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

10 be t r a ns i t i ona l be t w e e n m i gm a t i t i c m e t a s e di m e nt a nd S - t ype gr a n i t e , a nd ha s a h i ghl y m a gne t i c r e s pons e ( up t o 5000 x 10 - 5 S I uni t s ) . I t s r a d i om e t r i c r e s pons e i s m a r ke dl y l e s s t ha n t ha t of L P gw 1 , pr i m a r i l y i ndi c a t i ng l ow e r K c onc e nt r a t i on. LPgw 3 T hi s s ubuni t i s m i ne r a l ogi c a l l y s i m i l a r t o L P gw 1 but i s distinctively finer grained and mostly equigranular. A l t h ough i t l oc a l l y di s pl a ys l a ye r i ng, i t l a c ks t he di s t i nc t i ve flow-aligned phenocrysts of LPgw 1 . ga r ne t phe noc r ys t s a r e of s i m i l a r s i z e t o t hos e i n L P gw 1 , but ha ve a c l ot t e d a ppe a r a nc e w i t h s t r ongl y e m ba ye d m a r gi ns . T he r e f e r e nc e a r e a i s a r ound 4320 53m e 7533884m n. S ubuni t L P gw 3 i s a l s o di s t i nc t f r om L P gw 1 i n t ha t i t ha s a ve r y va r i a bl e m a gne t i c i nt e ns i t y a nd i t s r a di om e t r i c s i gna t ur e i s a l s o i nc ons i s t e nt . A r e a s of ve r y hi gh m a gne t i c i nt e ns i t y , i n non- out c r oppi ng a r e a s s how n a s L P gw 3 on the simplified geology map inset, may reflect the pr e s e nc e of m i gm a t i t e ( L P gw 2 ) a nd/ or m e t a s e di m e nt a r y r oc ks of t h e A ni r a M e t a m or phi c s . LPgw 4 T h i s s u b u n i t o c c u p i e s a c e n t r a l p o s i t i o n 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 , s o u t h o f t h e M o u n t I d a S h e a r Z o n e . I t d o e s n o t i n c l u d e o u t c r o p s i m m e d i a t e l y s o u t h o f t h e s h e a r z o n e , which are finer grained and generally strongly weathered and s h e a r e d . L P g w 4 c o m p r i s e s c o a r s e - g r a i n e d p o r p h y r i t i c g r a n i t e s i m i l a r t o L P g w 1 , b u t g e n e r a l l y l a c k i n g g a r n e t . S u b o r d i n a t e medium-grained equigranular granite is also present. Minor garnet has been identified locally and, in some places, the g r a n i t e c o n t a i n s s p h e r i c a l c l o t s o f b i o t i t e , w h i c h m a y r e p r e s e n t r e t r o g r e s s e d f o r m e r g a r n e t . T h e r e f e r e n c e a r e a i s a r o u n d 4 3 1 4 0 0 m e 7 5 2 3 0 0 0 m n. S u b u n i t L P g w 4 h a s t h e l o w e s t m a g n e t i c r e s p o n s e o f a l l s u b u n i t s o f 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 , b e i n g a l m o s t n o n - m a g n e t i c . T h i s a l a r g e r c o m p o n e n t o f i t s r a d i o m e t r i c s i g n a t u r e t h a n i n o t h e r g r a n i t i c u n i t s i n W oodgreen, m a n i f e s t e d i n K / T h r a t i o s i n t h e r a n g e 0 . 0 2 0 . 0 3 ( m o s t g r a n i t e s o n W oodgreen t y p i c a l l y h a v e K / T h > 0 . 0 3 ) . LPgw 5 T hi s s ubuni t i s t he m os t s out he r l y a nd i s s e pa r a t e d f r om L P gw 4 by a m a j or f a ul t or s he a r z one . I t c om pr i s e s t w o c ont r a s t i ng pha s e s t ha t a r e i n t e r c a l a t e d on a s c a l e t ha t doe s not a l l ow di s t i nc t i on on t he m a ps he e t ( Fig u re 10 ) . T he dom i na nt pha s e c om pr i s e s di s t i nc t i ve por phyr i t i c gr a ni t e w i t h a da r k bi ot i t e - r i c h gr oundm a s s ( Fig u re 1 1 ) . Thin sections show significant dynamic deformation and evidence of recrystallisation, including significant quantities of s e c onda r y e pi dot e i n t he gr oundm a s s . T he s ub or di na t e pha s e c om pr i s e s m e di um - gr a i ne d l e uc oc r a t i c gr a ni t e . I s ol a t e d out c r ops of non- por phyr i t i c bi ot i t e gr a ni t e ne a r t he w e s t e r n l i m i t of e xpos ur e ( e g a t 428690m e 7521369m n) ha ve a l s o be e n i nc l ude d i n L P gw 5 . T he r e f e r e nc e a r e a i s a r ound 433000m e 7519000m n, w hi c h i s a l s o t he t ype l oc a l i t y of t he e nt i r e W oodgr e e n gr a ni t e C om pl e x, a s nom i na t e d by S ha w a nd W a r r e n ( 1975) . T he uni t ha s a r e l a t i ve l y uni f or m , moderate to high magnetic response, with measured field s us c e pt i bi l i t i e s of up t o 2700 x 10 - 5 S I uni t s a s s oc i a t e d w i t h t he por phyr i t i c pha s e . M ollie G ranite Compl e x ( LP gm ) B a s e d o n a e r o m a g n e t i c i n t e r p r e t a t i o n , t h e s c a t t e r e d o u t c r o p s o f g r a n i t o i d r o c k s t h a t l i e i n a n o r t h w e s t - t r e n d i n g b e l t f r o m t h e U t o p i a t a n t a l i t e p r o s p e c t s t o t h e s m a l l o u t c r o p a t 4 2 6 7 0 0 m e 7 5 5 6 9 0 0 m e a r e l i k e l y t o c o m p r i s e a s i n g l e b o d y a n d a r e d i s t i n g u i s h e d o n t h e m a p a s M o l l i e gr a n i t e C o m p l e x ( n e w n a m e ; s e e Appendix 1 ) . H o w e v e r , a w i d e l i t h o l o g i c a l r a n g e i s p r e s e n t , e v e n i n a s i n g l e o u t c r o p , a n d i t i s u n c e r t a i n w h e t h e r a l l p h a s e s a r e c o m a g m a t i c o r w h e t h e r t h e y c o m p r i s e t w o o r m o r e u n r e l a t e d i n t r u s i o n s . I n t e r p r e t a t i o n i s c o m p l i c a t e d b y t h e f a c t t h a t m o s t o u t c r o p s a r e d e e p l y w e a t h e r e d , a l t h o u g h s m a l l f r e s h d o m e o r t o r o u t c r o p s , g e n e r a l l y w i t h l i t t l e r e l i e f , h a v e b e e n f o u n d i n s e v e r a l a r e a s ( e g 4 3 2 4 5 9 m e 7 5 5 2 7 7 3 m n, 4 4 3 9 9 9 m e 7 5 4 5 6 2 6 m n, 4 4 2 9 3 6 m e 7 4 5 3 6 3 2 m n, 4 4 4 3 0 9 m e 7 5 4 1 7 7 5 m n) . on e o f t h e b e s t e x p o s u r e s i s a r o u n d 4 3 2 4 5 9 m e 7 5 5 2 7 7 3 m n, e a s t - n o r t h e a s t o f ne w B o r e , 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 a r e a f o r t h i s c o m p l e x . A t t h i s l o c a l i t y , a n e a r l y , d a r k b i o t i t e - r i c h g r a n o d i o r i t e w i t h a b u n d a n t d a r k e n c l a v e s i s i n t r u d e d b y l e u c o c r a t i c m i c r o g r a n i t e a n d l e u c o c r a t i c p o r p h y r i t i c g r a n i t e , w i t h a distinctive flow foliation of tabular K-feldspar phenocrysts. T h e l a t e r p h a s e s a r e i n t i m a t e l y i n t e r l a y e r e d a n d a p p e a r t o b e comagmatic. Similar variants can be tentatively identified Figu re 10 . W oodgr e e n gr a ni t e C om pl e x ( L P gw 5 ) . T ypi c a l e xpos ur e s how i ng c oa r s e , da r k por phyr i t i c pha s e i nt e r l a ye r e d w i t h finer, leucocratic non-porphyritic phase. 432901m e 7518722m n, 6.5 k m W nW of U gna da B or e .


Aboriginal and Torres Strait Islander people are advised that this website may contain the names, voices and images of people who have died, as well as other culturally sensitive content. Please be aware that some collection items may use outdated phrases or words which reflect the attitude of the creator at the time, and are now considered offensive.

We use temporary cookies on this site to provide functionality.
By continuing to use this site without changing your settings, you consent to our use of cookies.