Breccia cored columnar rosettes in a rubbly pahoehoe lava flow, elephanta island, deccan traps, and a model for their origin

Breccia cored columnar rosettes in a rubbly pahoehoe lava flow, Elephanta Island, Deccan Traps, and a model for their origin Accepted Manuscript Breccia cored columnar rosettes in a rubbly pahoehoe la[.]

Breccia-cored columnar rosettes in a rubbly pahoehoe lava flow, Elephanta Island,

Deccan Traps, and a model for their origin

Hetu Sheth, Ishita Pal, Vanit Patel, Hrishikesh Samant, Joseph D’Souza

DOI: 10.1016/j.gsf.2016.12.004

Received Date: 4 October 2016

Revised Date: 6 December 2016

Accepted Date: 18 December 2016

Please cite this article as: Sheth, H., Pal, I., Patel, V., Samant, H., D’Souza, J., Breccia-cored columnar rosettes in a rubbly pahoehoe lava flow, Elephanta Island, Deccan Traps, and a model for their origin,

Geoscience Frontiers (2017), doi: 10.1016/j.gsf.2016.12.004.

This is a PDF file of an unedited manuscript that has been accepted for publication As a service to our customers we are providing this early version of the manuscript The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Major oxide and LOI (wt.%) and trace element (ppm) data and CIPW

norms (italics) for the Elephanta Island rubbly pahoehoe lava flow

Comp B,sa B,sa B,sa Ref Meas

ELF 1 ELF 2 IP2 W-2a W-2a

Notes: Sample ELF1 represents the massive, non-vesicular lower part of

the rubbly pahoehoe flow, and samples ELF2 and IP2 come from

columnar zones above, sampled at different locations mentioned in the

text Composition “B, sa” implies subalkalic basalt Mg# = 100

×Mg2+/(Mg2+ + Fe2+), atomic, assuming 85% of the total Fe to be in the

Fe2+ form For U.S.G.S reference material W-2a, the reference (ref.) and

measured (meas.) values provide an idea of analytical accuracy The

former values are from Stephen A Wilson of the U.S Geological Survey

(http://crustal.usgs.gov/geochemical_reference_standards/diabase.html)

Belgaum Koynanagar

Sheva

Nhva

Cre

ekjetty (Mumbai boats)

abandoned quarry

column set

subvertical column

subhorizontal column set

horizontal substrate surface

direction of lava flow advance

thickening and fracturing of upper crust

(a) Lobe emplacement

(b) Slabby pahoehoe formation

(c) Rubbly pahoehoe formation

rapid

inflation

rapid inflation continuing and

brecciation of pahoehoe slabs

new crust of breakout, fracturing to slabs (and later brecciating) as breakout inflates; the whole process (a-d) continues many times

flow advance

flow advance

flow advance

(f) Final situation, post-solidification

large surge in lava supply causing breakout

possible invasive flow behaviour,

to form

isotherm

subhorizontal columns to form

thick columns

to form

Research highlights (Sheth et al.)

Breccia-cored columnar rosettes in a rubbly pahoehoe lava flow from Elephanta Island (western Deccan Traps), and a model for their origin

• Unique volcanic structures with radial joint columns and flow-top-breccia cores

• Reported only from the Deccan flood basalts; new example from Elephanta Island

• Previously thought to form by FTB somehow sinking into molten flow interior

• Our model based on rubbly pahoehoe inflation and transitional character to ‘a’ā

• FTB rubble dropped by thick lava flow incorporated by itself during advance

• Roughly spherical isotherms around cold FTB inclusions produce radial jointing