\makeatletter
\@ifundefined{HCode}
{\documentclass[screen,CRGEOS,Unicode,Thematic]{cedram}
%\usepackage[sort&compress,square,comma,authoryear]{natbib}
\usepackage[square,comma,authoryear]{natbib}
\newenvironment{Table}{\begin{table}}{\end{table}}
\renewcommand\bibsection{\section*{\refname}}
\newenvironment{noXML}{}{}
\def\thead{\noalign{\relax}\hline}
\def\endthead{\noalign{\relax}\hline}
\def\tbody{\noalign{\relax}}
\def\tsup#1{$^{{#1}}$}
\def\tsub#1{$_{{#1}}$}
\RequirePackage{etoolbox}
\usepackage{upgreek}
\def\jobid{crgeos20221272}
%\graphicspath{{/tmp/\jobid_figs/web/}}
\graphicspath{{./figures/}}
\def\myRef{\ref}
\newcounter{runlevel}
\usepackage{multirow} 
\def\nrow#1{\@tempcnta #1\relax%
\advance\@tempcnta by 1\relax%
\xdef\lenrow{\the\@tempcnta}}
\def\morerows#1#2{\nrow{#1}\multirow{\lenrow}{*}{#2}}
\let\MakeYrStrItalic\relax
\def\refinput#1{}
\def\back#1{}
\csdef{Seqnsplit}{\\}
\DOI{10.5802/crgeos.232}
\datereceived{2022-12-30}
\daterevised{2023-05-27}
\datererevised{2023-07-25}
\dateaccepted{2023-08-17}
\ItHasTeXPublished
}
{
\PassOptionsToPackage{authoryear}{natbib}
\documentclass[crgeos]{article}
\usepackage[T1]{fontenc} 
\def\CDRdoi{10.5802/crgeos.232}
\makeatletter
\def\CDRsupplementaryTwotypes#1#2{}
 \def\selectlanguage#1{} 
\let\newline\break
}
\makeatother

\dateposted{2023-12-18}
\begin{document}

\begin{noXML}

%\makeatletter
%\def\TITREspecial{\relax}
%\def\cdr@specialtitle@english{Tribute to Jean Dercourt}
%%\def\cdr@specialtitle@french{Hommage \`a Jean Dercourt}
%\makeatother

\title{Rifting and seafloor spreading in the South China sea: a
subduction-related extension on the down-going plate?}

\alttitle{Ouverture de la Mer de Chine du Sud~: extension au sein
d'une plaque plongeante ?}

\author{\firstname{Sung-Ping} \lastname{Chang}\CDRorcid{0000-0002-5305-0939}}
\address{Ocean Center, 
National Taiwan University, 
Taiwan}
\email[S.-P. Chang]{chang.sung-ping@gs.ncku.edu.tw}

\author{\firstname{Manuel} \lastname{Pubellier}\CDRorcid{0000-0002-3064-9391}\IsCorresp}
\address{CNRS UMR 8538, 
Ecole Normale Sup\'{e}rieure, 
Laboratoire de G\'{e}ologie, 
PSL Research University, 
France}
\email[M. Pubellier]{manupub.pubellier@gmail.com}

\keywords{\kwd{South China Sea}
\kwd{Subduction}
\kwd{Proto South China Sea}
\kwd{Rifting}
\kwd{Spreading}
\kwd{Stratigraphic--tectonic correlations}}

\altkeywords{\kwd{Mer de Chine du Sud}
\kwd{Subduction}
\kwd{Proto Mer de Chine du Sud}
\kwd{Extension}
\kwd{Oceanisation}
\kwd{Corr\'elation Tectono--stratigraphiques}}

\begin{abstract} 
Active margins are sensitive to several subduction-related processes
which include rapid opening and closure of neighboring basins. The
stages of rifting, spreading and the cessation, of activity the South
China Sea basin in Cenozoic appears to be coeval with the progressive
closure of the Proto-South China Sea which ended with collision in
Borneo and Palawan. The evolution bracketed between 45~Ma and 16~Ma,
migrated through time from NE to SW. This dual simultaneous tectonic
evolution illustrates how far-field subduction process may impact the
regional tectonics in terms of both rifting and contraction of the
crust from initiation to termination.
\end{abstract}

\begin{altabstract} 
{La Mer de Chine M\'{e}ridionale (SCS), plus grand bassin d'Asie du SE,
s'ouvre au sein de la plaque plongeante et ses \'{e}tapes de rifting,
de propagation et de cessation d'activit\'{e} du bassin au
C\'{e}nozo\"{i}que semblent \^{e}tre contemporaines de la disparition
progressive du bassin voisin~; la Proto-mer de Chine (PSCS). Cependant,
si les \^{a}ges des \'{e}tages de rifting de la Mer de Chine sont
relativement bien contraints, la datation des \'{e}tapes de la
fermeture n\'{e}cessite une discussion des discordances successives.
Cette \'{e}tude corr\`{e}le le remplissage s\'{e}dimentaire, la
subsidence, les styles structuraux et le magmatisme du couple SCS et
PSCS. Les principales \'{e}tapes R0, R1 et R2 de l'extension de la
cro\^{u}te continentale de la SCS avant son oc\'{e}anisation sont
d\'{e}crites sur trois coupes s\'{e}ri\'{e}es. On y constate une
migration du NE vers le SO du breakup, avec des variations entre
\'{e}tirement crustal important d\'{e}butant au Pal\'{e}oc\`{e}ne et
durant jusqu'\`{a} l'Eoc\`{e}ne vers 45~Ma. Il est suivi par un
amincissement crustal basculant les blocs jusqu'\`{a} 37~Ma et par un
breakup \`{a} 32~Ma. Les autres coupes montrent des coupures
d\'{e}cal\'{e}es \`{a} 45, 28 et 23~Ma pour la coupe centrale, et 35, 23
et 15~Ma pour la coupe sud respectivement. Par opposition, la fermeture
de la PSCS montre, un changement d'environnement de d\'{e}p\^{o}t \`{a}
45~Ma et des discordances progressives jusqu'\`{a} la collision
compl\`{e}te \`{a} 16~Ma. Cette \'{e}volution tectonique simultan\'{e}e
sugg\`{e}re que la disparition d'une lithosph\`{e}re (PSCS) pourrait
affecter le style de rifting et la cr\'{e}ation de lithosph\`{e}re
oc\'{e}anique (SCS) dans l'autre.}
\end{altabstract} 

\maketitle

\twocolumngrid

\end{noXML}

\section{Introduction}\label{sec1} 
\begin{figure*}
{\vspace*{1pt}}
\includegraphics{fig01}
{\vspace*{1pt}}
\caption{\label{fig1}Schematic models illustrating three possible
scenarii for the South China Sea opening. (A)~Slab-pull model
suggesting a southward subduction of the Proto-South China Sea 
\citep{TaylorHayes1983,Hall2002,Pubellieretal2003,Morley2016}. 
(B)~Back-arc model suggesting that the South China Sea opened on the
overriding plate while Proto-South China Sea either subducted
northward, or was undergoing double-sided subduction 
\citep{WuSuppe2017,Lietal2020,Linetal2020}. A variation of this option
is an oceanward subduction followed by a continentward subduction 
\citep{Larvetetal2022}. (C)~Block extrusion induced by the
India-Eurasia collision which opened the South China Sea along
strike-slip fault 
\citep{Tapponnieretal1982,Briaisetal1993,Leloupetal2001}.}
{\vspace*{1pt}}
\end{figure*}

The original causes for the opening of large oceans are difficult to
decipher because the conditions of their onset is generally obscured by
their later development. On the other hand, marginal basins open as a
result of mechanisms which can be identified easily, and include
several subduction-related processes encompassing back-arc or forearc
setting, and often follow gravity collapse of older existing orogens.
In Southeast Asia, many basins have formed in convergence setting and
most of them are young enough to have it preserved 
\citep{PubellierMorley2014,Ranginetal1990b}, such as the Philippine Sea
\citep{Karig1974}, the Sulu Sea \citep{Rangin1989}, the Celebes Sea or
the Banda/Damar seas. The extension responsible for the opening is
observed on both upper and lower plate, and the rifting/spreading of
basins is often coeval with closure of the neighboring ones 
\citep{PubellierMeresse2013}. The stages of rifting, spreading and the
cessation of activity of the SCS basin in Cenozoic appear to be coeval
with the progressive closure of the Proto-South China Sea (PSCS) which
ended with collision in Borneo and Palawan 
\citep{Frankeetal2014,HallBreitfeld2017}. However, if the ages of the
rifting stages are relatively well constrained, the dating of the
closure is blurred and requires a
discussion of the successive regional\unskip\break 
unconformities.

Mature marginal basins are usually underlain by oceanic crust and are
semi-isolated from the open ocean by a tectonic or volcanic ridge
\citep{Zhou2014}. They are formed as a result of several processes
encompassing back-arc or fore-arc setting, and deformed by adjacent
boundary forces, such as for instance, trench retreat, block rotations
or collision \citep{Cheninetal2017}. The evolution of the basins, and
theirs adjacent structures, can be interpreted from their stratigraphic
record. The temporal and spatial variation at regional scale, allows
invoking a geodynamic scenario of evolution. Their short-lived cycle
also provides easier correlation across short distance between the
basin margins and their surrounding tectonic realms. 

\begin{figure*}
\includegraphics{fig02}
%\vspace*{-2pt}
\caption{\label{fig2}Cross-section lithosphere sections across the SCS
and the PSCS. (A)~Subduction of the Paleo-Pacific Plate went underneath
the Eurasia Plate and forming the Proto-SCS as a back-arc setting in
Cretaceous. Sampaguita, Kalamansi and Caolao wells are projected
reference drill sites. (B)~Same section during Late Neogene times.}
%\vspace*{-3pt}
\end{figure*}

Many studies had suggested the opening of the SCS, and the closure of
the PSCS, took place simultaneously in Cenozoic time 
\citep{Holloway1982,TaylorHayes1983,Zhouetal1995,Pubellieretal2003,Frankeetal2014,HallBreitfeld2017,Lunt2019,Lietal2020,Linetal2020}.
Different geodynamic and boundary forces have been suggested and
debated  (Figure~\ref{fig1}), such as the India-Eurasia collision
inducing extrusion of the Indo-China Block
\citep{Tapponnieretal1982,Briaisetal1993,Leloupetal2001}, the opening
of a supra-subduction basin \citep{WuSuppe2017,Lietal2020,Linetal2020},
or a basin opening in the midst of the downgoing plate 
\citep{TaylorHayes1983,Hall2002,Pubellieretal2003,Morley2016,Lietal2020}. The discussion of the different tectonic models of evolution in East and Southwest South China Sea, although still debated, has been reviewed recently 
\citep{Morley2016,Hennig-Breitfeldetal2019,Wangetal2020}.

The South China Sea, although a far field product of the subduction, is
difficult to consider as a back-arc basin, unless involving a
double-verging subduction \citep{WuSuppe2017,Lietal2020, Linetal2020},
and has been created as the result of tectonics involving either the
extrusion of the Indochina block 
\citep{Tapponnieretal1982,Briaisetal1993,Leloupetal2001}, or the
slab-pull triggered by the southward subduction of the Proto-South
China Sea 
\citep{TaylorHayes1983,Hall2002,Pubellieretal2003,Morley2016}. Indeed,
all these processes have somehow interacted; the global back-arc
location of all the marginal basins of Southeast Asia 
\citep{Ranginetal1990a,Pubellieretal2003}, the existence of the large
Red River and Wang Chau strike-slip faults, and the trench pull of the
PSCS. The latter of these options was confronted to the observation
that no active example exists on earth, although this configuration is
admitted for the demise of the successive Tethysian basins, and that it
was difficult to model, prior to the studies of 
\citet{Larvetetal2022}. 

In order to approach this issue, this study overviews the tectonic
evolution of two marginal seas; the South China Sea (SCS) and the
vanished Proto-South China Sea (PSCS), which have been studied
extensively in the past decades 
\citep{TaylorHayes1980,TaylorHayes1983,Holloway1982,Larsenetal2018}. In
view of the complexity of the different extensional and contractional
features of this paired configuration, the study attempts to establish
tectono-stratigraphic correlations across the opposite margins of the
SCS, and the PSCS. Various tectonic stages represented by the selected
unconformities and integrating multi-disciplinary evidences are
combined to reconcile the different hypotheses for the tectonic
evolution of this dual system. 
\vspace*{-2pt}

\section{Geological background}\label{sec2} 
\vspace*{-2pt}
South China Sea is located at the junction between the Eurasia Plate,
the Philippine Sea Plate, and the Indian--Australian Plate. Convergence
around the Sunda Plate encompasses seismically active plate boundaries
such as the Taiwan/Philippines Mobile Belt in the east, the Sumatra
subduction zone in the south and east, up to the Himalaya collision in
the west. Since Jurassic times, a northward subduction beneath the
Eurasia Plate, initiated an extension and a SE migration of the
subduction 
\citep{Yanetal2014a,PubellierMorley2014,Lietal2018,Lietal2020}. Several
intra-plate marginal seas were formed  (Figure~\ref{fig2}) 
\citep{Karigetal1978,Jolivetetal1989,Ranginetal1990b,Schellartetal2019},
in a global setting which is within the upper plate of the
Pacific/Indian Ocean subduction system.

The South China Sea is one of these marginal basins which opened along
the SE China and the Vietnam continental margins. Its rifted margins
developed along inherited structures, for instance, fold limbs 
\citep{Savvaetal2014,Yeetal2020}, or extensive granite massif 
\citep{Kudrassetal1986,Yanetal2014b,Xiaoetal2019,Miaoetal2021}. Many
syn-rift unconformities are described since the Paleogene, in response
to the development of half-grabens marked by detachment faults while
the continental crust extended over 600 km in both conjugated margins.
A rapid breakup  \citep{Larsenetal2018}, forming a significant V-shaped
formed between 32 to 16~Ma  [Figure~\ref{fig3},
\citealp{Briaisetal1993,LePourhietetal2018}] with a narrow COT and
localized magmatism \citep{Nirrengartenetal2020}. A diachronous
migration of the rifting and seafloor spreading has been proposed
\citep{Frankeetal2014}. 

\begin{figure*}
\includegraphics{fig03}
\caption{\label{fig3}(A)~Elevation in SE Asia illustrating oceanic
basins including SCS: South China Sea, SS: Sulu Sea, CS: Celebes Sea,
BS: Banda Sea, BBW: Beibuwan Basin, L: Luconia Basin, NCS: Nam Con Son
Basin, NWPB: NW Palawan Basin, PK: Phu Khanh Basin, PRMB: Pearl River
Mouth Basin, QDN: Qiongdongnan Basin, SH-Y: Song Hong-Yinggehai Basin,
TXN: Taixinan Basin. The bathymetric map has a non-linear color bar to
assist in highlighting certain features. Red lines represent the
location of seismic profiles and black solid dots represent the
locations of the wells. Reference to boreholes; A for Pearl River area,
B for ``Dangerous Grouds Area (e.g., Sampaguita-1 and Malampaya wells),
C for Hainan shelf, E for Nam Con Son (NCS), D for Spratleys Shelf, F
for Luconia Shelf. (B)~The black dashed lines demonstrate the tentative
location of the closure zone of the PSCS  
\citep[modified from][]{Zhouetal2008,Hall2012,Liuetal2014,Zhangetal2017}.}
\end{figure*}


\begin{figure*}
\includegraphics{fig04}
\caption{\label{fig4}Selected portions of seismic lines and major
horizons underlying the stratigraphic sequences R1, R2 and R3 discussed
in text for Domain 1 (NE of the SCS). Location of the seismic profiles
and wells see Figure~\ref{fig3}. The intra-rift unconformity (green
solid lines) separates the underlain R1 units and the overlying R2
units. The R2 characterizes detachment-related extension and onlapping
onto the intra-rift unconformity, corresponding to the acceleration of
rifting rate. The breakup unconformity (red solid lines) indicates the
breakup time and the incipient seafloor spreading. Subsidence curve
modified from  \citet{Tangetal2014},  \citet{Xieetal2014}; 
\citet{Cliftetal2015}. ROU is the base of R1, IRU is between the 2
thinning events (between R1 and R2), and BU (Breakup Unconformity)
marks the end of the rifting and the onset of the spreading at the
domain location.}
\end{figure*}


Another basin, known as the Proto South China Sea (PSCS), existed prior
to the opening of the SCS, to its SE, but is presently totally
subducted  \citep{Ranginetal1990b,HallBreitfeld2017}, and only present
as ophiolitic remnants  \citep{OmangBarber1996,Dycocoetal2021}. The
ocean-floored Proto-South China Sea (PSCS) was probably formed as a
back-arc basin also referred to as the Rajang Sea 
\citep{Ranginetal1990b} although a connection with the easternmost
Tethys is possible. The existence of this ancient basin is based on the
presence of ophiolite complexes and imbricated fold-and-thrust belt in
both NW Borneo and Palawan  (Figure~\ref{fig2}). The ages of the
ophiolites clustered in two main groups as Early Cretaceous and Middle
Eocene 
\citep{Ranginetal1990b,OmangBarber1996,Gravesetal2000,Keenanetal2016,Chienetal2019,Gibagaetal2020,Rahmatetal2020,Dycocoetal2021}. 
Many stratigraphic hiatuses and changes of sediment sources from the
hinterlands reveal successive tectonic events since the Eocene 
\citep{Cullen2010,Hennig-Breitfeldetal2019}. The termination of the
last of these events (Sabah Orogeny) is dated from Late Miocene to
Pleistocene
\citep{Tongkul2003,LuntMadon2017,Sapinetal2013,HallBreitfeld2017}. Few
granite intrusions along Borneo and Palawan suggest the presence of a
broken lithospheric slab in Late Miocene 
\citep{Prouteauetal1996,EncarnacionMukasa1997,Hutchisonetal2000,Cottametal2010,Sapinetal2013,Forsteretal2015}. 

\section{Methodology}\label{sec3} 
This paper reviews the unconformities which are indicators of tectonic
instabilities of the margins, but also changes of seismic facies and
subsidence history, in three different domains from East to Southwest
(D1 to D3 on  Figure~\ref{fig3}) following  \citet{Savvaetal2014}. We
extracted key published seismic profiles and wells (locations see 
Figure~\ref{fig3}) to analyze the rift evolution on the grounds of
seismic stratigraphy, bio-stratigraphy, and structures. Subsidence
history is also examined. In a general, we identify Ro as a 
``stretching stage'' in the sense of  \citet{Peron-Pinvidicetal2007}
which is characterized by numerous steeply dipping normal faults, R1
and R2 the thinning stages with an unconformity in the middle (IRU).
These rifting stages are followed by the breakup.

In Section~\ref{sec4}, the correlation of stratigraphic cuts related to
the contraction is established through domains 1 to 3 in order to
explore the timing of the collision. Observations in the field onshore
and on seismic lines offshore is used to underline and date the crucial
convergence-related unconformities. The facies changes in the deposits
are also taken into account to evaluate fluctuations in the
depositional environment and possible uplift periods. Ultimately, we
try to evaluate chronological links between the two opposite margins 
(Section~\ref{sec6}). 

\section{Tectono-stratigraphy of the rifting and\newline 
spreading in the South
China Sea}\label{sec4} 

\subsection{Rifting stratigraphy in Domain 1}\label{sec4.1} 
On the China margin, the stratigraphy had been established confidently
in the past decades according to the intense industrial research
exploration.  

Within the syn-rift sequence, some internal significant unconformities
are found in the Pearl River Mouth Basin (PRMB) in front of Hong-Kong 
\citep{Chanetal2010,Morley2016,Lunt2019}, 
as well as in the Tainan
Basin SW of Taiwan  \citep{Linetal2003}. The timing of breakup and
rifting has been interpreted as a diachronous event from east to
southwest  \citep{Frankeetal2014}. Although the onset of rifting has
been long debated due to insufficient number of drillings 
\citep{Morley2016}, the age of the detachment fault during rifting, and
the age of the breakup show a diachronous evolution as shown on 
Figure~\ref{fig4}  \citep{Frankeetal2014,Savvaetal2014}. An early phase
of diffuse stretching Ro begins possibly as early as Late Cretaceous 
\citep{Chanetal2010}, after the end of the compressional deformation 
\citep{Nannietal2017} and ended 45~Ma  \citep{Xieetal2019}. The
syn-rift I (R1) was deposited on a basement cut by high-angle normal
faults (orange on  Figure~\ref{fig4}) and bracketed between 45~Ma and
37~Ma  \citep{Linetal2003}. An Intra-Rift
Unconformity (IRU) separates
a second rifting period (R2) from 37 to 32~Ma. It is marked
simultaneously on the SE China and Palawan margins by a significant
hiatus, and a strong sagging period  \citep{Linetal2003,Xieetal2019}.
This period is characterized by thickly sedimented U-shaped seismic
units in the lower part (green to pink horizon on  Figure~\ref{fig4}),
typically expressed in the Liwan sag  \citep{Larsenetal2018}. The thick
R2 represents the last stage of the rifting prior to breakup. Spreading
started around 32~Ma  
\citep{Briaisetal1993,Larsenetal2018,Chaoetal2021},
and ceased at ca. 16~Ma  
\citep{Briaisetal1993,Lietal2015}. If the
extension alone can be invoked for the stretching and thinning of the
SE China margin, the southern conjugate margin may in addition have
suffered from a flexural fore-bulge effect induced by the subduction in
Palawan  \citep{Steueretal2014}. The most continuous record at Well
Sampaguita-1 documented a
stratigraphic boundary formed around 49~Ma
between the transition from the shelf to calcareous shale 
\citep{TaylorHayes1980,Yaoetal2012}. An extensive unconformity occurred
in Sampaguita-1 and Malampaya at 37~Ma  [T80; 
\citealp{Fournieretal2005,Yaoetal2012,Steueretal2014}], and this
unconformity can be extended along the seismic profiles showing its
distinct distribution in the Offshore Palawan Margin. There, to the
south of Domain 1, the breakup unconformity is drawn around 28--30~Ma,
possibly
indicating a small lag time, or at least an asymmetry for the
start of spreading  \citep{Nirrengartenetal2020}. The age is witnessed
by the drilling and seismic evidences 
\citep{Holloway1982,Fournieretal2005,Frankeetal2011,Yaoetal2012,Steueretal2013,Steueretal2014,Pengetal2020}.
\looseness=-1

The tectonic subsidence and the subsidence rate are integrated from
previous publications  \citep{Tangetal2014,Xieetal2014,Cliftetal2015},
and deduced from the seismic observation. The initial rifting
corresponds to the minor subsidence  (Figure~\ref{fig4}), coinciding
the R0 and R1 stratigraphy bounded by high-angle normal faults. The
increase of the subsidence rate within the R2 is vigorously related to
the detachment faults which thin the crust and generated a Late Eocene
unconformity onlapped by the concave-up R2 units in SE China and NW
Palawan Margins\unskip\break 
(Figure~\ref{fig4}). This acceleration of extension
rate is also suggested in the modelling prior to the rapid breakup in
the SCS  \citep{Bruneetal2016,LePourhietetal2018}.\looseness=1

\subsection{Rifting stratigraphy in Domain 2}\label{sec4.2} 
On the E Vietnam Margin, extension is localized both along sharp
segments  \citep{Marquisetal1997,Roquesetal1997,Fyhnetal2009}, and
along wide extremely stretched areas showing detachment features 
\citep{LeiRen2016,Savvaetal2014,Changetal2022}. Similarly, the
southwestern margin also developed extensive basins with detachment
faults  \citep{Liangetal2019} resulting ultimately in an even thinner
crust  (Figure~\ref{fig5}). 

\begin{figure*}
\includegraphics{fig05}
\caption{\label{fig5}Selected portions of seismic lines and major
horizons underlying the stratigraphic sequences R1, R2 and R3 discussed
in text for Domain 2 (Central part of the SCS). Location of the seismic
profiles and wells see  Figure~\ref{fig3}. ROU is the base of R1, IRU
is between the 2 thinning events (between R1 and R2), and BU (Breakup
Unconformity) marks the end of the rifting and the onset of the
spreading at the domain location).}
\end{figure*}

Likewise in Domain 1, the beginning of stretching is unclear (Late
Cretaceous?) and ended up at 38~Ma \citep{LeiRen2016}. The distinct ROU
(regional onset unconformity) is reported mainly at 37~Ma (T80, bottom
of Yacheng Fm.) or slightly older around 45~Ma (within Shixin Fm.), and
documented locally around proximal domain such as the Beibuwan Basin or
the Qiong Dong Nan Basin
[\citealp{Fyhnetal2009,Wuetal2009,Savvaetal2013,Vuetal2017,Zhouetal2018,Wangetal2020}, 
Figure~\ref{fig4}]. The intra-rift unconformity (T70, bottom of Linshui
Fm.) is an angular one around 28~Ma highlighting the development of
detachment faults particularly in both proximal and distal margin such
as in PK basin  \citep{Savvaetal2013,LeiRen2016,Changetal2022}. The
breakup unconformity is identified as 23~Ma (T60) marking a significant
hiatus. In the Dangerous Ground Margin, the earliest unconformity is
recorded around 37~Ma and observed within thick syn-rift sequences 
\citep{YanLiu2004}. An intra-rift unconformity around 30~Ma is
observed and dated by biostratigraphy data in the adjacent wells  [T7, 
\citealp{Hutchison2004,YanLiu2004,HutchisonVijayan2010,Dingetal2014,Zhangetal2020}].
The breakup unconformity main consensus is around 23~Ma, namely the MMU
in many studies  \citep{Steueretal2014,SongLi2015}.

The main character of R2 is its homogeneous upper syn-rift thickness,
which correlates well the northern and southern margins. The horizon of
upper R2 flattens in several basins (Phu Khanh, Nam Con Son (NCS), and
the COT of Nanshan Islands), and is offset slightly by normal faults.
This stage illustrates the space accommodation which develops
preferably horizontally rather than vertically. The possible age of R2
on the Northern margin is 28 to 23~Ma  \citep{LeiRen2016}. In the NW
Borneo Margin, the same age of R2 is extracted from the Sampagita Well,
although situated just N of the boundary with Domain 1,and its end
correlates nicely to that of the incipient oceanic crust 
\citep{Sibuetetal2016,Changetal2022}. The breakup occurred at 23~Ma and
the spreading lasted until 16~Ma. Likewise the Domain 1, the forebulge
region resulted in a widespread area of shallow-water depositional
environment, which developed a significant carbonate layer  [Nido
carbonates, \citealp{Hatley1980,Williams1997,Steueretal2014}]. It is
however deepening toward the Borneo-Palawan Trough, although a built-up
reef exists along the crest of the horst in the Dangerous Ground area 
\citep{Jamaludinetal2017}. 

\begin{figure*}
\includegraphics{fig06}
\vspace*{-3pt}
\caption{\label{fig6}Selected portions of seismic lines and major
horizons underlying the stratigraphic sequences R1, R2 and R3 discussed
in text for Domain 3 (NE of the SCS). Location of the seismic profiles
and wells see  Figure~\ref{fig3}. ROU is the base of R1, IRU is between
the 2 thinning events (between R1 and R2), and BU (Breakup
Unconformity) marks the end of the rifting and the onset of the
spreading at the domain location.}
\vspace*{-3pt}
\end{figure*}

Subsidence curves and subsidence rates from well logging and speculated
from seismic lines show a mild subsidence until the middle of the
Oligocene corresponding to the R0 and R1 units  [Figure~\ref{fig5},
\citealp{Fangetal2016,Shietal2017,Zhaoetal2018}].
A stronger subsidence
began since 33~Ma and accelerated afterward. This sequence corresponds
to R2, and onlaps on the seismic images prior to the breakup
unconformity  (Figure~\ref{fig5}).

\subsection{Rifting stratigraphy in Domain 3}\label{sec4.3} 
In Domain 3, no oceanic crust was developed because the opening of the
South China Sea aborted just before the breakup at 16~Ma. The
continental crust recorded two stages of rifting and the extensional
structures of the NCS and Luconia basins are influenced by the adjacent
neighboring mid-ocean ridge 
\citep{XiaZhou1993,Huchonetal2001,Hutchison2004,Dingetal2016,Luoetal2021,MadonJong2022}.
Several unconformities predated apparently the mature syn-rift units by
around 40~Ma and 32~Ma  \citep{Matthewsetal1997,Madonetal2013},
probably representing the rift onset in this region. One main
unconformity suggested the major rifting period from 24~Ma until the
extension terminated around 16~Ma as the\unskip\break 
propagator ceased 
\citep{Matthewsetal1997,Madonetal2013,Lietal2014}. 

The early stage of rifting is obscured, and R0 and R1 (Cycle I;
pre-24~Ma, in the Luconia province offshore Malaysia) cannot be
undoubtedly discriminated. The Mesozoic basement was encountered at the
bottom of the R0/R1 unit \citep{Areshevetal1992,WuYang1994}. 
Syn-rift
units are separated into two groups (I and II), showing similarities in
the NCS and Luconia basins 
\citep{Frankeetal2014,Madonetal2013,Clercetal2018,MadonJong2022}.
Until 23~Ma, The R2 (Cycle II and Cycle III for petroleum geologists of the S
margin of the SCS) remains\unskip\break 
characterized by horizontal to
sub-horizontal seismic facies overlying the intra-rift unconformities,
but without a breakup unconformity atop  [Figure~\ref{fig6},
\citealp{Hutchison2004,Lietal2014,Clercetal2018,Pengetal2018}]. Most of
the normal faults terminate at an horizon dated around 16~Ma  [red
horizon on  Figure~\ref{fig6};
\citealp{Madonetal2013,Savvaetal2014,Lietal2014,Lunt2019}]. 

\begin{figure*}
\vspace*{3pt}
\includegraphics{fig07}
\vspace*{1pt}
\caption{\label{fig7}Rifting diachronism by juxtaposing D1 to D3. The
diachronism appeared from R1 unit and goes on until the termination of
seafloor spreading. ROU is the base of R1, IRU is between the 2
thinning events (between R1 and R2), and BU (Breakup Unconformity)
marks the end of the rifting and the onset of the spreading at the
domain location.}
\vspace*{5pt}
\end{figure*}

Paleo-water depth gradually deepened by the witness of the well logging
and also the pseudo-well  
\citep{Lietal2014,Madonetal2013}. Subsidence
rate curves did not record the R0 and R1 subsidence curve in the
published data. The distinct acceleration found in the previous
sections began at 23~Ma, which corresponded to the detachment
development, and decreased after 16~Ma both in NCS and Luconia 
[Figure~\ref{fig6}; \citealp{Lietal2014,Jamaludin2022}].

\subsection{Diachronous rifting and seafloor spreading in the SCS
Margin}\label{sec4.4}
According to the above mentioned temporal recording, most of the
classical stages of evolution of a margin can be seen in the South
China Sea, but appear at a time that varies from D1 to D3. A simple
evolutionary age-table is compiled on  Figure~\ref{fig7} to illustrate
the diachronism of the extensional events. Although the end-members
ages of the extension\unskip\break 
history of the SCS are not significantly
different (Late Cretaceous for Ro to 16~Ma for the end of sea-floor
spreading), the
different markers of the rifting vary from the East to
the West. The bracket of ages for R1 to BU is younger toward the south;
from 45--32 in D1, 38 to 23 in D2, and 45? to 16 in D3. Indeed, a ridge
jump with a shift in spreading direction at 23~Ma 
\citep{Sibuetetal2016} is known and constitutes an important point in
time of the extension history. This event marks the end of a rifting
style controlled by N--S wrench faults and pull-apart basins 
\citep{Changetal2022}, which marks the early stage of the opening of
the SCS, both for the rifting  \citep{Chanetal2010} and for the
spreading  \citep{Briaisetal1993}. 

\begin{figure*}
\includegraphics{fig08}
\caption{\label{fig8}(Left)~Simplified geological map of Borneo and
Palawan and main stratigraphic elements for the convergence 
(Right)~Tectono-stratigraphy of the closure of the PSCS from D3 to D1. The
segment locations shown in  Figure~\ref{fig3}. Diachronism illustrated
by the beginning of uplift in Sarawak (D3) migrating toward Palawan
(D1). The termination of the orogenic event is around 16~Ma.} 
\end{figure*}

\section{Convergent tectono-stratigraphy in Borneo and
Palawan}\label{sec5} 
The tectonic evolution of the convergent margin in Borneo and Palawan
is also marked by key unconformities which represent different stages
of subduction and subsequent collision, as the thinned continental
margin of the south of the SCS progressively entered into the
subduction zone of the PSCS. In general, the core of the orogenic belt
exposes older and metamorphosed rocks of the Cretaceous to Late Eocene
Rajang Formation along the backbone in the central Borneo (grey shades
in  Figure~\ref{fig8}). The ophiolitic complexes attributed to the
relics of the PSCS are distributed in Palawan and Sabah (purple color
in  Figure~\ref{fig8}) and show two juxtaposed clusters of ages 
[Eocene and Mesozoic, 
\citealp{Burton-Johnsonetal2020,Dycocoetal2021}]. The metamorphism and
ages of the sedimentary formations decrease outward in the case of the
NW and SE Borneo edifices  (Figure~\ref{fig8}), in accordance to a
normal wedge (actually a fold-and-thrust belt) proceeding toward the
NW. On the NW side, the imbricated wedge gradually narrow toward
Palawan  \citep{Aurelioetal2014}. This section reviews the
stratigraphic unconformities and thermo-chronological data highlighting
the initiation of uplift induced by subduction/collision in each domain
(D1 to D3). The syn-tectonic and post-collision magmatism is also
integrated to assess the closure history of 
the\unskip\break PSCS. 

\subsection{Tectonic-related stratigraphy in Domain 3}\label{sec5.1} 
In the Sarawak region, each sedimentary formation has been analyzed in
terms of biostratigraphy and detrital zircon 
\citep{Galinetal2017,Hennig-Breitfeldetal2019}. The Sarawak Orogeny
Unconformity (or Rajang Unconformity,  Figure~\ref{fig8}) is documented
on the ground of a stratigraphic hiatus extensively distributed in
central Borneo and along the Bukit Mersing Line separating the Sibu and
Miri Zone 
\citep{Hutchison2005,Cullen2010,Hall2013,vanHattumetal2013,HallBreitfeld2017,Hennig-Breitfeldetal2019}.
After a generally continuous deposition, another widespread
unconformity, the Nyalau Unconformity dated around 16~Ma is found 
\citep{Hennig-Breitfeldetal2019}.

The Rajang Group mainly consists of deep-sea depositional environment
in Sibu Zone (SW Borneo) bearing sediments transported from Kuching
hinterland toward the north 
\citep{Haile1974,Tan1979,Bakaretal2007,Galinetal2017,Hennig-Breitfeldetal2019}. 
The water depth of the deposition appeared have shallowed since 45~Ma
without a distinct stratigraphic hiatus in Sarawak  [Figure~\ref{fig8},
\citealp{Haile1974,Tan1979,Hutchison1996,
Bakaretal2007,Galinetal2017,HallBreitfeld2017}]. 
The shallowing may suggest an uplift of sedimentary slices induced by
the embryonic subduction of the PSCS between 45 and 37~Ma. Acidic
magmatism was produced within this period of time 
\citep{Prouteauetal1996}. Above the Late Eocene unconformity, the
Nyalau Unconformity is underlain by Neogene strata, which is found in
offshore stratigraphy \citep{Hageman1987}, and is characterized by
gravity-driven deformation in the offshore fold-and-thrust belt of the
Borneo-Palawan\unskip\break 
Trough.

\subsection{Tectonic-related stratigraphy in Domain 2}\label{sec5.2} 
In Sabah (NW Borneo), the Late Eocene unconformity dated around 37~Ma
is similarly found  \citep{Cullen2010,Sapinetal2011,Hall2013}, resting
on the ophiolite exposed at the surface  [Figure~\ref{fig8},
\citealp{OmangBarber1996,Gravesetal2000,Chienetal2019,Gibagaetal2020}].
During latest Eocene to Mid-Miocene, the well-studied Rajang and
Crocker groups, constitute the distal and proximal sediments of the
PSCS, now thrusted in the NW Borneo wedge. Then During the Miocene, a
slight hiatus is recognized around 16~Ma and interpreted as the
Deep-Regional Unconformity  [DRU,  Figure~\ref{fig8},
\citealp{Levell1987,TanLamy1990,HazebroekTan1993,Changetal2019}] or the
Nyalau Unconformity in  \citet{Hennig-Breitfeldetal2019}. It is
followed by the Shallow Regional Unconformity (SRU) dated at Late
Miocene in most of Sabah area  \citep{Balaguruetal2003}.

Abundant literature exist on these sediments of the central part of the
NW Borneo wedge. The deep-sea sediments of the distal part of the PSCS
(Rajang 
Group) exposed northernmost Borneo (Trusmadi, Kudat Peninsula
area) are of early Paleogene. The sediments were transported from the
Schwaner granitic province of Southern Borneo, as shown by
paleo-current measurements and the prominent peak of detritus zircon 
\citep{Jacksonetal2009,Tongkul2003}. Later, the depositional
environment changed from deep-sea to marginal marine or shallow marine
in Croker Formation and Setap Shale in Sabah around Oligocene to Early
Miocene  \citep{Jacksonetal2009,Zakariaetal2013}, suggesting a period
of uplift in the neighboring land masses. Paleo-drainage
reconstructions based on the age population of detrital zircon
according to the sediment source suggest the NE--SW backbone in Borneo
was extensively uplifted since Miocene, also resulting in the
displacement of the paleo-coastline from NW--SE to NE--SW 
\citep{Menieretal2017,Hennig-Breitfeldetal2019}. After DRU, horizontal
to sub-horizontal strata appear to be restricted to close to the
coastline or in the offshore above the Middle Miocene Unconformity
(MMU)  \citep{Clennell1996,Cullen2010,Changetal2019}. The deltaic and
nearshore sedimentary input in the large Balingan and Baram deltas
indicated thrusting activity by this time was replaced by gravity
sliding  \citep{Sapinetal2012}. During the post-collision period, the
gravity-driven deformation involves a late Neogene fold-and-thrust belt
in offshore, surrounding circularly the Mount Kinabalu and accompanied
with E--W transfer zones in tip of Borneo 
\citep{Cullen2010,Frankeetal2008,Steueretal2014,Changetal2019}. 

\begin{figure*}
\includegraphics{fig09}
\caption{\label{fig9}Correlation between the SCS passive margin and the
closure of the PSCS.  (A)~Correlation of rifting events on the SCS
margins. (B)~Correlation of contractional events on the PSCS, basing
on unconformities and deformation in NW Borneo and Palawan Island. 
(C,D)~Two representations of the correlation between the events in the
neighboring basins between the Early Eocene and the Middle Miocene.
Post Middle Miocene is mostly affected by post-tectonic vertical
movements.}
\end{figure*}

\subsection{Tectonic-related stratigraphy in Domain 1}\label{sec5.3} 
In Palawan, an early Cenozoic structural contact exists between the
Cretaceous ophiolite and the Eocene formation, suggesting the absence
of the original deep sea sediments overlying the Cretaceous crust of
the PSCS \citep{Aurelioetal2014,Ilaoetal2018}. In the offshore Palawan,
the ophiolite and its metamorphic sole have been dated at 35~Ma,
suggesting that the subduction may have initiated at the PSCS mid-ocean
ridge  \citep{Keenanetal2016,Dycocoetal2021}. During the same period,
and until the Early Miocene, a significant hiatus is observed onshore
(although we have limited formation exposure)  (Figure~\ref{fig8}). A
later extensively distributed unconformity, the (MMU), with a hiatus,
seals the deformation around 15--20~Ma of the Nido Platform offshore
and onshore. In the past decades, the timing of this MMU was debated
due to the discrepancies in age from an area to another and because it
may represent the end of the contraction of the wedge as well as the
beginning of the gravity sliding period 
\citep{Hutchison2004,Ilaoetal2018}. 

In more detail, the Eocene stratigraphy (Panas Formation) consists of
sandstone interbedded with shale and mudstone showing a deep-sea
environment in the early history. With limited information on Oligocene
formation, the Nido Carbonate shows the shallow water depth around Late
Oligocene  \citep{Steueretal2013}. The Isugod Formation commenced
receiving the deposits derived from ophiolite while the Panas Formation
characterizing deep-sea sediments 
\citep{Suggateetal2014,Shaoetal2017}. Meanwhile, the Nido Carbonate was
thrusted in offshore Palawan, suggesting the timing of uplifting in D1
region by the end of Early Miocene 
\citep{Cullenetal2010,Steueretal2014,KesslerJong2016}. In Palawan, the
last stage of deformation is bracketed by the end of the Pagasa wedge
post-dating the Nido Limestone (16~Ma) and before the deposition the
Tabon Limestone  [9~Ma, \citealp{Taguibaoetal2012,Ilaoetal2018}]. 
A gravity-driven structureaffects a narrow belt induced by the shale
tectonic in offshore in post-orogeny tectonic  \citep{Ilaoetal2018}. 

\section{Integration SCS and PSCS: correlation of a paired extensional
and contractional system}\label{sec6} 
The evolution of the paired system can be assessed by unconformities on
the two margins. Although many unconformities are described during the
Tertiary evolution of SE Asia, this study selects widespread events of
the area encompassing the SCS and PSCS area. In the South China Sea,
three main unconformities including the rift-onset unconformity (ROU),
the intra-rift unconformity (IRU), and the breakup unconformity (BU)
may illustrate in a simple way the diachronism of the rifting process
from east to southwest  (Figure~\ref{fig9}). The extensional events
marked by the unconformities are found everywhere on the margins of the
SCS but at a different time. In parallel, several main unconformities
of the contractional realm of Borneo, illustrate the shortening of the
PSCS. Although it is more difficult to pin point the ages of the
different stages of the convergence, it is relevant to see if
correlation between the opening of a basin and the closure of the other
is relevant. 

The IRU and the Sarawak Orogeny Unconformity where documented, are
located within the Eocene  (Figure~\ref{fig9}). The latest Oligocene
(23~Ma) highlights the initiation of shifting the extensional direction
in the SCS, and the related unconformity (Top Croker 
Unconformity---TCU) can be traced widespread c. 23~Ma 
\citep[][and reference herein]{Briaisetal1993,Sibuetetal2016,Lunt2019}.
In the SCS, N--S rifting direction and seafloor spreading
lasted until 23~Ma and changed progressively to a NW--SE direction.
Precisions for the shift is recorded by a total of 30\textdegree\ between
the final rifting in N--S direction and the oceanic formation in NW--SE
direction  (Figure~\ref{fig9}), and is seen in the magnetic anomalies
and the bathymetry on oceanic crust 
\citep{Briaisetal1993,LeeLawver1995,Sibuetetal2016}. It is also seen in
the\unskip\break  
structural
mapping of the Phu Khank Basin  \citep{Savvaetal2013}.
This modification was interpreted as a ridge jump in the oceanic
formation. The counterclockwise change is however relatively less
obvious in the East Sub-Basin.

The next unconformity, known as the deep-regional unconformity (DRU) or
Middle-Miocene Unconformity (MMU), has been documented and debated for
decades. It marks the termination of orogeny in Borneo and Palawan 
\citep{Ilaoetal2018,Changetal2019}. \citet{Changetal2019} suggested
that this unconformity is diachronous along the collision zone, which
is dated at 16~Ma in Sarawak and appears northward around Palawan at c.
12~Ma  \citep{Steueretal2014}.

After the cessation of the opening, the SRU appeared extensively in
Sabah and also the MMU in the offshore Palawan. Mobile shale was
remobilized  \citep{Changetal2019}. This period is also marked by
several unconformities which are rather related to magmatism. They are
for instance the Mount Kinabalu in Sabah, the Mount Capoas in the
northern Palawan, and intra-plate Scarborough seamounts. 

\subsection{Temporality of events on reconstructions}\label{sec6.1} 
The succession of events around the South China Sea shows striking
indicators of correlation, but also of discrepancies. The global
picture is that there is a general time-link between the subduction and
closure of a basin, or a series of small basins, located south of the
South China Sea (referred to as the Proto South China Sea), and the
timing of rifting, spreading, change of spreading direction, and
cessation of spreading followed by bathymetric collapse. The second
order is that the precise review of the ages actually shows a migration
of both the opening of the SCS and the subduction of the PSCS followed
by the collision in NE Borneo. We illustrate this proposition in a
series of simple sections and sketch maps  (Figure~\ref{fig10}).

\begin{figure*}
\includegraphics{fig10}
\caption{\label{fig10}Schematic joint evolution of the PSCS/SCS; 
(A)~opening of the PSCS as a back-arc basin.  (B)~Beginning of closure
in N. Borneo and incipient rifting of the SCS. (C)~Subduction of the
PSCS. Right: beginning of rifting of the SCS and incipient sea floor
spreading of the SCS in the Xisha Trough. (D)~Shift in opening of the
SCS (propagation of the SW sub-basin), following the subduction of the
thinned continental margin of the SCS, beginning of the rotation of N.
Borneo. (E)~Suture of the PSCS basin and beginning of the opening of
the Sulu Sea. (F)~Post-collision setting in N. Borneo, with plutonic
activity (Kinabalu Mt) and opening of the Sulu Sea propagating toward
the SW. Arrow for the rotation of Borneo. Solid and open triangles for
active and extinct subduction. Red dots for plutons.}
\end{figure*}

\subsubsection{Before the Eocene times (Figure~\myRef{fig10} top
left)}\label{sec6.1.1}  
The first-stage rifting of the margins
in the SCS is well documented with an early extension starting from the
end of the Cretaceous to the Paleocene. The rifting occurred from SCS
extending toward NE to the East China Sea 
\citep{TengLin2004,Guanetal2016,Chengetal2021}. During this period, the
oceanic crust of PSCS was located to the south that juxtaposed with
Dangerous Ground and the Borneo.

\subsubsection{During Eocene to Oligocene (45--23~Ma)}\label{sec6.1.2}
The subduction initiated in Borneo and Palawan  (Figure~\ref{fig10} top
right), resulting in the beginning of developing detachment faults to
accelerate thinning the continental crusts in the SCS. The crustal
architectures suggest extensive development of the detachment faults
associating the dramatic subsidence solely in the SCS while no similar
impact on the East China Sea. While the collision occurred in Sarawak,
the Sabah and Palawan areas continued subduction coincided the
beginning of the rapid breakup in the East Sub-Basin in the SCS,
following the hyperextension stages around 32~Ma. The first propagator
migrating from East to West, stalling near the edge of the former
granitic arc, with a slight E--W compression 
\citep{LePourhietetal2018}. The Southwest of the SCS continued the
rifting, developing detachment faults in the main half grabens 
\citep{Savvaetal2013,Changetal2022,MadonJong2022},
mostly in N--S
direction extension (Figure~\ref{fig10} top right).

\subsubsection{The latest Oligocene (23~Ma) and early Miocene 
(23--16~Ma)}\label{sec6.1.3} 
Highlight the shift of extensional direction in the SCS and the block
rotation in Borneo. The spreading propagator continued operating
southwestward and the spreading rate decreased from 25 to 
$15~\mathrm{mm}{\cdot}\mathrm{yr}^{-1}$ 
in half spreading rate until it stopped at 16~Ma 
\citep{Briaisetal1993,Dengetal2018,Sibuetetal2016}. This may reflect a
regional deceleration on both margins of the subduction-driven process.
This rearrangement modified accordingly the extensional direction in
the vicinity of Spratly Islands and also the Phu Khann Basin
\citep{Savvaetal2013,Changetal2022}. The mountain ranges progressively
migrated northward to the Sabah region and modified the river
drainages, suggesting the frontal wedge proceeding NW toward direction
in Sabah and Palawan. The development of CCW rotation was accommodated
by the trench which also proceeding northwestward. Back-arc extension
started as a result in the Sulu Sea \citep{Rangin1989}. 

\subsubsection{The middle Miocene to recent (after
16~Ma)}\label{sec6.1.4}  
Stage suggests that the end of orogeny is followed by the magmatism
induced by slab breakoff, for instance, the Mount Kinabalu in Sabah and
the Mount Capoas in the northern Palawan 
\citep{EncarnacionMukasa1997,Forsteretal2015}, and the ages clustering
around 16--17~Ma of adakites found in Sarawak indicating asthenospheric
upwelling after convergence 
\citep{Prouteauetal1996,Prouteauetal2001,Breitfeldetal2019,WuSuppe2017}. 
A slab break-off magmatism followed this pattern and located the suture
zones where the locations of the slabs detached underneath 
\citep{Ranginetal1999,Sapinetal2011,HallSpakman2015,WuSuppe2017}.

The collapse of post-collision sedimentary packages characterized
diapiric mobile shale or remobilization of sedimentary m\'{e}lange 
\citep{MorleyGuerin1996,Morleyetal2003,Sapinetal2012,Ilaoetal2018,Changetal2019}, 
induced by the magmatic intrusion and uplift. Without further mountain
building, Late Neogene fold-and-trust belt\unskip\break 
developed in the offshore
Borneo and Palawan. Several magmatism-related unconformities are also
noticed during in the SCS, while no significant crustal thinning and
seafloor spreading in this period 
\citep{Jiangetal2018,Xiaetal2018,Fanetal2019,Gaoetal2019,Sunetal2020,Lietal2022}.

\section{Discussion}\label{sec7} 
The correlation of the divergent and convergent margins provides a rare
opportunity to evaluate the tectonic processes in the geodynamic
perspective. The various timing of orogeny was often suggested
resulting from arrival time of the thinned continental crust, derived
from the South China, to the suture zone varying in time and space. The
former PSCS margin geometry thus was implied a speculation of a
V-shaped oceanic closure in the PSCS 
\citep{Hall2002,Pubellieretal2003}, while coeval diachronism manifests
the V-shaped oceanic opening in the SCS. This result strengthens the
hypothesis that the SCS opening in response the neighboring subduction.

The driving forces such as slab pull and retreat are acknowledged to be
the main driving forces for opening and closure of marginal basins,
although no active example of active opening in the lower plate exists
on Earth. The mechanism of opening within the down-going (or lower
plate) is however always invoked for the evolution of the Tethysides.
In this setting, the subduction of the Tethys, is coeval with the
rifting of belts on the northern margin of Gondwana. The process can be
nowadays be modelled \citep{Larvetetal2022}. On the other hand, the
down-going plate consists of heterogeneities of the crust such as
lithologic variations, thickness and thermal conditions, and these
parameters may vary along strike the collision. Additional forces have
been proposed in the asthenospheric mantle, for the closure of a
V-shaped marginal sea  \citep{Wallaceetal2009}, and may also account
for the example of the SCS/PSCS dual system. The collision zone remains
relatively immobile and the subduction front proceeds and moves toward
to the trench, also suggested as a buoyant indentor. Examples of
subduction varying sharply exit in many active places, such as the
North arm of Sulawesi \citep{Surmontetal1994}. Relevant production of
igneous crust such as back-arc extension initiates behind or within the
volcanic arc, as shown by the temporal and spatial variation in the
Eastern Mediterranean Sea  \citep{Menantetal2016}. An additional
driving force in the asthenosphere is invoked in some numerical
simulations to propose that toroidal flows induced when the slab teared
and triggers the rotation on the overriding  crust 
\citep{Menantetal2016,Magnietal2017}.

\section{Conclusion}\label{sec8} 
The rifting-to-drifting history of the South China Sea may at least be
correlated in terms of stratigraphic cuts with the subduction-collision
of the Proto South China Sea history observed in the NW Borneo wedge
and Palawan Island. The initial rifting in the SCS is coeval with the
beginning of the subduction in the south, and the seafloor spreading of
the SCS started when the probably collision related classic sediments
of the Crocker group were shed in the PSCS. The ridge jump in the SCS
at 23~Ma may be connected with the rotation in Borneo and Palawan
during the Sarawak Orogeny. Both horizontal movements terminated at
16~Ma, when tectonics was marked by vertical movements illustrated by
mass wasting on the Borneo-Palawan margins and abnormal subsidence in
both margins. This interpretation is in line with a PSCS and a SCS
linked in the Cenozoic. This rare example of the paired PSCS and SCS
system may constitute an analogue to ancient orogenies in the world.
Variations along the subduction of a marginal sea, including the
rotation of the upper plate, may actually condition the rifting, the
breakup, and the variation of spreading direction of another basin in
the lower plate the lower plate.

\section*{Declaration of interests}
The authors do not work for, advise, own shares in, or receive funds
from any organization that could benefit from this article, and have
declared no affiliations other than their research organizations.

\section*{Dedication}
This paper is dedicated to Jean Dercourt, who taught MP (the 2nd
author), stratigraphy and the meaning of unconformities.

\section*{Acknowledgements}
MCS data processing had been performed at ENS-PSL/CNRS under the
project ``Mer de Chine T985''. We thank CGG for giving us access to the
CGG Geovation 2013 software. The raw seismic data set can be found
online (\url{www.geologie.ens.fr/imagerie/}). We are also grateful for
the useful suggestions of anonymous reviewers.

\back{}

\bibliographystyle{crgeos}
\bibliography{crgeos20221272}
\refinput{crgeos20221272-reference.tex}

\end{document}
