Res. Lett.,31, L11612, doi:10.1029/2004GL020347.
Lap, N. K. (1988), Seismic activity in northwestern Vietnam, Acta Geophys. Pol.,36, 375380.
Leloup, P. H., T. M. Harrison, F. J. Ryerson, C. Wenji, L. Qi, P. Tapponnier, and R. Lacassin (1993), Structural, petrological and themal evolution o
a Tertiary ductile strike-slip zone, Diancang Shan, Yunnan,J. Geophys. Res.,98, 67156743, doi:10.1029/92JB02791.
Leloup, P. H., R. Lacassin, P. Tapponnier, U. Schrer, Z. Dalai, L. Xiaohan, Z. Liangshang, J. Shaocheng, and P. T. Trinh (1995), The ASRR shea
zone (Yunnan, China), Tertiary transform boundary of Indochina, Tectonophysics,251, 384.
Leloup, P. H., N. Arnaud, R. Lacassin, J. R. Kienast, T. M. Harrison, T. T. P. Trong, A. Replumaz, and P. Tapponnier (2001), New constraints on the
structure, thermochronology, and timing of the Ailao Shan-Red River shear zone, SE Asia, J. Geophys. Res.,106, 66836732, doi:10.1029/
2000JB900322.
Maluski, H., C. Lepvrier, L. Jolivet, A. Carter, D. Roques, O. Beyssac, T. T. Tang, D. N. Thang, and D. Avigad (2001), Ar/Ar and ssiontrack ages in
the Song Chay massif: Early Triassic and Cenozoic tectonics in northern Vietnam,J. Asian Earth Sci.,19, 233248.
Michel, G. W., et al. (2001), Crustal motion and block behavior in SE-Asia from GPS measurements, Earth Planet. Sci. Lett.,187, 239244.
Nguyen, L. M., T.-L. Lin, Y.-M. Wu, B.-S. Huang, C.-H. Chang, W.-G. Huang, T. S. Le, Q. C. Nguen, and V. T. Dinh (2012), The rst peak ground
motion attenuation relationships for North of Vietnam, J. Asian Earth Sci.,43, 241253, doi:10.1016/j.jseaes.2011.09.012.
Acknowledgments
The study is an outcome of the ongoing
joint Vietnamese-Danish research
program termed the ENRECA Project
(ENhanced REsearch CApacity building)
sponsored by the Danish Ministry of
Foreign Affairs and supported by
PetroVietnam and Vietnam Petroleum
Institute. Vietnam Petroleum Institute
and PetroVietnam made data available
to the project group and are thanked
together with GEUS for permission to
publish. Center of Marine Geology and
Resources, Hanoi, provided shallow
seismic data. Data are propriety data
owned by PetroVietnam and cannot be
released according to Vietnamese law.
The ENRECA team has contributed
with stimulating discussions, and L.H.
Nielsenis thankedfor commentingon an
earlier version of the manuscript.
J. Halskov is acknowledged for the
gure artwork. The constructive reviews
by A. Replumaz and L. Schoenbohm are
highly appreciated.
Tectonics 10.1002/2014TC003674
FYHN AND PHACH 2015. American Geophysical Union. All Rights Reserved. 311
http://dx.doi.org/10.1029/2000JB900092http://dx.doi.org/10.1016/j.tecto.2009.08.002http://dx.doi.org/10.1016/j.marpetgeo.2007.07.014http://dx.doi.org/10.1016/j.marpetgeo.2013.07.012http://dx.doi.org/10.1016/j.tecto.2012.03.030http://dx.doi.org/10.1016/j.tecto.2012.03.030http://dx.doi.org/10.1029/2004GL020347http://dx.doi.org/10.1029/92JB02791http://dx.doi.org/10.1029/2000JB900322http://dx.doi.org/10.1029/2000JB900322http://dx.doi.org/10.1016/j.jseaes.2011.09.012http://dx.doi.org/10.1016/j.jseaes.2011.09.012http://dx.doi.org/10.1029/2000JB900322http://dx.doi.org/10.1029/2000JB900322http://dx.doi.org/10.1029/92JB02791http://dx.doi.org/10.1029/2004GL020347http://dx.doi.org/10.1016/j.tecto.2012.03.030http://dx.doi.org/10.1016/j.tecto.2012.03.030http://dx.doi.org/10.1016/j.marpetgeo.2013.07.012http://dx.doi.org/10.1016/j.marpetgeo.2007.07.014http://dx.doi.org/10.1016/j.tecto.2009.08.002http://dx.doi.org/10.1029/2000JB9000927/23/2019 Fyhn and Phac, 2015
23/23
Nielsen, L.H., A. Mathiesen, T. Bidstrup, O. V. Vejbk, P. T. Dien, andP. V. Tiem (1999), Modelling the hydrocarbongeneration in the Cainozoi
Song Hong Basin, Vietnam: A highly prospective basin, J. Asian Earth Sci.,17, 269294.
Payton, C. E. (Ed.) (1977), Seismic stratigraphy: Applications to hydrocarbon exploration, AAPG Mem.,26, 313.
Petersen, H. I., M. B. W. Fyhn, L. H. Nielsen, C. D. H. A. Tuan, C. D. Quang, N. T. Tuyen, P. V. Thang, N. T. Tham, N. K. Oang, and I. Abatzis (2014),
World-class Paleogene oil-prone source rocks from a cored lacustrine syn-rift succession, Bach Long Vi Island, Song Hong Basin, offshore
northern Vietnam,J. Pet. Geol.,37, 373389.
Pubellier, M., C. Rangin, P. V. Phach, B. C. Que, D. T. Hung, and C. L. Sang (2003), The Cao Bang-Tien Yen fault implications on the relationshipbetween the Red River and the South China coast belt, Adv. Nat. Sci.,4, 347361.
Rangin, C., M. Klein, D. Roques, X. Le Pichon, and L. V. Trong (1995), The Red River fault system in the Tonkin Gulf, Vietnam, Tectonophysics
243, 209222.
Replumaz, A., and P. Tapponnier (2003), Reconstruction of the deformed collision zone Between India and Asia by backward motion of
lithospheric blocks,J. Geophys. Res.,108(B6), 2285, doi:10.1029/2001JB000661.
Replumaz, A., R. Lacassin, and P. H. Leloup (2001), Large river offset and PlioQuaternary dextral slip rate on the Red River fault (Yunnan,
China),J. Geophys. Res.,106, 819836, doi:10.1029/2000JB900135 .
Schoenbohm, L. M., K. X. Whipple, B. C. Burchel, and L. Chen (2004), Geomorphic constraints on surface uplift, exhumation, and plateau
growth in the Red River region, Yunnan Province, China, Geol. Soc. Am. Bull.,116, 895909, doi:10.1130/B25364.1.
Schoenbohm, L. M., B. C. Burchel, C. Liangzhong, and Y. Jiyun (2005), Exhumation of the Ailao Shan shear zone recorded by Cenozoic
sedimentary rocks, Yunnan Province, China, Tectonics,24, TC6015, doi:10.1029/2005TC001803 .
Schoenbohm, L. M., B. C. Burchel, C. Liangzhong, and Y. Jiyun (2006), Miocene to present activity along the Red River fault, China, in the
context of continental extrusion, upper-crustal rotation, and lower-crustal ow,Geol. Soc. Am. Bull. ,118, 672688, doi:10.1130/B25816.1
Sengr, A. M. C., N. Grr, and F. Saroglu (1985), Strike-slip faulting and related basin formation in zones of tectonic escape: Turkey as a case
study, inStrike-Slip Deformation, Basin Formation, and Sedimentation , edited by K. T. Biddle and N. Christie-Blick, Soc. Econ. Paleontol.
Mineral. Spec. Publ.,37, 227264.
Shen, Z.-K., J. L, M. Wang, and R. Brgmann (2005), Contemporary crustal deformation around the southeast borderland of the TibetianPlateau,J. Geophys. Res.,110 B11409, doi:10.1029/2004JB003421.
Simons, W. J. F., et al. (2007), A decade of GPS in Southeast Asia: Resolving Sundaland motion boundaries,J. Geophys. Res.,112, B06420,
doi:10.1029/2005JB003868 .
Sun, Z., Z. Zhong, D. Zhou, X. Qiu, and X. Li (2004), Experimental constraints on Cenozoic development of Ying-Qiong basin in NW SCS, in
Continent-Ocean Interactions Within East Asian Marginal Seas ,Geophys. Monogr. Ser., vol. 149, edited by P. Clift et al., pp. 109120, AGU,
Washington, D. C.
Tapponnier, P., G. Peltzer, A. Y. LeDain, R. Armijo, and P. Cobbold (1982), Propagating extrusion tectonics in Asia: New insight from simple
experiments with plasticine,Geology,10, 611616.
Tapponnier, P., G. Peltzer, and R. Armijo (1986), On the mechanics of the collision between India and Asia, in Collision Tectonics, edited by
M. P. Coward and A. C. Ries, Geol. Soc. London Spec. Publ.,19, 115157.
To, T. D., N. T. Yem, D. C. Cong, V. Q. Hai, Z. Witold, C. N. Quoc, and N. N. Viet (2013), Recent crustal movements of northern Vietnam from GPS
data,J. Geodyn.,69, 510, doi:10.1016/j.jog.2012.02.009.
Trinh, P. T., N. V. Liem, N. V. Huong, H. Q. Vinh, B. V. Thom, B. T. Thao, M. T. Tan, and N. Hoang (2012), Late Quaternary tectonics and
seismitectonics along the Red River fault zone, North Vietnam, Earth Sci. Rev.,114, 224235, doi:10.1016/j.earscirev.2012.06.008.
Viola, G., and R. Anczkiewicz (2008), Exhumation history of the Red River shear zone in northern Vietnam: New insights from zircon and
apatitession-track analysis,J. Asian Earth Sci.,33, 7890, doi:10.1016/j.jseaes.2007.08.006.
Zhang, Z., R. McCaffrey, and P. Zhang (2013), Relative motion across the eastern Tibetian plateau: Contributions from faulting, internal strainand rotation rates,Tectonophysics,584, 240256, doi:10.1016/j.tecto.2012.08.006.
Zhao, S. (1995), Joint inversion of observed gravity and GPS baseline changes for the detection of the active fault segment at the Red River
fault zone,Geophys. J. Int.,122, 7088.
Zhao, S., D. Chao, and X. Jusheng (1993), Determination of current active segments at the Red River Fault Zone by inversion of GPS baseline
changes,J. Geodyn.,17, 145154.
Zhu, M., S. Graham, and T. McHargue (2009), The Red River Fault Zone in the Yinggehai basin, South China Sea, Tectonophysics,476, 397417
doi:10.1016/j.tecto.2009.06.015.
Zuchiewicz, W., and N. Q. Cuong (2009), Quarternary tectonics of the Red River Fault Zone in Vietnam A morphotectonic approach,
Geologia,35, 367374.
Zuchiewicz, W., N. Q. Cuong, J. Zasadni, and N. T. Yem (2013), Late Cenozoic tectonics of the Red River Fault Zone, Vietnam, in the light o
geomorphic studies,J. Geodyn.,69, 1130, doi:10.1016/j.jog.2011.10.008.
Tectonics 10.1002/2014TC003674
http://dx.doi.org/10.1029/2001JB000661http://dx.doi.org/10.1029/2000JB900135http://dx.doi.org/10.1130/B25364.1http://dx.doi.org/10.1029/2005TC001803http://dx.doi.org/10.1130/B25816.1http://dx.doi.org/10.1029/2004JB003421http://dx.doi.org/10.1029/2005JB003868http://dx.doi.org/10.1016/j.jog.2012.02.009http://dx.doi.org/10.1016/j.earscirev.2012.06.008http://dx.doi.org/10.1016/j.jseaes.2007.08.006http://dx.doi.org/10.1016/j.tecto.2012.08.006http://dx.doi.org/10.1016/j.tecto.2009.06.015http://dx.doi.org/10.1016/j.jog.2011.10.008http://dx.doi.org/10.1016/j.jog.2011.10.008http://dx.doi.org/10.1016/j.tecto.2009.06.015http://dx.doi.org/10.1016/j.tecto.2012.08.006http://dx.doi.org/10.1016/j.jseaes.2007.08.006http://dx.doi.org/10.1016/j.earscirev.2012.06.008http://dx.doi.org/10.1016/j.jog.2012.02.009http://dx.doi.org/10.1029/2005JB003868http://dx.doi.org/10.1029/2004JB003421http://dx.doi.org/10.1130/B25816.1http://dx.doi.org/10.1029/2005TC001803http://dx.doi.org/10.1130/B25364.1http://dx.doi.org/10.1029/2000JB900135http://dx.doi.org/10.1029/2001JB000661