New Ideas Concerning the Ultrahigh Pressure Metamorphic Rocks of the North-South China Block Suture By Chiu Hon Chim (2002315825) EASC3114 Regional Geology and Tectonics: Practicals Session 30 November 2004 Water Painting of Qinling http://www.silk2000soie2000.com/Galleries/Artwork/index.htm

I am going to talk about … The North-South China Block Suture and Ultrahigh Pressure Metamorphic Rocks Existing Concepts New Ideas Timeframe and Extent Exhumation Model Ductile Shear Zones

The North-South China Block Suture and Ultrahigh Pressure Metamorphic Rocks

Existing Concepts

New Ideas

Timeframe and Extent

Exhumation Model

Ductile Shear Zones

I am going to talk about … The North-South China Block Suture and Ultrahigh Pressure Metamorphic Rocks Existing Concepts New Ideas Timeframe and Extent Exhumation Model Ductile Shear Zones

The North-South China Block Suture and Ultrahigh Pressure Metamorphic Rocks

Existing Concepts

New Ideas

Timeframe and Extent

Exhumation Model

Ductile Shear Zones

North-South China Block Suture Qinling-Dabie Orogenic Complex From Collision of two continental blocks Yangtze Craton Sino-Korean Craton http://www-personal.une.edu.au/~imetcalf/ Sino-Korean Craton Yangtze Craton

Qinling-Dabie Orogenic Complex

From Collision of two continental blocks

Yangtze Craton

Sino-Korean Craton

Collision History They Collided in Late Permian  Triassic May have previous subduction of oceanic lithosphere http://www.paleomag.net/members/baochunhuang/images/paleorec.html

They Collided in Late Permian  Triassic

May have previous subduction of oceanic lithosphere

Outline The North-South China Block Suture and Ultrahigh Pressure Metamorphic Rocks Existing Concepts New Ideas Timeframe and Extent Exhumation Model Ductile Shear Zones

The North-South China Block Suture and Ultrahigh Pressure Metamorphic Rocks

Existing Concepts

New Ideas

Timeframe and Extent

Exhumation Model

Ductile Shear Zones

Ultrahigh Pressure (UHP) Metamorphic Rocks

What are these? Inclusions of high-pressure minerals coesite and/or diamonds indicate that these rocks have experienced pressures of more than 3000 MPa during subduction to depths as great as 135 km

Inclusions of high-pressure minerals

coesite and/or diamonds

indicate that these rocks have experienced pressures of more than 3000 MPa

during subduction to depths as great as 135 km

Coesite is a polymorph of quartz , It forms quickly at high pressures, above 20 00 MPa . The structure of coesite is Coesite? What’s that? http://www.geol.ucsb.edu/faculty/hacker/geo102C/lectures/coesitePPL.jpg much more compact than the other members of the quartz group. Coesite is only metastable at normal surface temperatures;

Coesite is a polymorph of quartz ,

It forms quickly at high pressures, above 20 00 MPa .

The structure of coesite is

much more compact than the other members of the quartz group.

Coesite is only metastable at normal surface temperatures;

Outline The North-South China Block Suture and Ultrahigh Pressure Metamorphic Rocks Existing Concepts New Ideas Timeframe and Extent Exhumation Model Ductile Shear Zones

The North-South China Block Suture and Ultrahigh Pressure Metamorphic Rocks

Existing Concepts

New Ideas

Timeframe and Extent

Exhumation Model

Ductile Shear Zones

Discovered to be 2000km long http://www.geol.ucsb.edu/faculty/hacker/geo102C/lectures/EChinaMap.jpg

Extent Before 2002 findings Dabie Shan and Su-Lu terrane Segmented by active, India collisional related N-S trending faults

Before 2002 findings

Dabie Shan and Su-Lu terrane

Segmented by active, India collisional related N-S trending faults

Generation of UHP Collisional history Yangtze and Sino-Korean Cratons separated by ocean during most of Proterozoic Palaeomagnetic data indicated they met in late Paleozoic Yangtze indented into Sino-Korean, progressing E  W Promote Rotation of Yangtze clockwise in Triassic-Jurassic

Collisional history

Yangtze and Sino-Korean Cratons separated by ocean during most of Proterozoic

Palaeomagnetic data indicated they met in late Paleozoic

Yangtze indented into Sino-Korean, progressing E  W

Promote Rotation of Yangtze clockwise in Triassic-Jurassic

Continental Blocks … Sino-Korean Archaean Basement Yangtze Craton Proterozoic Basement http://www.sciencemag.org/cgi/content/full/287/5456/1215

Sino-Korean

Archaean Basement

Yangtze Craton

Proterozoic Basement

Subduction Style (?) Thinned passive margin of Yangtze subducted beneath Sino-Korean Metamorphism reached stability field of coesite and diamond At around 240Ma Some continental material reached upper mantle depths (>120km) from petrological evidence

(?) Thinned passive margin of Yangtze subducted beneath Sino-Korean

Metamorphism reached stability field of coesite and diamond

At around 240Ma

Some continental material reached upper mantle depths (>120km) from petrological evidence

Metamorphic Sequence Shear Zone Ecologite w/ Coesite w/ Quartz Amphibole Blueschist Yangtze Fold-Thrust Belt

Shear Zone

Ecologite

w/ Coesite

w/ Quartz

Amphibole

Blueschist

Yangtze Fold-Thrust Belt

Massive Eclogite Indicates High Pressure Metamorphism http://www.geosciences.univ-rennes1.fr/ch/gautier/Onglets/Fig23_small.jpg

Exhumation Exposing features at a lower sequence Must be fast – no reverse reaction of coesite  quartz occurs http://www.geol.ucsb.edu/faculty/hacker/geo102C/lectures/coesiteSchreyer.jpg

Exposing features at a lower sequence

Must be fast – no reverse reaction of coesite  quartz occurs

“ Unroofing” Exhumation only first stage But this first stage happened very rapid so as to preserve UHPM minerals Rate is slower thereafter Slab has to be very cold, very dense to support a high exhumation rate Deposition of basin sediments indicates start of erosion only in Late Jurassic

Exhumation only first stage

But this first stage happened very rapid so as to preserve UHPM minerals

Rate is slower thereafter

Slab has to be very cold, very dense to support a high exhumation rate

Deposition of basin sediments indicates start of erosion only in Late Jurassic

Outline The North-South China Block Suture and Ultrahigh Pressure Metamorphic Rocks Existing Concepts New Ideas Timeframe and Extent Exhumation Model Ductile Shear Zones

The North-South China Block Suture and Ultrahigh Pressure Metamorphic Rocks

Existing Concepts

New Ideas

Timeframe and Extent

Exhumation Model

Ductile Shear Zones

Latest Findings- Timeframe and Extent From the discovery of a new UHPM belt Location: Altun-North Qaidam Significance: Coesite Bearing Age: Early Palaeozoic Correlation : Finding metamorphic diamond in between Westward Extension

From the discovery of a new UHPM belt

Location: Altun-North Qaidam

Significance: Coesite Bearing

Age: Early Palaeozoic

Correlation :

Finding

metamorphic

diamond

in between

Making Two Distinct UHP Events Early Palaeozoic (“North Qaidam-Altun”) From closure of ocean basin Evidence : Subduction related island-arc volcanic rocks and granites Triassic (“Dabie-Su-lu”) Final subduction and collision event

Early Palaeozoic (“North Qaidam-Altun”)

From closure of ocean basin

Evidence : Subduction related island-arc volcanic rocks and granites

Triassic (“Dabie-Su-lu”)

Final subduction and collision event

Discovery of Microscopic Diamond In N Qinling Bridges the Older Altun-Qaidam Belt and the Younger Dabie-SuLu Belt http://www.geol.ucsb.edu/faculty/hacker/geo102C/lectures/diamond.jpg

In N Qinling

Bridges the Older Altun-Qaidam Belt and the Younger Dabie-SuLu Belt

Central Orogeny 1000Ma  Accreted to form part of Rodinia 800-750 Ma  Rifting (basalts) Late Proterozoic  Ocean Closure (ophiolites, gneisses) Early Palaeozoic  First stage Subduction in the belt Triassic  Final amalgamation of N/SCB

1000Ma  Accreted to form part of Rodinia

800-750 Ma  Rifting (basalts)

Late Proterozoic  Ocean Closure (ophiolites, gneisses)

Early Palaeozoic  First stage Subduction in the belt

Triassic  Final amalgamation of N/SCB

Outline The North-South China Block Suture and Ultrahigh Pressure Metamorphic Rocks Existing Concepts New Ideas Timeframe and Extent Exhumation Model Ductile Shear Zones

The North-South China Block Suture and Ultrahigh Pressure Metamorphic Rocks

Existing Concepts

New Ideas

Timeframe and Extent

Exhumation Model

Ductile Shear Zones

Old Exhumation Model Triassic Indentation Triassic Vertical Extrusion and Erosion Shearing at 200-180Ma Horizontal Shortening and Vertical Extension Deformation: Cretaceous Plate Margin Transtension However, this c annot be the case it does not match erosion rates No signs of erosion before Cretaceous

Triassic Indentation

Triassic Vertical Extrusion and Erosion

Shearing at 200-180Ma

Horizontal Shortening and Vertical Extension

Deformation:

Cretaceous Plate Margin Transtension

However, this c annot be the case

it does not match erosion rates

No signs of erosion before Cretaceous

Seismic Reflection Profiling Crustal Dome

What does it indicate? Two stage mechanism of return From >100km to 30-40km Buoyancy is the major force Returned to the lower crust From 30-40km to surface Crustal-scale dome From intra-crustal uplift Almost entirely ductile flows

Two stage mechanism of return

From >100km to 30-40km

Buoyancy is the major force

Returned to the lower crust

From 30-40km to surface

Crustal-scale dome

From intra-crustal uplift

Almost entirely ductile flows

Importance Exhumation is not because of a special geological feature rather it should be a more common event throughout the world Distinction of UHP and non-UHP Lies only in exhumation Only rapid exhumations can preserve UHP minerals

Exhumation is not because of a special geological feature

rather it should be a more common event throughout the world

Distinction of UHP and non-UHP

Lies only in exhumation

Only rapid exhumations can preserve UHP minerals

Outline The North-South China Block Suture and Ultrahigh Pressure Metamorphic Rocks Existing Concepts New Ideas Timeframe and Extent Exhumation Model Ductile Shear Zones

The North-South China Block Suture and Ultrahigh Pressure Metamorphic Rocks

Existing Concepts

New Ideas

Timeframe and Extent

Exhumation Model

Ductile Shear Zones

Ductile Shear Zones In the past people focused in Dabie Shan area In Sulu Region, shear zones indicates a reversed tectonic setting

In the past people focused in Dabie Shan area

In Sulu Region, shear zones indicates a reversed tectonic setting

Postulations From Shear Zone evidences, North China plate was subducted New idea on UHP Metamorphism proposed As N China Plate subducted, it me e t constant pressure 2. At a temperature/pressure high enough ….

From Shear Zone evidences, North China plate was subducted

New idea on UHP Metamorphism proposed

As N China Plate subducted, it me e t constant pressure

2. At a temperature/pressure high enough ….

2. At a temperature/pressure high enough, a piece of the p l ate was broken and stayed in the shear zone 3. By detachment faulting, it exhumes quickly

2. At a temperature/pressure high enough, a piece of the p l ate was broken and stayed in the shear zone

3. By detachment faulting, it exhumes quickly

4. At mid-depth, it slows down again due to continued subduction

4. At mid-depth, it slows down again due to continued subduction

To Conclude … UHP Metamorphic Complexes in China, though one of the first to be discovered and largest in the world, Is still very debated and new findings and interpretation comes up Is essential to understanding plate tectonics, esp. collisional environments but interpretations are still open

UHP Metamorphic Complexes in China, though one of the first to be discovered and largest in the world,

Is still very debated and new findings and interpretation comes up

Is essential to understanding plate tectonics, esp. collisional environments but interpretations are still open

Chinese Exploration, 5km drillhole http://www.geol.ucsb.edu/faculty/hacker/geo102C/lectures/CCSD.jpg

The End

Additional Slides

http://www.geol.ucsb.edu/faculty/hacker/geo102C/lectures/UHPM.jpg

http://www.geol.ucsb.edu/faculty/hacker/geo102C/lectures/worldwideUHPM.jpg

Mineral Equilibria http://www.geol.ucsb.edu/faculty/hacker/geo102C/lectures/mantlePhaseRelations.jpg

Exhumation Models http://www.geol.ucsb.edu/faculty/hacker/geo102C/lectures/Exhumation.jpg

http://dunite.mr.nsysu.edu.tw/word-118.htm

Typical view of Dabie Shan http://www.geosciences.univ-rennes1.fr/ch/gautier/Figs/Fig21.jpg