| Citation: |
Dong-sheng Wang, Zong-qi Wang, Gang Wang, Xian-qing Guo, Yu-dong Wu, 2019. Characteristics of tectonic deformation of the melange zone in the Lachlan Orogen along eastern coast of Australia, China Geology, 2, 478-492. doi: 10.31035/cg2018131
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Characteristics of tectonic deformation of the melange zone in the Lachlan Orogen along eastern coast of Australia
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Abstract
The Narooma-Batemans Bay (NBB) area along the southeast coast of Australia is a part of the eastern zone of the Early Paleozoic Lachlan Orogen. In the NBB, a set of rock association consisting of turbidites, siliceous rock, basic lava, and argillaceous melange zone is mainly developed. According to systematic field geological survey, the deformation of 3 stages (D1, D2, and D3) was identified in the NBB. At stage D1, with the original bedding S0 in a nearly east-west trending as the deformation plane, tight folds, isoclinal folds, and other structures formed in the NBB accompanied by structural transposition. As a result, crenulation cleavage developed along the axial plane of the folds and schistosity S1 formed. At stage D2, with north-south-trending schistosity S1 as the deformation plane, a large number of asymmetrical folds and rotated porphyroclasts formed owing to thrusting and shear. At stage D3, left-lateral strike-slip occurred along the main north-south-trending schistosity. Based on the analysis of the characteristics of tectonic deformation in the NBB and summary of previous research results, it is determined that the early-stage (D1) deformation is related to Ordovician Macquarie arc-continent collision and the deformation at stages D2 and D3 is the result of the westward subduction of Paleo-Pacific Plate. That is, it is not the continuous westward subduction of the Paleo-Pacific Plate that constitutes the evolution model of the NBB as previously considered.
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Keywords:
- Australia /
- Narooma-Batemans Bay /
- Melanges /
- Tectonic deformation /
- Lachlan Orogen /
- Early Paleozoic /
- arc-continent collision
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References
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Dong-sheng Wang, Zong-qi Wang, Gang Wang, Xian-qing Guo, Yu-dong Wu, 2019. Characteristics of tectonic deformation of the melange zone in the Lachlan Orogen along eastern coast of Australia, China Geology, 2, 478-492. doi: 10.31035/cg2018131
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Figure 1.
Location (a) and tectonic unit distribution (b) of Lachlan Orogen (modified from Prendergast EI, 2007). Stereograms (1), (2), and (3) respectively refer to statistical diagram (great circles) of penetrative schistosity of melange zone in Batemans Bay, Wagonga Group in Narooma, and melange zone in Narooma (by equal-area lower-hemisphere projection). Narooma (Fig. 2a) and Batemans Bay (Fig. 2b) areas in the Lachlan Orogen are labeled with black dotted box.
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Figure 2.
Profiles of Ordovician turbidites (inner zone). a−Folds forming in original bedding owing to deformation; b-1, b-2−coarse sandstone in Merrimbula Group; c−sandstone inside sandy conglomerate; d−gravel distributed parallel to original sedimentary layer; e−Inside structure of sandy conglomerate; f−phyllite in fault contact with platy sandstone; g-1−slate obliquely crossing with the occurrence of phyllite; g-2−mineral composition inside platy sandstone; h-1−macro characteristics of phyllite; h-2−crenulation lineation developing on phyllite (f: axial plane of folds; lb: hinge of folds. Qtz-quartz; Fsp-feldspar; Ser-sericite).
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Figure 3.
Geological map of the structure of Narooma (a) (modified from Miller JM and Gray DR, 1996) and Batemans Bay (b) (modified from Fergusson CL and Frikken P, 2003).
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Figure 4.
Stratigraphic successions of rocks at Narooma and Batemans Bay areas (modified from Prendergast EI and Offler R, 2012).
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Figure 5.
Macro characteristics of the melange zone in Fosters Bay, Narooma. a−Tight folds developing in matrix of melange zone; b−blocks of different sizes in sandstone matrix; c−asymmetrical folds forming in schistosity due to shear; d−tight folds developing in banded siliceous rock (f: axial plane of folds; lb: hinge of folds. The same hereinafter).
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Figure 6.
Macro characteristics of Wagonga Group in Wagonga Head, Narooma. a−Lenticular basaltic breccia forming due to shear; b−amygdales in basic lava; c−pillow structures in basic lava; d−deformation of pillow basalt owing to shear; e−boundary between basic lava and siliceous rock; f−shear direction indicated by asymmetrical folds in siliceous rock.
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Figure 7.
Micro characteristics of Wagonga Group in Wagonga Head, Narooma. a−Basaltic breccia matrix (S01-1); b−basic angular fragments inside basaltic breccia (S01-3); c−andesitic breccia matrix (S01-2); d−micro folds developing inside basalt (S02-1). Qtz−quartz; Pl−feldspar; Cpx−clinopyroxene; Chl−chlorite; Ser−sericite.
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Figure 8.
Macro characteristics of the melange zone in Batemans Bay. a−Tight folds inside banded siliceous rock (Melville Point); b−asymmetrical folds developing along the boundary between siliceous rock and chlorite schist (Melville Point); c−tight folds developing inside siliceous rock (Circuit Beach); d−undeformed blocks in melange zone are lenticular and encapsulated in intensively deformed matrix (Lilli Pilli); e−streched blocks in melange zone (Wimbie Beach. la: stretching lineation); f−different-size lenticular blocks in melange zone (Lilli Pilli. S15-1 and S15-2 are location of samples in Figs. 9c, 9d).
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Figure 9.
Micro deformation characteristics of melange zone in Batemans Bay. a−Kinematic characteristics along XZ plane of an oriented thin section of chlorite schist (parallel to stretching lineation of stage D2 and vertical to schistosity; S14-1A, Melville Point); b−kinematic characteristics along XZ plane of an oriented thin section of chlorite schist (parallel to stretching lineation of stage D3 and vertical to schistosity; S14-1B, Melville Point); c−microstructure features of sandstone blocks in melange zone (S15-2, Lilli Pilli); d−microstructure features of phyllite matrix in melange zone (S15-1, Lilli Pilli). Qtz−quartz; Pl−feldspar; Ms−Muscovite; Chl−chlorite.
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Figure 10.
Macro characteristics of the rocks around the Batemans Bay. a−Characteristics of field distribution of turbidites (Mossy Point); b−diagonal bedding inside turbidites (Mossy Point); c−soft-sediment deformation inside turbidites (Mossy Point); d−original bedding in turbidites (Mossy Point); e−interface between melange zone and overlying Permian Sydney Basin (Myrtle Beach); f−Cambrian-Ordovician gravel developing inside Permian Sydney Basin (Myrtle Beach).
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Figure 11.
Tectonic evolution model of Early Paleozoic Lachlan Orogen (modified from Aitchison JC and Buckman S, 2012). a−Macquarie island arc originates on a plate offshore from eastern Australia; b−as a result of subduction, Macquarie island arc is transferred to the plate northward; c−west-directed subduction of the Paleo-Pacific became established under the Gondwana plate margin.