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
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 ni t e , a nd ha s a hi 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 di 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 he 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 nt 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 ( Figu 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 .