Woodgreen, Northern Territory : explanatory notes
Northern Territory Geological Survey
E-Publications; E-Books; PublicationNT; Australia 1:100 000 Geological Map Series
2007
Australia 1:100 000 Geological Map Wood 5458; Australia 1:250 000 Geological MapAlcoota SF5310; Australia 1:250 000 Geological MapAlcoota SF5310
1:100 000
Made available via the Publications (Legal Deposit) Act 2004 (NT); Available from GEMIS - Geoscience Exploration and Mining Information System
English
Geology; Georgina Basin; Arunta Region
Northern Territory Government; Northern Territory Government
Darwin
1st ed.
Australia 1:100 000 Geological Map Series
application/pdf
9780724571321
0811-6296
Attribution International 4.0 (CC BY 4.0)
Northern Territory Government
https://creativecommons.org/licenses/by/4.0/
https://geoscience.nt.gov.au/gemis/ntgsjspui/handle/1/81885 [GEMIS]
https://hdl.handle.net/10070/794795
https://hdl.handle.net/10070/794807
8 i n d i c a t e d b e l o w . W h e r e v e r p r a c t i c a l , m a p p a b l e s u b u n i t s w i t h i n t h e c o m p l e x h a v e b e e n d i s t i n g u i s h e d b y s u b s c r i p t n u m e r a l s a n d a r e d e s c r i b e d s e p a r a t e l y b e l o w . I n o t h e r a r e a s , p a r t i c u l a r l y w h e r e o u t c r o p i s p o o r , d e e p l y w e a t h e r e d o r s h e a r e d , t h e W o o d g r e e n gr a n i t e C o m p l e x r e m a i n s u n d i v i d e d . A s n o d e t a i l e d g e o c h e m i c a l s t u d i e s h a v e b e e n c o n d u c t e d , i t r e m a i n s u n c e r t a i n w h e t h e r t h e v a r i o u s e n t i t i e s a r e a l l p h a s e s o f a s i n g l e g r a n i t i c s u i t e , o r i f s e v e r a l u n r e l a t e d b u t b r o a d l y c o n t e m p o r a n e o u s i n t r u s i o n s a r e i n v o l v e d . T h e W o o d g r e e n gr a n i t e C o m p l e x h a s n o t b e e n d a t e d , b u t i t s l a c k o f r e g i o n a l d e f o r m a t i o n s u g g e s t s t h a t i t m a y b e r e l a t e d t o t h e 1 7 3 0 1 7 0 0 M a S t r a n g w a y s or o g e n y . W i t h t he e xc e pt i on of L P g w 1 3 , t he bou nda r i e s be t w e e n t he m a ppe d uni t s a r e f a ul t s o r s he a r z one s . T he w e s t - nor t hw e s t - t r e nd i ng M ount I da S he a r Z one s e pa r a t e s m os t l y ga r ne t - be a r i ng va r i a nt s ( L P g w 1 3 ) t o t he nor t h f r om ga r n e t - poor or ga r ne t - a bs e nt gr a ni t e s t o t he s out h ( L P g w 4 5 ) . U n d i v i d e d W o o d g r e e n gr a n i t e C o m p l e x , i m m e d i a t e l y t o t h e s o u t h o f t h i s s h e a r z o n e , i s g e n e r a l l y w e a t h e r e d a n d s t r o n g l y sheared. It is finer grained than subunits to the north and s o u t h , a n d a p p e a r s t o b e f r e e o f g a r n e t , a l t h o u g h t h i s c o u l d b e a f u n c t i o n o f r e t r o g r e s s i o n a n d / o r w e a t h e r i n g . U n i t s L P g w 4 a n d L P g w 5 a r e a l s o s e p a r a t e d b y a w e s t - n o r t h w e s t e r l y f a u l t o r s h e a r z o n e . T h e W o o d g r e e n gr a n i t e C o m p l e x i s i n f e r r e d t o i n t r u d e t h e de l n y M e t a m o r p h i c s i n t h e s o u t h , a l t h o u g h t h e a c t u a l e x p o s e d c o n t a c t i s a s h e a r z o n e . el s e w h e r e , e v i d e n c e o f t h e h o s t r o c k i s s p a r s e . ne a r 4 3 1 9 0 0 m e 7 5 3 0 7 0 0 m n, t h e W o o d g r e e n gr a n i t e C o m p l e x i n t r u d e s g r a n u l i t e - f a c i e s m e t a s e d i m e n t a r y r o c k s o f t h e A n i r a M e t a m o r p h i c s , w h i c h h a v e a l s o b e e n i n c o r p o r a t e d i n t o t h e g r a n i t e a s l a r g e r a f t s . T h e s i m i l a r i t y o f t h e g r a n i t e t o m e l t s e g r e g a t i o n s i n t h e m e t a s e d i m e n t a r y r o c k s s u g g e s t s t h a t t h e g r a n i t e m a y h a v e b e e n g e n e r a t e d a s p a r t o f t h e s a m e p r o c e s s e s t h a t r e s u l t e d i n g r a n u l i t e - f a c i e s p a r t i a l m e l t i n g i n t h e s e d i m e n t a r y r o c k s . T h e a b u n d a n c e o f g a r n e t a n d m e t a s e d i m e n t a r y e n c l a v e s i n L P g w 1 a n d L P g w 2 i s c o n s i s t e n t w i t h a n S - t y p e o r i g i n f o r t h e g r a n i t e . ot h e r o u t c r o p s o f h o s t r o c k s w i t h i n t h e W o o d g r e e n gr a n i t e C o m p l e x i n c l u d e d a r k g r e e n h o r n f e l s a t 4 2 7 8 1 8 m e 7 5 2 9 0 7 7 m n a n d e p i d o t e - r i c h r o c k s a r o u n d 4 2 9 8 0 0 m e 7 5 3 7 0 0 0 m n, b u t a s t h e s e o u t c r o p s a r e i s o l a t e d , i t i s u n c e r t a i n w h e t h e r t h e y r e p r e s e n t m a r g i n s t o t h e g r a n i t e o r a r e l a r g e r a f t s w i t h i n i t . M e t r e - s c a l e m e t a s e d i m e n t a r y e n c l a v e s a r e o f t e n p r e s e n t i n L P g w 2 , a n d a r e a l s o p r e s e n t a r o u n d 4 2 7 7 0 0 m e 7 5 3 3 9 0 0 m n. LPgw 1 T h i s s u b u n i t i s e x p o s e d n o r t h o f t h e M o u n t I d a S h e a r Z o n e a n d e x t e n d s e a s t w a r d t o t h e v i c i n i t y o f t h e S a n d o v e r H i g h w a y . A n e a s i l y a c c e s s i b l e r e f e r e n c e l o c a l i t y i s n o m i n a t e d a r o u n d 430409mE 7534109mN, ust west of the Sandover Highway a n d n o r t h o f t h e W o o d g r e e n M o u n t S k i n n e r b o u n d a r y f e n c e . T h e g r a n i t e i s b i o t i t e b e a r i n g a n d m o s t l y c o a r s e g r a i n e d , being typified by a distinctive flow alignment of large t a b u l a r K - f e l d s p a r p h e n o c r y s t s , w h i c h i n p l a c e s r e a c h 1 0 c m i n l e n g t h ( Fig u re 7 ) . T h e p l a t y a l i g n m e n t t y p i c a l l y d i p s s o u t h w e s t a t a n g l e s a v e r a g i n g a b o u t 3 0 . Layers of fine to m e d i u m e q u i g r a n u l a r g r a n i t e a r e p r e s e n t a t s o m e l o c a l i t i e s , b u t t h i s v a r i a n t m a k e s u p o n l y a s m a l l p e r c e n t a g e o f t h e t o t a l . ga r n e t i s u b i q u i t o u s a n d o c c u r s b o t h a s r a n d o m l y s c a t t e r e d , s u b s p h e r i c a l e m b a y e d p h e n o c r y s t s , t y p i c a l l y 1 0 2 0 m m i n s i z e , a n d i n l o c a l c l u s t e r s a n d l a y e r s ( Fig u re 8 ) . I s o l a t e d b i o t i t e - r i c h m a s s e s a n d s c h l i e r e n a r e o f t e n p r e s e n t , b u t a r e r a r e l y c o m m o n . T h e u n i t h a s a d i s t i n c t i v e l y u n i f o r m w e a k l y m a g n e t i c r e s p o n s e ( u p t o 3 0 0 x 1 0 - 5 S I u n i t s ) a n d a h i g h r a d i o m e t r i c r e s p o n s e . LPgw 2 T h i s s u b u n i t i s m a i n l y e x p o s e d e a s t o f t h e S a n d o v e r H i g h w a y , w h e r e i t a p p e a r s t o o c c u p y a n o r t h e a s t - t e n d i n g z o n e s e p a r a t i n g L P g w 1 a n d L P w 3 , b u t i t i s a l s o w e l l d e v e l o p e d i n a n i s o l a t e d o u t c r o p a t 4 2 8 9 3 0 m e 7 5 3 7 1 7 8 m n, w h i c h i s n o m i n a t e d a s a r e f e r e n c e l o c a l i t y . T h e r o c k s a r e s t r o n g l y l a y e r e d , a n d c o m m o n l y m i g m a t i t i c w i t h d i s t i n c t i v e b i o t i t e - r i c h d a r k l a y e r s a l t e r n a t i n g w i t h l e u c o c r a t i c l a y e r s ( Fig u re 9 ) . L e u c o c r a t i c l a y e r s v a r y w i d e l y i n g r a i n s i z e f r o m m i c r o g r a n i t e t o p e g m a t i t i c a n d a r e o f t e n p o r p h y r i t i c . ga r n e t i s p r e s e n t a n d t e n d s t o b e c o n c e n t r a t e d i n d i s c r e t e l a y e r s . M e t r e - s c a l e e n c l a v e s o f e p i d o t e - r i c h m e t a m o r p h i c r o c k s a r e p r e s e n t a t t h e r e f e r e n c e l o c a l i t y a n d e l s e w h e r e . T h e l a y e r i n g t y p i c a l l y d i p s s o u t h w e s t . An outcrop ad acent to the Sandover Highway at 427981mE 7 5 3 1 8 5 4 m n i n c l u d e s bi ot i t e - c or di e r i t e m i gm a t i t e of pr oba bl e m e t a s e di m e nt a r y or i gi n. U ni t L P gw 2 i s i nt e r pr e t e d t o Figu re 6 . M a s s i ve C r ooke d H ol e gr a ni t e ( hi l l t op) i nt r udi ng s c hi s t of de l ny gne i s s ( f or e gr ound) . gr a ni t e f or m s t a bul a r body i nt r ude d pa r a l l e l t o l a ye r i ng a nd s c hi s t os i t y i n de l ny gne i s s , he r e ne a r l y hor i z ont a l . 435064m e 7 51 1961m n, 6 km S W of U gna da B or e .