Territory Stories

Woodgreen, Northern Territory : explanatory notes

Details:

Title

Woodgreen, Northern Territory : explanatory notes

Issued by

Northern Territory Geological Survey

Collection

E-Publications; E-Books; PublicationNT; Australia 1:100 000 Geological Map Series

Date

2007

Location

Australia 1:100 000 Geological Map Wood 5458; Australia 1:250 000 Geological MapAlcoota SF5310; Australia 1:250 000 Geological MapAlcoota SF5310

Map scale

1:100 000

Notes

Made available via the Publications (Legal Deposit) Act 2004 (NT); Available from GEMIS - Geoscience Exploration and Mining Information System

Language

English

Subject

Geology; Georgina Basin; Arunta Region

Publisher name

Northern Territory Government; Northern Territory Government

Place of publication

Darwin

Edition

1st ed.

Series

Australia 1:100 000 Geological Map Series

File type

application/pdf

ISBN

9780724571321

ISSN

0811-6296

Use

Attribution International 4.0 (CC BY 4.0)

Copyright owner

Northern Territory Government

License

https://creativecommons.org/licenses/by/4.0/

Related links

https://geoscience.nt.gov.au/gemis/ntgsjspui/handle/1/81885 [GEMIS]

Parent handle

https://hdl.handle.net/10070/794795

Citation address

https://hdl.handle.net/10070/794807

Page content

20 Q u artz gr av e l (Cz q) This symbol is used where abundant quartz float is c onc e nt r a t e d i n a r e a s s ur r oundi ng out c r oppi ng qua r t z ve i ns , or i n on e c a s e , i s t he r e s ul t of di s i nt e gr a t i on of a qua r t z pe bb l e - r i c h c ongl om e r a t e . cons i de r i ng t he hi ghl y s t a bl e nature of quartz and the amount of quartz float surrounding a r e l a t i ve l y s m a l l s our c e , t he pe r i od of a c c um ul a t i on dur i ng de nu da t i on m a y be c ons i de r a bl e . S oil ov e r s u bc rop ( Cz / S ) thi s s ym bol i s us e d f or s ha l l ow s oi l s de ve l ope d f r om t he in situ br e a kdow n of gr a ni t i c a nd m e t a m or phi c r oc ks (s) a nd m a y a l s o i nc l ude s om e m a t e r i a l be i ng t r a ns por t e d r a di a l l y a w a y f r om s uc h a r e a s . the s oi l i s c om m onl y sandy and gritty, containing significant feldspar and mica components, as well as quartz float. Such areas are generally s l i gh t l y e l e va t e d a bove s ur r oundi ng Q ua t e r na r y s oi l s a nd a r e c om p a r a t i ve l y s pa r s e l y ve ge t a t e d. the y c om m onl y f or m s ha l os a r ou nd m a ppe d out c r ops of gr a ni t e a nd m e t a m or phi c r oc ks , a nd of t e n c ont a i n s m a l l , l ow out c r ops of w e a t he r e d a nd/ o r f r e s h pa r e nt r oc k t ha t a r e t oo s m a l l t o r e pr e s e nt on t he m a p. on a e r i a l phot ogr a phs a nd s a t e l l i t e i m a ge s , t he y are distinguished by their pale reflective nature and bedrock t r e nd s a r e s om e t i m e s vi s i bl e . the s e s oi l s a r e t he pr oduc t of l ong pe r i ods of s l ow w e a t he r i ng, a nd a l t hough t hi s pr oc e s s i s on goi ng t oda y , t he y a r e c a t e gor i s e d a s ce noz oi c r a t he r t ha n Q ua t e r na r y . Q u ate rnary s e di me nt (Q c, Q r, Q s , Q p, Q a) the di s t r i but i on of Q ua t e r na r y uni t s s how n on t he m a pf a c e ha s l a r ge l y be e n i nt e r pr e t e d f r om a e r i a l phot ogr a p hs a nd la nd s a t i m a ge r y . the m os t w i de s pr e a d Q ua t e r na r y uni t i n Woodgreen i s colluvial red soil (Q r ) pl a i ns , w hi c h a r e pa r t i c ul a r l y w e l l de ve l ope d i n t he w e s t e r n ha l f of t he s he e t a r e a . Whe r e m os t de ve l ope d, t he y a r e c ha r a c t e r i s e d by a r c ua t e s t a nds of m ul ga (Acacia aneura) a nd ot he r ve ge t a t i on t ype s , w hi c h a r e c l e a r l y vi s i bl e on a e r i a l phot ogr a phs a nd la nds a t i m a ge s . suc h ve ge t a t i on pa t t e r ns ha ve be e n r e f e r r e d t o a s ba nde d m os a i c or t i ge r bus h a nd de ve l op through the progressive separation of bare sheet flood areas f r om dow ns l ope w a t e r - a nd s i l t - t r a ppi ng ve ge t a t e d z one s (WakelinKing 1999). Colluvial deposits (Q c ) i nc l ude a c t i ve gr a v e l f a ns a nd a dj a c e nt gr a ve l out w a s h a r ound r a nge s , t oge t he r w i t h m i nor t a l us s l ope s a r ound a r e a s of s t e e p r e l i e f . Alluvial deposits of s i l t , s a nd a nd gr a ve l (Q a ) oc c ur on active floodplains and in channels. Red soil plains (Qr) and c ol l u vi a l de pos i t s (Q c ) bot h ha ve gr a da t i ona l bou nda r i e s w i t h a l l uvi um (Q a ). Lacustrine deposits (Q p) c om pr i s e s i l t a nd c l a y de pos i t e d f r om s t a ndi ng w a t e r w i t hi n e ph e m e r a l pl a ya l a ke s a nd s w a m ps , a nd oc c ur m os t c om m onl y i n t he f a r no r t he a s t a nd nor t hw e s t of t he s he e t a r e a . Red aeolian sand (Q s ), w hi c h f or m s s he e t - l i ke de pos i t s s l i ght l y e l e va t e d a bov e s ur r oundi ng a r e a s of r e d c ol l uvi a l s oi l a nd a l l uvi um , i s m a i nl y f ound i n n or t he r n Woodgreen. ae ol i a n s a nd a l s o f or m s s l opi ng de pos i t s r i m m i ng t he s ou t he a s t e r n s i de s of hi l l s a nd r a nge s i n t hi s a r e a . al t hough l ow l i ne a r m ounds a r e pr e s e nt i n s om e a r e a s , t r ue dune s a r e a bs e nt f r om t he s he e t a r e a . StructurEAndMEtAMorphISM th e m e t a m o r p h i c g r a d e o f Pa l a e o p r o t e r o z o i c m e t a s e d i m e n t a r y u n i t s i n t h e ar u n t a re g i o n i n Woodgreen r a n g e s f r o m l o w e r a m p h i b o l i t e t o g r a n u l i t e f a c i e s . th e h i g h e s t m e t a m o r p h i c g r a d e i s i n t h e an i r a me t a m o r p h i c s , w h i c h h a v e u n d e r g o n e h i g h - t e m p e r a t u r e , l o w - p r e s s u r e g r a n u l i t e - f a c i e s m e t a m o r p h i s m . th e r e i s n o p e r v a s i v e f a b r i c d e v e l o p m e n t a s s o c i a t e d w i t h t h i s m e t a m o r p h i s m . th e h i g h v o l u m e o f m e l t i n m e t a p e l i t e s i s a c c o m p a n i e d b y a c o r d i e r i t e - a n d s p i n e l - b e a r i n g m e l a n o s o m e , a n d t h i s s u g g e s t s t h a t t h e r o c k s u n d e r w e n t t h e b i o t i t e d e h y d r a t i o n m e l t i n g r e a c t i o n : b i o t i t e + s i l l i m a n i t e + q u a r t z = c o r d i e r i t e + s p i n e l + m e l t . th i s r e a c t i o n i s c o m m o n i n t h e h i g h - t e m p e r a t u r e , l o w - p r e s s u r e r e g i o n a l a u r e o l e m e t a m o r p h i s m e v i d e n t i n a n u m b e r o f l o c a t i o n s t h r o u g h t h e n o r t h e r n ar u n t a re g i o n , most notably around Mount Stafford (NAPPERBY; Greenfield et al 1996) and in the Deep Bore Metamorphics (HUCKITTA; Scrimgeour et al 2 0 0 1 ). it i s c o n s i s t e n t w i t h m e t a m o r p h i c p r e s s u r e - t e m p e r a t u r e c o n d i t i o n s o f 34 kbar and 750800 c. it i s l i k e l y t h a t m e t a m o r p h i s m o c c u r r e d a t a b o u t 1 7 3 0 ma a n d t h a t t h e g r a n u l i t e s f o r m a n e x t e n s i o n o f t h e e a s t - t r e n d i n g z o n e o f h i g h - t e m p e r a t u r e , l o w - p r e s s u r e m e t a m o r p h i s m , n o r t h o f t h e de l n y sh e a r Zone in HUCKITTA (Jinka domain; Scrimgeour et al 2 0 0 1 ). th e de l n y me t a m o r p h i c s a n d cr o o k e d H o l e gr a n i t e h a v e a s t r o n g f o l i a t i o n t h a t m o s t c o m m o n l y t r e n d s n o r t h e a s t a n d d i p s s t e e p l y t o v e r t i c a l l y , a l t h o u g h e a s t o f ug n a d a ta n k , t h e f o l i a t i o n d i p s m o r e m o d e r a t e l y t o t h e s o u t h - s o u t h w e s t . th e s e u n i t s h a v e b e e n m e t a m o r p h o s e d t o l o w - p r e s s u r e l o w e r a m p h i b o l i t e f a c i e s , w i t h b i o t i t e - m u s c o v i t e a n d a l u s i t e a s s e m b l a g e s , a n d w i t h g r a d e i n c r e a s i n g t o m i d d l e a m p h i b o l i t e f a c i e s i n w e s t e r n m o s t o u t c r o p s o f t h e de l n y me t a m o r p h i c s i n Woodgreen, w h e r e s i l l i m a n i t e i s p r e s e n t . th e ma p a t a gn e i s s h a s b e e n m e t a m o r p h o s e d t o m i d d l e t o u p p e r a m p h i b o l i t e f a c i e s . th e n o r t h e r n ar u n t a re g i o n i n alcoota a n d H uckitta c o n t a i n s s t e e p l y s o u t h - d i p p i n g , w e s t - n o r t h w e s t - t r e n d i n g r e v e r s e f a u l t s a n d s h e a r z o n e s t h a t t r u n c a t e e a r l y Pa l a e o p r o t e r o z o i c f a b r i c s . th e s e i n c l u d e m a j o r s t r u c t u r e s s u c h a s t h e de l n y , mo u n t id a a n d Wa i t e ri v e r s h e a r z o n e s . The Delny Shear Zone (Scrimgeour and Raith 2001; f o r m e r l y t h e de l n y - mo u n t sa i n t h i l l Fa u l t zo n e o f Wa r r e n 1978) does not outcrop in Woodgreen, b u t i s i n t e r p r e t e d t o o c c u r i n t h e s u b s u r f a c e i n t h e s o u t h w e s t e r n c o r n e r o f t h e s h e e t a r e a . th e Wa i t e ri v e r sh e a r zo n e s e p a r a t e s t h e Wo o d g r e e n gr a n i t e co m p l e x i n t h e n o r t h f r o m t h e de l n y me t a m o r p h i c s t o t h e s o u t h . th e mo u n t id a Shear Zone (Shaw and Warren 1975) forms a number of p r o m i n e n t m y l o n i t e o u t c r o p s a n d s e p a r a t e s g a r n e t - b e a r i n g c o n s t i t u e n t s o f t h e Wo o d g r e e n gr a n i t e co m p l e x t o t h e n o r t h f r o m g a r n e t - a b s e n t c o n s t i t u e n t s t o t h e s o u t h . th e s e s h e a r z o n e s a r e l i k e l y t o h a v e h a d a s i m i l a r e v o l u t i o n t o t h e de l n y sh e a r zo n e i n H uckitta, w h i c h u n d e r w e n t d u c t i l e d e f o r m a t i o n t h a t c u l m i n a t e d i n t h e l a t e Devonian (365360 Ma) with a southup reverse sense o f m o v e m e n t (sc r i m g e o u r a n d ra i t h 2 0 0 1 ). th i s s h e a r s e n s e i s c o n s i s t e n t w i t h l o c a l l y p r e s e r v e d s- c f a b r i c s i n


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