Re-defining the allochthon in Timor: Tim Charlton & Dino Gandara

<strong>Re</strong>‐<strong>def<strong>in</strong><strong>in</strong>g</strong> <strong>the</strong> <strong>allochthon</strong> <strong>in</strong> <strong><strong>Tim</strong>or</strong>:<br />

Structural‐stratigraphic relationships at <strong>the</strong><br />

boundaries of <strong>the</strong> Lolotoi metamorphic complex <strong>in</strong><br />

<strong><strong>Tim</strong>or</strong>‐Leste, and implications for <strong>the</strong> Mutis Complex<br />

<strong>in</strong> <strong><strong>Tim</strong>or</strong> Barat, NTT<br />

<strong>Tim</strong> <strong>Charlton</strong> & D<strong>in</strong>o <strong>Gandara</strong><br />

charlton@manson.demon.co.uk<br />

New website: www.timcharlton.co.uk

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Tectonic models for <strong><strong>Tim</strong>or</strong><br />

(modified from <strong>Re</strong>ed et al., 1996)

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<strong>Charlton</strong> et al. (1991)<br />

Harris et al. (1998)

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<strong>Charlton</strong> (2002, slightly modified)<br />

Standley & Harris (2009)

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Onset of arc‐cont<strong>in</strong>ent collision<br />

‐ potential orig<strong>in</strong>s of metamorphic complexes<br />

Banda<br />

Arc<br />

Collisional<br />

metamorphism<br />

Australia<br />

‘Asian’<br />

basement<br />

Australian<br />

basement

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Lolotoi ‘type’<br />

massif

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New Suai cross‐section

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<strong>Charlton</strong> (2002).<br />

Orig<strong>in</strong>al boundary<br />

mapp<strong>in</strong>g by Grady &<br />

Berry (1977)

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Previous arguments for an Australian<br />

basement orig<strong>in</strong> for <strong>the</strong> Lolotoi Complex<br />

• Gravity <strong>in</strong>dicates high‐density ‘roots’<br />

• Lolotoi Complex extends from >1000m.a.s.l.<br />

to >2900m subsea beneath <strong>the</strong> Suai Bas<strong>in</strong><br />

• <strong>Re</strong>ported stratigraphic contacts with<br />

Australian cover sequences<br />

• Basement‐cover relationships => Cribas<br />

Anticl<strong>in</strong>e is basement‐cored

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The Mutis‐Lolotoi correlation

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‘…<strong>the</strong>re is no significant difference <strong>in</strong> composition<br />

between <strong>the</strong> Lolotoi and Mutis Complexes’ (Harris,<br />

2006)<br />

But…<br />

• P‐T conditions more restricted <strong>in</strong> Lolotoi (no granulite)<br />

• Different tim<strong>in</strong>g (e.g. zircon ages L ~83Ma; M ~35Ma)<br />

• Composition (e.g. quartz <strong>in</strong> metabasites L ~30%, M ~15%; <strong>in</strong><br />

metapelites L typically >40%, M typically

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Lolotoi<br />

Lu‐Hf weighted mean age of 45.4 ±<br />

0.7 Ma from garnets: <strong>in</strong>terpreted<br />

to represent peak metamorphism<br />

of Lolotoi Complex (Standley,<br />

2007)<br />

Harris (2006)<br />

Mutis<br />

Aileu

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Chang<strong>in</strong>g def<strong>in</strong>itions of <strong>the</strong><br />

<strong>allochthon</strong>

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Audley‐Charles (1968)

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Audley‐Charles (1981)

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Harris (2006)

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Haig et al. (2006)

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<strong>Charlton</strong> (post‐2002)

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The geometry of an <strong>allochthon</strong>

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Harris et al. (1998)<br />

Standley & Harris (2009)

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Field evidence<br />

Sou<strong>the</strong>rn front of <strong>the</strong> Lolotoe<br />

‘type’ massif

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Audley‐Charles (1968)

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Lolotoi boundary on<br />

<strong>the</strong> Ogues map sheet<br />

<strong>Re</strong>connaissance<br />

mapp<strong>in</strong>g based on<br />

limited fieldwork and<br />

Google Earth<br />

<strong>in</strong>terpretation

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Three‐way stratigraphic l<strong>in</strong>kage<br />

• Dartollu Formation unconformably on Lolotoi<br />

Complex<br />

• Maubisse Formation unconformably on<br />

Lolotoi Complex<br />

• Maubisse fragments reworked <strong>in</strong>to Dartollu<br />

‐ Maubisse Formation is def<strong>in</strong>itely Australianaff<strong>in</strong>ity<br />

=> Lolotoi (and Dartollu) are also Australianaff<strong>in</strong>ity

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Lunt (2003)<br />

Lunt (2003)<br />

Pellatispira <strong>in</strong> Eocene<br />

conglomerate with<br />

Triassic limestone<br />

clasts<br />

Dartollu Lst conta<strong>in</strong>s<br />

reworked Australianaff<strong>in</strong>ity<br />

Maubisse Fm.<br />

fragments<br />

Co-occurrence of<br />

Biplanispira and<br />

Lacaz<strong>in</strong>ella <strong>in</strong> same<br />

th<strong>in</strong> section<br />

Assil<strong>in</strong>a <strong>in</strong> Sahul<br />

Shoals-1 well

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Legumau Range

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Audley‐Charles<br />

(1968)

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‘Barique Formation’

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Audley‐Charles (1968)

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‘Barique<br />

Volcanics’

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Sou<strong>the</strong>rn front of <strong>the</strong> Laclubar/<br />

Bebe Susu massif

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Audley‐Charles (1968)

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Standley & Harris (2009)

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Caraulun‐Same and Mota Siu<br />

reconnaissance mapp<strong>in</strong>g

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Cablac‐Lolotoi relationships on Mount Cablac<br />

(Keep et al., 2009)

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Conclusions from fieldwork<br />

• Lolotoi Complex represents Australian<br />

cont<strong>in</strong>ental basement<br />

• Lolotoi Complex is overla<strong>in</strong> unconformably by:<br />

‐ Maubisse and Dartollu formations (proven)<br />

‐ Atahoc and Cribas formations (probable)<br />

‐ Cablac Formation (likely but not observed by us)<br />

• No equivalents of <strong>the</strong> Palelo Group observed<br />

<strong>in</strong> <strong><strong>Tim</strong>or</strong>‐Leste

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An alternative <strong>in</strong>terpretation of Standley &<br />

Harris’s (2009) geochemical data is required<br />

Particularly...<br />

• Petrogenetic <strong>in</strong>terpretations<br />

• The significance of radiometric dat<strong>in</strong>g

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‘Australian’<br />

‘Asian’

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‘Asian’

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Lolotoi<br />

Lu‐Hf weighted mean age of 45.4 ±<br />

0.7 Ma from garnets: <strong>in</strong>terpreted<br />

to represent peak metamorphism<br />

of Lolotoi Complex (Standley,<br />

2007) =Middle Eocene<br />

Harris (2006)<br />

=Late Cretaceous (Santonian‐Campanian)<br />

Mutis<br />

Aileu<br />

=Late Eocene

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<strong>Re</strong>vised <strong>in</strong>terpretation

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Buru<br />

Seram<br />

Banda metamorphic P‐T‐t conditions

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Lolotoi Complex<br />

Mutis Complex<br />

Viete et al. (2011)

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Compromise?<br />

Lolotoi Complex is Australian basement<br />

Is <strong>the</strong> Mutis Complex also derived from<br />

<strong>the</strong> Australian plate ra<strong>the</strong>r than <strong>the</strong><br />

Banda forearc?<br />

But <strong>the</strong>n <strong>the</strong> Palelo/Metan <strong>in</strong> West <strong><strong>Tim</strong>or</strong><br />

must also be Australian, non‐arc aff<strong>in</strong>ity

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Tests<br />

• Mutis Complex<br />

‐ Geochemical aff<strong>in</strong>ities (to Lolotoi Complex; and to Banda volcanic arc or<br />

Australian rift‐spread<strong>in</strong>g volcanics)<br />

• Metan Volcanics<br />

‐ Arc or Australian geochemistry?<br />

‐ Palaeomagnetism<br />

• ‘Cablac Limestone’<br />

‐ Age: Mesozoic or Miocene?<br />

‐ Structural‐stratigraphic relationships to Mutis/Palelo<br />

• Dartollu Limestone (Eocene)<br />

‐ Does this unit occur <strong>in</strong> West <strong><strong>Tim</strong>or</strong>?<br />

‐ Structural‐stratigraphic relationships (e.g. to Metan volcanics)<br />

‐ Palaeomagnetism<br />

This work needs to be done <strong>in</strong> West <strong><strong>Tim</strong>or</strong>

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Significance

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Acknowledgements<br />

Roc Oil Company<br />

Limited<br />

SERN<br />

Pr<strong>in</strong>cipal field assistants:<br />

Hercio Fernandes Xavier (‘Iko’)<br />

Joao Soares<br />

Cleto Amaral<br />

Mario Nicolau<br />

Driver: Helder Amado Vieira

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Terima Kasih<br />

Thank you<br />

Obrigadu